sd_bus_message_rewind - Return to beginning of message or current container
sd_bus_message_rewind() moves the "read pointer" in the message
m to either the beginning of the message (if complete is true)
or to the beginning of the currently open container. If no container is open,
complete has no effect.
On success, this function returns 0 or a positive integer. The value is zero if
the current container or whole message in case no container is open is empty,
and positive otherwise. On failure, it returns a negative errno-style error
Returned errors may indicate the following problems:
The m parameter is NULL.
The message m has not been sealed.
These APIs are implemented as a shared library, which can be compiled and linked
to with the libsystemd pkg-config(1) file.