Thread: FTP Client

I am a C Newbie. I have been working on this simple FTP client for my school, and I have been coming a particular issue with the FTP protocol. I cant seem to get a handle on the NVT-ASCII format. I try to send commands over the control connection based on my interpretation of the commands in the FTP protocol, and I am not getting anywhere. Any advice? But to show an example, I dont see any examples for sending an NLST command. The specs say 'NLST [<sp> <path-name>] <crlf>', and I interpret it as 'NLST \r\n', as if you want to specify the current directory, you need a null argument. am I on the right track? or are other things involved that I seem to be missing?

Thanks again for your help.

Ayo.

Thx for the prompt response, I will post my code shortly.

Thx again.

Its a little lengthy.

Code:

/* function: implementation of 'ls' 1=> success, -1=> fail*/
int nlst()
{
   struct sockaddr_in client;
   struct hostent *clientAddr;
   short portNum;
   char cmd[STDSIZE];
   int dataSockFD;
   socklen_t sin_size;

   if((dataSockFD = socket(AF_INET, SOCK_STREAM, 0)) == -1)
   {
     perror("socket call failed!");
     exit(0);
   }

   /* gethostname call */
   if(gethostname(hPtr,STDSIZE) == -1)
        printf("%s\n", strerror(errno));

   /* WORKS SO FAR */

   /* finding out my IP address  */
   if( (clientAddr = gethostbyname(hPtr)) == NULL)
   {
        printf("Gethostbyname error!");
        exit(1);
   }

//   short port;
   client.sin_family = AF_INET;	          
   client.sin_port = htons(0);
   client.sin_addr   = *((struct in_addr *)clientAddr->h_addr);
   memset(&(client.sin_zero), '\0', 8);  // zero the rest

   /* set sock option for port reuse */
   if(setsockopt(dataSockFD, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) == -1) {
     printf("setsockopt failed!");
     exit(1);
   }

   /* attempt to bind while it fails */
   if((bind(dataSockFD, (struct sockaddr *)&client, sizeof(struct sockaddr)) == -1))
   {
     printf("bind failed.");
     exit(1);
     }

   /* start listening for a connection from server-DTP */
   if(listen(dataSockFD, QUEUE) == -1)
   {
       printf("%s\nE:",strerror(errno));
       exit(1);
   }

   sin_size = sizeof(client);
   if(getsockname(dataSockFD,(struct sockaddr *)&client, &sin_size) == -1)
   {
       printf("getsockname failed.");
       exit(1);
   }

   // put it in 
   int IP = *( (int *)(clientAddr->h_addr_list[0]));
   IP = htonl(IP);
   sprintf(cmd,"PORT %d,%d,%d,%d,%d,%d\r\n",
         (IP & 0xFF000000) >> 24      ,
         (IP & 0x00FF0000) >> 16      ,
         (IP & 0x0000FF00) >>  8      ,
         (IP & 0x000000FF)            ,
 (client.sin_port & 0xFF00) >> 8      ,
 (client.sin_port & 0x00FF));
   char *c;

   char cmd1[STDSIZE];

   // send PORT command
  c = cmd;
  write(sockFD,c, strlen(c));   // sending PORT command
  if(receive() == 0) { }

   // if NLST
   strcpy(cmd1, "NLST  \r\n");  <--- issues at this point!!!! 
   c = cmd1;
   write(sockFD,c,strlen(c));
   if(receive() == 0) {
      int dataFD;

      if((dataFD = accept(dataSockFD, NULL, NULL)) == -1)
      {
         printf("%s\n",strerror(errno));
      }
      else
         printf("Accepted from server!");

   char l;
   if(read(dataFD, l, 1) > 0)	// test if anything has been written to socket by server
      printf("%c\n",l);
   }
   else
     printf("something wrong with 'NLST' command");

   //  receive again... after reading directory...
   if(receive() == -1) {
      printf("receive error 2\n");
      exit(0);
      }

   return 1;
}

I replaced that part with the ampersand. But I am going to try what you said using tcpdump to see the behavior with regular ftp clients, to compare with mine.

Thanks again.

I will tell you how it went soon.