PipeReader CopyToAsync an overload to copy To IBufferWriter<byte>

[oliverjanik]

At the moment (net core 3.1.1) PipeReader.CopyToAsync has 2 overloads:

• copy to Stream
• copy to PipeWriter (which implements IBufferWriter<byte>)

https://docs.microsoft.com/en-us/dotnet/api/system.io.pipelines.pipereader.copytoasync

I'm trying to copy PipeReader into ArrayBufferWriter<byte> which seems like a common use-case and there's no direct way to do it.

Of course I could use a MemoryStream but where's the fun in that?

[manandre]

In next release, a new Stream.CopyToAsync overload will be available as described in https://github.com/dotnet/corefx/issues/21472

public virtual Task CopyToAsync(Func<ReadOnlyMemory<byte>, object?, CancellationToken, ValueTask> callback, object? state, int bufferSize, CancellationToken cancellationToken)

Enabling this type of code:

await pipeReader
    .AsStream()
    .CopyToAsync((memory, state, _) => 
    {
        ((IBufferWriter<byte>)state).Write(memory.Span);
        return default;
    },
    state: bufferWriter,
    bufferSize: 4096,
    cancellationToken: default); 

Would it fit your need?

[oliverjanik]

Nah, I'm suggesting a convenience function. Your solution is longer than using ReadAsync in a while loop.

As a side note, is there any guidance on when to use streams vs the new pipelines?

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