abi-encoding

Development

Encode and decode Ethereum ABI data with Nethereum. Use when the user needs to encode function calls, decode contract output, work with event topics, parse ABI JSON, handle custom errors, or calculate function selectors.

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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;