Add Span overrides to BufferedReadStream

src/Http/WebUtilities/src/BufferedReadStream.cs

@@ -186,6 +186,12 @@ public override void Write(byte[] buffer, int offset, int count)
         _inner.Write(buffer, offset, count);
     }
 
+    /// <inheritdoc/>
+    public override void Write(ReadOnlySpan<byte> buffer)
+    {
+        _inner.Write(buffer);
+    }
+
     /// <inheritdoc/>
     public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken)
     {
@@ -203,19 +209,36 @@ public override int Read(byte[] buffer, int offset, int count)
     {
         ValidateBufferArguments(buffer, offset, count);
 
-        // Drain buffer
         if (_bufferCount > 0)
         {
-            int toCopy = Math.Min(_bufferCount, count);
-            Buffer.BlockCopy(_buffer, _bufferOffset, buffer, offset, toCopy);
-            _bufferOffset += toCopy;
-            _bufferCount -= toCopy;
-            return toCopy;
+            return DrainBuffer(buffer.AsSpan(offset, count));
         }
 
+        // Forward to the matching inner overload. Going through Read(Span<byte>) would
+        // fall back to Stream's rent-and-copy shim if the inner stream doesn't override it.
         return _inner.Read(buffer, offset, count);
     }
 
+    /// <inheritdoc/>
+    public override int Read(Span<byte> buffer)
+    {
+        if (_bufferCount > 0)
+        {
+            return DrainBuffer(buffer);
+        }
+
+        return _inner.Read(buffer);
+    }
+
+    private int DrainBuffer(Span<byte> buffer)
+    {
+        var toCopy = Math.Min(_bufferCount, buffer.Length);
+        _buffer.AsSpan(_bufferOffset, toCopy).CopyTo(buffer);
+        _bufferOffset += toCopy;
+        _bufferCount -= toCopy;
+        return toCopy;
+    }
+
     /// <inheritdoc/>
     public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
     {

src/Http/WebUtilities/src/PublicAPI.Unshipped.txt

@@ -1 +1,3 @@
 #nullable enable
+override Microsoft.AspNetCore.WebUtilities.BufferedReadStream.Read(System.Span<byte> buffer) -> int
+override Microsoft.AspNetCore.WebUtilities.BufferedReadStream.Write(System.ReadOnlySpan<byte> buffer) -> void

src/Http/WebUtilities/test/BufferedReadStreamTests.cs

@@ -72,8 +72,209 @@ public void ReadLine_LineSpanningMultipleBuffersWithinLimit_Succeeds()
         Assert.Equal(content, line);
     }
 
