Make HostedFileDownloadStream explicitly read-only (#7394)

* Initial plan

* Make HostedFileDownloadStream read-only by default

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

* Fix HostedFileDownloadStream write overload ordering

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

src/Libraries/Microsoft.Extensions.AI.Abstractions/Files/HostedFileDownloadStream.cs

@@ -51,6 +51,40 @@ protected HostedFileDownloadStream()
     /// </remarks>
     public virtual string? FileName => null;
 
+    /// <inheritdoc />
+    public override bool CanWrite => false;
+
+    /// <inheritdoc />
+    public override void SetLength(long value) => throw new NotSupportedException();
+
+    /// <inheritdoc />
+    public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state) =>
+        throw new NotSupportedException();
+
+    /// <inheritdoc />
+    public override void EndWrite(IAsyncResult asyncResult) => throw new NotSupportedException();
+
+    /// <inheritdoc />
+    public override void WriteByte(byte value) => throw new NotSupportedException();
+
+    /// <inheritdoc />
+    public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
+
+#if NET
+    /// <inheritdoc />
+    public override void Write(ReadOnlySpan<byte> buffer) => throw new NotSupportedException();
+#endif
+
+    /// <inheritdoc />
+    public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken) =>
+        throw new NotSupportedException();
+
+#if NET
+    /// <inheritdoc />
+    public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default) =>
+        throw new NotSupportedException();
+#endif
+
     /// <summary>
     /// Reads the entire stream content from its current position and returns it as a <see cref="DataContent"/>.
     /// </summary>

src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIFileDownloadStream.cs

@@ -61,9 +61,6 @@ public override Task<DataContent> ToDataContentAsync(CancellationToken cancellat
     /// <inheritdoc />
     public override bool CanSeek => _innerStream.CanSeek;
 
-    /// <inheritdoc />
-    public override bool CanWrite => false;
-
     /// <inheritdoc />
     public override long Length => _innerStream.Length;
 
@@ -94,22 +91,10 @@ public override int Read(byte[] buffer, int offset, int count) =>
     public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken) =>
         _innerStream.ReadAsync(buffer, offset, count, cancellationToken);
 
-    /// <inheritdoc />
-    public override void Write(byte[] buffer, int offset, int count) =>
-        throw new NotSupportedException();
-
-    /// <inheritdoc />
-    public override Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken) =>
-        throw new NotSupportedException();
-
     /// <inheritdoc />
     public override long Seek(long offset, SeekOrigin origin) =>
         _innerStream.Seek(offset, origin);
 
-    /// <inheritdoc />
-    public override void SetLength(long value) =>
-        _innerStream.SetLength(value);
-
     /// <inheritdoc />
     public override Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken) =>
         _innerStream.CopyToAsync(destination, bufferSize, cancellationToken);
@@ -135,13 +120,6 @@ protected override void Dispose(bool disposing)
     public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default) =>
         _innerStream.ReadAsync(buffer, cancellationToken);
 
-    /// <inheritdoc />
-    public override void Write(ReadOnlySpan<byte> buffer) => throw new NotSupportedException();
-
-    /// <inheritdoc />
-    public override ValueTask WriteAsync(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default) =>
-        throw new NotSupportedException();
-
     /// <inheritdoc />
     public override async ValueTask DisposeAsync()
     {

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Files/HostedFileDownloadStreamTests.cs

@@ -50,6 +50,31 @@ public async Task ToDataContentAsync_EmptyStream_ReturnsEmptyData()
         Assert.Empty(content.Data.ToArray());
     }
 
+    [Fact]
+    public void CanWrite_ReturnsFalse()
+    {
+        using var stream = new MinimalDownloadStream([1, 2, 3]);
+        Assert.False(stream.CanWrite);
+    }
+
+    [Fact]
+    public async Task WriteApis_ThrowNotSupportedException()
+    {
+        using var stream = new MinimalDownloadStream([1, 2, 3]);
+
+        Assert.Throws<NotSupportedException>(() => stream.SetLength(1));
+        Assert.Throws<NotSupportedException>(() => stream.Write([4], 0, 1));
+        Assert.Throws<NotSupportedException>(() => stream.WriteByte(4));
+        await Assert.ThrowsAsync<NotSupportedException>(() => stream.WriteAsync(new byte[] { 4 }, 0, 1));
+        Assert.Throws<NotSupportedException>(() => stream.BeginWrite([4], 0, 1, callback: null, state: null));
+        Assert.Throws<NotSupportedException>(() => stream.EndWrite(Task.CompletedTask));
+
+#if NET
+        Assert.Throws<NotSupportedException>(() => stream.Write([4]));
+        await Assert.ThrowsAsync<NotSupportedException>(() => stream.WriteAsync(new byte[] { 4 }).AsTask());
+#endif
+    }
+
     /// <summary>
     /// Minimal implementation that does not override MediaType or FileName, testing the default behavior.
     /// </summary>
@@ -64,14 +89,11 @@ public MinimalDownloadStream(byte[] data)
 
         public override bool CanRead => _inner.CanRead;
         public override bool CanSeek => _inner.CanSeek;
-        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() => _inner.Flush();
         public override int Read(byte[] buffer, int offset, int count) => _inner.Read(buffer, offset, count);
         public override long Seek(long offset, SeekOrigin origin) => _inner.Seek(offset, origin);
-        public override void SetLength(long value) => _inner.SetLength(value);
-        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
 
         protected override void Dispose(bool disposing)
         {
@@ -102,14 +124,11 @@ public MetadataDownloadStream(byte[] data, string? mediaType, string? fileName)
         public override string? FileName { get; }
         public override bool CanRead => _inner.CanRead;
         public override bool CanSeek => _inner.CanSeek;
-        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() => _inner.Flush();
         public override int Read(byte[] buffer, int offset, int count) => _inner.Read(buffer, offset, count);
         public override long Seek(long offset, SeekOrigin origin) => _inner.Seek(offset, origin);
-        public override void SetLength(long value) => _inner.SetLength(value);
-        public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
 
         protected override void Dispose(bool disposing)
         {