sd_bus_message_new_method_call

systemd

sd_bus_message_new_method_return

Create a method call message

#include <systemd/sd-bus.h>

int

sd_bus_message_new_method_call

sd_bus *

bus

sd_bus_message **

const char *

destination

const char *

path

const char *

interface

const char *

member

int

sd_bus_message_new_method_return

sd_bus_message *

call

sd_bus_message **

Description

The sd_bus_message_new_method_call() function creates a new bus message object that encapsulates a D-Bus method call, and returns it in the m output parameter. The call will be made on the destination destination, path path, on the interface interface, member member.

Briefly, the destination is a dot-separated name that identifies a service connected to the bus. The path is a slash-separated identifier of an object within the destination that resembles a file system path. The meaning of this path is defined by the destination. The interface is a dot-separated name that resembles a Java interface name that identifies a group of methods and signals supported by the object identified by path. Methods and signals are collectively called members and are identified by a simple name composed of ASCII letters, numbers, and underscores. See the D-Bus Tutorial for an in-depth explanation.

The destination parameter may be NULL. The interface parameter may be NULL, if the destination has only a single member with the given name and there is no ambiguity if the interface name is omitted.

Note that this is a low level interface. See sd_bus_call_method(3) for a more convenient way of calling D-Bus methods.

The sd_bus_message_new_method_return() function creates a new bus message object that is a reply to the method call call and returns it in the m output parameter. The call parameter must be a method call message. The sender of call is used as the destination.

Return Value

On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code.

Errors

Returned errors may indicate the following problems:

-EINVAL
The output parameter m is NULL.

The destination parameter is non-null and is not a valid D-Bus service name (org.somewhere.Something), the path parameter is not a valid D-Bus path (/an/object/path), the interface parameter is non-null and is not a valid D-Bus interface name (an.interface.name), or the member parameter is not a valid D-Bus member (Name).

The call parameter is not a method call object.

-ENOTCONN
The bus parameter bus is NULL or the bus is not connected.

-ENOMEM
Memory allocation failed.

-EPERM
The call parameter is not sealed.

-EOPNOTSUPP
The call message does not have a cookie.

Examples

Make a call to a D-Bus method that takes a single parameter

This defines a minimally useful program that will open a connection to the bus, create a message object, send it, wait for the reply, and finally extract and print the answer. It does error handling and proper memory management.

History

sd_bus_message_new_method_call() and sd_bus_message_new_method_return() were added in version 246.