Question

Trying to build a proxy server.
recv from client -> send to server -> recv from server -> send to client.

The proxy receives the correct data from the client.
But after that I recv 0 bytes from the server.

This is the packet i should recv from the client and send to the server

0A 00 2C 01 23 00 0C 00 B3 01

Here is my code;

    //intercept commu by server <-> client

    memset(buffer, 0, buffer_len);

    //recv from client
    if((bytecount = recv(*csock, buffer, buffer_len, 0))== -1){
        fprintf(stderr, "Err: receiving data %d\n", errno);
        return 0;
    }

    //display what we got from the client
    printf("Received bytes %d\n", bytecount);
    for ( int i = 0; i < bytecount; i++ ) {
    printf( "%02x ", static_cast<unsigned char>( buffer[i] ) );
    }
    printf("\n");

    //send to server what we got from the client
    if((gbytecount=send(gsock, buffer, buffer_len, 0))== -1){
    fprintf(stderr, "Error sending data %d\n", errno);
    goto FINISH;
    }


    //recv from server
    if((gbytecount = recv(gsock, buffer, buffer_len, 0))== -1){
        fprintf(stderr, "Error receiving data %d\n", errno);
        return 0;
    }

    printf("Received bytes %d\n", gbytecount);
    for ( int i = 0; i < gbytecount; i++ ) {
    printf( "%02x ", static_cast<unsigned char>( buffer[i] ) );
    }
    printf("\n");   

    //send back to client what we got from the server
    if((bytecount = send(*csock, buffer, buffer_len, 0))== -1){
        fprintf(stderr, "Err: sending data %d\n", errno);
        return 0;
    }

How do I check what the proxy is sending to the server after recv from the client?
And is there something wrong with my logic?

---

UPDATE

I guess i found the problem, its because of the buffer_len.

Now I have recv() bytes 93. But the server again sends another packet.
What do I do to my code?

Currently my code is:

recv from client -> send to server -> recv from server -> send to client.

How can I make this code like If the client/server sends something, it will

forward it to the other?

---

UPDATE

Got to solve it. Thanks.

Answer 1

I don’t know your server and client, but may be server actually close the socket that cause a 0 as result of recv, and the reason of closure may be is that you receive bytecount data from client but send buffer_len data to the server that may cause some invalid data after valid data to sent to the server!