sd_bus_message_get_cookie - Man Page
Returns the transaction cookie of a message
int sd_bus_message_get_cookie(sd_bus_message *message, uint64_t *cookie);
int sd_bus_message_get_reply_cookie(sd_bus_message *message, uint64_t *cookie);
sd_bus_message_get_cookie() returns the transaction cookie of a message. The cookie uniquely identifies a message within each bus peer, but is not globally unique. It is assigned when a message is sent.
sd_bus_message_get_reply_cookie() returns the transaction cookie of the message the specified message is a response to. When a reply message is generated for a method call message, its cookie is copied over into this field. Note that while every message that is transferred is identified by a cookie, only response messages carry a reply cookie field.
Both functions take a message object as first parameter and a place to store the 64-bit cookie in.
On success, these calls return 0 or a positive integer. On failure, they return a negative errno-style error code.
On success, the cookie/reply cookie is returned in the specified 64-bit unsigned integer variable.
Returned errors may indicate the following problems:
A specified parameter is invalid.
No cookie has been assigned to this message. This either indicates that the message has not been sent yet and hence has no cookie assigned, or that the message is not a method response message and hence carries a reply cookie field.
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.
systemd(1), sd-bus(3), sd_bus_new(3)
sd-bus(3), systemd.directives(7), systemd.index(7).
The man page sd_bus_message_get_reply_cookie(3) is an alias of sd_bus_message_get_cookie(3).