Question

我有一个TCP服务器，它只为客户端发送给服务器的某些消息将数据写回客户端。
它基本上是一个基于命令的服务器，服务器只为某些命令响应字符串，否则不会将任何内容发送回客户端。

下面给出的代码是一种方法，它假定如果服务器发送了任何数据，它会将其显示为“MESSAGE FROM SERVER”，附加了已发送的数据。

    class TcpEchoClient
    {
    static void Main(string[] args)
    {
    Console.WriteLine("Starting echo client...");


            string ipaddress = "127.0.0.1";
            TcpClient client = null;
            NetworkStream netstream = null;

            try
            {

                client = new TcpClient(ipaddress,1000);
                netstream = client.GetStream();

            }
            catch
            {
                Console.ReadKey();
                Environment.Exit(0);
            }


            while(true)
            {
                Console.WriteLine("Message :  ");
                string t = Console.ReadLine();
                string readdata = null;
                Console.WriteLine("\n");


                if (write(t,netstream))
                {
                    Console.WriteLine("Message sent.");

                    if (client.Available!=0)
                    {
                        readdata = read(netstream);
                        Console.WriteLine("MESSAGE FROM SERVER : "+readdata);
                    }


                }
                else
                {
                    Console.WriteLine("Unable to send message.");
                }
            }


        }

        static bool write(string dat, NetworkStream stream) 
        {

            try
            {

                StreamWriter writer = new StreamWriter(stream) { AutoFlush = true };


                try{writer.WriteLine(dat);}
                catch (IOException){return false;}

                if (SHAHash(dat, "DATA") != SHAHash(read(stream), "DATA"))
                    return false;
            }catch (InvalidOperationException){return false;}


            return true;        
        }

        static string read(NetworkStream stream)
        {

            StreamReader reader = new StreamReader(stream);

            string readdata = null;

            try
            {
                readdata = reader.ReadLine();
                reader.BaseStream.Flush();
            }
            catch(IOException)
            {
                return null;
            }

            return readdata;
        }
}

此帖子中未显示SHAHash函数。它的格式是SHAHash（消息，盐）。

面临的问题是服务器发送的消息并不总是由客户端读取。有时，服务器发送的数据会显示客户端控制台，有时则不会。

我应该对上面的代码进行哪些更正，这样我才能在发送数据时从服务器读取数据。也就是说，只有当服务器向客户端发送一些数据时才需要执行以下代码，否则不应该执行它。

readdata = read(netstream);
Console.WriteLine("MESSAGE FROM SERVER : "+readdata);

Answer 1

使用冲洗或自动冲洗时要谨慎。有时它会在发送/接收操作之前执行......但这通常在使用线程时发生。

我的第一个提示是流阅读器/编写器没有被正确破坏。尝试将它们打包成使用声明。

Answer 2

TCP不同步，因此您无法写入数据并希望响应立即可用。当您执行以下检查时

if (client.Available!=0)

无法保证服务器尚未发送任何响应。您需要继续检查，直到有可用数据或异步读取数据

我会使用NetworkStream.BeginRead和callbacks来获取服务器响应

class StreamData
{

    public NetworkStream netstream;

    public byte[] myReadBuffer;
}


class TcpEchoClient
{

    static void Main(string[] args)
    {
        Console.WriteLine("Starting echo client...");

        string ipaddress = "127.0.0.1";
        TcpClient client = null;
        NetworkStream netstream = null;

        try
        {
            client = new TcpClient(ipaddress, 13000);
            netstream = client.GetStream();
        }
        catch
        {
            Console.ReadKey();
            Environment.Exit(0);
        }
        var streamData = new StreamData
        {
            netstream = netstream,
            myReadBuffer = new byte[1024],
        };

        netstream.BeginRead(streamData.myReadBuffer, 0, streamData.myReadBuffer.Length,
                                                   new AsyncCallback(myReadCallBack),
                                                   streamData);

        while (true)
        {
            Console.WriteLine("Message :  ");
            string t = Console.ReadLine();
            Console.WriteLine("\n");

            if (write(t, netstream))
            {
                Console.WriteLine("Message sent.");
            }
            else
            {
                Console.WriteLine("Unable to send message.");
            }
        }
    }

    static void myReadCallBack(IAsyncResult ar)
    {
        var streamData = (StreamData)ar.AsyncState;
        int bytesRead = streamData.netstream.EndRead(ar);
        var readdata = Encoding.ASCII.GetString(streamData.myReadBuffer, 0, bytesRead);
        //Be aware that this might not be the complete message depending on the size of the message and the buffer size
        Console.WriteLine("You received the following message : " + readdata);

        //Start waiting for more data
        streamData.netstream.BeginRead(streamData.myReadBuffer, 0, streamData.myReadBuffer.Length,
                                                   new AsyncCallback(myReadCallBack),
                                                   streamData);
    }

    static bool write(string dat, NetworkStream stream)
    {
        try
        {
            StreamWriter writer = new StreamWriter(stream) { AutoFlush = true };

            try { writer.WriteLine(dat); }
            catch (IOException) { return false; }

            //if (SHAHash(dat, "DATA") != SHAHash(read(stream), "DATA"))
            //    return false;
        }
        catch (InvalidOperationException) { return false; }

        return true;
    }


}

找出TCP服务器是否已发送数据

2 个答案: