Handling inputs to a smart contract constructor

[oskarth]

Duplicate of waku-org/nwaku#323

Problem

The problem is about how to deploy a smart contract with its constructor's inputs using nim-web3.

Some thoughts:
The EthSend has a data field which embodies the compiled code of the contract, probably the constructor's parameters should be passed/encoded as part of the data field, like <smartcontract code><parameters of constructor> but couldn't find the encoding procedure in this library.

[oskarth]

Original issue by @staheri14. This is also an issue for SWAP accounting that also requires a constructor: waku-org/nwaku#323

@zah or someone else do you have any ideas for how to do this within nim-web3 library? Would be very useful. Also see previous discussion in Nimbus discord.

[staheri14]

A solution for this issue is implemented in this PR waku-org/nwaku#359 (in nim-waku repo), please see https://github.com/status-im/nim-waku/blob/master/tests/v2/test_utils.nim

[jangko]

@yglukhov , is #112 also addressing this issue?

[yglukhov]

Yes, contract dsl now supports constructors, but web3-send api is still missing for that. Here's an example of how one could implement it:

import web3, chronos

proc deployContractAux(web3: Web3, data: seq[byte], gasPrice = 0): Future[ReceiptObject] {.async.} =
  var tr: EthSend
  tr.`from` = web3.defaultAccount
  tr.data = data
  tr.gas = Quantity(30000000).some
  if gasPrice != 0:
    tr.gasPrice = some(gasPrice.Quantity)

  let r = await web3.send(tr)
  return await web3.getMinedTransactionReceipt(r)

proc send*[T](d: ContractDeployment[T, Web3]): Future[Sender[T]] {.async.} =
  let receipt = await d.sender.deployContractAux(d.data)
  result.sender = typeof(result.sender)(web3: d.sender, contractAddress: receipt.contractAddress.get)

let contractCode: seq[byte] = ... # Load contract code
contract TestContract:
  proc constructorNameDoesNotMatter(arg1, arg2: string) {.constructor.}

let web3 = waitFor newWeb3("ws://127.0.0.1:8545/")

let testContract: Sender[TestContract] = waitFor web3.deployContract(TestContract, contractCode, "arg1 value", "arg2 value").send()

[yglukhov]

Update:
With #118 merged, the deployment is even easier:

import web3, chronos
let contractCode: seq[byte] = ... # Load contract code
contract TestContract:
  proc constructorNameDoesNotMatter(arg1, arg2: string) {.constructor.}
let web3 = waitFor newWeb3("ws://127.0.0.1:8545/")
let testContract: Sender[TestContract] = waitFor web3.deployContract(TestContract, contractCode, "arg1 value", "arg2 value")