client socket sends data but server socket does not receive them. c++ buffered stream?

Question

I am working on a project where a partner provides a service as socket server. And I write client sockets to communicate with it. The communication is two way: I send a request to server and then receive a response from server.

The problem is that I send the data to the server but apparently the server cannot receive the data.

From my side I just use very simple implementation just like the example from http://www.linuxhowtos.org/C_C++/socket.htm

#include <sys/socket.h>

socket_connect();

construct_request_data();

send(socket, request_data, request_length, 0/*flag*/); // I set flag as 0

// now the server should receive my request and send response to me    

recv(socket, response_data, response_length, 0);   

socket_close();

And it seems that the server socket is implemented with a "binding" to std::iostream and it is buffered stream. (i.e. the socket send/recv is done in iostream::write/read.)

server_socket_io >> receive_data;

server_socket_io << response_data; 

Btw, I got a test client from my partner and it is wrapped in a iostream as well. The test socket client can communicate with the server without problem, but it must do iostream::flush() after every socket send.

But I want to just keep it simple not to wrap my socket client in iostream.

I just wonder whether the buffered iostream results in the problem: the data is not processed since the data the client socket sent is just in very small amount and still buffered.

Or could it be my problem? how can I know if I really send out the data? does my client socket also buffer the data?

I have tried some "bad" workaround with TCP_NODELAY but it didn't help!

How can I solve the problem? from client side? or server side? Should I close the socket after sending request and before receiving response, so that the data will be "flushed" and processed?

or should I wrap my socket in iostream and do flush?

or the server socket should use a "unbuffered" stream?

thanks for any suggestion and advice!

Answer 1

Further to Jay's answer, you can try any network packet sniffer and check whether your packets are getting to the server or not. Have a look at wireshark or tcpdump.

Answer 2

Let's use "divide and conquer" to solve the problem.

First, does the server work?

From your code look up the port number that your server is listening on.

Start your server program. Run the following command line program to see if the server is really listening:

netstat -an -p tcp

It will produce a list of connections. You should see a connection on your selected port when the server is running. Stop the server and run the command again to ensure the port is no longer in use.

Once you've verified the server is listening try to connect to it using the following command:

telnet your-server-address-here your-port-number-here

telnet will print what your server sends to you on the screen and send what you type back to the sever.

This should give you some good clues.

Answer 3

I had a similar issue once before. My problem was that I never 'accepted' a connection (TCP) on the server inorder to create the stream between server/client. After I accepted the connection on the server side, everything worked as designed.

Answer 4

You should check the firewall settings for both systems. They may not be passing along your data.