A connectionless client.c

A connectionless client

This example shows how to use User Datagram Protocol (UDP) to connect a connectionless socket client program to a server.

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 connectionless client.       */
/**************************************************************************/

/**************************************************************************/
/* 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     3555
#define BUFFER_LENGTH    100
#define FALSE              0
#define SERVER_NAME     "ServerHostName"

/* Pass in 1 parameter which is either the */
/* address or host name of the server, or  */
/* set the server name in the #define      */
/* SERVER_NAME                             */
void main(int argc, char *argv[])
{
   /***********************************************************************/
   /* Variable and structure definitions.                                 */
   /***********************************************************************/
   int    sd, rc;
   char   server[NETDB_MAX_HOST_NAME_LENGTH];
   char   buffer[BUFFER_LENGTH];
   struct hostent *hostp;
   struct sockaddr_in serveraddr;
   int    serveraddrlen = sizeof(serveraddr);

   /***********************************************************************/
   /* A do/while(FALSE) loop is used to make error cleanup easier.  The   */
   /* close() of the socket descriptor 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 UDP transport        */
      /* (SOCK_STREAM) will be used for this socket.                      */
      /********************************************************************/
      sd = socket(AF_INET, SOCK_DGRAM, 0);
      if (sd < 0)
      {
         perror("socket() failed");
         break;
      }

      /********************************************************************/
      /* If an argument was passed in, use this as the server, otherwise  */
      /* use the #define that is located at the top of this program.      */
      /********************************************************************/
      if (argc > 1)
         strcpy(server, argv[1]);
      else
         strcpy(server, SERVER_NAME);

      memset(&serveraddr, 0, sizeof(serveraddr));
         serveraddr.sin_family      = AF_INET;
         serveraddr.sin_port        = htons(SERVER_PORT);
         serveraddr.sin_addr.s_addr = inet_addr(server);
         if (serveraddr.sin_addr.s_addr == (unsigned long)INADDR_NONE)
      {
         /*****************************************************************/
         /* The server string that was passed into the inet_addr()        */
         /* function was not a dotted decimal IP address.  It must        */
         /* therefore be the hostname of the server.  Use the             */
         /* gethostbyname() function to retrieve the IP address of the    */
         /* server.                                                       */
         /*****************************************************************/
         hostp = gethostbyname(server);
         if (hostp == (struct hostent *)NULL)
         {
            printf("Host not found --> ");
            printf("h_errno = %d\n", h_errno);
            break;
         }

         memcpy(&serveraddr.sin_addr,
                hostp->h_addr,
                sizeof(serveraddr.sin_addr));
      }

      /********************************************************************/
      /* Initialize the data block that is going to be sent to the server */
      /********************************************************************/
      memset(buffer, 0, sizeof(buffer));
      strcpy(buffer, "A CLIENT REQUEST");

      /********************************************************************/
      /* Use the sendto() function to send the data to the server.        */
      /********************************************************************/
      rc = sendto(sd, buffer, sizeof(buffer), 0,
                  (struct sockaddr *)&serveraddr,
                  sizeof(serveraddr));
      if (rc < 0)
      {
         perror("sendto() failed");
         break;
      }

      /********************************************************************/
      /* Use the recvfrom() function to receive the data back from the    */
      /* server.                                                          */
      /********************************************************************/
      rc = recvfrom(sd, buffer, sizeof(buffer), 0,
                    (struct sockaddr *)&serveraddr,
                    & serveraddrlen);
      if (rc < 0)
      {
         perror("recvfrom() failed");
         break;
      }

      printf("client received the following: <%s>\n", buffer);
      printf("from port %d, from address %s\n",
             ntohs(serveraddr.sin_port),
             inet_ntoa(serveraddr.sin_addr));

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

   } while (FALSE);

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

Parent topic: Creating a connectionless socket

A connectionless server.c

A connectionless server

This example illustrates how to create a connectionless socket server program by using User Datagram Protocol (UDP).

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 connectionless 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     3555
#define BUFFER_LENGTH    100
#define FALSE              0

void main()
{
   /***********************************************************************/
   /* Variable and structure definitions.                                 */
   /***********************************************************************/
   int    sd=-1, rc;
   char   buffer[BUFFER_LENGTH];
   struct sockaddr_in serveraddr;
   struct sockaddr_in clientaddr;
   int    clientaddrlen = sizeof(clientaddr);

   /***********************************************************************/
   /* 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 UDP transport        */
      /* (SOCK_DGRAM) will be used for this socket.                       */
      /********************************************************************/
      sd = socket(AF_INET, SOCK_DGRAM, 0);
      if (sd < 0)
      {
         perror("socket() 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 means that the UDP port of 3555 will be    */
      /* bound to all IP addresses on the system.                         */
      /********************************************************************/
      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 server uses the recvfrom() function to receive that data.    */
      /* The recvfrom() function waits indefinitely for data to arrive.   */
      /********************************************************************/
      rc = recvfrom(sd, buffer, sizeof(buffer), 0,
                    (struct sockaddr *)&clientaddr,
                    &clientaddrlen);
      if (rc < 0)
      {
         perror("recvfrom() failed");
         break;
      }

      printf("server received the following: <%s>\n", buffer);
      printf("from port %d and address %s\n",
             ntohs(clientaddr.sin_port),
             inet_ntoa(clientaddr.sin_addr));

