1 files changed, 397 insertions, 0 deletions
diff --git a/tests/Jellyfin.Extensions.Tests/StreamExtensionsTests.cs b/tests/Jellyfin.Extensions.Tests/StreamExtensionsTests.cs
new file mode 100644
index 0000000000..cdbf2f8b1d
--- /dev/null
+++ b/tests/Jellyfin.Extensions.Tests/StreamExtensionsTests.cs
@@ -0,0 +1,397 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Jellyfin.Extensions.Tests;
+
+public class StreamExtensionsTests
+{
+    [Fact]
+    public async Task IsStreamIdenticalAsync_SeekableDifferentLengths_ReturnsFalse()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = new MemoryStream(new byte[] { 1, 2, 3 });
+        await using var b = new MemoryStream(new byte[] { 1, 2, 3, 4 });
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.False(result);
+    }
+
+    [Fact]
+    public async Task IsStreamIdenticalAsync_NonSeekableIdenticalStreams_ReturnsTrue()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = new NonSeekableReadStream(new byte[] { 1, 2, 3, 4 });
+        await using var b = new NonSeekableReadStream(new byte[] { 1, 2, 3, 4 });
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public async Task IsStreamIdenticalAsync_NonSeekableDifferentStreams_ReturnsFalse()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = new NonSeekableReadStream(new byte[] { 1, 2, 3, 4 });
+        await using var b = new NonSeekableReadStream(new byte[] { 1, 2, 9, 4 });
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.False(result);
+    }
+
+    [Fact]
+    public async Task IsFileIdenticalAsync_NonSeekableStream_ThrowsArgumentException()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var path = Path.Join(Path.GetTempPath(), Path.GetRandomFileName());
+        await File.WriteAllBytesAsync(path, new byte[] { 1, 2, 3, 4 }, cancellationToken);
+
+        try
+        {
+            await using var stream = new NonSeekableReadStream(new byte[] { 1, 2, 3, 4 });
+
+            await Assert.ThrowsAsync<ArgumentException>(async () =>
+                await stream.IsFileIdenticalAsync(path, cancellationToken));
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    // Both publiclyVisible values are exercised so the test runs once under the fast path
+    // (TryGetBuffer succeeds) and once under the slow path (TryGetBuffer returns false).
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public async Task IsFileIdenticalAsync_UsesStartOfStreamAndRestoresPosition_OnMatch(bool publiclyVisible)
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var path = Path.Join(Path.GetTempPath(), Path.GetRandomFileName());
+        var bytes = new byte[] { 10, 20, 30, 40, 50 };
+        await File.WriteAllBytesAsync(path, bytes, cancellationToken);
+
+        try
+        {
+            await using var stream = CreateMemoryStream(bytes, publiclyVisible);
+            stream.Position = 3;
+
+            var result = await stream.IsFileIdenticalAsync(path, cancellationToken);
+
+            Assert.True(result);
+            Assert.Equal(3, stream.Position);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public async Task IsFileIdenticalAsync_RestoresPosition_OnMismatch(bool publiclyVisible)
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var path = Path.Join(Path.GetTempPath(), Path.GetRandomFileName());
+        await File.WriteAllBytesAsync(path, new byte[] { 10, 20, 30, 40, 99 }, cancellationToken);
+
+        try
+        {
+            await using var stream = CreateMemoryStream(new byte[] { 10, 20, 30, 40, 50 }, publiclyVisible);
+            stream.Position = 2;
+
+            var result = await stream.IsFileIdenticalAsync(path, cancellationToken);
+
+            Assert.False(result);
+            Assert.Equal(2, stream.Position);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public async Task IsStreamIdenticalAsync_BothMemoryStreams_NonZeroPositions_SeeksToStart(bool publiclyVisible)
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = CreateMemoryStream(new byte[] { 1, 2, 3, 4, 5 }, publiclyVisible);
+        await using var b = CreateMemoryStream(new byte[] { 1, 2, 3, 4, 5 }, publiclyVisible);
+        a.Position = 3;
+        b.Position = 1;
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.True(result);
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public async Task IsStreamIdenticalAsync_MemoryStreamPairedWithSeekableNonMemoryStream_NonZeroPositions_SeeksToStart(bool publiclyVisible)
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = CreateMemoryStream(new byte[] { 1, 2, 3, 4 }, publiclyVisible);
+        await using var b = new SeekableNonMemoryStream(new byte[] { 1, 2, 3, 4 });
+        a.Position = 2;
+        b.Position = 3;
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.True(result);
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public async Task IsStreamIdenticalAsync_NonMemoryStreamPairedWithMemoryStream_Swaps_ReturnsTrue(bool publiclyVisible)
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = new SeekableNonMemoryStream(new byte[] { 1, 2, 3, 4 });
+        await using var b = CreateMemoryStream(new byte[] { 1, 2, 3, 4 }, publiclyVisible);
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public async Task IsStreamIdenticalAsync_BothSeekableNonMemoryStreams_NonZeroPositions_SeeksToStart()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = new SeekableNonMemoryStream(new byte[] { 1, 2, 3, 4 });
+        await using var b = new SeekableNonMemoryStream(new byte[] { 1, 2, 3, 4 });
+        a.Position = 1;
+        b.Position = 2;
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public async Task IsStreamIdenticalAsync_NonSeekableShortReads_Identical_ReturnsTrue()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        var data = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
+        await using var a = new ShortReadingNonSeekableStream(data, maxReadSize: 3);
+        await using var b = new ShortReadingNonSeekableStream(data, maxReadSize: 5);
