Socket - UDP Datagram Server sample c code

Now you are equipped well enough to write a UDP datagram client and server program. In this section, you'll begin with a datagram server example (remember from my first post in this series, where you saw an example). This program took a strftime(3) format string as input and returned the formatted date and time string as a response. You are going to write a datagram server in this post, which will stand by itself, accept format strings as input datagrams. After the server formats a date string using the strftime(3) function, it will send the result back to the client program in another datagram as shown in Listing below,

 /* dgramsrvr.c:

  *

  * Example datagram server:

  */

  #include <stdio.h>

  #include <unistd.h>

  #include <stdlib.h>

  #include <errno.h>

  #include <string.h>

  #include <time.h>

  #include <sys/types.h>

  #include <sys/socket.h>

  #include <netinet/in.h>

  #include <arpa/inet.h>

 /*

  * This function reports the error and

  * exits back to the shell:

  */

  static void displayError(const char *on_what) {

     fputs(strerror(errno),stderr);

     fputs(": ",stderr);

     fputs(on_what,stderr);

     fputc('\n',stderr);

     exit(1);

  }

  int main(int argc,char **argv) {

     int z;

     char *srvr_addr = NULL;

     struct sockaddr_in adr_inet; // AF_INET

     struct sockaddr_in adr_clnt; // AF_INET

     int len_inet;                // length

     int s;                       // Socket

     char dgram[512];             // Recv buffer

     char dtfmt[512];             // Date/Time Result

     time_t td;                   // Current Time and Date

     struct tm tm;                // Date time values

 /*

  * Use a server address from the command

  * line, if one has been provided.

  * Otherwise, this program will default

  * to using the arbitrary address

  * 127.0.0.

  */

     if ( argc >= 2 ) {

        // Addr on cmdline:

        srvr_addr = argv[1];

     }

     else {

        // Use default address:

        srvr_addr = "127.0.0.23";

     }

 /*

  * Create a UDP socket to use:

  */

     s = socket(AF_INET,SOCK_DGRAM,0);

     if ( s == -1 ) {

        displayError("socket()");

     }

 /*

  * Create a socket address, for use

  * with bind(2):

  */

     memset(&adr_inet,0,sizeof adr_inet);

     adr_inet.sin_family = AF_INET;

     adr_inet.sin_port = htons(9090);

     adr_inet.sin_addr.s_addr =

     inet_addr(srvr_addr);

     if ( adr_inet.sin_addr.s_addr == INADDR_NONE ) {

        displayError("bad address.");

     }

     len_inet = sizeof adr_inet;

 /*

  * Bind a address to our socket, so that

  * client programs can contact this

  * server:

  */

     z = bind(s, (struct sockaddr *)&adr_inet, len_inet);

     if ( z == -1 ) {

        displayError("bind()");

     }

 /*

  * Now wait for requests:

  */

     for (;;) {

 /*

  * Block until the program receives a

  * datagram at our address and port:

  */

        len_inet = sizeof adr_clnt;

        z = recvfrom(s,            // Socket

                     dgram,        // Receiving buffer

                     sizeof dgram, // Max recv buf size

                     0,            // Flags: no options

                     (struct sockaddr *)&adr_clnt, // Addr

                     &len_inet);  // Addr len, in & out

        if ( z < 0 ) {

           displayError("recvfrom(2)");

        }

 /*

  * Process the request:

  */

        dgram[z] = 0; // null terminate

        if ( !strcasecmp(dgram,"QUIT") ) {

           break;     // Quit server

       }

 /*

  * Get the current date and time:

  */

        time(&td);            // Get current time & date

        tm = *localtime(&td); // Get components

 /*

  * Format a new date and time string,

  * based upon the input format string:

  */

        strftime(dtfmt,       // Formatted result

                 sizeof dtfmt,// Max result size

                 dgram,       // Input date/time format

                 &tm);        // Input date/time values

 /*

  * Send the formatted result back to the

  * client program:

  */

        z = sendto(s,             // Socket to send result

                   dtfmt,         // The datagram result to snd

                   strlen(dtfmt), // The datagram lngth

                   0,             // Flags: no options

                   (struct sockaddr *)&adr_clnt,// addr

                   len_inet);     // Client address length

       if ( z < 0 ) {

          displayError("sendto(2)");

      }

    }

 /*

  * Close the socket and exit:

  */

     close(s);

     return 0;

  }

/*

 * When we run this program our server will come in listen 

 * state and is waiting to accept the client connection

 *

 [sgupta@rhel55x86 chap6]$ gcc dgramserver.c -o dgramserver

 [sgupta@rhel55x86 chap6]$ ./dgramserver 192.168.22.55

 */

See the UDP datagram client from here for complete appication

See Also:

Socket Tutorial and Sample Codes

Advance Socket Tutorial and Sample Code