Abi Encoding

ABI Encoding with Nethereum

NuGet: Nethereum.ABI

Function selector calculation

var keccak = Sha3Keccack.Current;

var selector = keccak.CalculateHash("transfer(address,uint256)").Substring(0, 8);
// "a9059cbb"

var balanceOf = keccak.CalculateHash("balanceOf(address)").Substring(0, 8);
// "70a08231"

var approve = keccak.CalculateHash("approve(address,uint256)").Substring(0, 8);
// "095ea7b3"

Source: AbiEncodingDocExampleTests.ShouldCalculateFunctionSelector

Function encoding with Parameter array

var functionCallEncoder = new FunctionCallEncoder();
var sha3Signature = "a9059cbb";
var inputsParameters = new[]
{
    new Parameter("address", "to") { DecodedType = typeof(string) },
    new Parameter("uint256", "value") { DecodedType = typeof(BigInteger) }
};

var result = functionCallEncoder.EncodeRequest(sha3Signature, inputsParameters,
    "1234567890abcdef1234567890abcdef12345678", new BigInteger(1000));

Source: AbiEncodingDocExampleTests.ShouldEncodeBasicFunctionCall

Parameter attribute encoding

[Function("transfer")]
public class TransferFunction
{
    [Parameter("address", "to", 1)]
    public string To { get; set; }

    [Parameter("uint256", "amount", 2)]
    public BigInteger Amount { get; set; }
}

var input = new TransferFunction
{
    To = "1234567890abcdef1234567890abcdef12345678",
    Amount = new BigInteger(5000)
};

var result = new FunctionCallEncoder().EncodeRequest(input, "a9059cbb");

Source: AbiEncodingDocExampleTests.ShouldEncodeUsingParameterAttributes

Output decoding

var functionCallDecoder = new FunctionCallDecoder();
var outputParameters = new[]
{
    new ParameterOutput
    {
        Parameter = new Parameter("uint256", "balance") { DecodedType = typeof(BigInteger) }
    }
};

var encodedOutput = "0x" +
    "0000000000000000000000000000000000000000000000000000000000000045";

var result = functionCallDecoder.DecodeOutput(encodedOutput, outputParameters);
var balance = (BigInteger)result[0].Result; // 69

Source: AbiEncodingDocExampleTests.ShouldDecodeFunctionOutput

Event topic decoding

[Event("Transfer")]
public class TransferEventDTO
{
    [Parameter("address", "_from", 1, true)]
    public string From { get; set; }

    [Parameter("address", "_to", 2, true)]
    public string To { get; set; }

    [Parameter("uint256", "_value", 3, true)]
    public BigInteger Value { get; set; }
}

var topics = new[]
{
    "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
    "0x0000000000000000000000000000000000000000000000000000000000000000",
    "0x000000000000000000000000c14934679e71ef4d18b6ae927fe2b953c7fd9b91",
    "0x0000000000000000000000000000000000000000000000400000402000000001"
};

var transferDto = new TransferEventDTO();
new EventTopicDecoder().DecodeTopics(transferDto, topics, "0x");

Source: AbiEncodingDocExampleTests.ShouldDecodeTransferEventTopic

ABI JSON deserialization

var abi = @"[{""constant"":false,""inputs"":[{""name"":""a"",""type"":""uint256""}],
""name"":""multiply"",""outputs"":[{""name"":""d"",""type"":""uint256""}],""type"":""function""}]";

var des = new ABIJsonDeserialiser();
var contract = des.DeserialiseContract(abi);
// contract.Functions, contract.Events

Source: AbiEncodingDocExampleTests.ShouldDeserializeContractAbi

Custom error decoding

var error = new ErrorABI("InsufficientBalance");
error.InputParameters = new[]
{
    new Parameter("address", "account", 1),
    new Parameter("uint256", "balance", 2)
};

var errorSelector = error.Sha3Signature;
var encodedData = "0x" + errorSelector +
    "000000000000000000000000c14934679e71ef4d18b6ae927fe2b953c7fd9b91" +
    "0000000000000000000000000000000000000000000000000000000000000064";

var decoder = new FunctionCallDecoder();
var decoded = decoder.DecodeError(error, encodedData);
// decoded[0].Result = address, decoded[1].Result = BigInteger(100)

Source: AbiEncodingDocExampleTests.ShouldDecodeCustomError

Individual type encoding

var addressEncoded = new AddressType().Encode("1234567890abcdef1234567890abcdef12345678");
var intEncoded = new IntType("uint256").Encode(new BigInteger(42));
var boolEncoded = new BoolType().Encode(true);

var bytes32Value = new byte[32];
bytes32Value[0] = 0xAB;
var bytes32Encoded = new Bytes32Type("bytes32").Encode(bytes32Value);
// All produce 32-byte padded output

Source: AbiEncodingDocExampleTests.ShouldEncodeIndividualTypesWithPadding

Required usings

using Nethereum.ABI;
using Nethereum.ABI.ABIDeserialisation;
using Nethereum.ABI.FunctionEncoding;
using Nethereum.ABI.FunctionEncoding.Attributes;
using Nethereum.ABI.Model;
using Nethereum.Hex.HexConvertors.Extensions;
using Nethereum.Util;
using System.Numerics;