inet_aton()... Noob needs help with sockets :|

**Maz** · 11-22-2005

Hi dee Ho again.

I started learning how to toy with sockets yesterday... Well, I am utterly confused with the structures && functions dealing with ports & hostnames, with client & server sockets, with this & that

Basically what I would like to do is connect to certain server(s) & be able to send & receive data. I've done that with php sockets, so I assume I should be able to do it with c++ too

I prepared following class for that:
connect.h:

Code:

#ifndef _CONNECT
#define _CONNECT
#include <iostream>
#include <string.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

using namespace std;

class Connect {

private:

        int sock;
        struct sockaddr_in serv_addr;

public:
        Connect(){;}
        ~Connect()
                {
                close(this->sock);
                }
        int con(string host, int port); //open socket
        int send_command(string command);
        int send_payload(string command);
        char *receive();
};

#endif

and connect.cpp:

Code:

#include "connect.h"
#include <iostream>
#include <string.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <ctype.h>
#include <stdlib.h>
#include <netdb.h>

using namespace std;

int Connect::con(string host, int port)
{
        struct hostent *h;



        char *ip;

        //int success;


        if((h=gethostbyname(host.c_str()))==NULL)
        {
                herror("gethostbyname");
                exit(1);
        }

        ip=inet_ntoa(*((struct in_addr *)h->h_addr));


        if((this->sock = socket(AF_INET, SOCK_STREAM, 0)) < 0 )   //Lets make the filedescriptor
        {
                cout << "Smelly Socks!" << endl;
                exit(-666);
        }

        /*Lets connect to server*/
        serv_addr.sin_family = AF_INET;
        if( inet_aton(ip,&serv_addr.sin_addr) !=0 )
        {
                cout << "invalid ip format: " << ip << endl;
                exit(1);
        }
        serv_addr.sin_port = htons(port);

        if(connect(sock,(struct sockaddr *) &serv_addr, sizeof(serv_addr))<0)
        {
                cout << "Connecting to " << ip << " failed" << endl;
                exit(-666);
        }
        return 1;
}

int Connect::send_command(string command)
{
        int len;
        len=strlen(command.c_str())+2;

        command=command+"\r\n";
        write(sock,command.c_str(),len);
        cout << "SENT : " << command << endl;
        return 1;
}

int Connect::send_payload(string command)
{
        int len;
        len=strlen(command.c_str());
        cout << "SENT : " << command << endl;

        write(sock,command.c_str(),len);
        return 1;

}

char *Connect::receive()
{
        char *buf;
        int nread;
        nread=read(this->sock,buf,1024);
        cout << "GOT : " << buf << endl;
        return buf;
}

Now when I try to use it to connect to a certain server & send command inet_aton fails (it returns something that's not 0, and according to man pages it should not.)

(this

Code:

 if( inet_aton(ip,&serv_addr.sin_addr) !=0 )
        {
                cout << "invalid ip format: " << ip << endl;
                exit(1);
        }

Any ideas what's wrong? And can use this kind of class to do the connection? As I said, I am a noob with sockets, and the structures & handling of ip's / hostnames are mostly just taken from examples...

If someone feels like explaining them (structures & functions to manipulate hostnames/ips) well, feel free, (that would really help me understanding them better, cause the tutos I found just stated there is such structures, but the purpose is not terribly clear :/) but I would also be gratefull if someone just could tell me why inet_aton does not work.

Oh, BTW. I am using linux & g++ compiler.

**Stuka** · 11-22-2005

Here's a good guide to low-level socket programming:
http://beej.us/guide/bgnet/output/html/
<edit> Updated to the current page</edit>

And here's an implementation of an iostream-friendly socket class hierarchy that works on Linux, and probably other Unix systems:
http://www.linuxhacker.at/socketxx

The first one will explain the structures/functions pretty well, and the second can show you how to use them in C++ (or just let you use a nicely built socket library as-is).

