Rlp Encoding

RLP Encoding

NuGet: Nethereum.RLP

Source: tests/Nethereum.ABI.UnitTests/RlpDocExampleTests.cs

Important: Alias the encoder to avoid ambiguity with the namespace:

using RlpEncoder = Nethereum.RLP.RLP;

Required Usings

using System.Numerics;
using Nethereum.Hex.HexConvertors.Extensions;
using Nethereum.RLP;
using RlpEncoder = Nethereum.RLP.RLP;

Encode Strings

// Empty string encodes to 0x80
byte[] emptyBytes = "".ToBytesForRLPEncoding();
byte[] encodedEmpty = RlpEncoder.EncodeElement(emptyBytes);
// encodedEmpty.ToHex() == "80"

// Single character (< 0x80) encodes as itself
byte[] singleBytes = "d".ToBytesForRLPEncoding();
byte[] encodedSingle = RlpEncoder.EncodeElement(singleBytes);
// encodedSingle.ToHex() == "64"

// Short string: length prefix + data
byte[] dogBytes = "dog".ToBytesForRLPEncoding();
byte[] encodedDog = RlpEncoder.EncodeElement(dogBytes);
// encodedDog.ToHex() == "83646f67"

// Decode back
IRLPElement decoded = RlpEncoder.Decode(encodedDog);
string decodedStr = decoded.RLPData.ToStringFromRLPDecoded();
// decodedStr == "dog"

Encode Integers

// Zero encodes to 0x80 (same as empty)
byte[] zeroBytes = 0.ToBytesForRLPEncoding();
byte[] encodedZero = RlpEncoder.EncodeElement(zeroBytes);
// encodedZero.ToHex() == "80"

// Small int (< 128) encodes as single byte
byte[] smallBytes = 15.ToBytesForRLPEncoding();
byte[] encodedSmall = RlpEncoder.EncodeElement(smallBytes);
// encodedSmall.ToHex() == "0f"

// Larger int gets length prefix
byte[] mediumBytes = 1000.ToBytesForRLPEncoding();
byte[] encodedMedium = RlpEncoder.EncodeElement(mediumBytes);
// encodedMedium.ToHex() == "8203e8"

// Decode back
IRLPElement decoded = RlpEncoder.Decode(encodedMedium);
int decodedInt = decoded.RLPData.ToIntFromRLPDecoded();
// decodedInt == 1000

Encode BigInteger

byte[] hexBytes = "100102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f"
    .HexToByteArray();
BigInteger bigInt = hexBytes.ToBigIntegerFromRLPDecoded();

byte[] bigIntBytes = bigInt.ToBytesForRLPEncoding();
byte[] encoded = RlpEncoder.EncodeElement(bigIntBytes);
// encoded.ToHex() == "a0100102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f"

// Decode back
IRLPElement decoded = RlpEncoder.Decode(encoded);
BigInteger decodedBigInt = decoded.RLPData.ToBigIntegerFromRLPDecoded();
// decodedBigInt == bigInt

Encode Lists

// Empty list encodes to 0xc0
byte[][] emptyList = new byte[0][];
byte[] encodedEmpty = RlpEncoder.EncodeList(emptyList);
// encodedEmpty.ToHex() == "c0"

// List of strings: encode each element, then encode as list
string[] strings = { "cat", "dog" };
byte[][] stringBytes = strings.ToBytesForRLPEncoding();

byte[][] encodedElements = new byte[stringBytes.Length][];
for (int i = 0; i < stringBytes.Length; i++)
{
    encodedElements[i] = RlpEncoder.EncodeElement(stringBytes[i]);
}

byte[] encodedList = RlpEncoder.EncodeList(encodedElements);
// encodedList.ToHex() == "c88363617483646f67"

// Decode list
RLPCollection decodedList = RlpEncoder.Decode(encodedList) as RLPCollection;
string first = decodedList[0].RLPData.ToStringFromRLPDecoded();  // "cat"
string second = decodedList[1].RLPData.ToStringFromRLPDecoded(); // "dog"

Encode Raw Bytes

byte[] data = new byte[] { 0x01, 0x02, 0x03, 0x04 };
byte[] encoded = RlpEncoder.EncodeElement(data);

IRLPElement decoded = RlpEncoder.Decode(encoded);
byte[] decodedBytes = decoded.RLPData;
// decodedBytes == data

// Empty bytes
byte[] encodedEmpty = RlpEncoder.EncodeElement(new byte[0]);
// encodedEmpty.ToHex() == "80"

Extension Method Reference

RLP Encoding Rules Summary

1. Single byte < 0x80: encoded as itself
2. String 0-55 bytes: [0x80 + length] + data
3. String > 55 bytes: [0xb7 + length-of-length] + length + data
4. List total payload 0-55 bytes: [0xc0 + length] + items
5. List total payload > 55 bytes: [0xf7 + length-of-length] + length + items