Problem read/write to a socket opened for FTP

12-03-2008

#1 (permalink)

ariel_ro

Just Joined!

Join Date: Dec 2008

Posts: 9

Problem read/write to a socket opened for FTP

Hello everyone!
I have to build a FTP Client in C/C++ under Linux and right now I'm stuck. I can't seem to read responses from the FTP server after I've successfully connected to the server. After I send "USER myuser<CRLF>" the read function halts the execution.

Code:

int ConnectToServer::connectFTP()
{
	/* crearea socketului */
	if ((sd = socket (AF_INET, SOCK_STREAM, 0)) == -1)
	{
		cout<<"Eroare la socket()"<<endl;
		return errno;
	}

	server.sin_family = AF_INET; /* familia socket-ului */
	server.sin_addr.s_addr = inet_addr(_host.c_str()); /* adresa IP a serverului */
	server.sin_port = htons (21); /* portul de conectare */
		
        /* conectarea la server */
        if ( connect (sd, (struct sockaddr *) &server, sizeof (struct sockaddr)) == -1)
	{
	  cout<<"Eroare la connect()"<<endl;
	  return errno;
	}

        char _reply[255], _reply2[255], _reply3[255];
	bzero(_reply, 255);
	bzero(_reply2, 255);
	bzero(_reply3, 255);
	// citirea raspunsului dat de server  dupa crearea conexiunii
	if (read (sd, &_reply, sizeof(_reply)) < 0)
	{
	  cout<<"Eroare la read() de la server."<<endl;
	  return errno;
	}
	string response = _reply;
	cout<<"Am primit de la server: "<<atoi(response.substr(0, 3).c_str())<<endl;
	cout<<response<<endl;	
		
	while(true)
	{
	   // crearea comenzii pentru trimiterea user-ului
           string _comm("USER " + _username + "<CRLF>");
		cout<<_comm<<endl;
	    if (write (sd, &_comm, sizeof(_comm)) <= 0)
	    {
	        cout<<"Eroare la write() spre server. "<<endl;
	        return errno;
	    }
	    fflush(stdout);
	
            // citirea raspunsului dupa trimiterea username-ului 
	    if (read (sd, &_reply2, sizeof(_reply2)) < 0)
	    {
		 cout<<"Eroare la read() de la server."<<endl;
		 return errno;
	    }
            cout<<"Lungimea celui de-al doilea raspuns "<<strlen(_reply2)<<endl;
	    cout<<_reply2<<endl;
		
            // trimiterea comenzii coresp. parolei
	    string _comm2("PASS " + _password + "<CRLF>");
	    cout<<_comm2<<endl;
	    if (write (sd, &_comm2, sizeof(_comm2)) <= 0)
	    {
	          cout<<"Eroare la write() spre server. "<<endl;
	          return errno;
	    }
	    fflush(stdout);
		
	    // citirea raspunsului dupa trimiterea parolei 
	    if (read (sd, &_reply3, sizeof(_reply3)) < 0)
           {
		  cout<<"Eroare la read() de la server."<<endl;
		  return errno;
	    }
	    cout<<"Lungimea celui de-al treilea raspuns "<<strlen(_reply3)<<endl;
	    cout<<_reply3<<endl;
	    if(strlen(_reply3) > 3)
		break;
	}
	return 0;	
}

Here is the function that does the actual login. I wrapped the read/write sequence into a infinite loop(saw this in some other snippets). Any help would be greatly appreciated!

12-03-2008

#2 (permalink)

wje_lf

Linux Engineer

Join Date: Sep 2007

Location: Mariposa

Posts: 1,192

When you say:

Quote:

the read function halts the execution

I assume mean that you execute this code:

Code:

		 cout<<"Eroare la read() de la server."<<endl;
		 return errno;

Is that correct?

If it is, then you need to do something like this instead:

Code:

                 int error_temp;
                 error_temp=errno;
		 cout<<"Eroare la read() de la server."<<endl;
		 return error_temp;

to guard against the possibility that errno is modified before you can return it.

Once you've done that, could you please tell us what value was found in errno?

__________________
--
Bill

Old age and treachery will overcome youth and skill.

12-03-2008	#3 (permalink)
ariel_ro Just Joined! Join Date: Dec 2008 Posts: 9	Hi! Thanks for the reply wje_lf! Actually, it doesn't execute that portion. I connect to the desired FTP host, I get the response number 220 and than the program seems to wait for the response from the server(should be 331 User name ok, need password<CRLF>), which doesn't come. I guess it has something to do with the blocking behaviour of the read() function. I'm a beginner when it comes to C++ in Linux so my knowledge is limited. P.S.: I know that the first assumption might be that FTP server isn't working. Well, I manage to login successfully using regular ftp command and other clients.

12-04-2008	#4 (permalink)
wje_lf Linux Engineer Join Date: Sep 2007 Location: Mariposa Posts: 1,192	Maybe it's not the read(). Maybe it's the preceding write(). You send the user name to the server, correct? Do you follow that with a line feed (that is, a new line, that is, "\n")? Otherwise, the server will sit there waiting for the rest of the user name. If you already send down the "\n", could I see the code that includes the "\n"? __________________ -- Bill Old age and treachery will overcome youth and skill.

12-04-2008	#5 (permalink)
ariel_ro Just Joined! Join Date: Dec 2008 Posts: 9	Actually, I didn't append the "\n" to the end. Thank you very much! It works fine know!

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