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MagickImage.ReadAsync swallows non cancellation related exceptions from the stream it reads from

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Issue 类型
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技术栈
csharp
领域
backend

调研方向

首先定位 AsyncStreamWrapper.ReadAsync，以及等待它的 MagickImage.ReadAsync 路径。使用提供的 ThrowingStream 测试重现问题，然后验证其 IOException 能够传递到调用方，同时取消操作仍按预期运行。测试通过且不返回空图像即表示完成。

由索引模型根据 Issue 内容生成。

描述

Magick.NET version

14.17.2

Environment (Operating system, version and so on)

Mac / Linix

Description

AsyncStreamWrapper has this code:

    private async Task ReadAsync(CancellationToken cancellationToken)
    {
        while (true)
        {
            try
            {
                await _performRead.WaitAsync(cancellationToken).ConfigureAwait(false);
            }
            catch
            {
                _exceptionThrown = true;
                if (_performRead.Wait(0))
                    _readDone.Release();
                return;
            }

            if (_readCount == -1)
                return;

            try
            {
                _readCount = await _stream.ReadAsync(Data, 0, _readCount, cancellationToken).ConfigureAwait(false);
            }
            catch
            {
                _exceptionThrown = true;
            }
            finally
            {
                _readDone.Release();
            }
        }
    }

if _stream.ReadAsync throws the fact is logged so that subsequently in the caller the cancellation token has an opportunity to throw.

        var readTask = ReadAsync(cancellationToken);

        await Task.WhenAll(actionTask, readTask).ConfigureAwait(false);

        if (_exceptionThrown)
            cancellationToken.ThrowIfCancellationRequested();
    }

However this has an unfortunate side effect, and that is that non-cancellation related exceptions are swallowed. I discovered this because I use a wrapper around my network streams that throw under certain conditions. When this wrapper throws MagickImage.ReadAsync returns an RGB image of 0x0 dimensions rather than allowing the exception to percolate up.

Steps to Reproduce
    class ThrowingStream : MemoryStream
    {
        public ThrowingStream(byte[] buffer, bool writable) : base(buffer, writable)
        {
        }

        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            throw new IOException("Space Goat Failure");
        }
    }
    
    [TestMethod]
    public async Task SafeReadAsync_HealthyStream_ReadsTheImageBad()
    {
        using var image = new MagickImage();
        byte[] input = [1, 2, 3, 4, 5];

        await Assert.ThrowsAsync<Exception>(() => image.ReadAsync(new ThrowingStream(input, false)));
    }

The test fails because the exception is swallowed.

The screenshot is just a placeholder so I could submit the issue, it is of no relevance.

Images

Screenshot 2026-10-01 at 16.48.56.png

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  3. Fork 仓库，在一个分支上完成修改。
  4. 提交 Pull Request，并在描述里引用这个 Issue 编号。

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