sd_bus_add_match

systemd
Julian Orth ju.orth@gmail.com
sd_bus_add_match 3
sd_bus_add_match Add a match rule for message dispatching

    #include <systemd/sd-bus.h>

int `sd_bus_add_match` sd_bus *bus sd_bus_slot **slot const char *match sd_bus_message_handler_t callback void *userdata typedef int (*`sd_bus_message_handler_t`) sd_bus_message *m void *userdata sd_bus_error *ret_error

## Description

`sd_bus_add_match()` installs a match rule for incoming messages received on the specified bus connection object bus. The syntax of the match rule expression passed in match is described in the D-Bus Specification. The specified handler function callback is called for eaching incoming message matching the specified expression, the userdata parameter is passed as-is to the callback function.

On success, and if non-`NULL`, the slot return parameter will be set to a slot object that may be used as a reference to the installed match, and may be utilized to remove it again at a later time with sd_bus_slot_unref 3. If specified as `NULL` the lifetime of the match is bound to the lifetime of the bus object itself, and the match cannot be removed independently.

The message m passed to the callback is only borrowed, that is, the callback should not call sd_bus_message_unref 3 on it. If the callback wants to hold on to the message beyond the lifetime of the callback, it needs to call sd_bus_message_ref 3 to create a new reference.

If an error occurs during the callback invocation, the callback should return a negative error number. If it wants other callbacks that match the same rule to be called, it should return 0. Otherwise it should return a positive integer.

## Return Value

On success, `sd_bus_add_match()` returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

## See Also

systemd 1, sd-bus 3