problems with linux UDP server

Lopizda · 04-24-2007, 04:28 PM

Hello, this is my first attempt at creating an UDP client server application. The server (linux) receives a command from the client (windows) and returns the result of that command. The problem is that, for some reason, the server won't bind the socket(the debug printf messages don't show up on the screen), and it stops me from further debugging the program. Here is the source code for the server:

Code:

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
 
#define MAXLEN 100
#define SERVER_PORT 6069

int main()
{
     struct sockaddr_in serv,client; 
     int sd,sd2,len,len2;
     char command[MAXLEN];
     char line[100];

     sd=socket(AF_INET,SOCK_DGRAM,0);
     if(sd<0)
         {
          fprintf(stderr,"Can't create socket\n");
          return 1;
         }
     printf("socket created\n");

     memset((char*)&serv,0,sizeof(serv));

     serv.sin_family=AF_INET;
     serv.sin_addr.s_addr=INADDR_ANY; //i used also -- inet_addr("127.0.0.1");
     serv.sin_port=htons(SERVER_PORT);

     len2=sizeof(serv);

     printf("binding now");

     if (bind(sd,(struct sockaddr*)&serv,len2) < 0)
          {
          perror("error binding");
          }
     printf("bound and waiting");

     len=sizeof(client);

     for( ; ; )
          {
          recvfrom(sd,command,MAXLEN,0,(struct sockaddr*)&client,&len);
                            //receives the command 
          FILE* f;

          printf("\n Command '%s' executing now\n",command);
          f=popen(command,"r");

          if(f!=NULL)
               {
               while(fgets(line,MAXLEN,f)!=NULL)
                    {
                    sendto(sd,line,strlen(line),0,(struct sockaddr*) &client,len); 
                              //sends result to client
                    }
               sendto(sd,line,0,0,(struct sockaddr*) &client,len); 
                            //sending 0 to stop the client
               }
               else
               {
               strcpy(line,"error popening");
               sendto(sd,line,strlen(line),0,(struct sockaddr*) &client,len);
               }
          pclose(f);
          }
close(sd);
return 0;
}

brewbuck · 04-24-2007, 05:59 PM

Quote:

Originally Posted by Lopizda

Hello, this is my first attempt at creating an UDP client server application. The server (linux) receives a command from the client (windows) and returns the result of that command. The problem is that, for some reason, the server won't bind the socket(the debug printf messages don't show up on the screen), and it stops me from further debugging the program.

So the bind() call fails and perror() prints an error message? What message does it print?

Lopizda · 04-25-2007, 05:17 AM

nevermind, solved it. thanks anyway

**Salem** · 04-25-2007, 05:35 AM

> nevermind, solved it. thanks anyway
Well tell us then, so others can learn from it.

It's just like reading a book only to find the last page missing!

Lopizda · 04-26-2007, 07:53 AM

i will just post the code that's relevant. i still don't know what exactly went wrong, even though i did found one of that ellusive windows carriage return-line feed character hiding somewhere (i compiled the program under cygwin). i also moved the "len2=sizeof(serv);" function, but i doubt that one of these two things were the causes. cheers!

Code:

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define MAXLEN 100
#define SERVER_PORT 6069

int main()
{
  struct sockaddr_in  serv,client; //addresses of the server and the client
  int sd,sd2,len,len2,n;
  char command[MAXLEN];
  char line[100];

  sd=socket(AF_INET,SOCK_DGRAM,0);
  
  if(sd<0)
	{
	 fprintf(stderr,"Can't create socket\n");
	 return 1;
	}

  printf("socket created\n");

  len2=sizeof(serv);

  memset((char*)&serv,0,sizeof(serv));

  serv.sin_family=AF_INET;
  serv.sin_addr.s_addr=inet_addr("127.0.0.1");
  serv.sin_port=htons(SERVER_PORT);

  printf("binding now\n");
  if (bind(sd,(struct sockaddr*)&serv,len2) < 0)
	{
	 perror("error binding");
	}
  printf("bound and waiting\n");

brewbuck · 04-26-2007, 08:42 AM

Quote:

Originally Posted by Lopizda

i still don't know what exactly went wrong

Then you haven't solved anything.

04-25-2007, 05:17 AM	#3
Lopizda Registered User Join Date: Apr 2007 Posts: 3	nevermind, solved it. thanks anyway
Lopizda is offline

04-25-2007, 05:35 AM	#4
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,695	> nevermind, solved it. thanks anyway Well tell us then, so others can learn from it. It's just like reading a book only to find the last page missing! __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

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