sock_programming/bind

bind.c

  int tcp_sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
  // AF_INET to create a IPv4 socket
  // SOCK_STREAM to use a stream-based protocol
  // IPPROTO_TCP to use the TCP protocol

  // we create a struct to store ip address data;
  struct sockaddr_in address_info;

  // zero out the data in the struct
  memset(&address_info, 0, sizeof(address_info));

  // set the address family to be an internet address
  address_info.sin_family = AF_INET;

  // we let the system pick out the internet address by specifying the
  // wildcard `INADDR_ANY`
  address_info.sin_addr.s_addr = htonl(INADDR_ANY);

  // we pick the port we expect incoming connections
  in_port_t local_port = 42;
  address_info.sin_port = htons(local_port);

  // use `bind` to connect the socket with to the address specified in the
  // address_info struct. The most common reason for `bind` failing is that
  // another socket is already connected to this port.
  if (bind(tcp_sock, (struct sockaddr*) &address_info, sizeof(address_info)) < 0) {
    fputs("bind() failed", stderr);
    exit(1);
  }

  int max_connections = 10;
  // `listen()` lets the system know to allow incoming connections
  if (listen(tcp_sock, max_connections) < 0) {
    fputs("listen() failed", stderr);
    exit(1);
  }

  struct sockaddr_in incoming_addr;
  socklen_t incoming_addr_len = sizeof(incoming_addr);

  // infinite loop
  for (;;) {
    // `accept()` is a blocked until an incoming connection is made. At that point, accept returns
    // a descriptor for a new socket, which is connected to a remote socket. Note upon success, this also fils the incoming_addr struct with the ip address and port of the remote connection.
    int remote_sock = accept(tcp_sock, (struct sockaddr *) &incoming_addr, &incoming_addr_len);
    if (remote_sock < 0){
      fputs("accept() failed", stderr);
      exit(1);
    }

    char remote_address_str[INET_ADDRSTRLEN];
    // `inet_ntop` takes an address struct and writes the ip address from binary form into dotted-quad string format.
    // `ntohs` stands for network short to host, which converts a converts a port number from network byte-order
    // to host byte-order (more on this later).
    if (inet_ntop(AF_INET, &incoming_addr.sin_addr.s_addr, remote_address_str, sizeof(remote_address_str)) != NULL)
      printf("Handling remote connection. remote ip and port: %s/%d\n", remote_address_str, ntohs(incoming_addr.sin_port));
    else
      printf("Unable to get client address");

    int const BUFSIZE = 256;
    char buffer[BUFSIZE];
    // `recv()` is blocking until something is received or the connection is closed.
    ssize_t num_bytes_received = recv(remote_sock, buffer, BUFSIZE, 0);
    if (num_bytes_received < 0) {
      fputs("recv() failed", stderr);
      exit(1);
    } else {
      // handle the data in buffer
    }
    close(remote_sock);
  }