modbus_tcp_listen(3)

create and listen a TCP Modbus socket (IPv4)

Section 3 libmodbus-dev bookworm source

Description

MODBUS_TCP_LISTEN

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(3) 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);