add EncodeCheckSkipZeroes and new EncodeCheck and TryDecodeCheck variants with variable length prefix strings

Author: ssg

src/Base58.cs

@@ -5,6 +5,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Runtime.Serialization;
 using System.Security.Cryptography;
 
 namespace SimpleBase;
@@ -28,9 +29,9 @@ public sealed class Base58(Base58Alphabet alphabet) : DividingCoder<Base58Alphab
     const int reductionFactor = 733;
 
     const int maxCheckPayloadLength = 256;
+    const int minCheckDecodedBufferSize = 5;
     const int sha256Bytes = 32;
     const int sha256DigestBytes = 4;
-
     static readonly Lazy<Base58> bitcoin = new(() => new Base58(Base58Alphabet.Bitcoin));
     static readonly Lazy<Base58> ripple = new(() => new Base58(Base58Alphabet.Ripple));
     static readonly Lazy<Base58> flickr = new(() => new Base58(Base58Alphabet.Flickr));
@@ -87,17 +88,57 @@ public string EncodeCheck(ReadOnlySpan<byte> payload, byte version)
             throw new ArgumentException($"Payload length {payload.Length} is greater than {maxCheckPayloadLength}", nameof(payload));
         }
 
-        int versionPlusPayloadLen = payload.Length + 1;
-        int outputLen = versionPlusPayloadLen + sha256DigestBytes;
+        ReadOnlySpan<byte> prefix = [version];
+        return EncodeCheck(payload, prefix);
+    }
+
+    /// <summary>
+    /// Generate a Base58Check string out of a prefix buffer and payload.
+    /// </summary>
+    /// <param name="payload">Address data.</param>
+    /// <param name="prefix">Prefix buffer.</param>
+    /// <returns>Base58Check address.</returns>
+    /// <exception cref="ArgumentException">If <paramref name="payload"/> is empty.</exception>
+    public string EncodeCheck(ReadOnlySpan<byte> payload, ReadOnlySpan<byte> prefix)
+    {
+        int totalLength = prefix.Length + payload.Length;
+        int outputLen = totalLength + sha256DigestBytes;
         Span<byte> output = (outputLen < Bits.SafeStackMaxAllocSize) ? stackalloc byte[outputLen] : new byte[outputLen];
-        output[0] = version;
-        payload.CopyTo(output[1..]);
+        prefix.CopyTo(output);
+        payload.CopyTo(output[prefix.Length..]);
         Span<byte> sha256 = stackalloc byte[sha256Bytes];
-        computeDoubleSha256(output[..versionPlusPayloadLen], sha256);
-        sha256[..sha256DigestBytes].CopyTo(output[versionPlusPayloadLen..]);
+        computeDoubleSha256(output[..totalLength], sha256);
+        sha256[..sha256DigestBytes].CopyTo(output[totalLength..]);
         return Encode(output);
     }
 
+    /// <summary>
+    /// Generate a Base58Check string out of a prefix buffer and payload
+    /// by skipping leading zeroes in <paramref name="payload"/>.
+    /// Platforms like Tezos expects this behavior.
+    /// </summary>
+    /// <param name="payload">Address data.</param>
+    /// <param name="prefix">Prefix buffer.</param>
+    /// <returns>Base58Check address.</returns>
+    /// <exception cref="ArgumentException">
+    ///     If <paramref name="payload"/> is empty or only contains zeroes.
+    /// </exception>
+    public string EncodeCheckSkipZeroes(ReadOnlySpan<byte> payload, ReadOnlySpan<byte> prefix)
+    {
+        int firstNonZeroIndex = payload.IndexOfAnyExcept((byte)0);
+        if (firstNonZeroIndex < 0)
+        {
+            throw new ArgumentException("Payload cannot be empty or all zeroes", nameof(payload));
+        }
+
+        if (firstNonZeroIndex > 0)
+        {
+            payload = payload[firstNonZeroIndex..];
+        }
+
+        return EncodeCheck(payload, prefix);
+    }
+
     /// <summary>
     /// Try to decode and verify a Base58Check address.
     /// </summary>
@@ -111,28 +152,47 @@ public bool TryDecodeCheck(
         Span<byte> payload,
         out byte version,
         out int bytesWritten)
+    {
+        Span<byte> versionBuffer = stackalloc byte[1];
+        bool result = TryDecodeCheck(address, payload, versionBuffer, out bytesWritten);
+        version = versionBuffer[0];
+        return result;
+    }
+
+    /// <summary>
+    /// Try to decode and verify a Base58Check address.
+    /// </summary>
+    /// <param name="address">Address string.</param>
+    /// <param name="payload">Output address buffer.</param>
+    /// <param name="prefix">Prefix decoded, must have the exact size of the expected prefix.</param>
+    /// <param name="payloadBytesWritten">Number of bytes written in the output payload.</param>
+    /// <returns>True if address was decoded successfully and passed validation. False, otherwise.</returns>
+    public bool TryDecodeCheck(
+        ReadOnlySpan<char> address,
+        Span<byte> payload,
+        Span<byte> prefix,
+        out int payloadBytesWritten)
     {
         Span<byte> buffer = stackalloc byte[maxCheckPayloadLength + sha256DigestBytes + 1];
-        if (!TryDecode(address, buffer, out bytesWritten) || bytesWritten < 5)
+        if (!TryDecode(address, buffer, out int decodedBufferSize) || decodedBufferSize < minCheckDecodedBufferSize)
         {
-            version = 0;
+            payloadBytesWritten = 0;
             return false;
         }
 
