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A standard interface for non-fungible EOS tokens.
The following standard allows the implementation of a standard API for NFTs within EOS smart contracts. This standard provides basic functionality to track and transfer NFTs.
NFTs can represent ownership over digital or physical assets:
- Physical property — houses, unique artwork
- Cryptocollectibles — unique collectibles or instances which are part of limited-edition collections.
- "Negative value" assets — loans, burdens and other responsibilities
NFTs are distinguishable and you must track the ownership of each one separately.
A standard interface allows wallet/broker/auction applications to work with any NFT on EOS blockchain. A simple eosio.nft smart contract is provided.
This standard is inspired by the eosio.token standard. eosio.token is insufficient for tracking NFTs because each asset is distinct (non-fungible) whereas each of a quantity of tokens is identical (fungible).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
/// @title eosio.nft public interface
/// @dev See https://github.com/jafri/eosio.nft/blob/master/README.md
#include <eosiolib/eosio.hpp>
#include <eosiolib/asset.hpp>
#include <string>
#include <vector>
using namespace eosio;
using std::string;
using std::vector;
typedef uint128_t uuid;
typedef uint64_t id_type;
typedef string uri_type;
CONTRACT nft : public eosio::contract {
public:
using contract::contract;
nft( name receiver, name code, datastream<const char*> ds)
: contract(receiver, code, ds), tokens(receiver, receiver.value) {}
/// Creates token with a symbol name for the specified issuer account.
/// Throws if token with specified symbol already exists.
/// @param issuer Account name of the token issuer
/// @param symbol Symbol code of the token
ACTION create(name issuer, std::string symbol);
/// Issues specified number of tokens with previously created symbol to the account name "to".
/// Each token is generated with an unique token_id assigned to it. Requires authorization from the issuer.
/// Any number of tokens can be issued.
/// @param to Account name of tokens receiver
/// @param quantity Number of tokens to issue for specified symbol (positive integer number)
/// @param uris Vector of URIs for each issued token (size is equal to tokens number)
/// @param name Name of issued tokens (max. 32 bytes)
/// @param memo Action memo (max. 256 bytes)
ACTION issue(name to,
asset quantity,
vector<string> uris,
string name,
string memo);
/// Transfers 1 token with specified "id" from account "from" to account "to".
/// Throws if token with specified "id" does not exist, or "from" is not the token owner.
/// @param from Account name of token owner
/// @param to Account name of token receiver
/// @param id Unique ID of the token to transfer
/// @param memo Action memo (max. 256 bytes)
ACTION transferid(name from,
name to,
id_type id,
string memo);
/// Transfers 1 token with specified symbol in asset from account "from" to account "to".
/// Throws if amount is not 1, token with specified symbol does not exist, or "from" is not the token owner.
/// @param from Account name of token owner
/// @param to Account name of token receiver
/// @param quantity Asset with 1 token
/// @param memo Action memo (max. 256 bytes)
ACTION transfer(name from,
name to,
asset quantity,
string memo);
/// @notice Burns 1 token with specified "id" owned by account name "owner".
/// @param owner Account name of token owner
/// @param id Unique ID of the token to burn
ACTION burn(name owner,
id_type token_id);
/// @notice Sets owner of the token as a ram payer for stored data.
/// @param payer Account name of token owner
/// @param id Unique ID of the token to burn
ACTION setrampayer(name payer,
id_type id);
/// Structure keeps information about the balance of tokens
/// for each symbol that is owned by an account.
/// This structure is stored in the multi_index table.
TABLE account {
asset balance;
uint64_t primary_key() const { return balance.symbol.code().raw(); }
};
/// Structure keeps information about the total supply
/// of tokens for each symbol issued by "issue" account.
/// This structure is stored in the multi_index table.
TABLE stats {
asset supply;
name issuer;
uint64_t primary_key() const { return supply.symbol.code().raw(); }
uint64_t get_issuer() const { return issuer.value; }
};
/// Structure keeps information about each issued token.
/// Each token is assigned a global unique ID when it is issued.
/// Token also keeps track of its owner, stores assigned URI and its symbol code.
/// This structure is stored in the multi_index table "tokens".
TABLE token {
id_type id; // Unique 64 bit identifier,
uri_type uri; // RFC 3986
name owner; // token owner
asset value; // token value (1 SYS)
string tokenName; // token name
id_type primary_key() const { return id; }
uint64_t get_owner() const { return owner.value; }
string get_uri() const { return uri; }
asset get_value() const { return value; }
uint64_t get_symbol() const { return value.symbol.code().raw(); }
string get_name() const { return tokenName; }
// generated token global uuid based on token id and
// contract name, passed as argument
uuid get_global_id(name self) const
{
uint128_t self_128 = static_cast<uint128_t>(self.value);
uint128_t id_128 = static_cast<uint128_t>(id);
uint128_t res = (self_128 << 64) | (id_128);
return res;
}
string get_unique_name() const
{
string unique_name = tokenName + "#" + std::to_string(id);
return unique_name;
}
};
/// Account balance table
/// Primary index:
/// owner account name
using account_index = eosio::multi_index<"accounts"_n, account>;
/// Issued tokens statistics table
/// Primary index:
/// token symbol name
/// Secondary indexes:
/// issuer account name
using currency_index = eosio::multi_index<"stat"_n, stats,
indexed_by< "byissuer"_n, const_mem_fun< stats, uint64_t, &stats::get_issuer> > >;
/// Issued tokens table
/// Primary index:
/// token id
/// Seconday indexes:
/// owner account name
/// token symbol name
using token_index = eosio::multi_index<"token"_n, token,
indexed_by< "byowner"_n, const_mem_fun< token, uint64_t, &token::get_owner> >,
indexed_by< "bysymbol"_n, const_mem_fun< token, uint64_t, &token::get_symbol> > >;
private:
token_index tokens;
};In order to query information stored in tables, it is possible to use cleos commands:
display all issued tokens info
cleos get table eosio.nft eosio.nft token
display "tester1" tokens balance
cleos get table eosio.nft tester1 accounts
or
cleos get currency balance eosio.nft tester1
display current supply of tokens with symbol "NFT"
cleos get table eosio.nft NFT stat
Build command for EOSIO.CDT v1.4.0
eosio-cpp -o eosio.nft.wasm eosio.nft.cpp --abigen --contract nft
- Download the "eosio.contracts" repository and follow instructions on how to build it.
- Clone the "eosio.nft" repository into the "eosio.contracts" folder
- Add the following line to CMakeLists.txt in the "eosio.contracts" folder
...
add_subdirectory(eosio.token)
add_subdirectory(eosio.nft) <-- add this
...
- Copy files ("contractshpp.hpp.in" and "eosio.nft_tests.cpp") from the "eosio.contracts/eosio.nft/tests" folder to "eosio.contracts/tests"
- Rebuild the "eosio.contracts"
- Copy the file "eosio.nft.abi" from "eosio.contracts/eosio.nft" to "eosio.contracts/build/eosio.nft"
- Go to the "eosio.contracts/build/tests" folder and run the following command
./unit_test -t eosio_nft_tests
- Add secondary indices - done
- Add approval?
- Transfer between contracts