Name

modbus_tcp_listen - create and listen a TCP Modbus socket (IPv4)

Synopsis

int modbus_tcp_listen(modbus_t *ctx, int nb_connection);

Description

The modbus_tcp_listen() function shall create a socket and listen to maximum nb_connection incoming connections on the specified IP address. The context ctx must be allocated and initialized with modbus_new_tcp ⟨modbus_new_tcp.md⟩ before to set the IP address to listen, if IP address is set to NULL or '0.0.0.0', any addresses will be listen.

Return value

The function shall return a new socket if successful. Otherwise it shall return -1 and set errno.

Example

For detailed examples, see source files in tests directory:

• unit-test-server.c, simple but handle only one connection
• bandwidth-server-many-up.c, handles several connections at once

  ...
  /* To listen any addresses on port 502 */
  ctx = modbus_new_tcp(NULL, 502);
  /* Handle until 10 established connections */
  server_socket = modbus_tcp_listen(ctx, 10);
  /* Clear the reference set of socket */
  FD_ZERO(&refset);
  /* Add the server socket */
  FD_SET(server_socket, &refset);
  if (select(server_socket + 1, &refset, NULL, NULL, NULL) == -1) {
  }
  ...
  close(server_socket);
  modbus_free(ctx);
      

See also

• modbus_new_tcp ⟨modbus_new_tcp.md⟩
• modbus_tcp_accept ⟨modbus_tcp_accept.md⟩
• modbus_tcp_pi_listen ⟨modbus_tcp_pi_listen.md⟩