+    [Fact]
+    public void Read_Span_DrainsBufferedDataBeforeReadingInner()
+    {
+        // The buffer is rented from the pool, so its actual size may exceed the requested size.
+        // The content is long enough that some of it always remains in the inner stream.
+        const string content = "0123456789abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz";
+        var stream = MakeStream(content, bufferSize: 5);
+        Assert.True(stream.EnsureBuffered(5));
+        var buffered = stream.BufferedData.Count;
+        Assert.InRange(buffered, 5, content.Length - 3);
+
+        Span<byte> buffer = stackalloc byte[3];
+
+        // A span smaller than the buffered data drains it partially.
+        var read = stream.Read(buffer);
+        Assert.Equal(3, read);
+        Assert.Equal(content.Substring(0, 3), Encoding.UTF8.GetString(buffer.Slice(0, read)));
+        Assert.Equal(buffered - 3, stream.BufferedData.Count);
+
+        // Each read returns only buffered data, so the last one returns the remainder
+        // rather than topping up from the inner stream.
+        var consumed = read;
+        while (stream.BufferedData.Count > 0)
+        {
+            var remaining = stream.BufferedData.Count;
+            read = stream.Read(buffer);
+            Assert.Equal(Math.Min(remaining, buffer.Length), read);
+            Assert.Equal(content.Substring(consumed, read), Encoding.UTF8.GetString(buffer.Slice(0, read)));
+            consumed += read;
+        }
+        Assert.Equal(buffered, consumed);
+
+        // With the buffer drained, the read falls through to the inner stream.
+        read = stream.Read(buffer);
+        Assert.Equal(3, read);
+        Assert.Equal(content.Substring(consumed, 3), Encoding.UTF8.GetString(buffer.Slice(0, read)));
+        Assert.Equal(0, stream.BufferedData.Count);
+    }
+
+    [Fact]
+    public void Read_Array_DrainsBufferedDataBeforeReadingInner()
+    {
+        const string content = "0123456789abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz";
+        var stream = MakeStream(content, bufferSize: 5);
+        Assert.True(stream.EnsureBuffered(5));
+        var buffered = stream.BufferedData.Count;
+        Assert.InRange(buffered, 5, content.Length - 3);
+
+        var buffer = new byte[3];
+
+        var read = stream.Read(buffer, 0, buffer.Length);
+        Assert.Equal(3, read);
+        Assert.Equal(content.Substring(0, 3), Encoding.UTF8.GetString(buffer, 0, read));
+        Assert.Equal(buffered - 3, stream.BufferedData.Count);
+
+        var consumed = read;
+        while (stream.BufferedData.Count > 0)
+        {
+            var remaining = stream.BufferedData.Count;
+            read = stream.Read(buffer, 0, buffer.Length);
+            Assert.Equal(Math.Min(remaining, buffer.Length), read);
+            Assert.Equal(content.Substring(consumed, read), Encoding.UTF8.GetString(buffer, 0, read));
+            consumed += read;
+        }
+        Assert.Equal(buffered, consumed);
+
+        read = stream.Read(buffer, 0, buffer.Length);
+        Assert.Equal(3, read);
+        Assert.Equal(content.Substring(consumed, 3), Encoding.UTF8.GetString(buffer, 0, read));
+        Assert.Equal(0, stream.BufferedData.Count);
+    }
+
+    [Fact]
+    public void Write_Span_WritesToInnerStream()
+    {
+        var inner = new MemoryStream();
+        var stream = new BufferedReadStream(inner, bufferSize: 16);
+
+        stream.Write("hello"u8);
+
+        Assert.Equal("hello", Encoding.UTF8.GetString(inner.ToArray()));
+    }
+
+    [Fact]
+    public void Read_Array_WithEmptyBuffer_ForwardsToInnerArrayOverload()
+    {
+        var inner = new OverloadCountingStream("hello"u8.ToArray());
+        var stream = new BufferedReadStream(inner, bufferSize: 16);
+        var buffer = new byte[5];
+
+        var read = stream.Read(buffer, 0, buffer.Length);
+
+        Assert.Equal(5, read);
+        Assert.Equal("hello", Encoding.UTF8.GetString(buffer, 0, read));
+        Assert.Equal(1, inner.ArrayReads);
+        Assert.Equal(0, inner.SpanReads);
+    }
+
+    [Fact]
+    public void Read_Span_WithEmptyBuffer_ForwardsToInnerSpanOverload()
+    {
+        var inner = new OverloadCountingStream("hello"u8.ToArray());
+        var stream = new BufferedReadStream(inner, bufferSize: 16);
+        Span<byte> buffer = stackalloc byte[5];
+
+        var read = stream.Read(buffer);
+
+        Assert.Equal(5, read);
+        Assert.Equal("hello", Encoding.UTF8.GetString(buffer.Slice(0, read)));
+        Assert.Equal(1, inner.SpanReads);
+        Assert.Equal(0, inner.ArrayReads);
+    }
+
+    [Fact]
+    public void Write_Array_ForwardsToInnerArrayOverload()
+    {
+        var inner = new OverloadCountingStream([]);
+        var stream = new BufferedReadStream(inner, bufferSize: 16);
+        var data = "hello"u8.ToArray();
+
+        stream.Write(data, 0, data.Length);
+
+        Assert.Equal("hello", Encoding.UTF8.GetString(inner.ToArray()));
+        Assert.Equal(1, inner.ArrayWrites);
+        Assert.Equal(0, inner.SpanWrites);
+    }
+
+    [Fact]
+    public void Write_Span_ForwardsToInnerSpanOverload()
+    {
+        var inner = new OverloadCountingStream([]);
+        var stream = new BufferedReadStream(inner, bufferSize: 16);
+
+        stream.Write("hello"u8);
+
+        Assert.Equal("hello", Encoding.UTF8.GetString(inner.ToArray()));
+        Assert.Equal(1, inner.SpanWrites);
+        Assert.Equal(0, inner.ArrayWrites);
+    }
+
     private static BufferedReadStream MakeStream(string text, int bufferSize)
     {
         return new BufferedReadStream(new MemoryStream(Encoding.UTF8.GetBytes(text)), bufferSize);
     }
+
+    // Overrides both the array and span overloads so a test can tell which one BufferedReadStream
+    // forwarded to. It wraps a MemoryStream rather than deriving from one because MemoryStream's
+    // span overloads defer to Stream's base implementation for derived types, which rents an array
+    // and calls the array overload, hiding the difference.
+    private sealed class OverloadCountingStream : Stream
+    {
+        private readonly MemoryStream _inner;
+
+        public OverloadCountingStream(byte[] data)
+        {
+            _inner = new MemoryStream();
+            _inner.Write(data, 0, data.Length);
+            _inner.Position = 0;
+        }
+
+        public int ArrayReads { get; private set; }
+        public int SpanReads { get; private set; }
+        public int ArrayWrites { get; private set; }
+        public int SpanWrites { get; private set; }
+
+        public byte[] ToArray() => _inner.ToArray();
+
+        public override bool CanRead => true;
+        public override bool CanSeek => false;
+        public override bool CanWrite => true;
+        public override long Length => _inner.Length;
+        public override long Position
+        {
+            get => _inner.Position;
+            set => throw new NotSupportedException();
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            ArrayReads++;
+            return _inner.Read(buffer, offset, count);
+        }
+
+        public override int Read(Span<byte> buffer)
+        {
+            SpanReads++;
+            return _inner.Read(buffer);
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            ArrayWrites++;
+            _inner.Write(buffer, offset, count);
+        }
+
+        public override void Write(ReadOnlySpan<byte> buffer)
+        {
+            SpanWrites++;
+            _inner.Write(buffer);
+        }
+
+        public override void Flush() => _inner.Flush();
+        public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
+        public override void SetLength(long value) => throw new NotSupportedException();
+    }
 }