크립토 좀비 

https://cryptozombies.io

프로그래머스

https://programmers.co.kr/pages/blockchain

자바스크립트로 블록체인 코인 클론

https://academy.nomadcoders.co/p/nomad-coin

Document Metadata

• Creators: @ned; @theoretical

• Developers: @theoretical; @vandeberg; @itwasntme; @zgredek; @pychol-mychol;

@small.minion; @youkaicountry; @picokernel

• Contributors:

@sneak; @vandeberg; @valzav; @youkaicountry; @justinw;

@goldibex; et al.

• Sketch designs: @pkattera

• Copyright (c) Steemit, Inc. 2017

• GitHub: https://github.com/steemit/smt-whitepaper/blob/master/smt-manual/

manual.md

Smart Media Tokens (SMTs)

A Token Protocol for Content Websites, Applications, Online

Communities and Guilds Seeking Funding, Monetization and

User Growth

Steem’s Smart Media Tokens (SMTs) give anyone the power to launch and sell Proof-ofBrain [1] tokens, which are tokens distributed by “upvote” and “like”-based algorithms

and can be integrated with websites to align incentives and spur growth, while websites are

empowered to adopt sustainable, currency-centric revenue models. This model has been

tested and continues to be proven by steemit.com, busy.org, chainbb.com, dsound.audio,

dtube.video and other Steem interfaces, which are monetizing content, tokens and media

in a way never before seen.

Several popular token protocols, such as Ethereum’s ERC-20, allow you to create and

launch arbitrary tokens, but no protocol enables content businesses to leverage those tokens by aligning incentives between users and applications. Due to suboptimal transaction

cost structures that incur fees for basic actions such as voting or posting, misalignment

of interests between meta and core tokens that aren’t built for influencing distributions

based on Proof-of-Brain, private key hierarchies that don’t cater to social versus financial

operations, and slow transaction speeds that are out of sync with real-time websites - none

of these protocols could ever provide an acceptable user experience for content websites,

such as Twitter, Reddit (even subreddits) or The New York Times.

For content websites and tokens, incentive alignment between websites and users comes

from a steady, as well as decentralized and mathematically guaranteed, release of new

tokens, and incentives that must be allocated to the users - including bloggers, vloggers,

commenters and curators. The distribution of new tokens occurs based on stake-weighted

voting to prevent gaming and eliminate the need for a counterparty. Quality user experience comes from tokens that can be transacted safely (through separate private keys for

distinct sets of actions), without fees, and at real-time speeds. Further incentive alignment comes from a company’s ability to raise capital in ICOs. All Smart Media Tokens

have built-in ICO support, should the issuer wish to launch one.

1

Table of Contents

Document Metadata

1

Smart Media Tokens (SMTs)

A Token Protocol for Content Websites, Applications, Online Communities and

Guilds Seeking Funding, Monetization and User Growth . . . . . . . . . .

1

1

Introduction

Leveraging Tokens for Autonomous User Growth . . . . . .

New Fundraising Opportunities . . . . . . . . . . . . . . . .

Immediate Liquidity . . . . . . . . . . . . . . . . . . . . . .

Shared Bootstrap Tools . . . . . . . . . . . . . . . . . . . .

Monetizing with Shared Token Rewards . . . . . . . . . . .

Can My Entity Participate in SMTs? . . . . . . . . . . . . .

Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 - Content Publishers - Single Token Support . . . . .

2 - Forums - Multiple Token Support . . . . . . . . . .

3 - Comments Widget for Online Publishers . . . . . .

4 - Sub-Community Moderators and Managers . . . .

5 - Arbitrary Assets - Tokens Representing Real World

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Owner’s manual

Create a control account . . . . . . . . . . . .

Control account security . . . . . . . . .

Token consensus . . . . . . . . . . . . .

Token Generation and Initialized Parameters

SMT object creation . . . . . . . . . . .

SMT pre-setup . . . . . . . . . . . . . .

SMT setup . . . . . . . . . . . . . . . .

Token units . . . . . . . . . . . . . . . .

Unit ratios . . . . . . . . . . . . . . . .

Cap and min . . . . . . . . . . . . . . .

Hidden caps . . . . . . . . . . . . . . . .

Generation policy data structure . . . .

Examples and rationale . . . . . . . . .

Launch . . . . . . . . . . . . . . . . . .

Full JSON examples . . . . . . . . . . .

Inflation Parameters . . . . . . . . . . .

Named token parameters . . . . . . . .

Parameter constraints . . . . . . . . . . . . .

SMT vesting semantics . . . . . . . . . . . . .

Content rewards . . . . . . . . . . . . . . . .

Curve definitions . . . . . . . . . . . . . . . .

Target votes per day . . . . . . . . . . . . . .

SMT Setup GUI Sketch . . . . . . . . . . . .

Votability and Rewardability . . . . . . . . .

Static Token Parameters . . . . . . . . . . . .

Mandatory token parameters . . . . . . . . .

SMT interaction with existing operations . .

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Automated Market Makers for SMTs

Setup . . . . . . . . . . . . . . . . . . .

Basic Definitions . . . . . . . . . .

Notes on Conventions . . . . . . .

Finite Trades . . . . . . . . . . . . . . .

Basic Definitions . . . . . . . . . .

Computing the Restoring Trade . .

Computing the Equilibrium Price .

Example . . . . . . . . . . . . . . .

Infinitesimal Trades . . . . . . . . . . .

Setting up the Problem . . . . . .

Solving the DE’s . . . . . . . . . .

Qualitative discussion . . . . . . . . . .

FAQ . . . . . . . . . . . . . . . . . . . .

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Costs of SMT Operations And Bandwidth Rate Limiting

Fee-less Operations Necessary for Quality User Experience . . . . . . . . . . . .

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Decentralized Exchange

Automatic Order Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diverse Asset Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Zero Trading and Transfer Fees . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Augmenting SMTs with Additional Native Contracts

Community Building with Paid Positions . . . . . . . . . . . . .

Democratic SMTs using Whitelist Oracles . . . . . . . . . . . . .

Secondary ICOs for Contiguous Fundraising . . . . . . . . . . . .

Bandwidth Sharing with SMTs Based on Reserve Liquidity Pools

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What Makes SMTs Better Suited to Application-Specific Blockchains, such

as Steem, than Application-General Blockchains, such as Ethereum?

SMTs are Safer and More Cost Effective in Application-Specific Blockchain Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SMTs on Steem have Aligned Proof-of-Brain Incentives with the Core Token .

SMTs on Steem Have Transaction Pricing that Contributes to a Quality User

Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SMTs Benefit from a Blockchain that has Scaling Processes Programmed to a

Specialized Set of Applications . . . . . . . . . . . . . . . . . . . . . . . .

SMTs Benefit from a Blockchain with Content Management System (CMS)

Primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Increasing Market Demand for STEEM with SMTs and Implicit Value

Drivers rather than Fees

STEEM Purchased for Transaction Bandwidth Enables Maximally Profitable

Participation across SMTs . . . . . . . . . . . . . . . . . . . . . . . . . . .

STEEM Supply is Locked into Liquidity Pools by Automated Market Makers .

STEEM and SMT Demand Increases with Advent of New Powers of Influence .

STEEM Demand Increases with Proliferation of SMT ICOs . . . . . . . . . . .

Steem: The World’s Advertising Network . . . . . . . . . . . . . . . . . . . . .

Steem Ecosystem Support for SMTs

Integrating SMTs into Websites and Apps . . . . . . . . . . . . . . . . . . . . .

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APIs and Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . .

Shared Tools for Account Creation, Key Signing, and Wallet Functions . .

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Conclusion

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References

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Appendix

Implementation Notes . . . . . . . . . . . . . .

SMT naming standards . . . . . . . . . .

Asset directory standards . . . . . . . . .

UI guidelines for SMT names . . . . . . .

Operational guidelines for asset directories

Asset directory formats . . . . . . . . . .

Unit Tests . . . . . . . . . . . . . . . . . . . . .

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Introduction

Smart Media Tokens (SMTs) is a proposal to build a consensus-level token issuance protocol on the Steem blockchain. Inspired by the revolutionary properties of the STEEM

token, including automatic distributions to content creators, SMTs will be an upgrade

beyond previously created blockchain token issuance protocols due to carefully designed

token sale programmability, automated liquidity providers, decentralized token markets

and dynamic token distribution parameters, as well as a large ecosystem of tools (open

source wallets, shared key signing tools, etc.) for integrations at website and application

layers.

SMTs are an evolution of the successful relationship established between STEEM and

the social websites sitting atop of it, such as steemit.com, which has grown to be a top

2100 website in Alexa rankings in less than one year, solely from integrating the incentive

model of STEEM. With SMTs, any website or content library across the internet may have

one or more tokens integrated into its interface to facilitate fundraising and autonomous

growth.

These tokens are designed to allow website operators flexibility during the integration of

the token into their community by choosing from many parameters that may be structured

creatively at outset or refined over time. Any tokens launched as SMTs shall benefit from a

blockchain ecosystem built with an inbuilt decentralized exchange, as well as an ecosystem

of open-source applications and libraries to support successful deployment, fundraising,

and growth.

Leveraging Tokens for Autonomous User Growth

SMTs are a breakthrough for bridging the world’s content applications to tokens in a way

that aligns incentives between the users of a network and the entrepreneurs building the

applications. By leveraging the concepts of inflation (new token emissions) and token allocations by post-based voting, SMTs exist in a manner where value must be distributed

to users who are participating in their related content networks and applications. Entrepreneurs may now create tokens to integrate with their blog, application, or an entire

network of applications and topics. With SMTs, the entrepreneurs have the flexibility

to decide on the economics of the tokens they integrate into their products, from the

inflation rates to the algorithms that distribute the tokens.

Two unique properties align incentives and make SMTs “smart and social” compared to

other tokens (such as bitcoin, ether and ERC-20s). The first is a pool of tokens dedicated

to incentivizing content creation and curation (called the “rewards pool”). The second

is a voting system that leverages the wisdom of the crowd to assess the value of content

and distribute tokens to it. These two unique properties when combined are referred

to as Proof-of-Brain, which is an entendre based on Proof-of-Work, meant to emphasize

the human work required to distribute tokens to community participants. Proof-of-Brain

positions SMTs as a tool for building perpetually growing communities, which encourage

their members to add value to the community through the built in rewards structure.

Entrepreneurs and established entities may rely on SMTs to grow their content network

because of the automated and continuous generation of new tokens that are allocated

to producers of content by the holders of the existing tokens, through the process of

competitive voting. As the tokens are distributed to users of the network, the interests of

5

existing token holders are further aligned with content creators, the businesses running

the applications, and the entrepreneurs that support them. These unique properties of

the tokens’ economics continue to provide incentives for new users to join and participate

in growing the network. Any application, whether it is an existing publisher behemoth or

a stealth-mode social media startup, will be able to integrate and leverage these special

tokens for their own growth.

New Fundraising Opportunities

Blockchain-based tokens, beginning strongly with the advent of ERC20 on Ethereum,

represent a new manner of bringing capital into an organization through the process of

Initial Coin Offerings (ICOs). ICOs are an opportunity for one group to sell an initial

supply of tokens, privately or publicly, for-specific-purpose, for-profit or not-for-profit.

Depending on how these tokens are sold, different regulatory bodies could see them as

commodities, securities, derivatives, or as none of the above. Regardless, it is clear we

have seen north of one billion dollars (USD) raised through ICOs in 2017, and to support

this trend, it is possible to conveniently launch and sell tokens via the built in ICO contract

of SMTs. The launch of SMTs can be structured for ICOs with hard, soft, and no caps,

and can be tailored to receive STEEM and cryptocurrencies on other blockchains.

Immediate Liquidity

By leveraging a recently designed automated market maker concept [2], SMT-based ICOs

allow a portion of STEEM tokens received to be sent into an SMT’s on-chain, off-orderbook market maker in order to provide liquidity to the SMT at a specified reserve ratio.

Beyond the social and specialized distribution mechanisms of SMTs, this feature advances

the concept of automated market makers by pairing it alongside SMT’s decentralized

markets, which also facilitate bids and asks by human participants. The combination

of these two markets enables on-chain and trustless exchange opportunities for market

makers while enabling liquidity for token users.

Shared Bootstrap Tools

SMTs may be created with reward pool parameters tuned for “Shared Influence” between

Steem Power and other vesting SMTs, which means a SMT creator may specify that

Steem Power can control a portion of the SMT’s rewards pool for an unlimited or limited

amount of time, with increasing or decreasing influence. Altogether, Shared Influence may

allow SMTs to be wholly or partially bootstrapped by the interest of existing and active

Steem or other SMT community members. Through these tools, community managers

and entrepreneurs launching a token may leverage existing user bases to accelerate the

distribution of the SMT to a target market.

Monetizing with Shared Token Rewards

All Steem based interfaces have the option of splitting token rewards among a set of

arbitrary recipients, which could include an interface, community manager, referrer, a

paid position donation pool, and more. An interface can also provide this optionality

6

of how to split the tokens to the authors. The number of potential Reward Sharing

beneficiaries is initially soft capped by block producers at eight while the feature proves

its use, however the blockchain is capable of handling up to 256 beneficiaries per post.

Can My Entity Participate in SMTs?

An SMT can be launched by a person or entity; they only need 1 USD to cover the network

fee (this fee prevents spam and unused tokens while accruing value to the network), and

a namespace on Steem - which can be obtained by registering at anon.steem.network,

steemit.com, steemconnect.com, or any other Steem sign-up service.

Once an account name to register the token with is secured, the account issues the token

by using a Steem-based command line tool or any tool created in the future to support

token launches. The token can be structured to support an initial sale or distribution of

the token. Certain properties of an SMT, such as its inflation rate, must also be defined

by the person or entity creating the token. These properties dictate how the token is used

inside applications and respective communities.

From launch, the token becomes immutable on the blockchain, and leveraged correctly,

the token can have dramatic effects on the growth of businesses that choose to integrate

these tokens.

Use Cases

We have identified five ways in which existing businesses and future entrepreneurs can

leverage specially designed SMTs to transform the internet. Among these use cases you

may discover other ways of structuring and leveraging tokens inside applications. This list

is by no means exhaustive, and we will update this paper as more use cases demonstrate

their value.

1 - Content Publishers - Single Token Support

A mainstream media website’s growth has been slowing and they are looking for ways

to get ahead of the changing tech landscape. The website migrates to a Disqus-like

application based on Steem, or taps directly into Steem APIs for a custom integration.

Now their subscribers can be rewarded with cryptocurrency while commenting. When

the website is ready, they can issue their own token through the comments interface - the

token will allow them to 1) raise capital by selling tokens 2) catalyze autonomous growth.

7

Figure 1: Single Token Content Publishers

2 - Forums - Multiple Token Support

An up-and-coming forum business is looking to integrate cryptocurrency to create cash

flow and spark growth to get the business to the next level, however they are not cryptocurrency security experts and would prefer not to host a cryptocurrency wallet. They

issue an SMT and integrate it into their website. Focusing solely on the social aspects, the

forum business can integrate other applications, such as SteemConnect into their forum

to handle the wallet and transfer capabilities. This allows them to focus on their business

(growing communities) without focusing on the security aspects of cryptocurrency. The

forum enables additional tokens to be exposed or launched, to represent specific topics

of discussion. The ability to launch these tokens can be retained by the company behind

the website, or granted to the website’s community managers. Tokens dedicated to the

website’s specific topics will further spur autonomous growth of the website niche by niche.

An example of this multi-token model could eventually be found in organizations such as

ChainBB (chainbb.com) if it were to enable its own globally available token on its domain,

8

as well as narrowly available tokens for specific community niches - such as “gardening.”

Figure 2: Multiple tokens Forum

3 - Comments Widget for Online Publishers

One of the ways in which publishers will be onboarded faster to SMT integrations is by

offering a Steem-based comments widget that can easily be integrated into existing blogs

that are built on software such as WordPress and Blogger. The developer employing

the widget would be able to take a percentage of the tokens (called “Shared Rewards”)

distributed to the commenters for themselves, thereby creating a business opportunity for

the next generation of Disqus-like companies that are cryptocurrency enabled. It would

alleviate the burdens of transaction signing support, private key management, wallet

functionality, and hosting costs for the publisher - by outsourcing all of these functions

to the comments widget maintainer.

9

Figure 3: Comment Widget

4 - Sub-Community Moderators and Managers

Imagine you are a moderator for a specific topic inside a forum, such as a Reddit “subreddit” or a Steemit “community”. If a website integrates SMTs for these specific topics,

then the topic moderator/s can launch these tokens to empower the subscribers of their

topic, raise funds, and increase the quality of content curation for the community.

10

Figure 4: Sub-community

5 - Arbitrary Assets - Tokens Representing Real World Assets

Let’s examine an instance in which an entrepreneur is looking to provide liquidity in the

Steem ecosystem. The entrepreneur can issue an SMT without inflation properties, and

imply that they will provide structure to peg it to USD (or any other debt, contract, or

asset), making it like an IOU or basic derivative. The structure they provide to the asset

includes buying and selling it near $1, similar to Tether. The entrepreneur sets up bank

wire capabilities for buying and selling, and takes a small % on each transaction. The

derivative trades against STEEM, and also brings capital into the ecosystem to be used

across all tokens.

11

Figure 5: IOU Asset Token Exchange

Owner’s manual

This manual will explain the nuts and bolts of how SMTs work. The intended audience

is technical users who want to create their own SMT.

Create a control account

The first step to creating an SMT is to create a control account for the SMT. Any STEEM

account may serve as a control account, however it is highly recommended to create a

dedicated account solely for the purpose. It is also highly recommended that a control

account does not post, vote, or hold any STEEM, SBD, or other tokens (other than a

small amount of vested STEEM for transaction bandwidth).

12

The control account’s name will not occupy a high visibility position in most user interfaces, so it does not much matter if the control account’s name is not the best match for

the SMT brand.

Control account security

Security on the control account is important for persons who plan to use the account post

launch:

• The control account should use 2-of-3 or 3-of-5 multi-signature security.

• The control account’s authorities should have other accounts, not specific keys, as

multi-signature members.

• For additional security, each of the accounts in the control account’s multi-signature

group should itself use multi-signature security.

• A subset of keys should be kept offline, in air-gapped machines.

• Transactions should be generated by an online interface, and physically transferred

to the air-gapped machines via removable media.

• Signatures should be returned via physically removable media to the online system

for transmission via the UI.

Of course, once authorities are set up, you should verify the account is still able to transact.

It is advisable to test your authorities and transaction signing setup using a testnet, or a

less-important account on the main network.

Once the token is launched, you may consider burning the account’s keys by assigning

them to @null, initiating a token for which the dynamic properties can never be adjusted.

Token consensus

Since tokens participate in atomic transactions also involving STEEM, they have been

designed as part of the STEEM blockchain’s consensus.

Token Generation and Initialized Parameters

SMT object creation

The first operation to be executed is an smt_create_operation. This operation creates

an SMT object in the blockchain state. After executing the smt_create_operation, the

newly created SMT object is not yet fully configured.

Most of the configuration occurs in subsequent operations (smt_set_setup_parameters_operation,

smt_setup_inflation_operation and smt_setup_operation). These later operations

may occur in the same transaction, but they may also occur at any later point in time.

struct smt_create_operation

{

account_name_type control_account;

asset

smt_creation_fee;

asset_symbol_type symbol;

extensions_type

extensions;

};

13

Numerical asset identifiers

An SMT is referred to by a numerical asset identifier or NAI, consisting of two at-signs

followed by nine decimal digits, for example @@314159265. The blockchain enforces that

the identifier placed by a UI into the smt_create_operation must match the result of

the get_next_smt_identifier RPC. Therefore, an NAI cannot be chosen freely by the

SMT creator. It is not even possible to “mine” a “vanity NAI” (analogous to the “vanity

Bitcoin address” some people use).