**Maz** · 11-22-2005

Oh. The problem with inet_aton() was so silly... I had misread the manpages

inet_aton() returns 0 if theres error, othervice it returns something else

So I had the errorchecking wrong way

Anyways, now when I use the class with following "main" function:

Code:

#include "connect.h"
#include <iostream>
#include <string.h>
#include <string.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <ctype.h>
#include <stdlib.h>
#include <ctype.h>

using namespace std;

std::string itoa(int value, unsigned int base);

int main()
{
        char *dumb;
        int trid=0,socketti;
        Connect msn;
        string command;

        socketti=msn.con("messenger.hotmail.com",1863);
        command="VER "+itoa(trid++,10)+" MSNP9 CVR0\r\n";

        msn.send_command(command);
        cout << msn.receive();
}

/*
The following itoa() has been found from the web with google.
I just can't remember who the author was.
Anyways, I have not done it, and if someone knows the
author, please mention him :)

*/

std::string itoa(int value, unsigned int base)
{

        const char digitMap[] = "0123456789abcdef";
        std::string buf;

        // Guard:
        if (base == 0 || base > 16) {
                // Error: may add more trace/log output here
                return buf;
        }

        // Take care of negative int:

        std::string sign;
        int _value = value;

        // Check for case when input is zero:
        if (_value == 0) return "0";
        if (value < 0) {
                _value = -value;
                sign = "-";
        }

        // Translating number to string with base:
        for (int i = 30; _value && i ; --i) {
                buf = digitMap[ _value % base ] + buf;
                _value /= base;
        }
        return sign.append(buf);
}

It outputs following text:

SENT : VER 0 MSNP9 CVR0

GOT : VER 0 MSNP9 CVR0

VER 0 MSNP9 CVR0
14212: binding file ./msn to /usr/lib/libstdc++.so.5: normal symbol `_ZNSi6ignoreEii' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSi6sentryC1ERSib' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt15basic_streambufIcSt11char_traitsIcEE6sbump cEv' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt13basic_filebufIcSt11char_traitsIcEE19_M_und erflow_commonEb' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt12__basic_fileIcE6xsgetnEPci' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /lib/tls/libc.so.6: normal symbol `fread' [GLIBC_2.0]
14212: binding file ./msn to /usr/lib/libstdc++.so.5: normal symbol `_ZStrsIcSt11char_traitsIcEERSt13basic_istreamIT_T 0_ES6_PS3_' [GLIBCPP_3.2]

14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt12__basic_fileIcE10sys_ungetcEi' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /lib/tls/libc.so.6: normal symbol `ungetc' [GLIBC_2.0]

ds
14212: binding file ./msn to /lib/tls/libc.so.6: normal symbol `close' [GLIBC_2.0]
14212: binding file ./msn to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt8ios_base4InitD1Ev' [GLIBCPP_3.2]
14212:
14212: calling fini: /usr/lib/libstdc++.so.5
14212:
14212: binding file /usr/lib/libstdc++.so.5 to /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt8ios_base4InitD1Ev' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt8ios_base4Init14_S_ios_destroyEv' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt13basic_filebufIcSt11char_traitsIcEE5closeEv ' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt13basic_filebufIcSt11char_traitsIcEE26_M_des troy_internal_bufferEv' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt12__basic_fileIcE5closeEv' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt12__basic_fileIcED1Ev' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt13basic_filebufIwSt11char_traitsIwEE5closeEv ' [GLIBCPP_3.2]
14212: binding file /usr/lib/libstdc++.so.5 to /usr/lib/libstdc++.so.5: normal symbol `_ZNSt13basic_filebufIwSt11char_traitsIwEE26_M_des troy_internal_bufferEv' [GLIBCPP_3.2]
14212:
14212: calling fini: /lib/tls/libm.so.6
14212:
14212: binding file /lib/tls/libm.so.6 to /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
14212:
14212: calling fini: /lib/libgcc_s.so.1
14212:
14212: binding file /lib/libgcc_s.so.1 to /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
14212:
14212: calling fini: /lib/libnss_files.so.2
14212:
14212: binding file /lib/libnss_files.so.2 to /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
14212:
14212: calling fini: /lib/libnss_dns.so.2
14212:
14212: binding file /lib/libnss_dns.so.2 to /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
14212:
14212: calling fini: /lib/libresolv.so.2
14212:
14212: binding file /lib/libresolv.so.2 to /lib/tls/libc.so.6: normal symbol `__cxa_finalize' [GLIBC_2.1.3]
14212:
14212: calling fini: /lib/tls/libc.so.6
14212:

Well, that's not actually what I did expect... Does anyone notice any more errors? Perhaps theres something wrong in the way I output the contents of the socket??? or??

Please do not toast me if this question is silly, I really am a newbie with sockets

**Maz** · 11-22-2005

Okay, I found the bug. It was really stupid one...
I accidentally added \r\n twice at the end of the command, once in main.cpp and then again in send_command function... Sorry for bugging you

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