为什么我的TCP应用程序在快速发送时会错过一些数据包

Question

我正在使用异步套接字用C#编写一个多客户端/服务器应用程序。连接上的每个客户端发送10个项目。问题是，当快速启动大量客户机时，每个客户机发送的条目都少于10个，有时什么也不发送，服务器只记录它们的连接。

private void Recieve(IAsyncResult iar) //Called when socket receives something.
{
    Socket server_conn = (Socket)iar.AsyncState;

    if (!SocketConnected(server_conn))
    {
        server_conn.Close();
        logthis("Client Disconnected");
        return;
    }
    int n = server_conn.EndReceive(iar);  //Stop Receiving and parse data, n is number of bytes received

    ClientData asdf = null;
    foreach (ClientData cls in clientlist)
    {
        if (server_conn.RemoteEndPoint == cls.clientsock.RemoteEndPoint) //Who sent this data
        {
            asdf = cls; //cls is who sent this data

            //Start a new thread and pass received bytes to it in order to be parsed
            var t = new Thread(() => parse(cls, n,cls.recvbuffer));
            t.Start();
            Thread.Sleep(100);
            break;
        }
    }

    asdf.recvbuffer = new byte[1024];      //Clear buffer of client
    server_conn.BeginReceive(asdf.recvbuffer, 0, asdf.recvbuffer.Length, SocketFlags.None, new AsyncCallback(Recieve), server_conn); //Start receiving again

}

private void parse(ClientData theclient, int nobytesreceived, byte[] bytesreceived)
{
    ClientData cls = theclient;
    int n = nobytesreceived;
    byte[] receivedbytes = bytesreceived;


    lock(s)
    {
    if (!cls.dataphase)  //If there's no fragmented packets still waiting to be read
    {
        cls.dataphase = true;   
        byte[] sizeinbytes = new byte[4];
        for (int i = 0; i < 4; i++)
        {
            sizeinbytes[i] = receivedbytes[i];
        }
        int size = BitConverter.ToInt32(sizeinbytes, 0);  //Read first four bytes of packet to get size of data

        if ((n - 4) == size)  //If received number of bytes - 4 is equals to datasize
        {
            byte[] payload = new byte[size];
            Array.Copy(receivedbytes, 4, payload, 0, (n - 4)); //Copy data to separately to payload array to be displayed to user
            logthis(cls.clientsock.RemoteEndPoint.ToString());
            logthis(Encoding.ASCII.GetString(payload));
            cls.dataphase = false;       //packet read successfully 
        }
        else if ((n - 4) < size) //If received amount of bytes is less than data size (fragmented data)
        {
            cls.data = new byte[size];
            for (int i = 4; i <= n - 4; i++)
            {
                cls.data[i - 4] += receivedbytes[i];
            }

            cls.datasize = size; //And cls.dataphase will remain true so it can be handled correctly the next time we receive something from same client
        }
        else if((n-4) > size)  //If received amount of bytes is bigger than data (lumped packets)
        {
            byte[] payload = new byte[size];
            byte[] otherpacket = new byte[(n - 4) - size];

            for(int i = 0; i < size; i++)
            {
                payload[i] += receivedbytes[i + 4];

            }

            logthis(cls.clientsock.RemoteEndPoint.ToString());
            logthis(Encoding.ASCII.GetString(payload));
            Array.Copy(receivedbytes, (size + 4), otherpacket, 0, ((n - 4) - size));
            receivedbytes = new byte[(n - 4) - size];
            receivedbytes = otherpacket;
            cls.dataphase = false;
            parse(cls, ((n - 4) - size), receivedbytes); //Send rest of packet to read again
        }

    }
    else
    {
        //not implemented, supposed to handle fragmented packets
        if (n >= cls.datasize)
        {

        }
        else if (n < cls.datasize)
        {

        }

    }

}

Answer 1

你的问题来自

else
{
    //not implemented, supposed to handle fragmented packets

我会把钱放在这样一个事实上，即您正在访问else语句并丢失数据。一旦您没有完全读取从read函数返回的一个或两个集总在一起的数据包（这比您想象的要常见得多），您的客户机就会陷入cls.dataphase=true；中，永远无法摆脱它。