The reason for this restriction is that the blockchain designers want to discourage users

from using the consensus level identifiers as symbol names, and instead use a nonconsensus directory system to attach human meaningful symbols to assets. Distinguishing

a “namesquatter” from the legitimate owner of a brand is not something that a blockchain

can do, especially if the squatter is willing to pay the SMT creation fee.

SMT naming

The solution to the namesquatting problem is to publish an asset directory mapping NAIs

to names. An asset directory is non-consensus, meaning that all blockchain operations

are serialized only with NAIs. Asset names are only used for UI presentation.

A UI may include an asset directory as a file, URL, or a blockchain account which publishes

directory entries with custom operations. The publisher of an asset directory should

ensure that directory entries meet whatever standards of legitimate brand ownership the

publisher chooses to enforce.

SMT creation fee

Issuing a smt_create_operation requires payment of smt_creation_fee. The amount

required is set by the smt_creation_fee field of dynamic_global_properties_object.

This field may contain a value in STEEM or SBD. If specified in SBD, an equivalent

amount of STEEM will be accepted, at the current price feed.

Initially, smt_creation_fee will be set to 1 SBD, and no means will be provided

to update it. Updates to the smt_creation_fee amount may occur in future hardforks, however, so user-agents should read the smt_creation_fee value from the

dynamic_global_properties_object. User-agents should not assume the fee will

always be 1 SBD and they should be prepared to charge a separate fee paid to the

user-agent if the aim of the interface is to enable only a curated set of tokens.

The fee is destroyed by sending it to STEEM_NULL_ACCOUNT.

SMT pre-setup

Two pre-setup operations are included:

smt_setup_inflation_operation and

smt_setup_parameters. These operations must be issued after smt_create_operation,

and before smt_setup_operation. They may be issued in the same transaction, or in

prior blocks.

The reason pre-setup operations are not made a part of smt_setup_operation is to allow

a large number of pre-setup operations to be executed over multiple blocks.

14

SMT setup

Each SMT has an associated descriptor object which has permanent configuration

data. This data cannot be changed after launch! The descriptor is set by the

smt_setup_operation:

struct smt_setup_operation

{

account_name_type

control_account;

asset_symbol_type

smt_name;

int64_t

max_supply = STEEM_MAX_SHARE_SUPPLY;

smt_generation_policy

initial_generation_policy;

time_point_sec

time_point_sec

time_point_sec

time_point_sec

generation_begin_time;

generation_end_time;

announced_launch_time;

launch_expiration_time;

extensions_type

extensions;

};

The symbol precision in smt_setup_operation is authoritative. It may differ from, and

will override, any previously specified operations’ precision. Subsequently issued operations must have matching precision.

The operation must be signed by the control_account key. The named SMT must have

been created earlier by the control_account. The symbol’s embedded decimal places

may be distinct from prior smt_setup_operation.

The decimal_places field is used by UIs to display units as a number of decimals.

The generation_begin_time is when participants can begin to contribute to the ICO.

It is allowed to be in the future so users have time to study the ICO’s final terms before

the ICO begins.

The generation_end_time is when the ICO stops accepting contributions, and

the announced_launch_time is when the ICO token is created (assuming the ICO

reached the minimum participation level). Some pause is allocated between the

generation_end_time and announced_launch_time to allow for the possibility of

ICOs that wish to have hidden caps that aren’t revealed while the ICO is open for

contributions. It also gives the ICO creator time to use the final ICO numbers to aid in

pre-launch business activities.

At launch_expiration_time, if the ICO has not yet launched, all contributors will be

automatically refunded (with virtual operations) and the ICO will be cancelled. The

symbol will remain reserved to the specified control_account. However, in order to

launch the token, an smt_create_operation must be issued and the smt_creation_fee

must be paid again.

15

Token units

Initial token generation is driven by a contributions of STEEM units from contributors.

To simplify rounding concerns, a contribution must be an integer number of STEEM

units. The ICO creator sets the size of a STEEM unit - it can be large or small. It is

better to keep the unit small (for example, 1 STEEM or 0.1 STEEM), as this allows the

ICO to be accessible to the maximum possible audience.

A STEEM unit also specifies a routing policy which determines where the STEEM goes

when the token launches. (STEEM for tokens which do not launch may be refunded on

demand.) The routing policy may split the STEEM in the unit among multiple parties.

When the ICO occurs, the tokens are generated in token units. Multiple token units are

generated per STEEM unit contributed. Token units also have a routing policy.

The units and their routing policies are specified in the smt_generation_unit structure:

struct smt_generation_unit

{

flat_map< account_name_type, uint16_t >

flat_map< account_name_type, uint16_t >

};

steem_unit;

token_unit;

Each (key, value) pair in the flat_map determines the routing of some satoshis. The

total STEEM/tokens in each unit is simply the sum of the values.

Unit ratios

When an SMT launches, token units are created for STEEM units in a R-for-1 ratio. The number R is called the unit ratio. Maximum and minimum allowable values

for R are specified respectively in the min_unit_ratio and max_unit_ratio fields of

smt_generation_policy.

The maximum number of token units that can be created in the ICO is limited to

max_token_units_generated, a parameter which is set by the ICO creator. (More tokens can be created after the token has launched, but this later creation is called inflation

and is not considered to be part of the ICO.)

The unit ratio is set to the largest integer that would not result in exceeding

max_token_units_generated for the number of STEEM units actually contributed.

Cap and min

ICOs may specify a minimum number of STEEM units min_steem_units. If the ICO

does not reach min_steem_units before generation_end_time, then it does not occur,

and contributors become eligible for refunds.

Likewise, ICOs may specify two maximum numbers of STEEM units: A hard cap and

a soft cap. Units in excess of the soft cap have different routing for their STEEM and

tokens. STEEM units in excess of the hard cap are rejected and do not generate any

SMTs.

16

The effects of the soft cap are divided proportionally among all contributors. I.e. if a

ICO has a soft cap of 8 million STEEM, and 10 contributors each contribute 1 million

STEEM, then 0.2 million of each user’s STEEM is routed via the soft cap’s policy.

The effects of the hard cap fall solely on the last contributors. I.e. if a ICO has a hard

cap of 8 million STEEM, and 10 contributors each contribute 1 million STEEM, then

the first 8 users fully participate in the ICO, and the last 2 users are refunded 1 million

STEEM.

Hidden caps

The min and hard caps are hidden in the generation policy. This means that these

numbers are fixed at setup time, but the ICO creator has the option to keep them secret.

This functionality is implemented by a commit/reveal cryptographic protocol: A hash

called the commitment is published at setup time, and the actual amount must match

the commitment. (A nonce is also included in the hash to prevent an attacker from finding

the hidden cap with a brute-force guess-and-test approach.)

The SMT designer may wish to pre-publish a guarantee that the hidden values are within

a certain range. The lower_bound and upper_bound fields provide this functionality: A

revealed amount that is not in the specified range is treated the same as a hash mismatch.

struct smt_cap_commitment

{

share_type

lower_bound;

share_type

upper_bound;

digest_type

hash;

};

struct smt_revealed_cap

{

share_type

uint128_t

};

amount;

nonce;

struct smt_cap_reveal_operation

{

account_name_type

control_account;

smt_revealed_cap

cap;

extensions_type

extensions;

};

All caps are hidden, but the cap may be revealed at any point in time. Therefore, an

ICO with a non-hidden minimum or cap may be implemented by simply including the

smt_cap_reveal_operation in the same transaction as the smt_setup_operation. UIs

should provide functionality for this.

A UI should provide one or more of the following means to ensure the nonce and amount

are recoverable:

• Force the user to type in the amount and nonce again, as confirmation they have

been backed up.

17

• Set nonce to some deterministic function of the private key and public data, for example nonce = H(privkey + control_account + lower_bound + upper_bound

+ current_date).

• Provide functionality to brute-force the uncertain fields when the nonce is known

(e.g. the current date and amount).

• Require the amount to be low-entropy to facilitate brute-forcing when the nonce is

known (e.g. a number between 1-999 times a power of 10).

Generation policy data structure

The SMT generation policy data structure looks like this:

struct smt_capped_generation_policy

{

smt_generation_unit pre_soft_cap_unit;

smt_generation_unit post_soft_cap_unit;

smt_cap_commitment

smt_cap_commitment

min_steem_units_commitment;

hard_cap_steem_units_commitment;

uint16_t

soft_cap_percent = 0;

uint32_t

uint32_t

min_unit_ratio = 0;

max_unit_ratio = 0;

extensions_type

extensions;

};

Note, the max_token_units_generated parameter does not appear anywhere in the operation. The reason is that it is actually a derived parameter: max_token_units_generated

= min_unit_ratio * hard_cap_steem_units.

Additionally, the smt_generation_policy is defined as a static_variant, of which

smt_capped_generation_policy is the only member:

typedef static_variant< smt_capped_generation_policy > smt_generation_policy;

This typedef allows the potential for future protocol versions to allow additional generation policy semantics with different parameters.

Examples and rationale

Example ICO

ALPHA wants to sell a token to the crowd to raise funds where: 70% of contributed

STEEM goes to the Alpha Organization Account (@alpha_org), 23% of contributed

STEEM goes to Founder Account A (@founder_a), and 7% of contributed STEEM goes

to Founder Account B (@founder_b).

ALPHA defines a STEEM unit as:

steem_unit = [["alpha_org", 70], ["founder_a", 23], ["founder_b", 7]]

18

This STEEM-unit contains 100 STEEM-satoshis, or 0.1 STEEM.

For every 1 STEEM contributed, an ALPHA contributer will receive 5 ALPHA tokens,

and Founder Account D will receive 1 ALPHA token. This five-sixths / one-sixth split is

expressed as:

token_unit = [["$from", 5], ["founder_c", 1]]

This ratio is defined in the following data structure:

struct smt_generation_unit

{

flat_map< account_name_type, uint16_t >

flat_map< account_name_type, uint16_t >

};

steem_unit;

token_unit;

This token-unit contains 6 ALPHA-satoshis, or 0.0006 ALPHA (if ALPHA has 4 decimal

places).

Next we define the unit ratio as the relative rate at which token_unit are issued as

steem_unit are contributed. So to match the specification of 6 ALPHA per 1 STEEM,

we need to issue 1000 ALPHA-units per STEEM-unit. Therefore the unit ratio of this

ICO is 1000. This unit ratio is placed in the min_unit_ratio and max_unit_ratio fields

of the smt_capped_generation_policy data structure:

min_unit_ratio = 1000

max_unit_ratio = 1000

A special account name, $from, represents the contributor.

Also supported is

$from.vesting, which represents the vesting balance of the $from account.

Why unit ratios?

Why does the blockchain use unit ratios, rather than simply specifying prices?

The answer is that it is possible to write ICO definitions for which price is ill-defined. For

example:

•

•

•

•

"$from" does not occur in token_unit.

"$from" occurs in both token_unit and steem_unit.

A combination of "$from" and "$from.vesting" occurs.

Future expansion allows new special accounts.

All of these ICO definitions have a unit ratio, but defining a single quantity to call “price”

is complicated or impossible for ICOs like these.

UI treatment of unit ratios

As a consequence of the above, the concept of “ICO price” is purely a UI-level concept.

UIs which provide an ICO price should do the following:

• Document the precise definition of “price” provided by the UI.

• Be well-behaved for pathological input like above.

• Have a button for switching between a unit ratio display and price display.

19

Hidden cap FAQ

• Q: Should my ICO have a cap?

• A: Some set of people stay away from uncapped ICOs due to perceived “greed”, or

want a guaranteed lower bound on the percentage of the ICO their contribution will

buy. If you want this set of people to participate, use a cap.

• Q: Should my cap be hidden?

• A: Some people like the transparency and certainty of a public cap. Other people

think a hidden cap creates excitement and builds demand. One possible compromise

is to publish the previous and next power of 10, for example “this ICO’s cap is

between 1 million and 10 million STEEM.”

• Q: How do I disable the cap?

• A: Set it so that the cap would occur above STEEM_MAX_SHARE_SUPPLY.

Launch

The effective launch time is the time at which tokens become transferable. Two possibilities occur based on the timing of revealing of the hard cap:

• When min_steem_units and hard_cap_steem_units are revealed before the

announced_launch_time, the launch is an on-time launch. The launch logic is

executed by the blockchain as soon as announced_launch_time arrives, regardless

of further user action.

• When min_steem_units and hard_cap_steem_units have not been revealed before

the announced_launch_time, the launch will be a delayed launch. The launch logic

is executed by the blockchain when min_steem_units and hard_cap_steem_units

have been revealed.

• If the launch is delayed, then any contributor may use smt_refund_operation to

get their STEEM back at any time after announced_launch_time, and before the

launch logic is executed.

The reasons for this design are as follows:

• The hidden cap isn’t published immediately (that’s the definition of hidden).

• Publishing the hidden cap is an action that must be done by the ICO creator (again,

any action requiring non-public information to occur cannot happen automatically

on a blockchain).

• If the ICO creator never acts, then the launch logic will never execute.

• In the case of such a malicious or unresponsive ICO creator, contributors’ STEEM

would effectively be trapped forever, and they would never receive any tokens.

• To keep the STEEM from being trapped in this way, the smt_refund_operation

is implemented.

struct smt_refund_operation

{

account_name_type

contributor;

asset

amount;

extensions_type

extensions;

};

20

Note, users are not required to use smt_refund_operation; each individual contributor

must opt-in to receiving a refund. If the ICO creator publicizes a legitimate reason they

failed to publish before announced_launch_time, it is possible that all/most contributors

will voluntarily choose not to use smt_refund_operation. In this case, the launch will

occur as soon as the ICO creator publishes the hidden values.

The launch logic considers a contribution followed by a refund to be equivalent to not

having contributed at all. Therefore, when a delayed launch occurs, each contributor will

be in exactly one of the following two states:

• The contributor has executed smt_refund_operation, received their STEEM back,

and will not participate in the ICO.

• The contributor has not been issued a refund, and will participate in the ICO.

It is possible for a delayed launch to have exceeded its min_steem_units value at the

announced launch time, but subsequently falls below its min_steem_units value as a

result of refunds. In such a case, the ICO will not occur; it will be treated as if it had

never reached its min_steem_units.

Full JSON examples

ALPHA

This example builds on the ALPHA example from earlier. This ICO has the following

characteristics:

•

•

•

•

•

•

•

•

70% of contributed STEEM goes to Alpha Organization Account (@alpha_org).

23% of contributed STEEM goes to Founder Account A (@founder_a).

7% of contributed STEEM goes to Founder Account B (@founder_b).

Minimum unit of contribution is 0.1 STEEM.

For every 1 STEEM contributed, the contributor gets 5 ALPHA (@contibutor_a).

For every 1 STEEM contributed, Founder Account C gets 1 ALPHA (@founder_c).

No minimum, hard cap, or soft cap.

No post-launch inflation after launch.

21

Figure 6: Alpha ICO Flow

These are the operations for the ALPHA launch:

[

["smt_setup",

{

"control_account" : "alpha",

"decimal_places" : 4,

"max_supply" : "1000000000000000",

"initial_generation_policy" : [0,

{

"pre_soft_cap_unit" : {

"steem_unit" : [["alpha_org", 70], ["founder_a", 23], ["founder_b", 7]],

"token_unit" : [["$from", 5], ["founder_c", 1]]

},

"post_soft_cap_unit" : {

"steem_unit" : [],

"token_unit" : []

},

"min_steem_units_commitment" : {

"lower_bound" : 1,

"upper_bound" : 1,

"hash" : "32edb6022c0921d99aa347e9cda5dc2db413f5574eebaaa8592234308ffebd2b"

},

22

"hard_cap_steem_units_commitment" : {

"lower_bound" : "166666666666",

"upper_bound" : "166666666666",

"hash" : "93c5a6b892de788c5b54b63b91c4b692e36099b05d3af0d16d01c854723dda21"

},

"soft_cap_percent" : 10000,

"min_unit_ratio" : 1000,

"max_unit_ratio" : 1000,

"extensions" : []

}

],

"generation_begin_time" : "2017-08-10T00:00:00",

"generation_end_time" : "2017-08-17T00:00:00",

"announced_launch_time" : "2017-08-21T00:00:00",

"smt_creation_fee" : "1000.000 SBD",

"extensions" : []

}

],

["smt_cap_reveal",

{

"control_account" : "alpha",

"cap" : { "amount" : 1, "nonce" : "0" },

"extensions" : []

}

],

["smt_cap_reveal",

{

"control_account" : "alpha",

"cap" : { "amount" : "166666666666", "nonce" : "0" },

"extensions" : []

}

]

]

Some things to note:

• We disable the soft cap by setting soft_cap_percent to STEEM_100_PERCENT =

10000.

• post_soft_cap_unit must be empty when the soft cap is disabled.

• The unit ratio does not change so min_unit_ratio / max_unit_ratio must be set

accordingly.

• We disable the hidden caps by using a zero nonce and setting lower_bound

==

upper_bound.

• We still need to reveal the caps with smt_cap_reveal_operation.

• The hard cap specified is the largest hard cap that does not result in created tokens

exceeding STEEM_MAX_SHARE_SUPPLY.

BETA

The BETA token is created with the following rules:

• For every 5 STEEM contributed, 3 STEEM go to founder account Fred.

23

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

For every 5 STEEM contributed, 2 STEEM go to founder account George.

10% of the initial token supply goes to founder account George.

20% of the initial token supply goes to founder acconut Henry.

70% of the initial token supply is divided among contributors according to their

contribution.

Each STEEM unit is 0.005 STEEM.

Each token unit is 0.0010 BETA.

The minimum raised is 5 million STEEM units, or 25,000 STEEM.

The maximum raised is 30 million STEEM units, or 150,000 STEEM.

Each contributor receives 7-14 BETA per STEEM contributed, depending on total

contributions.

George receives 1-2 BETA per STEEM contributed, depending on total contributions.

Harry receives 2-4 BETA per STEEM contributed, depending on total contributions.

If the maximum of 30 million STEEM units are raised, then min_unit_ratio

=

50 applies.

The maximum number of token units is min_unit_ratio times 30 million, or 1.5

billion token units.

Since each token unit is 0.0010 BETA, at most 1.5 million BETA tokens will be

generated.

If 75,000 STEEM or less is contributed, the contributors George and Harry will

receive the maximum of 14, 2, and 4 BETA per STEEM contributed (respectively).

If more than 75,000 STEEM is contributed, the contributors, George and Harry

will receive BETA in a 70% / 10% / 20% ratio, such that the total is fixed at 1.5

million BETA.

As a consequence of the hard cap, the contributors, George and Harry will receive

at least 7, 1, and 2 BETA per STEEM contributed (respectively).

This example is chosen to demonstrate how the ratios work. It is not a realistic example,

as most ICOs will choose to either set min_unit_ratio = max_unit_ratio like ALPHA,

or choose to use a large max_unit_ratio like BETA.

[

[

"smt_setup",

{

"control_account" : "beta",

"decimal_places" : 4,

"max_supply" : "1000000000000000",

"initial_generation_policy" : [0,

{

"pre_soft_cap_unit" : {

"steem_unit" : [["fred", 3], ["george", 2]],

"token_unit" : [["$from", 7], ["george", 1], ["henry", 2]]

},

"post_soft_cap_unit" : {

"steem_unit" : [],

"token_unit" : []

},

"min_steem_units_commitment" : {

"lower_bound" : 5000000,

"upper_bound" : 5000000,

24

"hash" : "dff2e4aed5cd054439e045e1216722aa8c4758b22df0a4b0251d6f16d58e0f3b"

},

"hard_cap_steem_units_commitment" : {

"lower_bound" : 30000000,

"upper_bound" : 30000000,

"hash" : "f8e6ab0e8f2c06a9d94881fdf370f0849b4c7864f62242040c88ac82ce5e40d6"

},

"soft_cap_percent" : 10000,

"min_unit_ratio" : 50,

"max_unit_ratio" : 100,

"extensions" : []

}

],

"generation_begin_time" : "2017-06-01T00:00:00",

"generation_end_time" : "2017-06-30T00:00:00",

"announced_launch_time" : "2017-07-01T00:00:00",

"smt_creation_fee" : "1000.000 SBD",

"extensions" : []

}

],

[

"smt_cap_reveal",

{

"control_account" : "beta",

"cap" : { "amount" : 5000000, "nonce" : "0" },

"extensions" : []

}

],

[

"smt_cap_reveal",

{

"control_account" : "beta",

"cap" : { "amount" : 30000000, "nonce" : "0" },

"extensions" : []

}

]

]

This spreadsheet will make the relationship clear.

GAMMA

The GAMMA token is like BETA, but with one difference: The large max_unit_ratio

means that the maximum issue of 1.5 million tokens is reached very early in the ICO.

This ICO effectively divides 1.5 million GAMMA tokens between contributors (provided

at least 5 STEEM is contributed).

[

[

"smt_setup",

{

25

"control_account" : "gamma",

"decimal_places" : 4,

"max_supply" : "1000000000000000",

"initial_generation_policy" : [0,

{

"pre_soft_cap_unit" : {

"steem_unit" : [["fred", 3], ["george", 2]],

"token_unit" : [["$from", 7], ["george", 1], ["henry", 2]]

},

"post_soft_cap_unit" : {

"steem_unit" : [],

"token_unit" : []

},

"min_steem_units_commitment" : {

"lower_bound" : 5000000,

"upper_bound" : 5000000,

"hash" : "dff2e4aed5cd054439e045e1216722aa8c4758b22df0a4b0251d6f16d58e0f3b"

},

"hard_cap_steem_units_commitment" : {

"lower_bound" : 30000000,

"upper_bound" : 30000000,

"hash" : "f8e6ab0e8f2c06a9d94881fdf370f0849b4c7864f62242040c88ac82ce5e40d6"

},

"soft_cap_percent" : 10000,

"min_unit_ratio" : 50,

"max_unit_ratio" : 300000,

"extensions" : []

}

],

"generation_begin_time" : "2017-06-01T00:00:00",

"generation_end_time" : "2017-06-30T00:00:00",

"announced_launch_time" : "2017-07-01T00:00:00",

"smt_creation_fee" : "1000.000 SBD",

"extensions" : []

}

],

[

"smt_cap_reveal",

{

"control_account" : "gamma",

"cap" : { "amount" : 5000000, "nonce" : "0" },

"extensions" : []

}

],

[

"smt_cap_reveal",

{

"control_account" : "gamma",

"cap" : { "amount" : 30000000, "nonce" : "0" },

"extensions" : []

}

26

]

]

DELTA

In this ICO we have one million DELTA tokens created for the founder, and none for

contributors. A modest contribution of 0.1 STEEM can be made by any user (including

the founder themselves) to trigger the generation.

[

[

"smt_setup",

{

"control_account" : "delta",

"decimal_places" : 5,

"max_supply" : "1000000000000000",

"initial_generation_policy" : [0,

{

"pre_soft_cap_unit" : {

"steem_unit" : [["founder", 1]],

"token_unit" : [["founder", 10000]]

},

"post_soft_cap_unit" : {

"steem_unit" : [],

"token_unit" : []

},

"min_steem_units_commitment" : {

"lower_bound" : 10000000,

"upper_bound" : 10000000,

"hash" : "4e12522945b8cc2d87d54debd9563a1bb6461f1b1fa1c31876afe3514e9a1511"

},

"hard_cap_steem_units_commitment" : {

"lower_bound" : 10000000,

"upper_bound" : 10000000,

"hash" : "4e12522945b8cc2d87d54debd9563a1bb6461f1b1fa1c31876afe3514e9a1511"

},

"soft_cap_percent" : 10000,

"min_unit_ratio" : 1000,

"max_unit_ratio" : 1000,

"extensions" : []

}

],

"generation_begin_time" : "2017-06-01T00:00:00",

"generation_end_time" : "2017-06-30T00:00:00",

"announced_launch_time" : "2017-07-01T00:00:00",

"smt_creation_fee" : "1000.000 SBD",

"extensions" : []

}

],

[

"smt_cap_reveal",

27

{

"control_account" : "delta",

"cap" : { "amount" : 10000000, "nonce" : "0" },

"extensions" : []

}

],

[

"smt_cap_reveal",

{

"control_account" : "delta",

"cap" : { "amount" : 10000000, "nonce" : "0" },

"extensions" : []

}

]

]

Vesting contributions

It is possible to send part or all of contributions to a vesting balance, instead of permitting

immediate liquidity. This example puts 95% in vesting.

"token_unit"

: [["$from.vesting", 95], ["$from", 5]]

Burning contributed STEEM

In this ICO, the STEEM is permanently destroyed rather than going into the wallet of

any person. This mimics the structure of the Counterparty ICO.

{

"steem_unit" : [["null", 1]],

"token_unit" : [["$from", 1]]

}

Vesting as cost

In this ICO, you don’t send STEEM to the issuer in exchange for tokens. Instead, you

vest STEEM (to yourself), and tokens are issued to you equal to the STEEM you vested.

{

"steem_unit" : [["$from.vesting", 1]],

"token_unit" : [["$from", 1]]

}

Non-STEEM & Hybrid ICO’s

ICOs using non-STEEM contributions – for example, SBD, BTC, ETH, etc. – cannot

be done fully automatically on-chain. However, such ICOs can be managed by manually

transferring some founder account’s distribution to buyers’ Steem accounts in proportion

to their non-STEEM contribution.

28

Inflation Parameters

Creation of SMT after launch is called inflation.

Inflation is the means by which the SMT rewards contributors for the value they provide.

Inflation events use the following data structure:

struct smt_inflation_unit

{

flat_map< account_name_type, uint16_t >

};

token_unit;

// Event: Support issuing tokens to target at time

struct token_inflation_event

{

timestamp

schedule_time;

smt_inflation_unit unit;

uint32_t

num_units;

};

This event prints num_units units of the SMT token.

Possible inflation target

The target is the entity to which the inflation is directed. The target may be a normal

Steem account controlled by an individual founder, or a multi-signature secured account

comprised of several founders.

In addition, several special targets are possible representing trustless functions provided

by the blockchain itself:

• Rewards. A special destination representing the token’s posting / voting rewards.

• Vesting. A special destination representing the tokens backing vested tokens.

Event sequences

Traditionally blockchains compute inflation on a per-block basis, as block production

rewards are the main (often, only) means of inflation.

However, there is no good reason to couple inflation to block production for SMTs. In fact,

SMTs have no block rewards, since they have no blocks (the underlying functionality of

block production being supplied by the Steem witnesses, who are rewarded with STEEM).

Repeating inflation at regular intervals can be enabled by adding interval_seconds and

interval_count to the token_inflation_event data structure. The result is a new

data structure called token_inflation_event_seq_v1:

// Event seq v1: Support repeatedly issuing tokens to target at time

struct token_inflation_event_seq_v1

{

timestamp

schedule_time;

smt_inflation_unit unit;

asset

new_smt;

29

int32_t

uint32_t

interval_seconds;

interval_count;

};

The data structure represents a token inflation event that repeats every interval_seconds

seconds, for interval_count times. The maximum integer value 0xFFFFFFFF is a special

sentinel value that represents an event sequence that repeats forever.

Note, the new_smt is a quantity of SMT, not a number of units. The number of units is

determined by dividing new_smt by the sum of unit members.

Adding relative inflation

Often, inflation schedules are expressed using percentage of supply, rather than in absolute

terms:

// Event seq v2: v1 + allow relative amount of tokens

struct token_inflation_event_seq_v2

{

timestamp

schedule_time;

smt_inflation_unit unit;

uint32_t

num_units;

int32_t

uint32_t

interval_seconds;

interval_count;

asset

uint32_t

abs_amount;

rel_amount_numerator;

};

Then we compute new_smt as follows from the supply:

rel_amount = (smt_supply * rel_amount_numerator) / SMT_REL_AMOUNT_DENOMINATOR;

new_smt = max( abs_amount, rel_amount );

If we set SMT_REL_AMOUNT_DENOMINATOR to a power of two, the division can be optimized

to a bit-shift operation. To gain a more dynamic range from the bits, we can let the shift

be variable:

// Event seq v3: v2 + specify shift in struct

struct token_inflation_event_seq_v3

{

timestamp

schedule_time;

smt_inflation_unit unit;

int32_t

uint32_t

interval_seconds;

interval_count;

asset

uint32_t

uint8_t

abs_amount;

rel_amount_numerator;

rel_amount_denom_bits;

};

Then the computation becomes:

30

rel_amount = (smt_supply * rel_amount_numerator) >> rel_amount_denom_bits;

new_smt = max( abs_amount, rel_amount );

Of course, the implementation of these computations must carefully handle potential

overflow in the intermediate value smt_supply * rel_amount_numerator!

Adding time modulation

Time modulation allows implementing an inflation rate which changes continuously over

time according to a piecewise linear function. This can be achieved by simply specifying the left/right endpoints of a time interval, and specifying absolute amounts at both

endpoints:

// Event seq v4: v3 + modulation over time

struct token_inflation_event_seq_v4

{

timestamp

schedule_time;

smt_inflation_unit unit;

int32_t

uint32_t

interval_seconds;

interval_count;

timestamp

timestamp

lep_time;

rep_time;

asset

asset

uint32_t

uint32_t

lep_abs_amount;

rep_abs_amount;

lep_rel_amount_numerator;

rep_rel_amount_numerator;

uint8_t

rel_amount_denom_bits;

};

Some notes about this:

• Only the numerator of relative amounts is interpolated, the denominator is the same

for both endpoints.

• For times before the left endpoint time, the amount at the left endpoint time is

used.

• For times after the right endpoint time, the amount at the right endpoint time is

used.

Code looks something like this:

if( now <= lep_time )

{

abs_amount = lep_abs_amount;

rel_amount_numerator = lep_rel_amount_numerator;

}

else if( now >= rep_time )

{

abs_amount = rep_abs_amount;

rel_amount_numerator = rep_rel_amount_numerator;

31

}

else

{

// t is a number between 0.0 and 1.0

// this calculation will need to be implemented

// slightly re-arranged so it uses all integer math

t = (now - lep_time) / (rep_time - lep_time)

abs_amount = lep_abs_amount * (1-t) + rep_abs_amount * t;

rel_amount_numerator = lep_rel_amount_numerator * (1-t) + rep_rel_amount_numerator * t;

}

Inflation operations

The inflation operation is specified as follows:

struct smt_setup_inflation_operation

{

account_name_type

control_account;

timestamp

smt_inflation_unit

schedule_time;

inflation_unit;

int32_t

uint32_t

interval_seconds = 0;

interval_count = 0;

timestamp

timestamp

lep_time;

rep_time;

asset

asset

uint32_t

uint32_t

lep_abs_amount;

rep_abs_amount;

lep_rel_amount_numerator = 0;

rep_rel_amount_numerator = 0;

uint8_t

rel_amount_denom_bits = 0;

extensions_type

extensions

};

The setup_inflation_operation is a pre-setup operation which must be executed before

the smt_setup_operation. See the section on pre-setup operations.

Inflation FAQ

• Q: Can the SMT inflation data structures express Steem’s current inflation scheme?

• A: Yes (except for rounding errors).

• Q: Can the SMT inflation data structures reward founders directly after X

months/years?

• A: Yes.

• Q: I don’t care about time modulation. Can I disable it?

32

• A: Yes, just set the lep_abs_amount == rep_abs_amount and lep_rel_amount_numerator

== rep_rel_amount_numerator to the same value, and set lep_time = rep_time

(any value will do).

• Q: Can some of this complexity be hidden by a well-designed UI?

• A: Yes.

• Q: Can we model the inflation as a function of time with complete accuracy?

• A: The inflation data structures can be fully modeled / simulated. For some issue

structures, the amount issued depends on how much is raised, so the issue structures

cannot be modeled with complete accuracy.

Named token parameters

Some behaviors of STEEM are influenced by compile-time configuration constants which

are implemented by #define statements in the steemd C++ source code. It makes sense

for the equivalent behaviors for SMTs to be configurable by the SMT creator.

These parameters are runtime_parameters and setup_parameters. The setup_parameters

are a field in smt_setup_operation; they must be set before smt_setup_operation, and

cannot be changed once smt_setup_operation is executed. The runtime_parameters

are a field in smt_set_runtime_parameters_operation, and they can be changed by

the token creator at any time.

These operations are defined as follows:

struct smt_set_setup_parameters_operation

{

account_name_type

flat_set< smt_setup_parameter >

extensions_type

control_account;

setup_parameters;

extensions;

};

struct smt_set_runtime_parameters_operation

{

account_name_type

flat_set< smt_runtime_parameter >

extensions_type

control_account;

runtime_parameters;

extensions;

};

Currently the following setup_parameters and runtime_parameters are defined:

struct smt_param_allow_vesting

struct smt_param_allow_voting

{ bool value = true;

{ bool value = true;

typedef static_variant<

smt_param_allow_vesting,

smt_param_allow_voting

> smt_setup_parameter;

struct smt_param_windows_v1

{

33

};

};

uint32_t cashout_window_seconds = 0;

// STEEM_CASHOUT_WINDOW_SECONDS

uint32_t reverse_auction_window_seconds = 0;

// STEEM_REVERSE_AUCTION_WINDOW_SECONDS

};

struct smt_param_vote_regeneration_period_seconds_v1

{

uint32_t vote_regeneration_period_seconds = 0; // STEEM_VOTE_REGENERATION_SECONDS

uint32_t votes_per_regeneration_period = 0;

};

struct smt_param_rewards_v1

{

uint128_t

content_constant = 0;

uint16_t

percent_curation_rewards = 0;

uint16_t

percent_content_rewards = 0;

curve_id

author_reward_curve;

curve_id

curation_reward_curve;

};

typedef static_variant<

smt_param_windows_v1,

smt_param_vote_regeneration_period_seconds_v1,

smt_param_rewards_v1

> smt_runtime_parameter;

UIs which allow inspecting or setting these parameters should be aware of the type and

scale of each parameter. In particular, percentage parameters are on a basis point scale

(i.e. 100% corresponds to a value of STEEM_100_PERCENT = 10000), and UIs or other

tools for creating or inspecting transactions must use the basis point scale.

Parameter constraints

Several dynamic parameters must be constrained to prevent abuse scenarios that could

harm token users.

• 0 < vote_regeneration_seconds < SMT_VESTING_WITHDRAW_INTERVAL_SECONDS

• 0 <= reverse_auction_window_seconds + SMT_UPVOTE_LOCKOUT < cashout_window_seconds

< SMT_VESTING_WITHDRAW_INTERVAL_SECONDS

SMT vesting semantics

SMTs have similar vesting (powerup / powerdown) semantics to STEEM. In particular:

• SMTs can be “powered up” into a vesting balance.

• SMTs in a vesting balance can be “powered down” over 13 weeks (controlled by static

SMT_VESTING_WITHDRAW_INTERVALS, SMT_VESTING_WITHDRAW_INTERVAL_SECONDS

parameters).

• Voting is affected only by powered-up tokens.

• Vesting balance cannot be transferred or sold.

34

Additionally, some token inflation may be directed to vesting balances. These newly

“printed” tokens are effectively split among all users with vesting balances, proportional

to the number of tokens they have vested. As the number of tokens printed is independent

of users’ vesting balances, the percentage rate of return this represents will vary depending

on how many tokens are vested at a time.

Content rewards

Tokens flow from SMT emissions into the reward fund. The blockchain uses algorithms

to decide:

• (1) How to divide the token-wide rewards among posts.

• (2) How to divide rewards within a post among the author and curators (upvoters)

of that post.

The algorithms to solve these problems operate as follows:

• (1) Posts are weighed against other posts according to the reward curve or rc.

• (2a) The curators collectively receive a fixed percentage of the post, specified by the

curation_pct parameter.

• (2b) The author receives the remainder (after applying any beneficiaries or limited/declined author reward).

• (2c) Curators are weighted against other curators of that post according to the

curation curve or cc.

Figure 7: Flow of initial tokens and SMT emissions

Curve definitions

The reward curve can be linear or quadratic. The linear reward curve rc(r) = r passes

the R-shares (upvotes) through unchanged. The quadratic reward curve rc(r) = rˆ2 +

35

2rs has increasing slope.

For an illustration of the meaning of reward curves, imagine grouping the most-upvoted

posts as follows:

• Section A consists of the top 10% of posts by upvotes.

• Section B consists of the next 10% of posts by upvotes.

Here’s how the rewards differ:

• With either reward curve, Section A posts will have greater rewards than Section

B posts, since they have more upvotes.

• With the quadratic reward curve, Section A posts will have an additional boost

relative to Section B posts, since Section A posts will get more rewards per upvote.

• With the linear reward curve, Section A and Section B will get the same reward

per upvote.

Possible curation curves are:

• Linear cc(r) = r

• Square-root cc(r) = sqrt(r)

• Bounded cc(r) = r / (r + 2s)

To help visualize, here are some plots called pie charts. Each colored area represents how

curation rewards are divided among curators with equal voting power.

36

Figure 8: Reward curves and curation curves

• The rectangular vertical column shows the immediate reward upon making an upvote.

• The colored area extending to the right shows how the rewards of a curator grow

as later curators vote.

• When both curves are linear, everyone gets the same curation reward regardless of

37

which post they vote on.

• In the case of rc_linear + cc_sqrt and rc_quadratic + cc_bounded, the same

height rectangles means everyone gets about the same initial curation reward, call

this ICR=.

• In the case of rc_linear + cc_bounded, the rectangles are decreasing in height.

This represents a progressive handicap against voting for already-popular posts, call

this ICR-.

• In the case of rc_quadratic + cc_sqrt and rc_quadratic + cc_linear, the

rectangles are increasing in height. Call this ICR+.

Fundamentally, curation is making a prediction that upvotes will occur in the future. As

reward system designers, our criterion for selecting a curve should be to reward successful

predictions. Which curve satisfies this criterion depends on the relationship between

current and future upvotes.

• If a post’s future upvotes are independent of its current upvotes, we should choose

an ICR= curve.

• If a post’s future upvotes are positively correlated with its current upvotes, we should

choose some ICR- curve, ideally somehow tuned to the amount of correlation.

• If a post’s future upvotes are negatively correlated with its current upvotes, we should

choose some ICR+ curve, ideally somehow tuned to the amount of correlation.

In practice, independence or a modest positive correlation should be expected, so an ICR=

or ICR- curve should be chosen. For STEEM itself, curation was originally the quadratic

ICR=, as of the Steem hard fork 19 it is the linear ICR=.

