Using getpeername()

This is a discussion on Using getpeername() within the Networking/Device Communication forums, part of the General Programming Boards category; Hey :-) I'm getting into network programming and want to be able to see the hostname connected on a specified ...

  1. #1
    Registered User
    Join Date
    Mar 2004
    Posts
    2

    Using getpeername()

    Hey :-)

    I'm getting into network programming and want to be able to see the hostname connected on a specified port, is this easy enough to do with getpeername() or is there another way to do it?

    Here's the code I have so far, i've bolded where I wanna use the hostname:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <errno.h>
    #include <string.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    #include <sys/wait.h>
    #include <signal.h>
     
    #define MYPORT 3490    // the port users will be connecting to
    #define BACKLOG 10     // how many pending connections queue will hold
     
    void sigchld_handler(int s) {
     while(wait(NULL) > 0);
    }
     
    int main() {
      int sockfd, new_fd;  // listen on sock_fd, new connection on new_fd
      struct sockaddr_in my_addr;    // my address information
      struct sockaddr_in their_addr; // connector's address information
      int sin_size;
      struct sigaction sa;
      int yes=1;
      FILE *filePointer = fopen("telnet_server.log", "a");;
      struct sockaddr *hostName_ptr;
      char hostName[128];
     
      if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
      }
     
      if (setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
        perror("setsockopt");
        exit(1);
      }
             
      my_addr.sin_family = AF_INET;         // host byte order
      my_addr.sin_port = htons(MYPORT);     // short, network byte order
      my_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
      memset(&(my_addr.sin_zero), '\0', 8); // zero the rest of the struct
     
      if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1) {
        perror("bind");
        exit(1);
      }
     
      if (listen(sockfd, BACKLOG) == -1) {
        perror("listen");
        exit(1);
      }
     
      sa.sa_handler = sigchld_handler; // reap all dead processes
      sigemptyset(&sa.sa_mask);
      sa.sa_flags = SA_RESTART;
       
      if (sigaction(SIGCHLD, &sa, NULL) == -1) {
        perror("sigaction");
        exit(1);
      }
     
      while(1) {  // main accept() loop
        sin_size = sizeof(struct sockaddr_in);
        if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) == -1) {
          perror("accept");
          continue;
        }
     
        fprintf(filePointer, "Server: Got connection from %s\n", inet_ntoa(their_addr.sin_addr)); 
     
          if (!fork()) { // this is the child process
          close(sockfd); // child doesn't need the listener
          if (send(new_fd, "Hello world!\n", 14, 0) == -1)
            perror("send");
            close(new_fd);
            exit(0);
          }
        close(new_fd);  // parent doesn't need this
      }
     
    return 0;
    }

    If there is anyone that could help it be much appreciated

  2. #2
    Yes, my avatar is stolen anonytmouse's Avatar
    Join Date
    Dec 2002
    Posts
    2,544
    getpeername() returns the remote address for the socket(which you already have). I think you are looking for gethostbyaddr(). This takes an ip address and returns a hostent structure which includes the host name in h_name.

    Search Google Groups for samples.

    It should be noted that getting the host name requires a dns lookup and is therefore not "instant".

  3. #3
    Registered User
    Join Date
    Mar 2004
    Posts
    2
    Thanks heaps anonytmouse - did a GG search and found something to what I needed, changed it a bit then added it... works perfectly :-)

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