-        buffer = buffer[..bytesWritten];
-        version = buffer[0];
+        buffer = buffer[..decodedBufferSize];
+        buffer[..prefix.Length].CopyTo(prefix);
         Span<byte> sha256 = stackalloc byte[sha256Bytes];
         computeDoubleSha256(buffer[..^sha256DigestBytes], sha256);
         if (!sha256[..sha256DigestBytes].SequenceEqual(buffer[^sha256DigestBytes..]))
         {
-            version = 0;
+            payloadBytesWritten = 0;
             return false;
         }
 
-        var finalBuffer = buffer[1..^sha256DigestBytes];
-        version = buffer[0];
+        var finalBuffer = buffer[prefix.Length..^sha256DigestBytes];
         finalBuffer.CopyTo(payload);
-        bytesWritten = finalBuffer.Length;
+        payloadBytesWritten = finalBuffer.Length;
         return true;
     }
 

src/PublicAPI.Unshipped.txt

@@ -1 +1,3 @@
-
+SimpleBase.Base58.EncodeCheck(System.ReadOnlySpan<byte> payload, System.ReadOnlySpan<byte> prefix) -> string!
+SimpleBase.Base58.EncodeCheckSkipZeroes(System.ReadOnlySpan<byte> payload, System.ReadOnlySpan<byte> prefix) -> string!
+SimpleBase.Base58.TryDecodeCheck(System.ReadOnlySpan<char> address, System.Span<byte> payload, System.Span<byte> prefix, out int payloadBytesWritten) -> bool

test/Base58/Base58CheckTest.cs

@@ -25,6 +25,16 @@ public class Base58CheckTest
         new object[] { 20, "00000000000000000000000000000000000000000000000000000000000000", "bi1EWXwJay2udZVxLJozuTb8Meg4W9c6xnmJaRDjg6pri5MBAxb9XwrpQXbtnqEoRV5U2pixnFfwyXC8tRAVC8XxnjK"},
     ];
 
+    // test vector taken from gotezos at https://github.com/goat-systems/go-tezos/blob/800cc714fad7313e92a5068407c23e0e397f5323/keys/key_test.go#L127
+    // see LICENSE.gotezos.txt for details
+    static object[][] zeroPrefixedLongVersionTestData = [
+        [ "0000861299624c9a3b52be10762c64bac282b1c02316", new byte[] { 6, 161, 159 }, "tz1XrwX7i9Nzh8e6UmG3VnFkAeoyWdTqDf3U" ],
+    ];
+
+    static object[][] longVersionTestData = [
+        [ "861299624c9a3b52be10762c64bac282b1c02316", new byte[] { 6, 161, 159 }, "tz1XrwX7i9Nzh8e6UmG3VnFkAeoyWdTqDf3U" ],
+    ];
+
     [Test]
     [TestCaseSource(nameof(testData))]
     public void EncodeCheck_ValidInput_ReturnsExpectedResult(int version, string payload, string expectedOutput)
@@ -34,6 +44,37 @@ public void EncodeCheck_ValidInput_ReturnsExpectedResult(int version, string pay
         Assert.That(result, Is.EqualTo(expectedOutput));
     }
 
+    [Test]
+    [TestCaseSource(nameof(zeroPrefixedLongVersionTestData))]
+    public void EncodeCheckSkipZeroes_ZeroPrefixes_ReturnsExpectedResult(string hexPayload, byte[] version, string expectedResult)
+    {
+        var payload = Convert.FromHexString(hexPayload);
+        string result = Base58.Bitcoin.EncodeCheckSkipZeroes(payload, version);
+        Assert.That(result, Is.EqualTo(expectedResult));
+    }
+
+    [Test]
+    [TestCaseSource(nameof(zeroPrefixedLongVersionTestData))]
+    public void TryDecodeCheck_ZeroPrefixedLongVersion_ValidInput_ReturnsExpectedResult(string expectedHexPayload, byte[] expectedVersion, string encoded)
+    {
+        var versionBuffer = new byte[expectedVersion.Length];
+        var outputBuffer = new byte[256];
+        bool result = Base58.Bitcoin.TryDecodeCheck(encoded, outputBuffer, versionBuffer, out int bytesWritten);
+        Assert.That(result, Is.True);
+        Assert.That(versionBuffer, Is.EquivalentTo(expectedVersion));
+        var expectedBuffer = Convert.FromHexString(expectedHexPayload.TrimStart('0'));
+        Assert.That(outputBuffer.AsSpan(0, bytesWritten).ToArray(), Is.EquivalentTo(expectedBuffer));
+    }
+
+    [Test]
+    [TestCaseSource(nameof(longVersionTestData))]
+    public void EncodeCheck_LongVersionOverload_DoesNotStripPrefixZeroes(string hexPayload, byte[] version, string expectedResult)
+    {
+        var payload = Convert.FromHexString(hexPayload);
+        string result = Base58.Bitcoin.EncodeCheck(payload, version);
+        Assert.That(result, Is.EqualTo(expectedResult));
+    }
+
     [Test]
     [TestCaseSource(nameof(testData))]
     public void TryDecodeCheck_ValidInput_ReturnsExpectedResult(int expectedVersion, string expectedOutput, string input)

test/LICENSE.gotezos.txt

@@ -0,0 +1,7 @@
+Copyright 2018 DefinitelyNotAGoat/MagicAglet
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.