README.md

Swap Asset Contract

this is an example of creating a swap asset (ERC20) contract with required Swapin and Swapout methods for cross chain bridge.

please ref. to CrossChain-Bridge.

How to deploy contract using truffle

0. install @openzeppelin/contracts

npm install

flatten contract

This has been already done. Mention here only for re-flatten if modified later.

mpm install -g truffle-flattener
truffle-flattener internal/BtcSwapAsset.sol | sed '/SPDX-License-Identifier:/d' | sed 1i'// SPDX-License-Identifier: MIT' > contracts/BtcSwapAsset.sol
truffle-flattener internal/EthSwapAsset.sol | sed '/SPDX-License-Identifier:/d' | sed 1i'// SPDX-License-Identifier: MIT' > contracts/EthSwapAsset.sol
truffle-flattener internal/UsdtSwapAsset.sol | sed '/SPDX-License-Identifier:/d' | sed 1i'// SPDX-License-Identifier: MIT' > contracts/UsdtSwapAsset.sol
truffle-flattener internal/Erc20SwapAsset.sol | sed '/SPDX-License-Identifier:/d' | sed 1i'// SPDX-License-Identifier: MIT' > contracts/Erc20SwapAsset.sol

1. Modify truffle config

truffle-config.js

Normally, you may meed to modify the following items:

host: the rpc host of the node
port: the rpc port of the node
network_id: the chain id

2. Add and modify contracts

Add and modify contracts in contracts directory.

like our example: BtcSwapAsset.sol.

3. Add migrations to deploy contract

Add an js file to depoly contract in migrations directory.

like our example: 2_deploy_contracts.js.

4. Compile contract

Use the following command to compile contracts:

truffle compile

or re-compile all contracts:

truffle compile --all

5. Deploy contract

5.1 Deploy contract directly

Use the following command to deploy contract:

truffle migrate

or re-deploy contract:

truffle migrate --reset

We may want to perform a test or 'dry run' migration firstly:

truffle migrate --dry-run

5.2 Deploy contract using DCRM

Because we need to build a raw contract creation transaction and sign this raw transaction using DCRM technology,

So we need the bytecode as the transaction input data to build a raw contract cteation transaction.

bytecode can be found in ./build/contracts/BtcSwapAsset.json

5.3 get byte code by solc

The bytecode files in bytecode/solc directory are generated by the following command, with solc version of 0.5.4+commit.9549d8ff.Emscripten.clang

solcjs --bin --output-dir solc --evm-version byzantium --optimize --runs=1500 contracts/*.sol

5.4 get byte code by remix

use remix: https://remix.ethereum.org/#optimize=true&evmVersion=null&version=soljson-v0.5.4+commit.9549d8ff.js&runs=200

5.5 how to get bytecode of contract with constructor arguments

the bytecode in truffle built contracts is runtime bytecode which has not the constructor argument info.

we should append the packed constructor arguments data (like abi encoding) to the end of the runtime bytecode to generage the creation bytecode which is used as contract creation transaction's input data.

the following is a way by attaching to full node:

abi = ...
runtime_bytecode = ...
creation_bytecode = eth.contract(abi).getData(param1,param2,...lastparam,{from:eth.coinbase,data:runtime_bytecode})

6. Access the deployed contract

6.1 Access from truffle terminal

We can access the above deployed contract in truffle console terminal.

Firstly log into truffle console terminal:

truffle console

Then assign an variable app to the deployed contract instance:

BtcSwapAsset.deployed().then(function(instance){ app = instance; })

For convenience, we can also assign all local accounts to accounts variable:

web3.eth.getAccounts().then(function(result){ accounts = result })

Now we can access the methods and attributes of the deployed contract.

For example,

app.Swapout("45678","2MxQaHFhqKgYyTgcJj8foYHbPJQLQxvXQjp",{from:accounts[1]})

6.2 Access by attaching IPC file

after attached to the running node, we can access the contract by the following infos:

app = eth.contract(abi).at(contractAddress)

abi can be found in ./build/contracts/BtcSwapAsset.json (after building)