A connection-oriented server.c

A connection-oriented server

This example shows how a connection-oriented server can be created.

You can use this example to create your own socket server application. A connection-oriented server design is one of the most common models for socket applications. In a connection-oriented design, the server application creates a socket to accept client requests.

Note: By using the examples, you agree to the terms of the Code license and disclaimer information.

/**************************************************************************/
/* This sample program provides a code for a connection-oriented server.  */
/**************************************************************************/

/**************************************************************************/
/* Header files needed for this sample program .                          */
/**************************************************************************/
#include "stdio.h"
#include "string.h"
#include "sys/types.h"
#include "sys/socket.h"
#include "netinet/in.h"
#include "arpa/inet.h"
#include "netdb.h"

/**************************************************************************/
/* Constants used by this program                                         */
/**************************************************************************/
#define SERVER_PORT     3005
#define BUFFER_LENGTH    250
#define FALSE              0

void main()
{
   /***********************************************************************/
   /* Variable and structure definitions.                                 */
   /***********************************************************************/
   int    sd=-1, sd2=-1;
   int    rc, length, on=1;
   char   buffer[BUFFER_LENGTH];
   fd_set read_fd;
   struct timeval timeout;
   struct sockaddr_in serveraddr;

   /***********************************************************************/
   /* A do/while(FALSE) loop is used to make error cleanup easier.  The   */
   /* close() of each of the socket descriptors is only done once at the  */
   /* very end of the program.                                            */
   /***********************************************************************/
   do
   {
      /********************************************************************/
      /* The socket() function returns a socket descriptor, which represents   */
      /* an endpoint.  The statement also identifies that the INET        */
      /* (Internet Protocol) address family with the TCP transport        */
      /* (SOCK_STREAM) will be used for this socket.                      */
      /********************************************************************/
      sd = socket(AF_INET, SOCK_STREAM, 0);
      if (sd < 0)
      {
         perror("socket() failed");
         break;
      }

      /********************************************************************/
      /* The setsockopt() function is used to allow the local address to  */
      /* be reused when the server is restarted before the required wait  */
      /* time expires.                                                    */
      /********************************************************************/
      rc = setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on));
      if (rc < 0)
      {
         perror("setsockopt(SO_REUSEADDR) failed");
         break;
      }

      /********************************************************************/
      /* After the socket descriptor is created, a bind() function gets a */
      /* unique name for the socket.  In this example, the user sets the  */
      /* s_addr to zero, which allows connections to be established from  */
      /* any client that specifies port 3005.                             */
      /********************************************************************/
      memset(&serveraddr, 0, sizeof(serveraddr));
      serveraddr.sin_family      = AF_INET;
      serveraddr.sin_port        = htons(SERVER_PORT);
      serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);

      rc = bind(sd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));
      if (rc < 0)
      {
         perror("bind() failed");
         break;
      }

      /********************************************************************/
      /* The listen() function allows the server to accept incoming       */
      /* client connections.  In this example, the backlog is set to 10.  */
      /* This means that the system will queue 10 incoming connection     */
      /* requests before the system starts rejecting the incoming         */
      /* requests.                                                        */
      /********************************************************************/
      rc = listen(sd, 10);
      if (rc< 0)
      {
         perror("listen() failed");
         break;
      }

      printf("Ready for client connect().\n");

      /********************************************************************/
      /* The server uses the accept() function to accept an incoming      */
      /* connection request.  The accept() call will block indefinitely   */
      /* waiting for the incoming connection to arrive.                   */
      /********************************************************************/
      sd2 = accept(sd, NULL, NULL);
      if (sd2 < 0)
      {
         perror("accept() failed");
         break;
      }

      /********************************************************************/
      /* The select() function allows the process to wait for an event to */
      /* occur and to wake up the process when the event occurs.  In this */
      /* example, the system notifies the process only when data is       */
      /* available to read.  A 30 second timeout is used on this select   */
      /* call.                                                            */
      /********************************************************************/
      timeout.tv_sec  = 30;
      timeout.tv_usec = 0;

      FD_ZERO(&read_fd);
      FD_SET(sd2, &read_fd);

      rc = select(sd2+1, &read_fd, NULL, NULL, &timeout);
      if (rc < 0)
      {
         perror("select() failed");
         break;
       }

      if (rc == 0)
      {
         printf("select() timed out.\n");
         break;
      }

      /********************************************************************/
      /* In this example we know that the client will send 250 bytes of   */
      /* data over.  Knowing this, we can use the SO_RCVLOWAT socket      */
      /* option and specify that we don't want our recv() to wake up until*/
      /* all 250 bytes of data have arrived.                              */
      /********************************************************************/
      length = BUFFER_LENGTH;
      rc = setsockopt(sd2, SOL_SOCKET, SO_RCVLOWAT,
                                          (char *)&length, sizeof(length));
      if (rc < 0)
      {
         perror("setsockopt(SO_RCVLOWAT) failed");
         break;
      }

      /********************************************************************/
      /* Receive that 250 bytes data from the client                      */
      /********************************************************************/
      rc = recv(sd2, buffer, sizeof(buffer), 0);
      if (rc < 0)
      {
         perror("recv() failed");
         break;
      }

      printf("%d bytes of data were received\n", rc);
      if (rc == 0 ||
          rc < sizeof(buffer))
      {
         printf("The client closed the connection before all of the\n");
         printf("data was sent\n");
         break;
      }

      /********************************************************************/
      /* Echo the data back to the client                                 */
      /********************************************************************/
      rc = send(sd2, buffer, sizeof(buffer), 0);
      if (rc < 0)
      {
         perror("send() failed");
         break;
      }

      /********************************************************************/
      /* Program complete                                                 */
      /********************************************************************/

   } while (FALSE);

   /***********************************************************************/
   /* Close down any open socket descriptors                              */
   /***********************************************************************/
   if (sd != -1)
      close(sd);
   if (sd2 != -1)
      close(sd2);
}

Parent topic: Creating a connection-oriented socket

Related reference

Using AF_INET address family

Example: A connection-oriented client