sd_bus_message_new

systemd
sd_bus_message_new 3
sd_bus_message_new sd_bus_message_ref sd_bus_message_unref sd_bus_message_unrefp SD_BUS_MESSAGE_METHOD_CALL SD_BUS_MESSAGE_METHOD_RETURN SD_BUS_MESSAGE_METHOD_ERROR SD_BUS_MESSAGE_SIGNAL sd_bus_message_get_bus Create a new bus message object and create or destroy references to it

    #include <systemd/sd-bus.h>

    enum {
          SD_BUS_MESSAGE_METHOD_CALL,
          SD_BUS_MESSAGE_METHOD_RETURN,
          SD_BUS_MESSAGE_METHOD_ERROR,
          SD_BUS_MESSAGE_SIGNAL,
    };

int `sd_bus_message_new` sd_bus *bus sd_bus_message **m uint8_t type sd_bus_message *`sd_bus_message_ref` sd_bus_message *m sd_bus_message *`sd_bus_message_unref` sd_bus_message *m void `sd_bus_message_unrefp` sd_bus_message **mp sd_bus *`sd_bus_message_get_bus` sd_bus_message *m

## Description

`sd_bus_message_new()` creates a new bus message object attached to the bus bus and returns it in the output parameter m. This object is reference-counted, and will be destroyed when all references are gone. Initially, the caller of this function owns the sole reference to the message object. Note that the message object holds a reference to the bus object, so the bus object will not be destroyed as long as the message exists.

Note: this is a low-level call. In most cases functions like sd_bus_message_new_method_call 3, sd_bus_message_new_method_error 3, sd_bus_message_new_method_return 3, and sd_bus_message_new_signal 3 that create a message of a certain type and initialize various fields are easier to use.

The type parameter specifies the type of the message. It must be one of `SD_BUS_MESSAGE_METHOD_CALL` — a method call, `SD_BUS_MESSAGE_METHOD_RETURN` — a method call reply, `SD_BUS_MESSAGE_METHOD_ERROR` — an error reply to a method call, `SD_BUS_MESSAGE_SIGNAL` — a broadcast message with no reply.

The flag to allow interactive authorization is initialized based on the current value set in the bus object, see sd_bus_set_allow_interactive_authorization 3. This may be changed using sd_bus_message_set_allow_interactive_authorization 3.

`sd_bus_message_ref()` increases the reference counter of m by one.

`sd_bus_message_unref()` decreases the reference counter of m by one. Once the reference count has dropped to zero, message object is destroyed and cannot be used anymore, so further calls to `sd_bus_message_ref()` or `sd_bus_message_unref()` are illegal.

`sd_bus_message_unrefp()` is similar to `sd_bus_message_unref()` but takes a pointer to a pointer to an sd_bus_message object. This call is useful in conjunction with GCC's and LLVM's Clean-up Variable Attribute. See sd_bus_new 3 for an example how to use the cleanup attribute.

`sd_bus_message_ref()` and `sd_bus_message_unref()` execute no operation if the passed in bus object address is `NULL`. `sd_bus_message_unrefp()` will first dereference its argument, which must not be `NULL`, and will execute no operation if that is `NULL`.

`sd_bus_message_get_bus()` returns the bus object that message m is attached to.

## Return Value

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

`sd_bus_message_ref()` always returns the argument.

`sd_bus_message_unref()` always returns `NULL`.

`sd_bus_message_get_bus()` always returns the bus object.

### Errors

Returned errors may indicate the following problems:

`-EINVAL`

  Specified type is invalid.

`-ENOTCONN`

  The bus parameter bus is `NULL` or the bus is not connected.

`-ENOMEM`

  Memory allocation failed.

## See Also

systemd 1, sd-bus 3, sd_bus_new 3, sd_bus_message_new_method_call 3, sd_bus_message_new_method_error 3, sd_bus_message_new_method_return 3, sd_bus_message_new_signal 3