Target votes per day

Each account has a voting_power, which is essentially a “mana bar” that fills from 0%

to 100% over time at a constant rate. That rate is determined by two parameters:

• (a) The time it takes to regenerate the bar to 100%, vote_regeneration_period_seconds.

• (b) The voting_power used by a maximum-strength vote.

The vote_regeneration_period_seconds is specified directly. For (b), instead of

specifying the voting power of a maximum-strength vote directly, instead you specify

votes_per_regeneration_period. Then the maximum-strength vote is set such that a

user casting that many max-strength votes will exactly cancel the regeneration.

38

SMT Setup GUI Sketch

39

Figure 9: SMT Configuration

Votability and Rewardability

In this section, we introduce the concepts of votability and rewardability.

•

•

•

•

A token is votable for a comment if the balance of that token influences the comment.

For a given vote, each votable token of the comment is either rewardable or advisory.

If a token is rewardable, then the vote affects the comment’s reward in that token.

If a token is advisory, then the vote does not affect the comment’s reward in that

token.

Advisory votes do not affect rewards or voting power. However, the ranking algorithms

and estimated reward calculations still apply advisory votes, so UIs may display advisory

posts accordingly.

The votable token set is determined by allowed_vote_assets which is a comment_options_extension.

struct allowed_vote_assets

{

flat_map< account_name_type, votable_asset_info >

};

votable_assets;

struct votable_asset_info_v1

{

share_type

max_accepted_payout

= 0;

bool

allow_curation_rewards = false;

};

typedef static_variant< votable_asset_info_v1 >

votable_asset_info;

The following rules are applied to determine whether tokens are votable:

• STEEM is votable for every post.

• A token is votable for a post if it appears in the post’s votable_assets.

• Otherwise, the token is not votable for this post.

And these are the rules for whether a token is rewardable:

• In order to be rewardable for a post, a token must be votable for that post.

• If, for some post/token, that post’s max_accepted_payout of the token is zero, then

the token is not rewardable for that post.

• If some voter (i.e. upvoter / downvoter) has a zero balance of a token, then that

token is not rewardable for that voter’s votes.

• If the max_accepted_payout for any non-STEEM token is nonzero, then

the max_accepted_payout for STEEM/SBD must be at least the default

max_accepted_payout.

Implementation notes:

• For an advisory vote, all rewards are zero, including curators and beneficiaries. This

is because the blockchain applies the max_accepted_payout cap before the curator

/ beneficiary computations.

40

• Currently (as of Steem hard fork 19), the Steem blockchain does deduct voting

power for advisory Steem votes. This behavior will be changed in a future Steem

hard fork (Steem issue #1380).

• At most two tokens may be specified in votable_assets. This means that each

post is voted with at most three tokens (including STEEM).

• The default max_accepted_payout is stored in max_accepted_steem_payout_latch

member of dynamic_global_properties_object.

Clients should populate

max_accepted_payout of a post based on this member, in case the default value

changes in a future version.

No consensus level restriction forces any particular post to have any particular

allowed_vote_assets. As a consequence, any post may mark itself as eligible to be

rewarded in any token. However, UI’s may impose their own non-consensus validation

rules on allowed_vote_assets, and hide posts that violate these non-consensus

validation rules.

For example, in a Hivemind community with a corresponding token, there may be a validation rule that the allowed_vote_assets specified in each post within that Hivemind

community must include the token of that community. This is a non-consensus validation rule, since the entire concept of a post existing within a Hivemind community is a

non-consensus concept. Since it is a non-consensus validation rule, no consensus logic can

enforce it. However, UIs that are aware of Hivemind communities may refuse to index or

display posts that violate this validation rule.

Static Token Parameters

Static parameters are configuration constants that affect the behavior of SMTs, but are

deliberately excluded from smt_setup_parameters or smt_runtime_parameters. The

reason they are designed to be non-configurable is that allowing these parameters to

significantly deviate from the values used for STEEM would result in significant risks,

such as:

•

•

•

•

May

May

May

May

result in a very complicated implementation.

result in extreme end-user frustration.

threaten the security and stability of the token.

threaten the security and stability of STEEM.

Here is the list of such static parameters:

• SMT_UPVOTE_LOCKOUT_HF17 : Static – This value locks out upvotes from posts at a

certain time prior to “CASH OUT”, to prevent downvote abuse immediately prior

to “CASH OUT.”

• SMT_VESTING_WITHDRAW_INTERVALS : Static

• SMT_VESTING_WITHDRAW_INTERVAL_SECONDS : Static

• SMT_MAX_WITHDRAW_ROUTES : Static

• SMT_SAVINGS_WITHDRAW_TIME : Static

• SMT_SAVINGS_WITHDRAW_REQUEST_LIMIT : Static

• SMT_MAX_VOTE_CHANGES : Static

• SMT_MIN_VOTE_INTERVAL_SEC : Static

• SMT_MIN_ROOT_COMMENT_INTERVAL : Static

• SMT_MIN_REPLY_INTERVAL : Static

• SMT_MAX_COMMENT_DEPTH : Static

41

• SMT_SOFT_MAX_COMMENT_DEPTH : Static

• SMT_MIN_PERMLINK_LENGTH : Static

• SMT_MAX_PERMLINK_LENGTH : Static

Mandatory token parameters

The token parameters set by smt_setup_parameters or smt_runtime_parameters have

default values. A few STEEM-equivalent parameters are specified by smt_setup_operation

fields. These are the parameters which do not have a default value, and thus, must be

specified for every asset.

• SMT_MAX_SHARE_SUPPLY : Set by smt_setup_operation.max_supply

• SMT_BLOCKCHAIN_PRECISION : Set by pow(10, smt_setup_operation.decimal_places)

• SMT_BLOCKCHAIN_PRECISION_DIGITS : Set by smt_setup_operation.decimal_places

SMT interaction with existing operations

• comment_payout_beneficiaries : The existing comment_payout_beneficiaries

will only redirect STEEM. In the future, comment_payout_beneficiaries functionality which allows redirecting SMT rewards may be added.

• comment_options : max_accepted_payout, allow_votes only affects STEEM, see

here to restrict max_accepted_payout for assets. allow_curation_rewards affects

all tokens.

• vote_operation : Multiple tokens in the comment’s votable set vote.

• transfer_operation : Supports all SMTs.

• Escrow operations: Do not support SMTs.

• transfer_to_vesting_operation : Supports all SMTs that support vesting.

• withdraw_vesting_operation : Supports all SMTs that support vesting.

• set_withdraw_vesting_route_operation : Does not support SMTs.

• account_witness_vote_operation : SMTs do not affect witness votes.

• account_witness_proxy_operation : SMTs do not affect witness votes.

• feed_publish_operation : Feeds may not be published for SMTs.

• convert_operation : SMTs cannot be converted.

• Limit order operations : Limit orders are fully supported by SMTs trading against

STEEM.

• transfer_to_savings_operation : SMTs support savings.

• decline_voting_rights_operation : Affects SMT votes as well as STEEM votes.

• claim_reward_balance_operation : Restrictions on this operation are relaxed to

allow any asset in any of the three fields, including SMTs.

• delegate_vesting_shares_operation : Supports all SMTs that support vesting.

• Multisig Native: There is nothing “special” about the handling of SMT operations

signed by multiple signatures. If you set up your account to require multi-signature

security, then everything your account signs will need to be signed with multiple

signatures, as you specified. This includes operations your account does as a control

account managing an SMT, and operations your account does as a user holding SMT

tokens.

42

Automated Market Makers for SMTs

Automated Market Makers are smart contracts, largely based on the Bancor Protocol [2],

that may be constructed during the initial ICO setup of an SMT for providing perpetual

liquidity to an SMT community. For simplicity, Automated Market Makers in Steem may

only trade between STEEM and any given SMT.

Setup

Basic Definitions

In this article, we’ll let s represent a quantity of STEEM, let t represent a quantity of

some token (SMT), and let p represent a price, such that pt is STEEM-valued (i.e. if

MYTOKEN is trading at p = 0.05 STEEM / MYTOKEN then t = 120 MYTOKEN has

a value of pt = (0.05 STEEM / MYTOKEN) · (120 MYTOKEN) = 6 STEEM.

Suppose we have a market maker (or any economic agent) with a two-asset “portfolio”

(inventory) of s STEEM and t tokens. If the price of tokens is t, then we may measure of

the value of this portfolio, in units of STEEM, as v(p, s, t) = s + pt.

One common portfolio management policy is to require that STEEM should be some

constant fraction r of the portfolio, i.e. s = rv(p, s, t) where 0 < r < 1. We call this

policy the constant portfolio ratio or CPR policy, and the equation s = rv(p, s, t) is the

CPR invariant.

A different portfolio management policy, discussed by the Bancor whitepaper, is called

CRR or constant reserve ratio. To discuss CRR, let us notate the total number of tokens

in existence as T . The CRR invariant is then defined as s = rv(p, 0, T − t).

Notes on Conventions

We must discuss where our convention varies from the Bancor whitepaper. At some times,

when some user Alice interacts with the market maker, Alice will remove some tokens

from her balance to get STEEM from the market maker’s balance. On the other hand,

Bob may add some tokens to his balance in exchange for sending STEEM to the market

maker’s balance.

Bancor takes the convention that in this example, the market maker destroys tokens in

its interaction with Alice, and creates tokens in its interaction with Bob. The Bancor

convention suggests the market maker is not an ordinary actor, but needs system-level

“special powers” – specifically, the privilege to operate the token printing press – in order

to function.

In this paper, we adopt the convention that the tokens sent by Alice to the market maker

are not destroyed, but are instead added to the inventory (balance) of the market maker.

Likewise, the tokens sent to Bob by the market maker are not created out of thin air; they

already exist and are merely transferred from the inventory of the market maker to Bob.

Thus, we show that the market maker is essentially an ordinary economic agent acting

according to a deterministic algorithm – it doesn’t actually need “special powers”!

43

Finite Trades

Basic Definitions

A trade is a change in the market maker’s balance from (s, t) → (s+∆s, t+∆t). The price

at which the trade occurs is defined as p = −∆s

∆t . We restrict ourselves to well-formed

trades where either ∆s = ∆t = 0, or ∆s and ∆t are both nonzero and have opposite sign.

Theorem: A trade at price p conserves value at price p. More rigorously, if ∆s, ∆t

represent a trade at price p, then v(p, s, t) = v(p, s + ∆s, t + ∆t).

Let us more rigorously define the market maker’s state as a tuple M = (s, t, T, r). Given

some price p, we may define the restoring trade at p (also called a relaxing trade or a

relaxation) to be a trade which occurs at price p and results in a state that satisfies the

CRR invariant.

Computing the Restoring Trade

The restoring trade consists of functions ∆s(M, p) and ∆t(M, p). We may actually compute these functions from the definition of price and the CRR invariant:

∆s = −p∆t

s + ∆s = rv(p, 0, T − (t + ∆t))

⇒ s − p∆t = rv(p, 0, T − t − ∆t)

= rp(T − t − ∆t)

= rpT − rpt − rp∆t

⇒ rp∆t − p∆t = rp(T − t) − s

rp(T − t) − s

⇒ ∆t =

rp − p

(

)(

)

1

s

=

− r(T − t)

1−r

p

⇒ ∆s = −p∆t

(

)

1

=

(rp(T − t) − s)

1−r

Computing the Equilibrium Price

Given a state M , there exists some price peq (M ) for which the restoring trade is zero;

call this price the equilibrium price. We may compute the equilibrium price by setting

∆s = 0:

44

∆s = (

0

)

1

=

(rpeq (T − t) − s)

1−r

⇒ rpeq (T − t) − s = 0

⇒ rpeq (T − t) =

⇒ peq

=

s

s

r(T − t)

Theorem: Relaxation is idempotent. That is, after relaxing at price p, the equilibrium

price of the resulting state is p, and a second relaxation at price p will be a zero trade.

Example

Example: Suppose M = (1200, 3600, 12000, 0.25) and p = 0.5. Then of the T = 12000

TOKEN in existence, t = 3600 TOKEN is held by the MM, so T −t = 12000−3600 = 8400

TOKEN are “circulating” (i.e. exist in balances outside the MM). These circulating tokens

are worth p(T − t) = 4200 STEEM total, so they “should be” backed by a target reserve

level of rp(T − t) = 4200 ∗ 0.25 = 1050 STEEM.

In this example, there is “too much” STEEM in the reserve, so relaxation will buy tokens

in the market. This sale will cause two effects: It will decrease the reserve STEEM, and

also decrease circulating tokens. The decrease in circulating tokens, in turn, causes the

target reserve level to decline. For every 1 STEEM used to buy tokens, the target reserve

level declines by r STEEM; since r < 1 eventually the declining reserve will “catch up”

to its more slowly declining target level.

(

)

1

The above algebra shows that we will catch up at ∆s = 1−r

(rp(T − t) − s) and

(

)(

)

1

s

∆t = 1−r

p − r(T − t) . Running the calculations with the numbers defined in this

example gives ∆s = −200 STEEM and ∆t = 400 TOKEN.

Let’s check that these computed values ∆s = −200, ∆t = 400 (a) represent a trade with

price 0.5, and (b) that the CRR invariant holds for the new state Mnew = (s + ∆s, t +

∆t, T, r). Calculating p = −∆s

∆t we indeed get p = 0.5. After this trade executes, the

market maker has snew = s + ∆s = 1200 − 200 = 1000 STEEM, and tnew = t + ∆t =

3600 + 400 = 4000 tokens.

To check condition (b), that the CRR invariant holds, we effectively repeat the analysis

in the initial paragraph of this example with the new numbers. We know Mnew =

(1000, 4000, 12000, 0.25) and p = 0.5. Then of the T = 12000 TOKEN in existence,

tnew = 4000 TOKEN is now held by the MM, so T −tnew = 12000−4000 = 8000 TOKEN

are now circulating. These circulating tokens are worth p(T − tnew ) = 4000 STEEM total,

so they “should be” backed by a target reserve level of rp(T − t) = 4000 ∗ 0.25 = 1000

STEEM. Since the target reserve level indeed exactly matches the actual reserve level of

snew = 1000 STEEM, we conclude that the CRR invariant is satisfied after this relaxing

trade.

45

Infinitesimal Trades

This section is fairly technical; the reader will need a good grasp of calculus and differential

equations to follow the results.

Setting up the Problem

Suppose we satisfy the invariant condition at some price p = pe q; by the CRR invariant

s = rv(p, 0, T − t) = rp(T − t). Suppose the price then increases to p + ∆p and a relaxing

trade ∆s, ∆t occurs at this new price.

In this section we consider the limiting situation where ∆p is infinitesimally small, so we

will use Leibniz notation (dp for a small change in p, ds for a small change in s, dt for a

small change in t).

Solving the DE’s

By applying the substitution p ← p+dp to the expression for ∆s computed in the previous

section, we obtain an expression which simplifies to a separable DE which can be solved:

ds

=

=

=

=

1

⇒ dp =

p

∫

1

⇒

dp =

p

⇒ ln(p) =

⇒p

1

(r(p + dp)(T − t) − s)

1−r

1

(rp(T − t) + rdp(T − t) − rp(T − t))

1−r

1

r(T − t)dp

1−r

( )

s

1

dp

1−r p

(

)

1

(1 − r)

ds

s

∫

1

(1 − r)

ds

s

(1 − r) ln(s) + C0

= k0 s1−r

Similarly for t, we can start from dt = −ds/p and again obtain and solve a separable DE:

46

= −ds/p

r

= −

(T − t)dp/p

1−r

( )

r

1

1

dt = −

dp

⇒

T −t

1−r p

(

)

1

1−r

1

⇒ dp =

dt

p

r

t−T

∫

∫

1−r

1

1

dp =

dt

⇒

p

r

t−T

1−r

⇒ ln(p) =

ln |t − T | + C1

r

1−r

⇒ p = k1 (T − t) r

dt

Qualitative discussion

In a CRR market maker, where does the “backing” for newly emitted tokens come from?

One option is to lower the reserve ratio r. This option results in no immediate market

activity, but will weaken the response of the market maker to any future price changes.

This is called the “pay later” option.

Another option is to change the dynamical system’s initial conditions, i.e. edit the constants of integration. This option will cause the equilibrium price peq to drop, meaning

the market maker will more aggressively sell tokens to replenish the reserve. If order

books are deep compared to the amount of emission, and there are adequate buyers for

the tokens, then the sales will be able to replenish the reserve and keep the equilibrium

price near its old value; the deep order books provide resistance to the price change being

driven by the market maker. If order books are thin compared to the amount of emission,

and there are few/no buyers for the tokens, then the equilibrium price will fall, breaking through the thin orders and lowering the market price. Even though few/no many

tokens were sold, so even though the absolute amount of STEEM in the reserve is still

nearly/exactly the same as before, the reserve’s value relative to the now-lower market

cap of the token has increased to the reserve ratio. This option is the “pay now” option.

FAQ

Q: What is the relevance of constant portfolio ratio policy?

A: It may become a supported market maker policy in the future.

Q: Can the reserve ratio go over 100 percent?

A: No.

Q: Can the reserve ratio be exactly 100 percent?

A: Not with the system described in this paper. It might be possible to code as a special

case.

47

Q: In a CRR market maker, where does the “backing” for newly emitted tokens come

from?

A: As blockchain designers, we have two options for sourcing the “backing”. One option

is to lower the reserve ratio r. This option results in no immediate market activity, but

will weaken the response of the market maker to any future price changes. This is called

the “pay later” option.

Another option is to change the dynamical system’s initial conditions, i.e. edit the constants of integration. This option will cause the equilibrium price peq to drop, meaning

the market maker will more aggressively sell tokens to replenish the reserve. If order

books are deep compared to the amount of emission, and there are adequate buyers for

the tokens, then the sales will be able to replenish the reserve to its target level while

keeping the equilibrium price near its old value. The deep order books provide resistance

to the price change being driven by the market maker.

If order books are thin compared to the amount of emission, and there are few/no buyers

for the tokens, then the equilibrium price will fall, breaking through the thin orders and

lowering the market price. Even though few/no many tokens were sold, so even though

the absolute amount of STEEM in the reserve is still nearly/exactly the same as before,

the reserve’s value relative to the now-lower market cap of the token has increased to the

reserve ratio. This option is the “pay now” option.

Q: Where’s the “don’t pay” option?

A: You have to come up with some answer to where the “backing” for newly emitted

tokens will come from. Unless there’s no emission. Or unless there’s no “backing” for any

tokens. So the “don’t pay” option would be to have an SMT with either no emission, or

no market maker.

Q: Don’t fractional exponents require floating point to implement?

A: Only if you need fairly high precision (we don’t), don’t care about bit-for-bit reproducibility across compilers, OS’s, CPU’s, etc (we do), and need to do massive numbers

of calculations quickly (we don’t). A fast, approximate, all-integer implementation is

possible.

Q: Does this market maker interact with the order book through the existing limit order

system, or is it a separate set of operations?

A: In theory, it could be implemented either way. However, the likely outcome is that

the market maker will be implemented outside of order-book markets to allow its code to

be modularized. In practice, if implemented as a completely separate subsystem, people

will run arbitrage bots which will trade away any price differences between the reserve

system and the existing market system.

Q: Where do the market maker’s initial token balances come from?

A: ICO units can specify the market maker as a destination. An ICO creator may direct

a percentage of their ICO’s STEEM contributions to the MM by specifying the market

maker similarly to specifying a founder. Or may use the soft cap system to specify all

STEEM above a pre-determined amount goes to the ICO. Likewise, a fixed or percentage

amount of tokens can be added in the ICO to increase the MM’s token balance.

Q: Can someone send STEEM or tokens to the market maker?

A: Yes.

48

Q: What are the side effects of sending STEEM or tokens to the market maker?

A: The constants of integration are re-initialized, meaning the equilibrium price will

change. The market maker will become more aggressive about selling the asset.

Q: Can’t this cause manipulation or appropriating the market maker’s inventory to private

profit?

A: Sending assets to the market maker does cause it to engage in trading activity which

affects the price. However, dumping an identical amount on the market will result in a

larger amount of trading activity and a larger effect on the price. If Eve is willing to

spend her tokens/STEEM to manipulate prices, she would prefer the strategy of simply

dumping tokens/STEEM on the market, as that strategy is more cost-effective for her.

Q: Does the market maker’s activity generate profits (losses)?

A: It depends on how you measure “profits”. If you measure the value of STEEM and

tokens in some external third currency such as US dollars or bitcoins, the market maker’s

inventory, valued in that currency, can definitely increase or decrease. If people voluntarily

send STEEM or tokens to the market maker, such activity definitely increases the value

of the market maker regardless of your measurement.

Another way to define profits is by the constants of integration. If both of the constants

of integration increase, or one increases while the other remains the same, a tiny increase

occurs with each trade when the market maker is in “taker” mode.

Q: What is “taker” mode? How can a market maker be set to operate in “taker” mode?

A: When orders execute, the order used to set the price is called the maker; the maker’s

counterparty is the taker. In the STEEM on-chain market (and on almost all trading

platforms) the older order is always the maker.

When the market maker is in taker mode, its actions are always considered to be taker

orders, which execute at the price specified by the user acting as its counterparty – this

price is always at least a little bit more favorable than the market maker is willing to

accept. When the market maker is not in taker mode, its actions are always considered

to be maker orders, which don’t generate changes in the constants of integration.

Taker mode is a runtime parameter that can be set by the SMT’s control account.

Q: Who benefits from the profits of a market maker in taker mode?

A: Maybe nobody, or maybe everybody. It’s decentralized.

Q: OK, if my SMT reaches a steady price, the STEEM in the reserve is basically locked

up forever. That seems not cool. How do I set it up so that this STEEM can be unlocked

for the benefits of my SMT users?

A: Set the DRR (decaying reserve ratio) setup parameter. If you set DRR, then the reserve

ratio will slowly drop over time to a pre-set value, using its excess STEEM reserves to

buy excess tokens. Setting DRR is an excellent, fair, decentralized way to return excess

capitalization to contributors in a more-popular-than-anticipated ICO that raises more

than the sponsor can effectively spend.

Q: If the reserve ratio can change over time due to pay-later emissions or DRR, it’s not

really a constant reserve ratio, is it?

49

A: No, they’re not. The reserve ratio’s called “constant” because it’s constant over the

short-term, in normal conditions, or in the conditions in Bancor which is where it was

named. But the name could be regarded as slightly misleading.

Q: If the constants of integration can change over time, they’re not really constants either,

are they?

A: No, they’re not. They’re called constants of integration because that’s their mathematical role in the calculation that introduces them. Maybe they’ll be differently named

in a future version of this paper.

Q: Can I specify a contribution to a DRR to be a pay-later contribution, that increases

its reserve ratio, the increase to be eventually negated over time by future decay? Why

would I want to?

A: Yes. This is effectively contributing to the market maker, subject to the condition

that it’s not allowed to immediately dump a portion of the contribution. It’s useful if

you want to make a large contribution to a market maker without causing it to create a

disturbance by immediately dumping a significant fraction of your contribution onto the

market.

Q: Can I specify a DRR with emission to use pay-later for emissions when the RR is

decaying?

A: Yes.

Q: Is the market maker specified here equivalent to a Bancor token changer?

A: No. A Bancor token changer has multiple reserve ratios that must sum to one hundred

percent, and involves a third token that effectively represents equity in the token changer.

This paper’s market maker has none of these features.

Q: I want to have an initial “price discovery” period where people trade without action

from the market maker, then have tokens and STEEM from the ICO gradually flow in

over time to the market maker so it has a delayed, slow start from zero to full power. Can

I do it?

A: This is called “gradual seeding” and it may be supported.

Q: What about numerical stability?

A: A market maker will be restricted to only operate when its balances exceed a certain

minimum for both assets. Also, reserve ratios will be restricted to a certain range, all

the mechanisms that can set / increase / decrease a reserve ratio will be restricted to not

allow it to move outside the range. Tentative numerical experiments suggests these limits

should be about 10,000 satoshis of both assets, 5 percent and 50 percent, respectively.

These values are subject to change based on future experimentation, worst-case analysis,

and testing.

Costs of SMT Operations And Bandwidth Rate Limiting

Like STEEM, SMTs can be transferred on the Steem blockchain with zero fees. Steem

replaces fees with bandwidth rate limiting based on the percentage of STEEM an ac-

50

count has staked, which means the blockchain calculates how much STEEM an account

has temporaily vested to determine how much bandwidth the account is permitted for

transfers, posting, and other operations across a period of time. In a future version of

Steem, possesion of an account name could permit some small degree of bandwidth to

allow for even greater user experience.

Fee-less Operations Necessary for Quality User Experience

Because of bandwidth rate limiting, Steem may never charge applications or users transaction fees for basic operations such as voting, posting, and transferring tokens. This lack

of fees allows Steem based apps to compete with their non-blockchain counterparts, such

as Facebook or Reddit, which certainly do not charge fees for actions such as ‘Like’ and

‘Upvote’. If these applications did charge fees, adoption would suffer.

Decentralized Exchange

One of the valuable features of SMTs is their immediate access to functioning unmanned

markets against the liquid asset, STEEM.

Automatic Order Matching

The Decentralized Exchange (DEX) structures of Steem allow assets to be automatically

matched for best possible price when bids and asks overlap, unlike other DEXs - which

require a “man in the middle” or user-agent to match orders. Automatic, rather than

middle-man-facilitated, order matching is important for the security of Steem-based assets,

and for the replicability and safety of DEX interfaces.

Diverse Asset Types

There are several assets that SMT users and creators will have access to by way of the

Steem DEX: STEEM, SBD, SMTs, and Simple Derivatives (IOUs). These neighboring

assets can increase the visibility and network effect of all created SMTs.

STEEM is the gateway token for assets issued on Steem, staying relevant by acting as

the bandwidth usage measuring stick across Steem’s SMTs. STEEM is also the common

denominator asset, acting as a trading pair for all of Steem’s SMTs.

SBD (Steem Blockchain Dollars) are an experimental asset on Steem that relate to the

US Dollar, originating with Steem’s launch in 2016. It is unclear if SBD will bring value

to holders of USD as they will compete, possibly poorly, with USD IOU tokens; however,

SBDs will bring value to speculators.

SMTs as described in this proposal are an important part of growing the token ecosystem,

and bringing crypto assets to the mainstream. SMTs will trade against STEEM across

the DEX.

Simple Derivatives (IOUs) will be possible via SMT issuance. For instance, if an SMT

is issued without inflation or rewards pool properties, then the issuer can reliably back

51

the token with another real world asset such as bitcoin or USD. In this instance, the

issuer could create a business functioning as a gateway, by trading their IOU for BTC

or USD. Users would buy the IOU to gain access to the Steem DEX. This market would

add diversity and value flow to the Steem ecosystem, while adding to the DEX’s network

effect.

Zero Trading and Transfer Fees

The Steem DEX is the first DEX to exist without trading fees, to the benefit of SMT

creators and traders alike. This is made possible by bandwidth rate limiting (described

in the original Steem Whitepaper and Bluepaper), as the process by which the blockchain

calculates transaction “prices” on a per byte basis, and deducts transaction bandwidth

available to an account temporarily. These “prices” are an internal blockchain accounting

and do not debit any token balances.

Augmenting SMTs with Additional Native Contracts

There are several potentially valuable programmable contracts that are not in the immediate scope of SMTs, however, these contract capabilities can be created as modular,

follow-on projects that increase the creativity entrepreneurs and communities may apply

to growth of SMT ecosystems.

Community Building with Paid Positions

SMT communities may be bolstered with paid positions, guild roles, or jobs that are

defined in programmable, native smart contracts and matched with continuously elected

participants. Rewards received through the elected position come from some portion of

the token’s Founder allocations or donations that are sent to a paid position contract.

Paid position contracts may be defined for length of position, frequency and volume of

payments, particular token used for stake-weighted elections, percentage of the token

required for a participant to be elected, and how tokens in paid position contracts are

socialized or forfeited given no participant is elected.

The paid roles may be leveraged to support various applications, games, and businesses

built around an SMT. A contract for a paid position, the postion’s reward schedule, and

the voting thresholds required to elect an account into a paid position may be created by

anyone for a fee. To establish the purpose of these positions, job descriptions or constitutions that encourage adherence to performance expectations may be established by the

issuer or the token’s community. There can be an unlimited number of paid positions,

and paid position contracts can receive any amount of a token’s Founder allocations or

community donations. The types of paid positions that may be employed includes everything from front end developer, to evangelist, including educational content creator,

business development representative, and many roles that have yet to be imagined.

52

Democratic SMTs using Whitelist Oracles

SMTs represent completely open access to tokens, however, some entities may wish to

enable one-whitelisted-account, one-vote-per-post and X-number-of-target-votes-per-day

algorithms to increase their token’s potential for accurate wisdom-of-the-crowd content

discovery mechanics and the democratic nature of their token community. To incorporate

this, the Rewards Pool for a token will need to have a manageable whitelist that can be

enabled only at launch. Whitelist management may be handled by the entity launching

the token or outsourced to an identity management service, such as Civic or Jumio. The

service would need to publish a feed of Steem usernames for known/identified people into

the Steem blockchain, along with periodic updates to ensure accuracy of the whitelist.

As the blockchain pays rewards to a token, it verifies the account receiving the token is

on the whitelist, otherwise the tokens are returned to the reward pool.

Secondary ICOs for Contiguous Fundraising

Entrepreneurs leveraging SMTs to finance ventures may want to have the option to perform token auctions after the initial launch of the token. The entrepreneur can reserve

Founders tokens at launch and earmark them for later sale, however, they may want to

auction these tokens rather than sell them into Bid/Ask order books or sell them OTC.

To enable secondary auction-style ICOs, a secondary auction contract may be established.

This contract requires definitions for when an ICO begins and how long it lasts, as well as

lockup periods for the tokens purchased. The lockup period allows the tokens to be sold

at a discount to the open markets and attract investment capital that would otherwise

stay out of the market. The entrepreneur will send tokens to this contract prior to the

beginning of the auction and the tokens will be distributed to the auction participants

immediately following the close of auction period.

Bandwidth Sharing with SMTs Based on Reserve Liquidity Pools

SMTs that use ICOs to create Automated Market Makers to boost token liquidity will

inherit bandwidth rights proportionate to the amount of STEEM in the Automated Market Maker’s reserve pool. This bandwidth inheritance confers transaction rights from

STEEM to all the of the “powered up” and vested SMT, basically permitting SMT owners to transact proportionate to their stake of SMT without owning STEEM outright.

Bandwidth Sharing based on liquidity pools enables new tokens to operate with an even

higher degree of independence while still contributing proportionate value to STEEM.

What Makes SMTs Better Suited to ApplicationSpecific Blockchains, such as Steem, than ApplicationGeneral Blockchains, such as Ethereum?

Throughout the history of software and hardware development, it has been observed

that specialized systems have the potential to greatly outperform generalized systems.

An example of this can be seen in GPUs outperforming CPUs through specialization,

which was followed by ASICs outperforming GPUs for particular tasks. In turn, some

53

wonder how a specialized blockchain, such as Steem, which hosts application-specific programmability, and static mechanics embedded in consensus, is more suited to SMTs than

application-general, open-programmability blockchains, such as Ethereum, which hosts

turing-complete (“infinitely”) programmable smart contracts in a layer beyond consensus, and has shown its use for discovering new cryptocurrency concepts. Without delving

into Steem’s advantages in network effect and developer team experience, the advantages

for SMTs on Steem can be seen through a set of computer science, consumer safety, and

economic perspectives.

SMTs are Safer and More Cost Effective in Application-Specific

Blockchain Environments

The value of SMTs in a native, specialized-programmability environment, such as Steem,

comes from reliability of the code and efficiencies created by that reliability, whereas

application-general platforms, such as Ethereum and Tezos, require costly and highlyassumptive audits on each new token and issuer to be deemed safe. Some of these

application-general protocols claim to have formal verification, which is valuable, however, the majority of the audit cost remains due to the need to audit the issuer’s choice

of token mechanics, choice of client for writing the code, and semantics of custom code

written to the token. Enabled by the purposeful design of its code, Steem enables SMTs

to support static (versus dynamic) crypto-economic properties that can be tuned after

the token’s launch without each change potentially harming their token holders. The

purposeful delineation between economic properties that should be static versus dynamic

makes the necessary token audits for safety simple and inexpensive to accomplish.

To elucidate this issue, imagine someone is offering you 20% of their currency in exchange

for $100 USD. You will have additional questions for the seller - essentially questions to

audit tertiary realities of the deal, such as: “does the seller maintain a right to print more

currency and therefore dilute me?” In SMTs, holders of SMTs will be able to rely on the

core economics of the SMTs they purchase due to static nature of the SMTs economic

properties - such as emissions or inflation rates, which cannot be changed by the issuer

after launch. Therefore, there can be no unexpected new currency emissions to harm

the consumer. In application-general, open-programmability blockchain protocols, such

as Ethereum and Tezos, there can be no such platform-spanning design principles and

reliabilities that protect consumer safety.

SMTs on Steem have Aligned Proof-of-Brain Incentives with the

Core Token

Unlike STEEM, core tokens (such as ETH) that do not carry Proof-of-Brain content

rewards, cannot offer monetization, primed active user-base, shared influence, and bootstrapping benefits to new SMT communities. STEEM, on the other hand, is able to lend

its reward pool features and primed-user base to new networks, to help them bootstrap,

market, and become successful independent clusters of participants on the network. Conversely, some entrepreneurs will identify and choose a strategy to employ SMTs largely

independent from STEEM, and like ERC20 to Ethereum, SMTs can run while only having STEEM run in the background to calculate the necessary bandwidth for transaction

costs.

54

SMTs on Steem Have Transaction Pricing that Contributes to a

Quality User Experience

Whether operating with bandwidth rate limiting, or outright fees, no general purpose

blockchain will price transactions effectively for more than a small fraction of its applications, and SMTs would have reduced user experience (UX) on application-general

blockchains (such as Ethereum) as a result. The clear example is that on blockchains

such as Ethereum, there are outright fees for all transactions, however, no content publisher would expect users to pay fees to leave comments or likes on their articles. With

SMTs on Ethereum, those fees would be required, which makes Ethereum a non-starter

as an SMT platform.

Unlike Ethereum, some open-programmability blockchains of the future may use bandwidth rate limiting as transaction costs, however, bandwidth rate limiting requires fine

tuning to meet the UX requirements of specific applications. As an example, in Steem,

bandwidth rate limiting is specifically tailored to support content applications and their

user interactions by leveraging bandwidth rights according to two objects: amount of

token ownership, and account ownership - and it’s taken over a year of production-level

research to refine the optimal bandwidth allowances to each. In general purpose, openprogrammability platforms, the burden and the need for accurate pricing may hinder the

ability for applications to have their users’ actions priced appropriately, and the problem may be exacerbated as a greater myriad of potential application experiments come

to exist, stretching and sharing the blockchain’s resources. Therefore, blockchains that

support native application-specificity may yield more suitable transaction pricing, as it

pertains to the UX with tokens in related applications.

SMTs Benefit from a Blockchain that has Scaling Processes Programmed to a Specialized Set of Applications

In blockchain scaling there are cutting-edge concepts of “sharding” (originated by Vitalik Buterin and the Ethereum project) and “multi-threaded parallelism” (originated by

Michael Vandeberg of Steem) that refer to how blockchains may scale by allowing multiple

operations to occur at once. General purpose platforms (such as Ethereum) are a great

test bed for these approaches to scaling, however, a platform that takes advantage of all

the product-market fit discovered by Ethereum, that then applies it to a more specialized,

iterative-upgrading model, such as Steem, can scale its processes more effectively to meet

the demand discovered by that product-market fit.

Looking to the 90s and early 00s for analogy, when the computer science world started

writing code specifically optimized for GPUs, the boundary pushing for greater scale occurred through FPGAs: field programmable gate arrays, which are chips that allow the

programmability of the set of logic gates into the form of any conceivable circuit, allowing for effectively a prototype ASIC (albeit with higher power consumption). This is not

quite the same performance per watt as an ASIC, but orders of magnitude faster than

a CPU for particular tasks. As these platforms move to more and more generalizations,

such as the idea that any contract may call on any other contract, they will move further away from ability to optimize for scale, as contracts that call on all other contracts

can reduce the capacity for multi-parallel processing to single-core processing. By analogy, like CPUs do not optimize better than GPUs, platforms like Ethereum, GEOS, and

Tezos do not optimize better than Turing-incomplete application-specific blockchains like

55

Steem. These CPU-like blockchains will be bottlenecked by unpredictable processing requirements, while the ultimate blockchain platforms will be specially-designed, like Steem,

and will scale by optimizing in the way FPGAs were optimized for parallel algorithms.

SMTs Benefit from a Blockchain with Content Management System (CMS) Primitives

Unlike application-general blockchains, such as Ethereum, that inherently avoid

application-specific primitives at the core of the protocol, Steem offers a structured

public content database for storing plain text and generic structured data in tandem with

content primitives that developers can build from: Account Names, Posts, Comments,

Votes and Account Balance. These primitives benefit the blockchain-based applications

by helping to establish application-interoperability and rapid developer on-boarding.

Without these primitives, second order databases need to be structured specifically for

a blockchain-based application, which may give rise to many second-order applicationspecific databases competing with each other. The rise of multiple second layer content

databases splits the potential network effect for the blockchain as a content management

system (CMS), and reduces the potential for application-interoperability, which provides

consumer safety benefits by allowing end users to move fluidly from one blockchain-based

application to another.

Increasing Market Demand for STEEM with SMTs and

Implicit Value Drivers rather than Fees

There are several new value drivers to STEEM with the creation of SMTs.

STEEM Purchased for Transaction Bandwidth Enables Maximally

Profitable Participation across SMTs

With the advent of SMTs, there is growing demand for users to hold STEEM, because

users need to increasingly hold STEEM in order to participate, consume, and use Steem

services at a rate maximally commensurate with their growing potentials in respective

SMT ecosystems. Put simply, as power users are growing their earning potential in SMT

communities, they need more STEEM to achieve the bandwidth allowance needed to

perform at their highest possible rate of return in SMT ecosystems. At an application

level, the demand for bandwidth may be satisfied by users or by businesses, which can

delegate surplus bandwidth to their users.

STEEM Supply is Locked into Liquidity Pools by Automated Market Makers

Each SMT that leverages Automated Market Makers augments the ratio of demand for

STEEM to available supply of STEEM. The effect of the Automated Market Maker to

STEEM is that each Automated Market Maker represents a permanent holding pool for

STEEM, which represents a decrease in available supply. Given demand were to stay

56

equal, the price of STEEM is caused to rise with the advent of each new Automated

Market Maker.

