Question

I’m using sockets to communicate between a server and client.
For some reason though, the client skips every second line that the server has sent.

Client’s code:

    ...

    out.println(console.readLine());                //Client initiates (sent to server)

    while ((userOut = in.readLine()) != null)       //Waits for response
    {
        System.out.println("Server says: " + userOut);  //Prints response

        userIn = console.readLine();                //Gets user input
        out.println(userIn);                        //Sends user input to server
    }

    ...

Servers Code:

    ...

    while ((clientIn = in.readLine()) != null)  //Waits for clients message
    {
        System.out.println("Client says: " + clientIn); //Print clients message

        //Send appropriate response
        if (clientIn.equals(CLIENT_INSTRUCTION_LOGCALC))
        {
            out.println(SERVER_RESPONSE_LOGCALC_OK); //Send response to client
            System.out.println("Message sent: " + SERVER_RESPONSE_LOGCALC_OK); //Print response sent
        }

        else if (clientIn.equals(CLIENT_INSTRUCTION_SB))
        {
            out.println(SERVER_RESPONSE_SB_CHANGE);
        }

        else if (clientIn.equals(CLIENT_INSTRUCTION_BYE))
        {
            out.println(SERVER_RESPONSE_BYE_OK);
        }

        else if (clientIn.equals(CLIENT_INSTRUCTION_END))
        {
            out.println(SERVER_RESPONSE_END_OK);
        }

        else
        {
            out.println(SERVER_RESPONSE_INPUT_ERR);
        }
        ...

An example of using this displays (client first):

 LOGCALC
 Server says: LOGCALC: OK
 LOGCALC
 Server says: 

Server:

Client says: LOGCALC
Message sent: LOGCALC: OK

Client says: LOGCALC
Message sent: LOGCALC: OK

Hopefully you can see that in the second LOGCALC message sent to the server, the server responded, but the client did not receive the servers response.

Any thoughts?

Answer 1

Looking at your output, it appears that you have an extra linebreak in SERVER_RESPONSE_LOGCALC_OK, since System.out.println("Message sent: " + SERVER_RESPONSE_LOGCALC_OK); has an extra line after it in the server output. I’d remove the extra newline or use a simple out.print(SERVER_RESPONSE_LOGCALC_OK) instead of out.println(SERVER_RESPONSE_LOGCALC_OK);. This should solve your skipping problem.

The underlying flaw you’re experiencing is because you only read one line at a time and then wait for user input before reading another line instead of as many lines as are available before waiting for user input. I’m betting that if you do something like the code below in the client you will see different output.

out.println(console.readLine());                //Client initiates (sent to server)

    while ((userOut = in.readLine()) != null)       //Waits for response
    {
        System.out.println("Server says: " + userOut);  //Prints response

        if(!in.available()){
          userIn = console.readLine();                //Gets user input
          out.println(userIn);                        //Sends user input to server
        }
    }