From 3e3e5c28ec44d02926ace0174546745484540df8 Mon Sep 17 00:00:00 2001
From: sakno <roman.sakno@gmail.com>
Date: Thu, 5 Dec 2024 19:10:42 +0200
Subject: [PATCH] Added helpers for one-shot encoding and decoding

---
 .../Buffers/Binary/Leb128Tests.cs             | 14 +++---
 .../Buffers/SpanReaderWriterTests.cs          | 23 +++++++++
 src/DotNext/Buffers/Binary/Leb128.cs          | 47 +++++++++++++++++++
 3 files changed, 77 insertions(+), 7 deletions(-)

diff --git a/src/DotNext.Tests/Buffers/Binary/Leb128Tests.cs b/src/DotNext.Tests/Buffers/Binary/Leb128Tests.cs
index 3efe04055..8433f2395 100644
--- a/src/DotNext.Tests/Buffers/Binary/Leb128Tests.cs
+++ b/src/DotNext.Tests/Buffers/Binary/Leb128Tests.cs
@@ -8,16 +8,13 @@ private static void EncodeDecode<T>(ReadOnlySpan<T> values)
         where T : struct, IBinaryInteger<T>
     {
         Span<byte> buffer = stackalloc byte[Leb128<T>.MaxSizeInBytes];
-        var writer = new SpanWriter<byte>(buffer);
-        var reader = new SpanReader<byte>(buffer);
 
         foreach (var expected in values)
         {
-            writer.Reset();
-            reader.Reset();
-
-            True(writer.WriteLeb128(expected) > 0);
-            Equal(expected, reader.ReadLeb128<T>());
+            True(Leb128<T>.TryGetBytes(expected, buffer, out var bytesWritten));
+            True(Leb128<T>.TryParse(buffer, out var actual, out var bytesConsumed));
+            Equal(bytesWritten, bytesConsumed);
+            Equal(expected, actual);
         }
     }
 
@@ -27,6 +24,9 @@ private static void EncodeDecode<T>(ReadOnlySpan<T> values)
     [Fact]
     public static void EncodeDecodeInt64() => EncodeDecode([0L, long.MaxValue, long.MinValue, 0x80L, -1L]);
 
+    [Fact]
+    public static void EncodeDecodeInt128() => EncodeDecode([0, Int128.MaxValue, Int128.MinValue, 0x80, Int128.NegativeOne]);
+
     [Fact]
     public static void EncodeDecodeUInt32() => EncodeDecode([uint.MinValue, uint.MaxValue, 0x80U]);
 }
\ No newline at end of file
diff --git a/src/DotNext.Tests/Buffers/SpanReaderWriterTests.cs b/src/DotNext.Tests/Buffers/SpanReaderWriterTests.cs
index 47c2ae35b..c246053ef 100644
--- a/src/DotNext.Tests/Buffers/SpanReaderWriterTests.cs
+++ b/src/DotNext.Tests/Buffers/SpanReaderWriterTests.cs
@@ -452,4 +452,27 @@ public static void WriteLengthPrefixedBytes(LengthFormat format)
         using var actual = reader.ReadBlock(format);
         Equal(expected, actual.Span);
     }
+    
+    private static void EncodeDecodeLeb128<T>(ReadOnlySpan<T> values)
+        where T : struct, IBinaryInteger<T>
+    {
+        Span<byte> buffer = stackalloc byte[Leb128<T>.MaxSizeInBytes];
+        var writer = new SpanWriter<byte>(buffer);
+        var reader = new SpanReader<byte>(buffer);
+
+        foreach (var expected in values)
+        {
+            writer.Reset();
+            reader.Reset();
+
+            True(writer.WriteLeb128(expected) > 0);
+            Equal(expected, reader.ReadLeb128<T>());
+        }
+    }
+    
+    [Fact]
+    public static void EncodeDecodeInt32() => EncodeDecodeLeb128([0, int.MaxValue, int.MinValue, 0x80, -1]);
+    
+    [Fact]
+    public static void EncodeDecodeInt64() => EncodeDecodeLeb128([0L, long.MaxValue, long.MinValue, 0x80L, -1L]);
 }
\ No newline at end of file
diff --git a/src/DotNext/Buffers/Binary/Leb128.cs b/src/DotNext/Buffers/Binary/Leb128.cs
index ff81fd9b6..8afd60b49 100644
--- a/src/DotNext/Buffers/Binary/Leb128.cs
+++ b/src/DotNext/Buffers/Binary/Leb128.cs
@@ -95,6 +95,53 @@ public T Value
     /// <returns></returns>
     public readonly Enumerator GetEnumerator() => new(value);
 
+    /// <summary>
+    /// Tries to encode the value by using LEB128 binary format.
+    /// </summary>
+    /// <param name="value">The value to encode.</param>
+    /// <param name="buffer">The output buffer.</param>
+    /// <param name="bytesWritten">The number of bytes written.</param>
+    /// <returns><see langword="true"/> if <paramref name="buffer"/> has enough space to save the encoded value; otherwise, <see langword="false"/>.</returns>
+    public static bool TryGetBytes(T value, Span<byte> buffer, out int bytesWritten)
+    {
+        bytesWritten = 0;
+        var index = 0;
+        foreach (var octet in new Leb128<T> { Value = value })
+        {
+            if ((uint)index >= (uint)buffer.Length)
+                return false;
+
+            buffer[index++] = octet;
+        }
+
+        bytesWritten = index;
+        return true;
+    }
+
+    /// <summary>
+    /// Decodes LEB128-encoded integer.
+    /// </summary>
+    /// <param name="buffer">The input buffer containing LEB128 octets.</param>
+    /// <param name="result">The decoded value.</param>
+    /// <param name="bytesConsumed">The number of bytes consumed from <paramref name="buffer"/>.</param>
+    /// <returns><see langword="true"/> if operation is successful; otherwise, <see langword="false"/>.</returns>
+    public static bool TryParse(ReadOnlySpan<byte> buffer, out T result, out int bytesConsumed)
+    {
+        bytesConsumed = 0;
+        var decoder = new Leb128<T>();
+        var successful = false;
+
+        foreach (var octet in buffer)
+        {
+            bytesConsumed += 1;
+            if (successful = !decoder.Append(octet))
+                break;
+        }
+
+        result = decoder.Value;
+        return successful;
+    }
+
     /// <summary>
     /// Represents an enumerator that produces 7-bit encoded integer as a sequence of octets.
     /// </summary>