STEEM and SMT Demand Increases with Advent of New Powers

of Influence

From a potential utility perspective, demand for STEEM increases as each SMT is created

with Influence Sharing for Steem Power over a SMT’s rewards pool. The advent of each

trace of Steem Power-based Shared Influence over an SMT’s Reward Pool gives new rights

and usage to STEEM, which in turn drives demand for STEEM. These rights can also

be granted from SMT to SMT, and the flow of value follows an identical pattern.

STEEM Demand Increases with Proliferation of SMT ICOs

At a platform level, other cause for demand may include exclusive financing opportunities,

such as ICOs, which attract new capital into ecosystems, first flowing into the base asset,

STEEM, and then flowing into SMTs. Increased capital in the ecosystem due to ICOs

always presents an opportunity for net positive capital retained in STEEM, and at worst,

a wash on the value of the base asset, where all of the STEEM is sold by the organization

making the offering. The example of the worst case scenario is that an ICO occurs and

$100 USD buys STEEM to buy the ICO’d SMT, then 100% of the STEEM received by the

ICO is sold for USD - and no explicit net effect related to the value of STEEM. However,

even when the net effect contribution of an ICO to the value of STEEM is apparently

zero, it is an implicit net benefit in terms of attention received by STEEM and the Steem

ecosystem, if we consider all new attention valuable. Further, it is reasonable to expect,

based on the behavior of ICOs in Ethereum, that the majority of the STEEM received

by the ICO’ing organization will continue to be held on a speculative or promissory basis,

therefore creating holding value.

Steem: The World’s Advertising Network

Along with these new value creating mechanisms, it is imperative to recognize the original

value created for STEEM as an implicit attention and advertising network that now

applies to all SMTs that utilize Proof-of-Brain rewards. Smart Media Tokens, such as

STEEM, have inherent curation properties, such as their Rewards Pools, that give them

reliability and credentials as an implicit advertising network. The Rewards Pool in SMTs

demands that fully-SMT-integrated interfaces, such as steemit.com, respect the pending

SMT payouts on posts and then rank these posts from highest to lowest pending payout

in pages often referred to as “Trending” - such that the posts can be audited by the

community of SMT holders. The effect of this, which applies equally to STEEM as other

SMTs, is a sorted “Trending” page that users (bloggers, vloggers, advertisers) can reliably

use to evaluate the potential returns on buying higher placement on the page to attain

more attention, and then these participants make decisions to buy or rent STEEM and

SMTs to promote content. Through this process, as advertisers choose to buy and

rent STEEM/SMTs to gain exposure, demand for STEEM/SMTs increases. These value

driving properties can be described in a way similar to “Ethereum: the world computer”,

but instead as “Steem: The world’s advertising network.”

57

Steem Ecosystem Support for SMTs

Integrating SMTs into Websites and Apps

APIs and Documentation

To be continuously updated for SMTs. Current Steem APIs exist here: http://steem.

readthedocs.io/en/latest/index.html and https://steemit.github.io/steemit-docs/

Shared Tools for Account Creation, Key Signing, and Wallet Functions

Several shared tools exist to support applications that wish to outsource signup, transaction signing, and wallet functions - such as SteemConnect. SteemConnect enables

applications to support SMTs while the applications are backed by entrepreneurs who

may have little to no cryptocurrency experience.

Conclusion

Through a combination of specialized designs for open asset-issuance, bandwidth rate limiting as transaction costs, permanent-availability of content, real-time transaction speeds,

autonomous distribution of tokens, decentralized exchange, automated market making

and ICO contracts, Steem offers the premier token protocol for publishers across the

internet.

References

[1] Steemit, Inc., 2017. Steem Bluepaper. A protocol for bringing smart, social currency to publishers and content businesses across the internet. (https://www.steem.io/

steem-bluepaper.pdf)

[2] Eyal Hertzog, Guy Benartzi & Galia Benartzi, 2017. Bancor Protocol. Continuous

Liquidity and Asynchronous Price Discovery for Tokens through their Smart Contracts.

(https://www.bancor.network/static/bancor_protocol_whitepaper_en.pdf)

Appendix

Implementation Notes

Here is a timeline / state diagram of the events in an SMT launch:

58

Figure 10: Timeline of SMT Launch

SMT naming standards

• An SMT name should consist of 3-10 uppercase ASCII letters (A-Z).

• An SMT name should not equal STEEM, SBD or VESTS.

Asset directory standards

A directory maps each NAI to one of the following states:

Listed

Deprecated

Unlisted

Blacklisted

Each possible asset name is mapped to one of the following states:

Free

Reserved

59

A Listed or Deprecated NAI has an associated name, which should be listed as Reserved

in the mapping.

UIs may provide asset directory union functionality to augment directories by combining

multiple asset directories into a single asset directory. Asset directory union should use

the following algorithm to resolve situations where an NAI is listed differently by different

directories:

• (1) If the NAI is Blacklisted in any component directory, return Blacklisted.

• (2) If the NAI is Listed or Deprecated in multiple component directories, and

all of the component directories do not agree on the associated name, return

Unlisted.

• (3) If the NAI is Listed in at least one component directory, return Listed.

• (4) If the NAI is Deprecated in at least one component directory, return

Deprecated.

• (5) Return Unlisted.

Likewise, here are the rules for resolving names listed differently by different directories:

• (1) If the name is Reserved in any component directory, return Reserved.

• (2) Return Free.

A dynamic directory (based on a URL or blockchain account) should not be cached more

than 5 minutes.

UI guidelines for SMT names

• A UI may, but need not, have a default asset directory.

• A UI may choose to hide unlisted NAIs.

• A UI should allow users to override or augment the UIs defaults with their own

asset directories.

• A UI should reconsider hiding unlisted NAIs in which the user has actively transacted.

Operational guidelines for asset directories

• An asset directory should not confuse users by setting a well-known NAI to refer to

a different name, or setting a well-known name to refer to a different NAI.

• An asset directory should make the process for listing clear to both SMT creators

seeking to add their asset to the directory, and UI developers considering adding

the directory to their UI.

Asset directory formats

URL and file-based asset directories will be a JSON format. The details will be developed concurrently with the implementation. Blockchain-based asset directories will use

a custom JSON operation. Again, the details will be developed concurrently with the

implementation.

60

Unit Tests

The details of the unit tests will be developed concurrently with the implementation.

61

2018년 3월 9일자 확인됨

우분투에 서버 설치하기

시작하기전 기본 설정

1. EC2 기본형 올리기 (프리티어급)
2. express 노드 앱이 준비 되어 있다는 가정
3. putty나 맥을 통해서 터미널로 접속이 가능해야함 (pem 파일 이미 등록된 상태)

DB는 AWS RDS 이용합니다.

파일 서버는 S3 이용합니다.

방화벽 설정하기

aws ec2는 콘솔에서 설정가능

참고 링크 :

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-with-ufw-on-ubuntu-16-04

ufw allow 80

Nginx 설치

일반적으로 우분투에 설치시 최신버전을 설치를 안한다. 그래서 저장소 키를 가져와서 직접 최신걸로 업데이트를 할 수 있다.

참고내용 :

https://websiteforstudents.com/install-nginx-latest-version-ubuntu-16-10-17-04/

https://bjornjohansen.no/install-latest-version-of-nginx-on-ubuntu

사인키 등록

// get nginx key
curl -O https://nginx.org/keys/nginx_signing.key

// install
apt-key add nginx_signing.key

$ sudo echo -e "deb https://nginx.org/packages/mainline/ubuntu/ `lsb_release -cs` nginx\ndeb-src https://nginx.org/packages/mainline/ubuntu/ `lsb_release -cs` nginx" > /etc/apt/sources.list.d/nginx.list

sudo apt-get update
sudo apt-get install nginx

업그레이드시

sudo apt-get dist-upgrade

버전 체크

nginx -v
-> nginx version: nginx/1.10.3 (Ubuntu)

명령어 모음

// 시작
$ sudo service nginx start
$ sudo systemctl start nginx
$ sudo /etc/init.d/nginx start

// 재시작
$ sudo service nginx restart
$ sudo systemctl restart nginx
$ sudo /etc/init.d/nginx restart

// 중지
$ sudo service nginx stop
$ sudo systemctl stop nginx
$ sudo /etc/init.d/nginx stop

// 상태
$ sudo service nginx status
$ sudo systemctl status nginx

// 설정 reload
$ sudo service nginx reload
$ sudo systemctl reload nginx
$ sudo nginx -s reload

FTP 설치

sudo apt-get install vsftpd

설정페이지

nano /etc/vsftpd.conf

기본 설정

# chroot 적용 
# 아래와 같은 설정을 할 경우 사용자들은 자신의 계정에서 상위 디렉토리로 이동할수 없게된다. 
chroot_local_user=YES

# 수정 가능
write_enable=YES

*chroot_local_user=YES 주석을 풀면 아래와 같은 에러가 발생하는 경우가 있음
500 OOPS: vsftpd: refusing to run with writable root inside chroot()
이러한 경우 vsftpd.conf 파일에

allow_writeable_chroot=YES  을 추가 저장

출처: http://nahosung.tistory.com/40 [nahos]

그리고 유저를 추가

adduser test
//비번 입력창 나오면 알아서 입력

FTP 권한 및 옵션 확인

echo 'allow_writeable_chroot=YES' >> /etc/vsftpd.conf //YES로 변경
chmod 777 /home/{유저이름}

sudo /etc/init.d/vsftpd restart //재가동

기본 설정

vsftpd.conf 와 관련된 내용



1. FTP의 포트를 바꾸고 싶으면 어떻게 해야 할까?



  listen=YES 라고 써 있는 부분 아래에

  listen_port=21022 (원하는 포트번호로 넣어줌) 적어준다





2. 비계정(guest)의 접속을 허용하게 하려면


  anonymous_enabled=NO 를 YES로 변경해 준다.





3. 업로드 가능하게 하려면?

  write_enable=YES에 걸려있는 주석을 제거해야 한다.





4. 파일 업로드 했을 때 파일의 권한을 설정하려면 어떻게 해야 하나?

  local_umask=022 (마스킹 처리가 되기 때문에 022로 하면 해당파일은 755 라고 설정된다)에 걸려있는 주석을 제거한다.





5. 계정사용자가 상위디렉토리(root 디렉토리)에 접근하는 것을 허용하려면?

  chroot_local_user=YES

  chroot_list_enable=YES

  chroot_list_file=/etc/vsftpd.chroot_list

  최초에 설치하면 주석이 걸려있는데 이것은 상위 디렉토리로 이동하는것을 막기 위함이다.

  이 주석을 제거하고 난 후에 chroot_list_file 항목에 적혀있는 경로로 파일을 만들고 그 안에 계정이름을 적으면 상위로 이동하 것이 허용된다.



  $sudo vi /etc/vsftpd.chroot_list

   user1

   user2



 이렇게 하면 user1과 user2는 상위 디렉토리로 이동이 가능해진다.



6. root 계접 접속을 허용하려면?

  $sudo vi /etc/ftpusers

  root 계정에 앞에 주석처리 해준다 (또는 삭제)

노드 설치

nvm 으로 설치

https://www.digitalocean.com/community/tutorials/how-to-install-node-js-on-ubuntu-16-04

또는 정식 설치

https://nodejs.org/en/download/package-manager/

curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -
sudo apt-get install -y nodejs

or

curl -sL https://deb.nodesource.com/setup_9.x | sudo -E bash -
sudo apt-get install -y nodejs

네이티브 애드온 설치

sudo apt-get install -y build-essential

노드를 백그라운드에서 돌릴수 있는 PM2 설치

sudo npm install pm2 -g 

pm2 startup systemd //서버 재시동시 자동으로 올릴수 있도록

pm2 start ./bin/www //express app.js 실행

그리고 pm2을 통해서 외부에서 모니터링 설치

https://app.keymetrics.io 추천 ( 1개까진 무료 )

//create bucket 후
pm2 link b3o4z****** rxio4******** //메뉴얼대로 진행

그러면 관리자화면이 자동으로 연동

이제 ngnix에서 내부 서버로 포워딩해야함

참고 사이트 :

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-node-js-application-for-production-on-ubuntu-16-04

vi /etc/nginx/sites-available/default

..........

# / 루트로 오는 경우 3000번으로 포워딩처리
location / { 
        proxy_pass http://localhost:3000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }

.........

혹시 site-avavailable 폴더가 안만들어진 경우...

cd /etc/nginx/sites-enabled 
//없는 폴더일 경우

//1. sites-enabled 폴더를 만든다. 
//2. default(사이트이름가능) 만든다. 
vi /etc/nginx/sites-enabled/default

///etc/nginx/sites-enabled/default 내용

server {
    listen 80;

    server_name  {도메인주소};

    location / {
        proxy_pass http://127.0.0.1:3000;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
    }
}

nginx sites-enabled에 symlink 생성하기

이제sites-available에 있는 파일들에 대해서sites-enabled에 symlink를 추가합시다

mkdir /etc/nginx/sites-enabled
sudo ln -s /etc/nginx/sites-available/[아까 만든 default] /etc/nginx/sites-enabled/

그리고 문법에 이상없는 지 체크

nginx -t
-> nginx: configuration file /etc/nginx/nginx.conf test is successful

그럼 ngnix 재시작

// 재시작은 아래에 있는 명령어 중 하나로 실행하시면 됩니다.
$ sudo service nginx restart
$ sudo systemctl restart nginx
$ sudo /etc/init.d/nginx restart

-> [ ok ] Restarting nginx (via systemctl): nginx.service.

그러면 포스트맨이나 웹에서 접속 테스트를 해본다.

도메인은 router 53에서 A 레코드로 하나 추가함.

그리고 value 에 해당 아이피를 입력함

시간이 다소 걸릴 수 있음

도메인 변경후 접속 테스트를 해서 통과가 되는 경우 HTTPS 설치로 넘어가자.

HTTPS 설치 - letsencrypt + certbot 이용

https://certbot.eff.org/

으로 가서 맞는 환경을 선택...

우선 우분투 버전 체크

lsb_release -a

--------------------------

Distributor ID: Ubuntu
Description:    Ubuntu 16.04.3 LTS
Release:        16.04
Codename:       xenial

certbot 환경선택 에서 우분투 16.04 + Nginx 선택

sudo apt-get update
sudo apt-get install software-properties-common
sudo add-apt-repository ppa:certbot/certbot
sudo apt-get update
sudo apt-get install python-certbot-nginx

그리고 certbot 인증 절차를 시작한다.

sudo certbot --nginx
// 이메일 등록하라고 함
// 기타 몇가지 설정하고 도메인이 꼭 설정이 되어 있어야 함
// 마지막은 http로 온걸 https로 리다이렉트할꺼냐 물어봄

그리고 letencrypt이용시 3개월마다 갱신해야 한다. 이걸 자동 등록할수 있다.

sudo certbot renew --dry-run

그리고 https로 접속 확인해본다.

마지막으로 제대로 되었는지 SSL 등급 테스트를 해보자

https://www.ssllabs.com/ssltest/

그럼 이제 완료가 되었다. 터미널 끄고 개발하면 된다..ㅠㅠ

추가적으로 nginx 에 파일업로드시 용량부족이 뜨는 경우가 있다.

sudo nano /etc/nginx/nginx.conf

.............
http 부분에
client_max_body_size 2M; //2M 부분에 원하는 용량 적으면 된다. 
.............
sudo /etc/init.d/nginx restart

배열과 연결된 리스트의 장단점

2장에서는 주된 설명은 배열과 연결된 리스트에 대한 비교 설명이 있었다.

배열은 검색이 빠른 반면 삽입이 느리다는 것

연결된 리스트의 경우 삽입이 빠르지만 검색부분에선 배열보다 느리다는 장단점이 있다.

선택정렬 (Selection Sort)

2번째 알고리즘 문제이다.

만약 주어진 배열이 있으면 그 배열을 정렬하고자 할 때 선택정렬을 사용할 수 있다.

기본 흐름은 다음과 같다. (순차적 정렬시)

1. 배열에 가장 작은 값 검색
2. 가장 작은 값 위치 값 획득
3. 그 위치 값을 배열에서 제거 하고 새로운 배열에 하나씩 추가함
4. 그렇게 해서 최종 새로운 배열로 결과값을 보여줌

Python3 으로 구현시 다음과 같다.

def findSmallest(arr):
    smallest = arr[0]
    smallest_index = 0
    for i in range(1, len(arr)):
        print(">> {0},{1},{2}".format(smallest, smallest_index, arr[i]))
        if arr[i] < smallest:            
            smallest = arr[i]
            smallest_index = i
    return smallest_index


def selectionSort(arr):
    newArr = []
    for i in range(len(arr)):
        print("arr => ", arr)
        smallest = findSmallest(arr)
        print("smallest => ", smallest)
        newArr.append(arr.pop(smallest)) # pop은 꺼낸 후 제거된다. 
    return newArr

print(selectionSort([5, 3, 6, 2, 10]))

2를 arr 에서 pop (2를 꺼내는 동시에 제거) 하고 다시 위의 반복문을 돌린다.

위 결과값 출력은 다음과 같다.

arr =>  [5, 3, 6, 2, 10]
>> 5,0,3
>> 3,1,6
>> 3,1,2
>> 2,3,10
smallest =>  3
arr =>  [5, 3, 6, 10]
>> 5,0,3
>> 3,1,6
>> 3,1,10
smallest =>  1
arr =>  [5, 6, 10]
>> 5,0,6
>> 5,0,10
smallest =>  0
arr =>  [6, 10]
>> 6,0,10
smallest =>  0
arr =>  [10]
smallest =>  0


[2, 3, 5, 6, 10] <== 최종 정렬된 값

다트 버전의 경우는 온라인 다트 편집기 에서 테스팅 가능하다.

void main() {
  print("result => ${selectionSort([5, 3, 6, 2, 10])}");
}

List<int> selectionSort(List<int> arr) {
  var newArr = [];
  var length = arr.length;
  for(var i = 0; i < length; i++) {    
      var smallestIndex = findSmallestIndex(arr);    
    newArr.add(arr[smallestIndex]);
    arr.removeAt(smallestIndex);
  }
  return newArr;
}

int findSmallestIndex(List<int> arr) {
  int smallest = arr[0];
  int smallestIdx = 0;

  var newArr = arr.sublist(1,arr.length);

  newArr.forEach((item) {    
    if(item < smallest) {
      smallest = item;
      smallestIdx = arr.indexOf(item);      
    }
  });  
  return smallestIdx;
}

................
result => [2, 3, 5, 6, 10]

빅오 표기법으로는 O(n^2) 이라고 한다.

이진탐색 (Binary Search)

시나리오

1~1000개 숫자 의 배열에서 특정 숫자만 뽑아내고 싶을 경우 어떻게 해야 될까?

1. 리스트로 한개씩 넣어서 검색해서 운좋으면 빠른 시간안에 검색이 될 수 있으나 최악의 경우 1000번의 수행을 해야 한다.
2. 이진탐색 알고리즘을 통해서 전체의 반을 검색하고 다시 반을 검색하는 방법을 사용할 수 있다.

예를 들어 100의 중간 50부터 시작되는 함수로 시작된다

4번만에 답을 찾은 경우이다. 그럼 log2 16 = 4 이라고 표시한다.

즉 로그는 거듭제곱의 반대말이다.

지수표현이 잘 안됨..

