c# - 使用 Reactive Extensions (Rx) 进行套接字编程实用吗？

Question

用 Rx 编写 GetMessages 函数最简洁的方法是什么:

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 ????????????? 
}

作为上述示例驱动程序的简单服务器:http://gist.github.com/452893#file_program.cs

关于使用Rx进行套接字编程

我一直在调查使用 Reactive Extensions对于我正在做的一些套接字编程工作。我这样做的动机是它会以某种方式使代码“更简单”。这是否意味着更少的代码，更少的嵌套。

然而到目前为止，情况似乎并非如此:

1. 我还没有找到很多使用 Rx 和套接字的例子
2. example s 我发现似乎并不比我现有的 BeginXXXX、EndXXXX 代码复杂
3. 虽然 Observable 有 FromAsyncPattern 的扩展方法，这不包括 SocketEventArgs 异步 API。

当前无效的解决方案

这是我目前所拥有的。这不起作用，它因堆栈溢出而失败(呵呵)我还没有弄清楚语义，所以我可以创建一个 IObservable 来读取指定数量的字节。

    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);
    }

Answer 1

按照这些思路可能会奏效。这没有经过测试，没有考虑异常和部分返回消息的情况。但除此之外，我相信这是一个正确的方向。

    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:为了处理不完整的读取，可以使用 Observable.While(在 GetSockedData 中)，正如 Dave Sexton 在 same thread on RX forum 中所建议的那样.

编辑:另外，请看一下 Jeffrey Van Gogh 的这篇文章:Asynchronous System.IO.Stream reading