      /********************************************************************/
      /* Echo the data back to the client                                 */
      /********************************************************************/
      rc = sendto(sd, buffer, sizeof(buffer), 0,
                  (struct sockaddr *)&clientaddr,
                  sizeof(clientaddr));
      if (rc < 0)
      {
         perror("sendto() failed");
         break;
      }

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

   } while (FALSE);

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

Parent topic: Creating a connectionless socket

Creating a connectionless socket

Connectionless sockets do not establish a connection over which data is transferred. Instead, the server application specifies its name where a client can send requests.

Connectionless sockets use User Datagram Protocol (UDP) instead of TCP/IP.
The following figure illustrates the client/server relationship of the socket APIs used in the examples for a connectionless socket design.

Socket flow of events: Connectionless server

The following sequence of the socket calls provides a description of the figure and the following example programs. It also describes the relationship between the server and client application in a connectionless design. Each set of flows contains links to usage notes on specific APIs. If you need more details on the use of a particular API, you can use these links. The first example of a connectionless server uses the following sequence of API calls:

1. The socket() API returns a socket descriptor, which represents an endpoint. The statement also identifies that the Internet Protocol address family (AF_INET) with the UDP transport (SOCK_DGRAM) is used for this socket.
2. After the socket descriptor is created, a bind() API gets a unique name for the socket. In this example, the user sets the s_addr to zero, which means that the UDP port of 3555 is bound to all IPv4 addresses on the system.
3. The server uses the recvfrom() API to receive that data. The recvfrom() API waits indefinitely for data to arrive.
4. The sendto() API echoes the data back to the client.
5. The close() API ends any open socket descriptors.

Socket flow of events: Connectionless client

The second example of a connectionless client uses the following sequence of API calls.

1. The socket() API returns a socket descriptor, which represents an endpoint. The statement also identifies that the Internet Protocol address family (AF_INET) with the UDP transport (SOCK_DGRAM) is used for this socket.
2. In the client example program, if the server string that was passed into the inet_addr() API was not a dotted decimal IP address, then it is assumed to be the host name of the server. In that case, use the gethostbyname() API to retrieve the IP address of the server.
3. Use the sendto() API to send the data to the server.
4. Use the recvfrom() API to receive the data from the server.
5. The close() API ends any open socket descriptors.

• Example: A connectionless server
  This example illustrates how to create a connectionless socket server program by using User Datagram Protocol (UDP).
• Example: A connectionless client
  This example shows how to use User Datagram Protocol (UDP) to connect a connectionless socket client program to a server.

Parent topic: Basic socket design

Related information

close()

socket()

bind()

recvfrom()

sendto()

gethostbyname()

connection-oriented client.c

A connection-oriented client

This example shows how to create a socket client program to connect to a connection-oriented server in a connection-oriented design.

The client of the service (the client program) must request the service of the server program. You can use this example to write your own client application.

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 client.  */
/**************************************************************************/

/**************************************************************************/
/* 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
#define SERVER_NAME     "ServerHostName"

/* Pass in 1 parameter which is either the */
/* address or host name of the server, or  */
/* set the server name in the #define      */
/* SERVER_NAME.                             */
void main(int argc, char *argv[])
{
   /***********************************************************************/
   /* Variable and structure definitions.                                 */
   /***********************************************************************/
   int    sd=-1, rc, bytesReceived;
   char   buffer[BUFFER_LENGTH];
   char   server[NETDB_MAX_HOST_NAME_LENGTH];
   struct sockaddr_in serveraddr;
   struct hostent *hostp;

   /***********************************************************************/
   /* A do/while(FALSE) loop is used to make error cleanup easier.  The   */
   /* close() of the socket descriptor 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;
      }

      /********************************************************************/
      /* If an argument was passed in, use this as the server, otherwise  */
      /* use the #define that is located at the top of this program.      */
      /********************************************************************/
      if (argc > 1)
         strcpy(server, argv[1]);
      else
         strcpy(server, SERVER_NAME);

      memset(&serveraddr, 0, sizeof(serveraddr));
      serveraddr.sin_family      = AF_INET;
      serveraddr.sin_port        = htons(SERVER_PORT);
      serveraddr.sin_addr.s_addr = inet_addr(server);
      if (serveraddr.sin_addr.s_addr == (unsigned long)INADDR_NONE)
      {
         /*****************************************************************/
         /* The server string that was passed into the inet_addr()        */
         /* function was not a dotted decimal IP address.  It must        */
         /* therefore be the hostname of the server.  Use the             */
         /* gethostbyname() function to retrieve the IP address of the    */
         /* server.                                                       */
         /*****************************************************************/

         hostp = gethostbyname(server);
         if (hostp == (struct hostent *)NULL)
         {
            printf("Host not found --> ");
            printf("h_errno = %d\n", h_errno);
            break;
         }

         memcpy(&serveraddr.sin_addr,
                hostp->h_addr,
                sizeof(serveraddr.sin_addr));
      }

