ReadStreamToArraySegment use BufferListStream directly when available

[danielmarbach]

Additional split of #19683

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[ghost]

Thank you for your contribution @danielmarbach! We will review the pull request and get back to you soon.

[danielmarbach]

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
AMD Ryzen 9 3950X, 1 CPU, 32 logical and 16 physical cores
.NET Core SDK=5.0.201
  [Host]     : .NET Core 3.1.13 (CoreCLR 4.700.21.11102, CoreFX 4.700.21.11602), X64 RyuJIT
  Job-AYYPIA : .NET Core 3.1.13 (CoreCLR 4.700.21.11102, CoreFX 4.700.21.11602), X64 RyuJIT

InvocationCount=800000  

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
ConvertViaMemoryStream	306.6 ns	6.13 ns	15.94 ns	1.00	0.00	0.1100	-	-	928 B
PatternMatch	132.8 ns	1.13 ns	0.88 ns	0.48	0.04	0.0325	-	-	280 B

[danielmarbach]

    using System;
    using System.IO;
    using System.Text;
    using BenchmarkDotNet.Attributes;
    using BenchmarkDotNet.Configs;
    using BenchmarkDotNet.Diagnosers;
    using BenchmarkDotNet.Exporters;
    using BenchmarkDotNet.Jobs;
    using Microsoft.Azure.Amqp;

    [Config(typeof(Config))]
    public class BufferListStreamDirectly
    {
        private BufferListStream stream;
        private AmqpMessage amqpMessage;

        private class Config : ManualConfig
        {
            public Config()
            {
                AddExporter(MarkdownExporter.GitHub);
                AddDiagnoser(MemoryDiagnoser.Default);
                AddJob(Job.Default.WithInvocationCount(800000));
            }
        }

        [IterationSetup]
        public void Setup()
        {
            stream = new BufferListStream(new[] {new ArraySegment<byte>(Encoding.UTF8.GetBytes("Hello"))});
            amqpMessage = AmqpMessage.Create(stream, false);
        }

        [IterationCleanup]
        public void Cleanup()
        {
            amqpMessage.Dispose();
        }

        private const int StreamBufferSizeInBytes = 512;

        [Benchmark(Baseline = true)]
        public ArraySegment<byte> ConvertViaMemoryStream()
        {
            using var messageStream = amqpMessage.ToStream();
            using var memStream = new MemoryStream(StreamBufferSizeInBytes);
            messageStream.CopyTo(memStream, StreamBufferSizeInBytes);
            return new ArraySegment<byte>(memStream.ToArray());
        }

        [Benchmark]
        public ArraySegment<byte> PatternMatch()
        {
            using var messageStream = amqpMessage.ToStream();
            return messageStream switch
            {
                BufferListStream bufferListStream => bufferListStream.ReadBytes((int) stream.Length),
                _ => throw new InvalidOperationException()
            };
        }
    }

[jsquire]

Thanks, @danielmarbach! I'll defer to Josh for approval and merge, but assuming that we're getting a BufferListStream back from the AMQP library in most cases, this looks like it could be a nice efficiency with little risk.

[JoshLove-msft]

Thanks, @danielmarbach! I'll defer to Josh for approval and merge, but assuming that we're getting a BufferListStream back from the AMQP library in most cases, this looks like it could be a nice efficiency with little risk.

As discussed in the other PR, we do always get back a BufferListStream, but looking in master it has been changed to a MemoryStream, so this still makes me a bit nervous. I don't think there are imminent plans to ship out of master though, and if others think this is a good calculated risk I'm happy to go with it. Still, it would be awesome if we could add coverage for the default case via a unit test, but we can always file an issue for that.

[danielmarbach]

sigh even the virtual was removed on that method. Basically, a complete breaking change also for all inheritors of that abstract class 🤷

[JoshLove-msft]

/azp run net - servicebus - tests

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