Support encoding constructor arguments

[kamikazechaser]

The ABI parser expects any function to be named. In some cases it would be useful to encode constructor args. (address) for example doesn't work. One way would be to reserve the constructor keyword in the lexer.

constructorFunc, err := w3.NewFunc("constructor(address)", "")
if err != nil {
	return nil, err
}

constructorArgs := []any{w3.A(0x765DE816845861e75A25fCA122bb6898B8B1282a)}

constructorBytecode, err := constructorFunc.EncodeArgs(constructorArgs...)
if err != nil {
	return nil, err
}

// Should return bytearray representing 000000000000000000000000765de816845861e75a25fca122bb6898b8b1282a

Not sure if this is within scope of w3 or should the abi package (abi.Pack) from geth be used instead.

[lmittmann]

There is one hacky way to do this rn. w3.Func exposes Func.Args of the "raw" geth type ab.Arguments. So you could use the constructorFunc from your example to call constructorFunc.Args.Pack.

This is definitely within the scope of w3. The problem is I don't really have a good idea how to handle constructors. Not sure if it is safe to reserve the "constructor" name. Does it even make sense to encode arguments without the deploy bytecode? How would you handle this in your code-example?

[kamikazechaser]

Does it even make sense to encode arguments without the deploy bytecode? How would you handle this in your code-example?

I would append the constructor args because the contract bytecode is fixed.

func PrepareContractBytecodeData(contractBin string, contractABIJSON string, constructorArgs []any) ([]byte, error) {
	constructorBytecode, err := encodeConstructorArgs(contractABIJSON, constructorArgs)
	if err != nil {
		return nil, err
	}

	return append(common.Hex2Bytes(contractBin), constructorBytecode...), nil
}

func encodeConstructorArgs(contractABI string, constructorArgs []any) ([]byte, error) {
	abi, err := abi.JSON(strings.NewReader(contractABI))
	if err != nil {
		return nil, err
	}

	constructorBytecode, err := abi.Pack("", constructorArgs...)
	if err != nil {
		return nil, err
	}

	return constructorBytecode, nil
}

Not sure if it is safe to reserve the "constructor" name.

Yeah, it might not be the best way as the library should be as flexible as possible