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public async Task IsStreamIdenticalAsync_NonSeekableShortReads_DifferentLengths_ReturnsFalse()
+    {
+        var cancellationToken = TestContext.Current.CancellationToken;
+        await using var a = new ShortReadingNonSeekableStream(new byte[] { 1, 2, 3, 4 }, maxReadSize: 3);
+        await using var b = new ShortReadingNonSeekableStream(new byte[] { 1, 2, 3, 4, 5 }, maxReadSize: 5);
+
+        var result = await a.IsStreamIdenticalAsync(b, cancellationToken);
+
+        Assert.False(result);
+    }
+
+    private static MemoryStream CreateMemoryStream(byte[] data, bool publiclyVisible)
+        => publiclyVisible
+            ? new MemoryStream(data, 0, data.Length, writable: false, publiclyVisible: true)
+            : new MemoryStream(data);
+
+    private sealed class NonSeekableReadStream : Stream
+    {
+        private readonly Stream _inner;
+
+        public NonSeekableReadStream(byte[] data)
+        {
+            _inner = new MemoryStream(data, writable: false);
+        }
+
+        public override bool CanRead => true;
+
+        public override bool CanSeek => false;
+
+        public override bool CanWrite => false;
+
+        public override long Length => throw new NotSupportedException();
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override void Flush()
+        {
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+            => _inner.Read(buffer, offset, count);
+
+        public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
+            => _inner.ReadAsync(buffer, cancellationToken);
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+            => _inner.ReadAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
+
+        public override long Seek(long offset, SeekOrigin origin)
+            => throw new NotSupportedException();
+
+        public override void SetLength(long value)
+            => throw new NotSupportedException();
+
+        public override void Write(byte[] buffer, int offset, int count)
+            => throw new NotSupportedException();
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _inner.Dispose();
+            }
+
+            base.Dispose(disposing);
+        }
+
+        public override async ValueTask DisposeAsync()
+        {
+            await _inner.DisposeAsync();
+            await base.DisposeAsync();
+        }
+    }
+
+    private sealed class SeekableNonMemoryStream : Stream
+    {
+        private readonly MemoryStream _inner;
+
+        public SeekableNonMemoryStream(byte[] data)
+        {
+            _inner = new MemoryStream(data, writable: false);
+        }
+
+        public override bool CanRead => true;
+
+        public override bool CanSeek => true;
+
+        public override bool CanWrite => false;
+
+        public override long Length => _inner.Length;
+
+        public override long Position
+        {
+            get => _inner.Position;
+            set => _inner.Position = value;
+        }
+
+        public override void Flush()
+        {
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+            => _inner.Read(buffer, offset, count);
+
+        public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
+            => _inner.ReadAsync(buffer, cancellationToken);
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+            => _inner.ReadAsync(buffer.AsMemory(offset, count), cancellationToken).AsTask();
+
+        public override long Seek(long offset, SeekOrigin origin)
+            => _inner.Seek(offset, origin);
+
+        public override void SetLength(long value)
+            => throw new NotSupportedException();
+
+        public override void Write(byte[] buffer, int offset, int count)
+            => throw new NotSupportedException();
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _inner.Dispose();
+            }
+
+            base.Dispose(disposing);
+        }
+
+        public override async ValueTask DisposeAsync()
+        {
+            await _inner.DisposeAsync();
+            await base.DisposeAsync();
+        }
+    }
+
+    private sealed class ShortReadingNonSeekableStream : Stream
+    {
+        private readonly Stream _inner;
+        private readonly int _maxReadSize;
+
+        public ShortReadingNonSeekableStream(byte[] data, int maxReadSize)
+        {
+            _inner = new MemoryStream(data, writable: false);
+            _maxReadSize = maxReadSize;
+        }
+
+        public override bool CanRead => true;
+
+        public override bool CanSeek => false;
+
+        public override bool CanWrite => false;
+
+        public override long Length => throw new NotSupportedException();
+
+        public override long Position
+        {
+            get => throw new NotSupportedException();
+            set => throw new NotSupportedException();
+        }
+
+        public override void Flush()
+        {
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+            => _inner.Read(buffer, offset, Math.Min(count, _maxReadSize));
+
+        public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
+            => _inner.ReadAsync(buffer[..Math.Min(buffer.Length, _maxReadSize)], cancellationToken);
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+            => _inner.ReadAsync(buffer.AsMemory(offset, Math.Min(count, _maxReadSize)), cancellationToken).AsTask();
+
+        public override long Seek(long offset, SeekOrigin origin)
+            => throw new NotSupportedException();
+
+        public override void SetLength(long value)
+            => throw new NotSupportedException();
+
+        public override void Write(byte[] buffer, int offset, int count)
+            => throw new NotSupportedException();
+
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                _inner.Dispose();
+            }
+
+            base.Dispose(disposing);
+        }
+
+        public override async ValueTask DisposeAsync()
+        {
+            await _inner.DisposeAsync();
+            await base.DisposeAsync();
+        }
+    }
+}