Editing Berkeley sockets (section)

==Client-server example using TCP==
The [[Transmission Control Protocol]] (TCP) is a [[Connection-oriented communication|connection-oriented]] protocol that provides a variety of error correction and performance features for transmission of byte streams. A process creates a TCP socket by calling the {{code|socket()}} function with the parameters for the protocol family ({{mono|''[[PF INET]]'', PF_INET6}}), the socket mode for [[stream socket]]s ({{mono|SOCK_STREAM}}), and the IP protocol identifier for TCP ({{mono|IPPROTO_TCP}}).

===Server===
Establishing a TCP server involves the following basic steps:
* Creating a TCP socket with a call to ''socket().''
* Binding the socket to the listening port ''bind()'' after setting the port number.
* Preparing the socket to listen for connections (making it a listening socket), with a call to ''listen()''.
* Accepting incoming connections (''accept()''). This blocks the process until an incoming connection is received, and returns a socket descriptor for the accepted connection. The initial descriptor remains a listening descriptor, and ''accept()'' can be called again at any time with this socket, until it is closed.
* Communicating with the remote host with the API functions ''send()'' and ''recv()'', as well as with the general-purpose functions ''write()'' and ''read()''.
* Closing each socket that was opened after use with function ''close()''

The following program creates a TCP server listening on port number 1100:

<syntaxhighlight lang="c">
  #include <sys/types.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <arpa/inet.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  
  int main(void)
  {
    struct sockaddr_in sa;
    int SocketFD = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (SocketFD == -1) {
      perror("cannot create socket");
      exit(EXIT_FAILURE);
    }
  
    memset(&sa, 0, sizeof sa);
  
    sa.sin_family = AF_INET;
    sa.sin_port = htons(1100);
    sa.sin_addr.s_addr = htonl(INADDR_ANY);
  
    if (bind(SocketFD,(struct sockaddr *)&sa, sizeof sa) == -1) {
      perror("bind failed");
      close(SocketFD);
      exit(EXIT_FAILURE);
    }
  
    if (listen(SocketFD, 10) == -1) {
      perror("listen failed");
      close(SocketFD);
      exit(EXIT_FAILURE);
    }
  
    for (;;) {
      int ConnectFD = accept(SocketFD, NULL, NULL);
  
      if (ConnectFD == -1) {
        perror("accept failed");
        close(SocketFD);
        exit(EXIT_FAILURE);
      }
  
      /* perform read write operations ... 
      read(ConnectFD, buff, size)
      */
  
      if (shutdown(ConnectFD, SHUT_RDWR) == -1) {
        perror("shutdown failed");
        close(ConnectFD);
        close(SocketFD);
        exit(EXIT_FAILURE);
      }
      close(ConnectFD);
    }

    close(SocketFD);
    return EXIT_SUCCESS;  
}
</syntaxhighlight>

===Client===
Programming a TCP client application involves the following steps:
* Creating a TCP socket.
* Connecting to the server (''connect()''), by passing a {{code|sockaddr_in}} structure with the {{code|sin_family}} set to {{mono|AF_INET}}, {{code|sin_port}} set to the port the endpoint is listening (in network byte order), and {{code|sin_addr}} set to the IP address of the listening server (also in network byte order).
* Communicating with the remote host with the API functions ''send()'' and ''recv()'', as well as with the general-purpose functions ''write()'' and ''read()''.
* Closing each socket that was opened after use with function ''close().''

<syntaxhighlight lang="c">
  #include <sys/types.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
  #include <arpa/inet.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  
  int main(void)
  {
    struct sockaddr_in sa;
    int res;
    int SocketFD;

    SocketFD = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (SocketFD == -1) {
      perror("cannot create socket");
      exit(EXIT_FAILURE);
    }
  
    memset(&sa, 0, sizeof sa);
  
    sa.sin_family = AF_INET;
    sa.sin_port = htons(1100);
    res = inet_pton(AF_INET, "192.168.1.3", &sa.sin_addr);

    if (connect(SocketFD, (struct sockaddr *)&sa, sizeof sa) == -1) {
      perror("connect failed");
      close(SocketFD);
      exit(EXIT_FAILURE);
    }
  
    /* perform read write operations ... */
  
    close(SocketFD);
    return EXIT_SUCCESS;
  }

</syntaxhighlight>