使用Reactive Extensions（Rx）进行套接字编程实用吗？

问题描述

用Rx编写 GetMessages 函数的最简洁的方式是：

What is the most succint way of writing the GetMessages function with Rx:

static void Main()
{
    Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

    var messages = GetMessages(socket, IPAddress.Loopback, 4000);
    messages.Subscribe(x => Console.WriteLine(x));

    Console.ReadKey();
}

static IObservable<string> GetMessages(Socket socket, IPAddress addr, int port)
{
    var whenConnect = Observable.FromAsyncPattern<IPAddress, int>(socket.BeginConnect, socket.EndConnect)(addr, port);

    // now will receive a stream of messages
    // each message is prefixed with an 4 bytes/Int32 indicating it's length. 
    // the rest of the message is a string

    // ????????????? Now What ????????????? 
}

作为上述示例的驱动程序的简单服务器：

A simple server as a driver for the above sample: http://gist.github.com/452893#file_program.cs

我一直在使用，用于我正在做的一些套接字编程工作。我这样做的动机是，它将以某种方式使代码更简单。这是否意味着更少的代码，更少的嵌套内容。

I've been investigating using Reactive Extensions for some socket programming work I am doing. My motivation for doing so would be that it would somehow make the code "simpler". Whether this would mean less code, less nesting something along those lines.

但是到目前为止，似乎并非如此：

However so far that does not seem to be the case:

1. I尚未找到使用Rx和套接字的很多示例


2. 我发现与我现有的BeginXXXX，EndXXXX代码一样，


3. 尽管 Observable 具有，这不包括 SocketEventArgs 异步API。

1. I haven't found very many examples of using Rx with sockets
2. The example I have found don't seem less complicated then my existing BeginXXXX, EndXXXX code
3. Although Observable has extension methods for FromAsyncPattern, this does not cover the SocketEventArgs Async API.

当前的非工作解决方案

这是我到目前为止的内容。这是行不通的，它会因堆栈溢出而失败（heh）我还没有弄清楚语义，因此我可以创建一个 IObservable 来读取指定数量的

    static IObservable<int> GetMessages(Socket socket, IPAddress addr, int port)
    {
        var whenConnect = Observable.FromAsyncPattern<IPAddress, int>(socket.BeginConnect, socket.EndConnect)(addr, port);

        // keep reading until we get the first 4 bytes
        byte[] buffer = new byte[1024];
        var readAsync = Observable.FromAsyncPattern<byte[], int, int, SocketFlags, int>(socket.BeginReceive, socket.EndReceive);

        IObservable<int> readBytes = null;
        var temp = from totalRead in Observable.Defer(() => readBytes)
                   where totalRead < 4
                   select readAsync(buffer, totalRead, totalRead - 4, SocketFlags.None);
        readBytes = temp.SelectMany(x => x).Sum();

        var nowDoSomethingElse = readBytes.SkipUntil(whenConnect);
    }

推荐答案

按以下方式工作。这未经测试，没有考虑异常和部分返回消息的情况。但是，否则，我认为这是正确的方向。

Something along these lines could work. This is not tested, does not take into account exceptions and the case when a message is returned partially. But otherwise, I believe this is a right direction to go.

    public static IObservable<T> GetSocketData<T>(this Socket socket,
        int sizeToRead, Func<byte[], T> valueExtractor)
    {
        return Observable.CreateWithDisposable<T>(observer =>
        {
            var readSize = Observable
                .FromAsyncPattern<byte[], int, int, SocketFlags, int>(
                socket.BeginReceive,
                socket.EndReceive);
            var buffer = new byte[sizeToRead];
            return readSize(buffer, 0, sizeToRead, SocketFlags.None)
                .Subscribe(
                x => observer.OnNext(valueExtractor(buffer)),
                    observer.OnError,
                    observer.OnCompleted);
        });
    }

    public static IObservable<int> GetMessageSize(this Socket socket)
    {
        return socket.GetSocketData(4, buf => BitConverter.ToInt32(buf, 0));
    }

    public static IObservable<string> GetMessageBody(this Socket socket,
        int messageSize)
    {
        return socket.GetSocketData(messageSize, buf =>
            Encoding.UTF8.GetString(buf, 0, messageSize));
    }

    public static IObservable<string> GetMessage(this Socket socket)
    {

        return
            from size in socket.GetMessageSize()
            from message in Observable.If(() => size != 0,
                socket.GetMessageBody(size),
                Observable.Return<string>(null))
            select message;
    }

    public static IObservable<string> GetMessagesFromConnected(
        this Socket socket)
    {
        return socket
            .GetMessage()
            .Repeat()
            .TakeWhile(msg => !string.IsNullOrEmpty(msg));
    }

    public static IObservable<string> GetMessages(this Socket socket,
        IPAddress addr, int port)
    {
        return Observable.Defer(() => 
        {
            var whenConnect = Observable
                .FromAsyncPattern<IPAddress, int>(
                    socket.BeginConnect, socket.EndConnect);
            return from _ in whenConnect(addr, port)
                   from msg in socket.GetMessagesFromConnected()
                       .Finally(socket.Close)
                   select msg;
        });
    }

编辑：要处理不完整的读取，可以使用Observable。可以使用（在GetSockedData中） ），如Dave Sexton在。

To handle incomplete reads, Observable.While can be used (within GetSockedData) as proposed by Dave Sexton in the same thread on RX forum.

编辑：另外，请看一下Jeffrey Van Gogh的文章：

Also, take a look at this Jeffrey Van Gogh's article: Asynchronous System.IO.Stream reading

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