      /********************************************************************/
      /* Use the connect() function to establish a connection to the      */
      /* server.                                                          */
      /********************************************************************/
      rc = connect(sd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));
      if (rc < 0)
      {
         perror("connect() failed");
         break;
      }

      /********************************************************************/
      /* Send 250 bytes of a's to the server                              */
      /********************************************************************/
      memset(buffer, 'a', sizeof(buffer));
      rc = send(sd, buffer, sizeof(buffer), 0);
      if (rc < 0)
      {
         perror("send() failed");
         break;
      }

      /********************************************************************/
      /* In this example we know that the server is going to respond with */
      /* the same 250 bytes that we just sent.  Since we know that 250    */
      /* bytes are going to be sent back to us, we can use the          */
      /* SO_RCVLOWAT socket option and then issue a single recv() and     */
      /* retrieve all of the data.                                        */
      /*                                                                  */
      /* The use of SO_RCVLOWAT is already illustrated in the server      */
      /* side of this example, so we will do something different here.    */
      /* The 250 bytes of the data may arrive in separate packets,        */
      /* therefore we will issue recv() over and over again until all     */
      /* 250 bytes have arrived.                                          */
      /********************************************************************/
      bytesReceived = 0;
      while (bytesReceived < BUFFER_LENGTH)
      {
         rc = recv(sd, & buffer[bytesReceived],
                   BUFFER_LENGTH - bytesReceived, 0);
         if (rc < 0)
         {
            perror("recv() failed");
            break;
         }
         else if (rc == 0)
         {
            printf("The server closed the connection\n");
            break;
         }

         /*****************************************************************/
         /* Increment the number of bytes that have been received so far  */
         /*****************************************************************/
         bytesReceived += rc;
      }

   } while (FALSE);

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

Parent topic: Creating a connection-oriented socket

Related reference

Using AF_INET address family

Example: A connection-oriented server

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

Creating a connection-oriented socket

These server and client examples illustrate the socket APIs written for a connection-oriented protocol such as Transmission Control Protocol (TCP).

The following figure illustrates the client/server relationship of the sockets API for a connection-oriented protocol.

Socket flow of events: Connection-oriented server

The following sequence of the socket calls provides a description of the figure. It also describes the relationship between the server and client application in a connection-oriented design. Each set of flows contains links to usage notes on specific APIs.

1. The socket() API returns a socket descriptor, which represents an endpoint. The statement also identifies that the Internet Protocol address family (AF_INET) with the TCP transport (SOCK_STREAM) is used for this socket.
2. The setsockopt() API allows the local address to be reused when the server is restarted before the required wait time expires.
3. After the socket descriptor is created, the bind() API 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 IPv4 client that specifies port 3005.
4. The listen() API allows the server to accept incoming client connections. In this example, the backlog is set to 10. This means that the system queues 10 incoming connection requests before the system starts rejecting the incoming requests.
5. The server uses the accept() API to accept an incoming connection request. The accept() call blocks indefinitely, waiting for the incoming connection to arrive.
6. The select() API 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 be read. A 30-second timeout is used on this select() call.
7. The recv() API receives data from the client application. In this example, the client sends 250 bytes of data. Thus, the SO_RCVLOWAT socket option can be used, which specifies that recv() does not wake up until all 250 bytes of data have arrived.
8. The send() API echoes the data back to the client.
9. The close() API closes any open socket descriptors.

Socket flow of events: Connection-oriented client

The following sequence of APIs calls describes the relationship between the server and client application in a connection-oriented design.

1. The socket() API returns a socket descriptor, which represents an endpoint. The statement also identifies that the Internet Protocol address family (AF_INET) with the TCP transport (SOCK_STREAM) is used for this socket.
2. In the client example program, if the server string that was passed into the inet_addr() API was not a dotted decimal IP address, then it is assumed to be the host name of the server. In that case, use the gethostbyname() API to retrieve the IP address of the server.
3. After the socket descriptor is received, the connect() API is used to establish a connection to the server.
4. The send() API sends 250 bytes of data to the server.
5. The recv() API waits for the server to echo the 250 bytes of data back. In this example, the server responds with the same 250 bytes that was just sent. In the client example, the 250 bytes of the data might arrive in separate packets, so the recv() API can be used over and over until all 250 bytes have arrived.
6. The close() API closes any open socket descriptors.

• Example: A connection-oriented server
  This example shows how a connection-oriented server can be created.
• Example: A connection-oriented client
  This example shows how to create a socket client program to connect to a connection-oriented server in a connection-oriented design.

Parent topic: Basic socket design

Related information

listen()

bind()

accept()

send()

recv()

close()

socket()

setsockopt()

select()

gethostbyname()

connect()