• 10^2^ = 100 -> log10100 = 2
• 10^3 = 100 -> log101000 = 3
• 2^3 = 8 -> log28 = 3 (결과값을 앞으로 보내면 된다.)
• 2^4 = 16 -> log216 = 4
• 2^5 = 32 -> log232 = 5

위의 경우에는 정렬된 배열에 한해 해당되는 내용이었다. 하지만 실무에서는 보통 정렬이 안되어있는 경우가 많은 편이다.

그럼 어떻게 구현이 될까? 파이썬으로 시작해보자.

우선 먼저 배열 전체 길이를 설정하자.

low = 0
high = len(list) - 1

그리고 가운데를 딱 나누어서 원소를 확인해보자.

mid = (low + high) / 2 //반으로 나눈값 설정
guess = list(mid) //리스트의 반이 무엇인지 예측

추측한 값이 너무 작으면 low 값을 다음과 같이 변경 처리

if guess < item:
  low = mid + 1

또 큰 경우 high 값을 설정

if guess > item
  hight = mid -1

표로 정리해보면 다음과 같다.

def binary_search(list, item):
    cnt = 0
    low = 0
    high = len(list) - 1
    print("찾는 문자 : ", item)

    while low <= high:
        mid = (low + high) // 2
        guess = list[mid]
        print("번호:",cnt, " low:", low, " high:", high, " mid:", mid, " guess:", guess )
        if guess == item:
            print("in ", guess, "==", item, " return ", mid)
            return mid
        if guess > item: #item보다 guess 가 큰경ㅇ 
            print("in ", guess, ">", item, " 작다")
            high = mid - 1
        else:
            print("in ", guess, "<", item, " 크다")
            low = mid + 1
        cnt=cnt+1    
        

    return None #아이템이 리스트에 없음


my_list = list(range(1,101))
print(binary_search(my_list, 57))

결과값

찾는 문자 :  57
번호: 0  low: 0  high: 99  mid: 49  guess: 50
in  50 < 57  크다
번호: 1  low: 50  high: 99  mid: 74  guess: 75
in  75 > 57  작다
번호: 2  low: 50  high: 73  mid: 61  guess: 62
in  62 > 57  작다
번호: 3  low: 50  high: 60  mid: 55  guess: 56
in  56 < 57  크다
번호: 4  low: 56  high: 60  mid: 58  guess: 59
in  59 > 57  작다
번호: 5  low: 56  high: 57  mid: 56  guess: 57
in  57 == 57  return  56
56

다트 버전

온라인 에디터 바로가기

void main() {
  //1~100까지 생성  
  int targetNum = 57;
  var list = new List<int>.generate(100, (i) => i+1);
  print("final result =  ${binary_search(list, targetNum)}");
}

int binary_search(List<int> list, int item) {
  //초기화  
  int low = 0;
  //리스트 갯수 - 1
  int high = list.length - 1;

  //while low <= high
  while(low <= high) {  
    int mid = ((low + high) / 2).floor();    
    int guess = list[mid];
    print("$low,$high,$mid,$guess");
    if(guess == item) {
      return mid;
    }else if(guess > item) {
      high = mid -1;      
    }else{
      low = mid + 1;
    }          
  }

  return 0;

}

결과

0,99,49,50
50,99,74,75
50,73,61,62
50,60,55,56
56,60,58,59
56,57,56,57
final result =  56

안녕하세요. 수지아빠입니다. 

요즘 알고리즘이 아주 핫합니다. 하지만 오랜 시간 개발을 해도 알고리즘을 따로 공부하지 않으면 늘 부족함을 느끼기 마련입니다. 

그리고 바쁜 직장인 일정에서 스터디도 하긴 시간도 부족하고 늘어지기 쉽죠. 

그래서 읽기 편한 알고리즘 왕초보 책 한권 우선 선정해서 다 같이 떼는 걸로 진행하는 온라인 스터디를 시작할 예정입니다. 

인증도 같이 해야 되니 꼭 공부하실 분만 오세요. 

인증방법은 챕터별 또는 공부한 내용에 대해서 GitHub 또는 자신의 블로그에 정리해서 

올리시고 그 링크를 공유를 해주셔야 합니다. 

정리하는 내용은 공부한 내용이므로 자세하지 않으셔도 됩니다. 자세하고 잘 적으시면 그만큼 더 뿌듯하셔도 됩니다. 멋지십니다. !!

다시 말하자면 이방은 아래 알고리즘 책 한권을 위한 방입니다. 

알고리즘에 대한 토론도 환영합니다.

책 한권 다 보고 정리해서 공유해서 다같이 공부하는 게 

이 온라인 스터디룸의 목표입니다. 

그리고 책을 한번 다 끝까지 다 본 경우 졸업생 홍길동 이런식으로 계속 방에 계셔도 되거나 졸업하셔서 나가시면 됩니다. 

http://www.yes24.com/24/Goods/37885448?Acode=101

공부하실분만 모십니다. 오랫동안 공부안하시면 강제 조퇴당할수 있습니다. 

밑의 사진 클릭시 입장가능합니다. 

Truffle를 활용한 Pet-Shop 튜터리얼 분석

광고 클릭시 많은 힘이 됩니다. 

Truffle 튜터리얼 중 펫샵을 활용해서 프론트 까지 적용해서 어떤식으로 웹에서 연동되는지 살펴보자.

아래 주소에 있는 내용은 깔끔하게 정리되어 있다.  따라해보는 걸 추천한다. 

• http://truffleframework.com/tutorials/pet-shop

여기 글은 펫샵에 사용되는 소스를 분석해보자 한다. 

이더리움 플랫폼 위 DAPP개발 프레임워크 중 하나인 truffle사용시 개발시 순서는 다음과 같다.

• 개발환경을 설정한다.
• truffle box( 보일러 플레이트처럼 만들어준다.)를 이용해서 pet-shop 을 해제
• 스마트 계약 소스를 (.sol) 작성한다.
• 컴파일 및 배포를 한다.
• Ganeche 를 통해 테스팅을 한다.
• 웹 브라우저에서 스마트 계약이 정상적으로 인터랙션이 제대로 이루어지는지 확인해본다.

아래 이미지는 결과 화면이다. Adopt 버튼을 통해서 success 이 제대로 이루어 지는 지 보면 된다.

MetaMask 를 통해서 창이 열리면서 Submit를 클릭해준다.

최종적으로 채택이 된 것을 웹에서 확인해볼 수 있다. ( 새로고침을 해야한다. )

결과물은 따라하다보면 쉽게 볼 수 있을것이다. 여기서 특이한 점은

MetaMask를 통한 Custom RPC 로 ganache private network 로 접속해서 진행

스마트 계약을 테스팅시 솔리디티 언어로 테스팅 하는 방법

우선 Adoption.sol 파일을 훝어보자.

pragma solidity ^0.4.17;

contract Adoption {
    address[16] public adopters;

    function adopt(uint petId) public returns (uint) {
        require(petId >= 0 && petId <= 15);

        adopters[petId] = msg.sender;

        return petId;
    }

    function getAdopters() public view returns (address[16]) {
        return adopters;
    }
}

주로 스마트 계약을 테스팅시 자바스크립트(mocha)로 계약 함수를 신뢰성을 테스트한다. 하지만 여기에선 바로 솔리디티 언어로 테스팅하는 걸 보여준다.

• http://truffleframework.com/docs/getting_started/solidity-tests

pragma solidity ^0.4.17;

//다양한 테스팅 도구 제공
import "truffle/Assert.sol";
//이미 서버에 배포된 계약 주소를 가져온다. 
import "truffle/DeployedAddresses.sol";
//계약 소스를 가져온다. 
import "../contracts/Adoption.sol";

contract TestAdoption {
    //Adoption 초기화
    Adoption adoption = Adoption(DeployedAddresses.Adoption());

    //Pet에 Adopt를 할수 있는지 테스트
    function testUserCanAdoptPet() public {
        //8번 아이디를 adopt 함수 실행
        uint returnedId = adoption.adopt(8);

        uint expected = 8;


        //값이 제대로 가져오는 지 체크
        Assert.equal(returnedId, expected, "Adoption of pet ID 8 should be recoreded");
    }

    //아이디를 통해 Adopter 주소를 가져오는 걸 테스팅
    function testGetAdopterAddressByPetId() public {
        //트랙잭션을 할 예정이므로 예상 값을 this로 설정 가능하다. (펫 구매한 사람 주소)
        address expected = this;

        //adopters 변수 설정되면 public getter 가 되므로 거기 위치에 8의 값을 가져와서 테스팅해본다. 
        address adopter = adoption.adopters(8);

        //값 맞게 들어오는지 체크
        Assert.equal(adopter, expected, "Owner of pet Id 8 should be recored");
    }

    function testGetAdopterAddressByPetIdInArray() public {
        //트랙잭션을 할 예정이므로 예상 값을 this로 설정 가능하다. (펫 구매한 사람 주소)
        address expected = this;

        //storeage, memory 를 설정해서 실제 물리적으로 저장 할 것인지 내부에서 저장할 건지 정한다. 
        //adoption 클래스에서 adopter 배열목록을 가져온다. 
        address[16] memory adopters = adoption.getAdopters();

        //가져온 adopter의 8번째가 맞는지 체크
        Assert.equal(adopters[8], expected, "Owner of pet ID 8 should be recorded.");
    }
}

그리고 다음과 같이 테스팅을 해본다.

> truffle test
or
devlope 모드일 경우 단지 test 만 입력

Using network 'development'.

   Compiling ./contracts/Adoption.sol...
   Compiling ./test/TestAdoption.sol...
   Compiling truffle/Assert.sol...
   Compiling truffle/DeployedAddresses.sol...

     TestAdoption
       ✓ testUserCanAdoptPet (91ms)
       ✓ testGetAdopterAddressByPetId (70ms)
       ✓ testGetAdopterAddressByPetIdInArray (89ms)


     3 passing (670

그리고 웹쪽 프론트에서 이 계약 함수들을 사용하는 내용이다. App.js 에서 볼 수 있다.

주석을 달아봄으로써 해당 기능을 알아볼 예정이다. 

App = {
  web3Provider: null,
  contracts: {},

  //초기화
  init: function() {
    //펫 배열을 가져와서 리스트를 만든다. 
    $.getJSON("../pets.json", function(data) {
      var petsRow = $("#petsRow");
      var petTemplate = $("#petTemplate");

      for (i = 0; i < data.length; i++) {
        petTemplate.find(".panel-title").text(data[i].name);
        petTemplate.find("img").attr("src", data[i].picture);
        petTemplate.find(".pet-breed").text(data[i].breed);
        petTemplate.find(".pet-age").text(data[i].age);
        petTemplate.find(".pet-location").text(data[i].location);
        petTemplate.find(".btn-adopt").attr("data-id", data[i].id);

        petsRow.append(petTemplate.html());
      }
    });
    
    //지갑설정 함수를 실행한다. 
    return App.initWeb3();
  },

  
  initWeb3: function() {
    // Is there an injected web3 instance?
    if (typeof web3 !== "undefined") {
      //Metamask 가 실행시 현 지갑을 리턴한다. 
      App.web3Provider = web3.currentProvider;
    } else {
      //만약 지정된 지갑이 없는 경우 미리 설정된 Ganeche 지갑을 리턴한다. 
      App.web3Provider = new Web3.providers.HttpProvider(
        "http://localhost:7545"
      );
    }
    web3 = new Web3(App.web3Provider);

    return App.initContract();
  },
  
  //계약 초기화
  initContract: function() {
    /*
    Adoption.JSON 형태 
    {
    "contractName": "Adoption",
    "abi": [
      {
        "constant": true,
        "inputs": [
          {
            "name": "",
            "type": "uint256"
          }
        ],
        "name": "adopters",
       ...............
    */
    //Adoption 은 컴파일 시 나온 ABI JSON이다 여기에 기본 함수들이 표시가 된다. 
    //웹에서는 이 ABI JSON을 보고 실행을 할 수 있다.
    $.getJSON("Adoption.json", function(data) {
      // Get the necessary contract artifact file and instantiate it with truffle-contract
      var AdoptionArtifact = data;
      //미리 제공된 truffleContract 를 통해 Adoption 인스턴스 생성
      App.contracts.Adoption = TruffleContract(AdoptionArtifact);
      
      //지갑 설정
      App.contracts.Adoption.setProvider(App.web3Provider);

      //
      // 이미 채택된 애완 동물이 있는 경우 함수를 호출해서 데이터 확인 후 업데이트 할수 있도록 한다. 
      return App.markAdopted();
    });

    return App.bindEvents();
  },

  //이벤트 바인딩
  bindEvents: function() {
    $(document).on("click", ".btn-adopt", App.handleAdopt);
  },

  //채택된 아이템이 있는 경우 버튼을 success 로 변경
  markAdopted: function(adopters, account) {
    var adoptionInstance;

    App.contracts.Adoption.deployed()
      .then(function(instance) {
        adoptionInstance = instance;
        
        //전체 adopte 배열 주소를 리턴한다. 
        return adoptionInstance.getAdopters.call();
      })
      .then(function(adopters) {
        //for 문 돌면서 adopte 만큼 버튼을 success 로 바꾸고 비활성화를 시킨다. 
        for (i = 0; i < adopters.length; i++) {
          if (adopters[i] !== "0x0000000000000000000000000000000000000000") {
            $(".panel-pet")
              .eq(i)
              .find("button")
              .text("Success")
              .attr("disabled", true);
          }
        }
      })
      .catch(function(err) {
        console.log(err.message);
      });
  },
  //Adopt 버튼 클릭시 adopt 함수 실행하는 함수이다. (트랙잭션이 발생된다.)
  handleAdopt: function(event) {
    //기본 이벤트 블럭함
    event.preventDefault();

    //펫 아이디를 id 를 통해 쿼리해옴
    var petId = parseInt($(event.target).data("id"));

    var adoptionInstance;
    
    //지갑상에 주소를 가져온다. 
    web3.eth.getAccounts(function(error, accounts) {
      if (error) {
        console.log(error);
      }

      //처음 주소를 가져온다. 
      var account = accounts[0];

      
      App.contracts.Adoption.deployed()
        .then(function(instance) {
          adoptionInstance = instance;
          
          
          //petId, account를 넣어서 adopt 함수를 실행한다. 
          return adoptionInstance.adopt(petId, { from: account });
        })
        .then(function(result) {
        //완료 된 후 success 버튼으로 변경...잘 안됨..
          return App.markAdopted();
        })
        .catch(function(err) {
          console.log(err.message);
        });
    });
  }
};

$(function() {
  $(window).load(function() {
  //초기화
    App.init();
  });
});

Truffle을 이용해서 손쉽게 테스팅 가능하며 배포도 쉽게 가능한 걸 볼수 있다. 잘 배워놓으면 도움이 많이 된다고 본다. 

Truffle기초 - 계약 디버깅과 테스팅

Truffle디버깅 및 테스팅 하는 방법을 알아보자.

Truffle 은 DAPP 개발을 편하게 해주는 프레임워크이다. 테스팅 및 컴파일, 배포까지 쉽게 해준다.

테스팅은 Ganache 를 이용한다. Ganache 은 개발모드에서 가상으로 테스팅 및 배포까지 하게 해주는 프레임워크

다른 웹에서 쉽게 테스팅을 할시 http://remix.ethereum.org/ 에서 쉽게 가능하다.

그리고 truffle에서도 지원한다.

우선 작업 할 폴더를 구성하자.

mkdif simple-contract
cd simple-contract

truffle을 초기화를 해서 기본 구성을 만들 수 있다.

truffle init

기본 구성은 위와 같이 나온다.

• build: 컴파일시 나오는 스마트 계약 빌드 파일이다. ABI파일이 나오는 걸로 보인다.
• contracts: 스마트 계약 파일들을 여기에서 보관한다.
• migrations: 이미 배폰 계약에 대해서 버전링을 하는 것이다. 자세한 내용은 여기를 참고하기 바란다.
• test: 계약을 테스팅 할 수 있다.

위에보이는 truffle.js 등은 서버설정 및 기타 설정이 가능하다.

초기화를 진행 한 후 스마트 계약(.sol) 을 만들어 보자.

여기에서는 visual stuio code 를 사용할 것이다.

플러그인으로는 solidity설치해서 재 시작한다.

pragma solidity ^0.4.17;

contract SimpleStorage {
    uint myVariable;

    function set(uint x) public {
        myVariable = x;
    }

    function get() constant public returns (uint) {
        return myVariable;
    }
}

두가지 간단한 함수들이 있다. Set, Get 등이다. 변수를 넣고 가져오는 계약이다.

이제 /migrations폴더에 배포함수를 넣어보자. 이름은 2_deploy_contracts.js 으로 하자.

var SimpleStorage = artifacts.require("SimpleStorage");

module.exports = function(deployer) {
  deployer.deploy(SimpleStorage);
};

그리고 컴파일을 해본다.

> truffle compile

...............
Compiling .\contracts\Store.sol...
Writing artifacts to .\build\contracts

컴파일 후에 build 폴더에 계약 관련 파일이 생성되었다.

실서버에 배포를 하기 전에 제대로 솔리디티에서 함수들의 신뢰성들을 테스팅 할 필요가 있다. Truffle 프레임워크 단에서 편하게 지원해주니 우린 잘 쓰면 된다.

그럼 개발 모드로 들어가본다.

> truffle develop

Connected to existing Truffle Develop session at http://127.0.0.1:9545/
truffle(develop)> //입장

개발 모드로 실행 및 세팅된 상태이다.

그럼 배포를 해보자.

migrate

배포를 한 후 결과값을 보면 다음과 같다.

  Replacing Migrations...
  ... 0x620c6bad3d8c76712a1262667b7944d125a882ac485f7ff73bb20af13b882035
  Migrations: 0x8acee021a27779d8e98b9650722676b850b25e11
Saving successful migration to network...
  ... 0x5ef83bc84690e0a14a30bb02f358bc1ff44f19ab487996f7323f063e95e417f4
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Deploying SimpleStorage...
  ... 0x79e9162e22395f000597903ac21f461f22240d4ccd22f51f2bcfde726147fb14
  SimpleStorage: 0x4e71920b7330515faf5ea0c690f1ad06a85fb60c
Saving successful migration to network...
  ... 0xa56b2ca521875b0ee0e9ab32d12ce376b0f56930043f4ae55674a0c04510f2ec
Saving artifacts...

그러면 테스팅 서버에 배포가 된 걸로 보인다.

이제 테스팅 코드를 작성해서 실제 값이 잘 넣고 가져오는 지 테스트를 해보자.

/test 폴더내 testing_simplestorage.js 를 만들자.

그리고 내용에 다음과 같이 자바스크립트로 테스팅을 해본다.

테스팅시 Promise 사용하는 방법과 Await 문법을 각각 사용해서 테스팅 해보았다.

자바스크립트 테스팅 관련 자세한 문서 바로가기

var SimpleStorage = artifacts.require("SimpleStorage");

contract("SimpleStorage", function(accounts) {
  it("should value is 0", function() {
    SimpleStorage.deployed()
      .then(function(instance) {
        return instance.get.call();
      })
      .then(function(value) {
        assert.equal(value, 0, "value is 0");
      })
      .catch(e => {
        console.log(e);
      });
  });
  it("should value is 4 when i put the 4 about value", async () => {
    try {
      let instance = await SimpleStorage.deployed();
      await instance.set(4); //4를 넣어본다.

      let instance2 = await SimpleStorage.deployed();
      let value = await instance2.get.call();
      assert.equal(value, 4, "value is 4"); // 그리고 결과값이 4로 나오는 지 확인해본다. 
    } catch (e) {
      console.log(e);
    }
  });
});

콘솔에서 바로 테스팅도 가능하다.

