C++ – Dr John's Tech Talk

Intro
I was looking around for a sample TCP socket program written in C++ that might make working with TCP sockets less mysterious. I expected to find a flood of things to pick from, but that really wasn’t the case.

The Details
OK, I only looked for a few minutes, to be honest. The one I did settle on seems adequate. It’s sufficiently old, however, that it doesn’t actually work as-is. Probably if it did I wouldn’t even mention it. So I thought it was worth repeating here, with some tiny semantic updates.

What I used is from this web page: http://cs.baylor.edu/~donahoo/practical/CSockets/practical/. I was really only interested in the TCP echo client. It’s a good stand-ion for any TCP client I think.

Here’s TCPechoClient.cpp:

/*
 *   C++ sockets on Unix and Windows
 *   Copyright (C) 2002
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
 
// taken from http://cs.baylor.edu/~donahoo/practical/CSockets/practical/TCPEchoClient.cpp
 
#include "PracticalSocket.h"  // For Socket and SocketException
#include <iostream>           // For cerr and cout
#include <cstdlib>            // For atoi()
#include <cstring>            // author forgot this
 
using namespace std;
 
const int RCVBUFSIZE = 32;    // Size of receive buffer
 
int main(int argc, char *argv[]) {
  if ((argc < 3) || (argc > 4)) {     // Test for correct number of arguments
    cerr << "Usage: " << argv[0]
         << " <Server> <Echo String> [<Server Port>]" << endl;
    exit(1);
  }
 
  string servAddress = argv[1]; // First arg: server address
  char *echoString = argv[2];   // Second arg: string to echo
// DrJ test
//  echoString = "GET / HTTP/1.0\n\n";
  int echoStringLen = strlen(echoString);   // Determine input length
  unsigned short echoServPort = (argc == 4) ? atoi(argv[3]) : 7;
 
  try {
    // Establish connection with the echo server
    TCPSocket sock(servAddress, echoServPort);
 
    // Send the string to the echo server
    sock.send(echoString, echoStringLen);
 
    char echoBuffer[RCVBUFSIZE + 1];    // Buffer for echo string + \0
    int bytesReceived = 0;              // Bytes read on each recv()
    int totalBytesReceived = 0;         // Total bytes read
    // Receive the same string back from the server
    cout << "Received: ";               // Setup to print the echoed string
    while (totalBytesReceived < echoStringLen) {
      // Receive up to the buffer size bytes from the sender
      if ((bytesReceived = (sock.recv(echoBuffer, RCVBUFSIZE))) <= 0) {
        cerr << "Unable to read";
        exit(1);
      }
      totalBytesReceived += bytesReceived;     // Keep tally of total bytes
      echoBuffer[bytesReceived] = '\0';        // Terminate the string!
      cout << echoBuffer;                      // Print the echo buffer
    }
    cout << endl;
 
    // Destructor closes the socket
 
  } catch(SocketException &e) {
    cerr << e.what() << endl;
    exit(1);
  }
 
  return 0;
}

/* * C++ sockets on Unix and Windows * Copyright (C) 2002 * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ // taken from http://cs.baylor.edu/~donahoo/practical/CSockets/practical/TCPEchoClient.cpp #include "PracticalSocket.h" // For Socket and SocketException #include <iostream> // For cerr and cout #include <cstdlib> // For atoi() #include <cstring> // author forgot this using namespace std; const int RCVBUFSIZE = 32; // Size of receive buffer int main(int argc, char *argv[]) { if ((argc < 3) || (argc > 4)) { // Test for correct number of arguments cerr << "Usage: " << argv[0] << " <Server> <Echo String> [<Server Port>]" << endl; exit(1); } string servAddress = argv[1]; // First arg: server address char *echoString = argv[2]; // Second arg: string to echo // DrJ test // echoString = "GET / HTTP/1.0\n\n"; int echoStringLen = strlen(echoString); // Determine input length unsigned short echoServPort = (argc == 4) ? atoi(argv[3]) : 7; try { // Establish connection with the echo server TCPSocket sock(servAddress, echoServPort); // Send the string to the echo server sock.send(echoString, echoStringLen); char echoBuffer[RCVBUFSIZE + 1]; // Buffer for echo string + \0 int bytesReceived = 0; // Bytes read on each recv() int totalBytesReceived = 0; // Total bytes read // Receive the same string back from the server cout << "Received: "; // Setup to print the echoed string while (totalBytesReceived < echoStringLen) { // Receive up to the buffer size bytes from the sender if ((bytesReceived = (sock.recv(echoBuffer, RCVBUFSIZE))) <= 0) { cerr << "Unable to read"; exit(1); } totalBytesReceived += bytesReceived; // Keep tally of total bytes echoBuffer[bytesReceived] = '\0'; // Terminate the string! cout << echoBuffer; // Print the echo buffer } cout << endl; // Destructor closes the socket } catch(SocketException &e) { cerr << e.what() << endl; exit(1); } return 0; }

Note the cstring header file I needed to include. The standard must have changed to require this since the original code was published.

Then I neeed PracticalSocket.h, but that has no changes from the original version: “http://cs.baylor.edu/~donahoo/practical/CSockets/practical/PracticalSocket.h, and his Makefile is also just fine: http://cs.baylor.edu/~donahoo/practical/CSockets/practical/Makefile. For the fun of it I also set up the TCP Echo Server: http://cs.baylor.edu/~donahoo/practical/CSockets/practical/TCPEchoServer.cpp.

Run

make TCPEchoclient

and you should be good to go. How to test this TCPEchoClient against your web server? I found that the following works:

~/TCPEchoClient drjohnstechtalk.com 'GET / HTTP/1.0
Host: drjohnstechtalk.com
 
' 80

which gives this output:

Received: HTTP/1.1 301 Moved Permanently
Date: Thu, 23 Feb 2012 17:19:02

which, now that I analyze it, looks cut-off. Hmm. Because with curl I have:

curl -i drjohnstechtalk.com

HTTP/1.1 301 Moved Permanently
Date: Thu, 23 Feb 2012 17:19:43 GMT
Server: Apache/2.2.16 (Ubuntu)
X-Powered-By: PHP/5.3.3-1ubuntu9.5
Location: http://www.drjohnstechtalk.com/blog/
Vary: Accept-Encoding
Content-Length: 2
Content-Type: text/html

I guess that’s what you get for demo code. At this point I don’t have a need to sort it out so I won’t. Perhaps we’ll come back to it later. Looking at it, I see the received buffer size is quite small, 32 bytes. I tried to set that to a reasonable value, 200 MBytes, but get a segmentation fault. The largest I could manage, after experiementation, is 10000000 bytes:

//const int RCVBUFSIZE = 32;    // Size of receive buffer
const int RCVBUFSIZE = 10000000;    // Size of receive buffer - why is 10 MB the max. value??

and this does indeed give us the complete output from our web server home page now.

Conclusion
There is some demo C++ code which creates a useable class for dealing with TCP sockets. There might be some work to do before it could be used in a serious application, however.