QRC20 Integration Technical Guide

This document explains the basics of interacting with an QRC20 contract with the qtumd CLI command tool.

The full example in PHP: Qrc20.php .

Intro

We recommend that an exchange use one main address to store tokens for all users. Below MAIN_QRC_ADDRESS is the main address.

The address of the QRC20 token contract is TOKEN_CONTRACT_ADDRESS.

gas limit is DEFAULT_GAS_LIMIT, recommended value is 250000
gas price is DEFAULT_GAS_PRICE，recommended value is 0.00000040

TOKEN_DECIMALS is the decimals of the token, which varies per token. Here we set it 8.

We'll use the following utility functions:

addressToHash160 - Convert base58 address to hash160 address.
to32bytesArg left-pad hex data to 32 bytes with 0.
addDecimals multiply the nominal token amount by the number of decimal places.

Running QTUMD

You should remember to enable the indexing service when starting qtumd, using the flags -logevents -txindex.

Interacting With QRC20

In the CLI examples below, please substitute {} with actual addresses and values.

Getting Token Balance

$userAddress is the deposit address

qtum-cli callcontract \
    {TOKEN_CONTRACT_ADDRESS} \
    70a08231{to32bytesArg(addressToHash160($userAddress))}

In the JSON output look for executionResult.output. This is the token balance.

Withdraw

$userAddress is the withdraw address
$amount the withdraw amount in unit token

qtum-cli sendtocontract \
    {TOKEN_CONTRACT_ADDRESS} \
    a9059cbb{to32bytesArg(addressToHash160($userAddress))}{to32bytesArg(addDecimals($amount)) \
    0 \
    {DEFAULT_GAS_LIMIT} \
    {DEFAULT_GAS_PRICE} \
    {MAIN_QRC_ADDRESS}

The command returns the txid of this transaction. You may use it to find information about this transaction (e.g. number of confirmations).

Generate a deposit address

For an exchange, a user may use the same address for both QTUM and other QRC20 tokens.

Use this command to generate a deposit address:

qtum-cli getnewaddress

Deposit and Witdraw Logs

$startingBlock is where you want to start looking (inclursive)
- You can start looking from 0, but for better efficiency, you should remember where to start looking.

qtum-cli searchlogs \
    STARTING_BLOCK \
    999999999 \
    '{ "addresses": ["TOKEN_CONTRACT_ADDRESS"]}' \
    '{"topics": ["ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]}'

The event type filtered is the Transfer event:

event Transfer(address indexed _from, address indexed _to, uint256 _value)

Look through the logs to filter by to or from addresses.

Checking Confirmations

Given a transaction id $txid:

qtum-cli gettransaction $txid

Use the property confirmations from output.

QRC20 Integration