테스팅전에 배포환경을 초기를 해야한다.

> migrate --reset

> test

> truffle develope
SimpleStorage.deployed().then(function(instance){return instance.get.call();}).then(function(value){return value.toNumber()});
> 0
SimpleStorage.deployed().then(function(instance){return instance.set(4);});

SimpleStorage.deployed().then(function(instance){return instance.get.call();}).then(function(value){return value.toNumber()});
> 4 //4로 나오는 걸 확인

자바스크립와 콘솔에서 테스팅시 차이점은 트랙잭션이 일어날시 로그가 좀 다르게 나온다.

// 트렉잭션 발생시켜본다.
SimpleStorage.deployed().then(function(instance){return instance.set(4);});

............................ 결과 출력
{ tx: '0x8a7d3343dd2aaa0438157faae678ca57cc6485825bb4ed2ebefe90609dd268ce',
  receipt:
   { transactionHash: '0x8a7d3343dd2aaa0438157faae678ca57cc6485825bb4ed2ebefe90609dd268ce',
     transactionIndex: 0,
     blockHash: '0xd66fc7ddf829f1d1ee4a655c0b6a7de537748865de39de28b2167d8485fd9e92',
     blockNumber: 5,
     gasUsed: 41642,
     cumulativeGasUsed: 41642,
     contractAddress: null,
     logs: [],
     status: '0x01',
     logsBloom: '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000' },
  logs: [] }

출력값을 사용자별로 다르게 나올수 있다.

위와 같은 내용은 정상적으로 계약이 이루어 질 경우이다.

디버깅

솔리디티(.sol) 에서 스마트 계약 개발시 컴파일은 되지만 런타임에서 디버깅을 해서 잘 동작되는지 체크 해볼 필요가 있다.

우선 솔리디티에서 강제적으로 오류를 발생시켜 보자.

계약 내 set 함수를 아래와 같이 바꾼 후 다시 배포를 해보자.

function set(uint x) public {
    assert(x == 0); //0일 경우에만 통과를 하도록 한다. 
    myVariable = x;
}

다시 배포를 해보자.

> migrate --reset

디버깅시 실행시 개발모드에서 로그도 출력을 볼 수 있다.

그러기 위해선 Terminal 을 따로 열어서 확인을 할 수 있다.

+을 클릭해서 터미널을 추가한다.

그리고 개발에서 로그모드로 다시 접속한다.

> truffle develop --log

Connected to existing Truffle Develop session at http://127.0.0.1:9545/

그리고 처음 콘솔로 가서 다시 트렉젝션을 실행 시켜본다.

truffle(develop)> migrate --reset // 배포 초기화

Compiling .\contracts\Store.sol...
Writing artifacts to .\build\contracts

Using network 'develop'.

Running migration: 1_initial_migration.js
  Replacing Migrations...
  ... 0xeab337bfe489629610d34f11044e77fbfc37cfbea4b614f2e12c87ec45ea6f35
  Migrations: 0x2c2b9c9a4a25e24b174f26114e8926a9f2128fe4
Saving successful migration to network...
  ... 0x9b51540f5a7d75a8fc920e3e5e4ec66792ba31fd006bd176901f0e6347af2dba
Saving artifacts...
Running migration: 2_deploy_contracts.js
  Replacing SimpleStorage...
  ... 0x6622a3183323a916e08b9e1d55ec0f848ca75174adae954ebe796e0e66d0ae3f
  SimpleStorage: 0xfb88de099e13c3ed21f80a7a1e49f8caecf10df6
Saving successful migration to network...
  ... 0x69eaa7ed49cc72426706d54c4f52ba70b742ed6910f1223eb0df5f250b4b8ec3
Saving artifacts...

//트렉잭션 실행하기
truffle(develop)> SimpleStorage.deployed().then(function(instance){return instance.set(4);});

실행시 오류내용을 확인할 수 있다.

Error: VM Exception while processing transaction: invalid opcode //0이 아니므로 오류 발생
    at XMLHttpRequest._onHttpResponseEnd (C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\xhr2\lib\xhr2.js:509:1)
    at XMLHttpRequest._setReadyState (C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\xhr2\lib\xhr2.js:354:1)
    at XMLHttpRequestEventTarget.dispatchEvent (C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\xhr2\lib\xhr2.js:64:1)
    at XMLHttpRequest.request.onreadystatechange (C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\web3\lib\web3\httpprovider.js:128:1)
    at C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\truffle-provider\wrapper.js:134:1
    at C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\web3\lib\web3\requestmanager.js:86:1
    at Object.InvalidResponse (C:\Users\tommy\AppData\Roaming\npm\node_modules\truffle\build\webpack:\~\web3\lib\web3\errors.js:38:1)

그리고 다시 2번째 콘솔로 가서 로그를 확인해본다.

Connected to existing Truffle Develop session at http://127.0.0.1:9545/

  ..............

  develop:testrpc eth_sendTransaction +2s
  develop:testrpc  +17ms
  develop:testrpc   Transaction: 0x2cc0d39fc0bec51835df91343e64577b34ae335f7d998143349d5ab8b3d63181 +1ms //이부분이 중요하다. 
  develop:testrpc   Gas usage: 6721975 +0ms
  develop:testrpc   Block Number: 11 +0ms
  develop:testrpc   Block Time: Sat Mar 31 2018 09:56:57 GMT+0900 (대한민국 표준시) +1ms
  develop:testrpc   Runtime Error: invalid opcode +0ms
  develop:testrpc  +1ms

Transaction: 0x2cc0d39fc0bec51835df91343e64577b34ae335f7d998143349d5ab8b3d63181

트렉잭션 아이디를 이용해서 디버깅이 가능하다. 첫번째 콘솔로 가서 아래와 같이 디버깅을 실행해본다.

debug 0x2cc0d39fc0bec51835df91343e64577b34ae335f7d998143349d5ab8b3d63181

Gathering transaction data...

Addresses affected:
 0xfb88de099e13c3ed21f80a7a1e49f8caecf10df6 - SimpleStorage

Commands:
(enter) last command entered (step next)
(o) step over, (i) step into, (u) step out, (n) step next
(;) step instruction, (p) print instruction, (h) print this help, (q) quit
(b) toggle breakpoint, (c) continue until breakpoint
(+) add watch expression (`+:<expr>`), (-) remove watch expression (-:<expr>)
(?) list existing watch expressions
(v) print variables and values, (:) evaluate expression - see `v`


Store.sol:

1: pragma solidity ^0.4.17;
2:
3: contract SimpleStorage {
   ^^^^^^^^^^^^^^^^^^^^^^^^

debug(develop:0x2cc0d39f...)>

Store.sol:

4:     uint myVariable;
5:
6:     function set(uint x) public {
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

debug(develop:0x2cc0d39f...)>

Store.sol:

5:
6:     function set(uint x) public {
7:         assert(x == 0); //0일 경우에만 통과를 하도록 한다.
                       ^

debug(develop:0x2cc0d39f...)>

Store.sol:

5:
6:     function set(uint x) public {
7:         assert(x == 0); //0일 경우에만 통과를 하도록 한다.
                  ^

debug(develop:0x2cc0d39f...)>

Store.sol:

5:
6:     function set(uint x) public {
7:         assert(x == 0); //0일 경우에만 통과를 하도록 한다.
                  ^^^^^^

debug(develop:0x2cc0d39f...)>

Store.sol:

5:
6:     function set(uint x) public {
7:         assert(x == 0); //0일 경우에만 통과를 하도록 한다.
           ^^^^^^^^^^^^^^

엔터를 누르면 차례로 진행되면서 오류가 발생되는 부분에 표시가 된다. 이런식으로 단계별로 디버깅을 할 수 있다.

Remix 를 통해서 디버깅이 쉽게 되는 점도 알아놓으면 도움이 많이 된다.

이 외에에도 다양한 케이스에서 테스팅가능하다.

소스 링크

참조 링크

• http://truffleframework.com/docs/getting_started/solidity-tests
• http://truffleframework.com/tutorials/debugging-a-smart-contract

광고 클릭시 많은 힘이 됩니다. 감사합니다. 

혹시 크립토키티 라는 걸 듣어보셨나요?  이더리움상에서 DAPP 형태로 고양이를 랜덤으로 만들어서 거래까지 가능한 플랫폼이다.

현재 매출은 1200억 달러를 넘어섰다고 한다. 

관련 기사 모음

• 블록체인으로 만든 게임, '크립토키티스' 다시금 화제
• 이더리움 가능성 - 한계 보여준 고양이 게임

이런 플랫폼 게임 개발시 필요한 DAPP 개발 지식을 무료로 튜터리얼식으로 만들어서 공유 하는 곳이 있다.

크립토좀비 바로가기

왼쪽에는 설명이 나오고 오른쪽은 코드 실습을 통해서 하나씩 배워나가는 방식이다.

개발 내용은 DAPP 개발시 필요한 솔리티디 언어로 진행한다. 

레벨이 현재 5개로 나누어 (계속 추가될 예정) 지며 각각의 레벨과 함께 게임도 같이 만들어 나가는 재미도 있다. 

이 글은 여기 튜터리얼에 나온 레벨별로 요약을 해보았다. 종종 훝어 보기 편하게..^^

unit[2] fixedArray; //2개의 원소를 담을 수 있는 고정길이 배열

string[5] stringArray; //또다른 고정 배열으로 5개의 스트링을 담을 수 있다. 

unit[] dynamicArray; //동적배열은 고정된 크기가 없으며 계속 크기가 커질 수 있다.

Person[] people: //이는 동적 배열로 원소를 계속 추가 가능함

Person[] public people //public이 중간에 붙는 걸 유의하자

Person satoshi = Person(172, "Satoshi");
people.push(satoshi) //이런식으로 추가 가능하다.

function eat(string _name, uint _amount) {
    //TODO
}

eat('hambuger',1000); //함수의 실행

function addToArray(uint _number) private {
  numbers.push(_number)
}

string greeting = "what's up dog"

function sayHello() public returns (string) { //string 타입으로 리턴합니다. 
  return greeting;
}

function sayHello() public view returns (string) {

}

function _multiply(uint a, uint b) private pure returns (uint) {
  return a * b;
}

//6e91ec6b618bb462a4a6ee5aa2cb0e9cf30f7a052bb467b0ba58b8748c00d2e5
keccak256("aaaab");
//b1f078126895a1424524de5321b339ab00408010b7cf0e6ed451514981e58aa9
keccak256("aaaac");

uint a = 5;
uint b = 6;
// a * b가 uint8이 아닌 uint를 반환하기 때문에 에러메세지가 나옴
uint8 c = a * b
// b를 unit8 으로 형변환해서 코드가 제대로 동작하기 위해서...
uint8 c = a * uint8(b);

event IntegersAdded(uint x, uint y, uint result);

function add(uint _x, uint _y) public {
    uint result = _x + _y;
    //이벤트를 실행하여 앱에게 add 함수가 실행되었음을 알린다. 
    IntegersAdded(_x, _y, result);
    return result;
}

//////////////// 호출은
MyContract.IntegerAdded(function(error,result){
    //결과와 관련된 행동을 취한다.     

0x0cE446255506E92DF41614C46F1d6df9Cc969183

mapping (address => uint) public accountBalance; //유저의 계좌 잔액을 보유 하는 uint 지정가능

mapping (uint => string) userIdToName; //key는 uint 이고 값은 string 이다.

mapping (address => uint) favoriteNumber;

function setMyNumber(uint _myNumber) public {
  favoriteNumber[msg.sender] = _myNumber;
}

function getMyNumber() public view returns (uint) {
  return favoriteNumber[msg.sender];
}

function checkName(string _name) public returns (string) {
    require(keccak256(_name) == keccak256("tommy"));

    return "toooooomy!!";
}

contract Animal {
    function eat() public returns (string) {
        return "eat";
    }
}

contract Dog is Animal {
    function eatAll() public returns (string) {
        return eat();
    }
}

import './testContract1.sol';

contract testContract2 is testContract1 {

}

contract SandwichFactory {
    struct Sandwich {
        string name;
        string status;
    }

    Sandwich[] sandwiches;

    function eatSandwich(uint _index) public {


        //Sandwich mySandwich = sandwiches[_index];
        //스토리지 변수에 넣으라는 경고 메세지를 볼수 있다(아래 그림 참고)

        Sandwich storage mySandwich = sandwiches[_index];
        //스토리지에 넣게 된다. 

        mySandwich.status = "Eaten!";
        //Save to storage sandwiches array items

        mySandwich.status = "Eaten!";
        //스토리즈로 저장됨

        Sandwich memory anotherSandwich = sandwiches[_index + 1];
        //하지만 복사객체를 만들어서 메모리상으로 만듬

        anotherSandwich.status = "Eaten!";
        //메모리상으로 복사객체에 넣게 되서 sandwiches 배열과는 무관함

        sandwiches[_index + 1] = anotherSandwich;
        //다시 스토리지로 저장된다. 

    }
}

pragma solidity ^0.4.17;

contract LuckyNumber {
    mapping(address => uint) numbers;

    function setNum(uint _num) public {
        numbers[msg.sender] = _num;
    }
    function getNum(address _myAddress) public view returns (uint) {
        return numbers[_myAddress];
    }
}

contract NumberInterface {
    //위 계약의 getNum 를 호출한다. 
    function getNum(address _myAddress) public view returns (uint); //껍데기만 정의한다. 
}

contract MyContract {
    address addr = 0xabcdef..... //이더상의 계약 주소

    NumberInterface numberContract = NumberInterface(addr);
    //생성한다.

     function someFunction() public {
         //이제 getNum을 호출한다. 
         uint num = numberContract.getNum(msg.sender);
         //이제 LuckyNumber 상의 getNum을 호출해서 사용할 수 있게 한다. 
     }     
}

function multipleReturns() internal returns(uint a, uint b, uint c) {
    return (1, 2, 3);
}

function processMultiReturns() external {
    uint a;
    uint b;
    uint c;
    //다수값을 설정함    
    (a, b, c) = multipleReturns();
}

function getLastReturnValue() external {
    uint c;
    //비어있는 건 빈값으로 설정가능
    (,,c) = multipleReturns();
}

function eatBLT(string sandwich) public {
    //스트링(문자)간의 동일 여부를 판단하기 위해선 keccak256 을 사용해서 해시값 비교를 해야한다는 점 유의
    if(keccak(sandwich) == keccak256("BLT")){
        eat();
    }
}

pragma solidity ^0.4.17;

contract Ownable {
    address public owner;
    event OwnerShipTransferred(address indexed previousOwner, address indexed newOwner);

    function Ownable() public {
        owner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0));
        OwnerShipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

.. Ownable 계약서에 있는
modifier onlyOwner() {
    require(msg.sender == owner);
    _
}

contract MyContract is Ownable {
    event eat(string food);

    function eatBread() external onlyOwner {
        eat("Bread");
    }
}

uint a;

uint32 a;

uint32 a;

uint32 b;

uint c;

uint32 a;

uint c;  

uint32 b;  

1 minutes = 60
1 hours = 3600 (60 * 60)
1 days = 86400 ( 24 * 1 hours)

uint lastUpdated;

function updateTimestamp() public {
    lastUpdated = now //now로 설정
}
//5분이 지난 경우 true , 아닌 경우 false
function fiveMinutesHavePassed() public view returns(bool) {
    return (now >= (lastUpdated + 5 minutes));
}

uint32(uint256 변수) //이런식으로 캐스팅함

function _doStuff(Zombie storage _zombie) internal {
    // _zombie 처리
}

// 사용자의 나이를 저장하는 매핑
mapping ( uint => uint ) public age;

//사용자의 특정 나이 이상인지 확인 하는 제어자
modifier olderThan( uint _age, uint _userId ) {
    require(age[_userId]) >= _age);
    _;
}

function buyAlchoDrinks(uint _userId) public orderThan(16, _userId) {
    //필요한 함수 내용들
}

external view //오직 읽기에만 사용가능하다. 

function getArray() external pure returns(uint[]){
    //배열의 크기는 항상 주어져야 한다. 이후에는 변경될 수 있을것이다. 
    uint[] memory values = new uint[](3);
        
    values.push(1);
    values.push(2);
    values.push(3);
    
    return values;
}

function getEvens() pure external returns(uint[]) {
    uint[] memory evens = new uint[](5);
    
    uint counter = 0;
    
    for(uint i = 0; i <= 10; i++ ){
        if(i % 2 == 0){
            evens[counter] = i;
            counter++;
        }
    }
    return evens;    
}

Contract OnlineStore {
    function buySomething() external payable {
        //함수 실행에 0.001이더가 보내졌는지 체크하는 함수 (> , <로도 이용가능)
        require(msg.value == 0.001 ether);
        transferthing(msg.sender); //이더를 이동..
    }
}

// `OnlineStore`는 자네의 이더리움 상의 컨트랙트를 가리킨다고 가정해야 한다. 
OnlineStore.buySomething({from: web3.eth.defaultAccount, value: web3.utils.toWei(0.001)})

contract GetPaid is Ownable {
    //Owner 인지 체크
    function withdraw() external onlyOwner {
        //계좌에 있는 금액을 트렌스퍼한다. 
        owner.transfer(this.balance);
    }
}

uint itemfee = 0.001 ether;
msg.sender.transfer(msg.value - itemFee); //입금하는 사람에게 출금하고 있다. 

seller.transfer(msg.value) //지정된 판매자에게 금액을 출금하고 있다. 

uint randNonce = 0;
uint random = uint(keccak256(now, msg.sender, randNounce)) % 100;
randNonce++;
uint random2 = uint(keccak256(now, msg.sender, randNounce)) % 100;

if (zombieCoins[msg.sender] > 100000000) {
    
}else{
    
}

contract ERC721 {
  event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
  event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);

  function balanceOf(address _owner) public view returns (uint256 _balance);
  function ownerOf(uint256 _tokenId) public view returns (address _owner);
  function transfer(address _to, uint256 _tokenId) public;
  function approve(address _to, uint256 _tokenId) public;
  function takeOwnership(uint256 _tokenId) public;
}

import "./erc721.sol"

//참고로 계약은 다중상속을 허용하고 있다. 
contrat A is B,C {
}

function balanceOf(address _owner) public view returns (uint256 _balance);
//Address 입력시 그 계정에 balance가 얼마나 있는지 조회할 수 있다.

function ownerOf(uint256 _tokenId) public view returns (address _owner);
//해당 토큰 아이디에 address를 리턴해준다.

uint number = 255;
number++; //이 경우 오버플로우 발생함

using SafeMath for uint256; //라이버러리를 사용하겠다고 정의

uint256 a = 5;
uint256 b = a.add(3);
uint256 c = a.mul(2);

library SafeMath {

  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

using SafeMath for uint;
uint test = 2;
test = test.mul(3); //인자가 2개가 필요하지만 자동으로 앞 변수(test)를 입력받게 된다.. 

//num++ 이 방법을 쓰지 말고
num = num.add(1); //이렇게 대체하면 됩니다.

/// @title A contract for basic math operations
/// @author H4XF13LD MORRIS 💯💯😎💯💯
/// @notice For now, this contract just adds a multiply function
contract Math {
  /// @notice Multiplies 2 numbers together
  /// @param x the first uint.
  /// @param y the second uint.
  /// @return z the product of (x * y)
  /// @dev This function does not currently check for overflows
  function multiply(uint x, uint y) returns (uint z) {
    // This is just a normal comment, and won't get picked up by natspec
    z = x * y;
  }
}

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