Gets a header field on @message.
The caller is responsible for checking the type of the returned #GVariant matches what is expected.
A 8-bit unsigned integer (typically a value from the #GDBusMessageHeaderField enumeration)
A #GVariant with the value if the header was found, %NULL otherwise. Do not free, it is owned by @message.
2.26
See Implementation
Gets a header field on @message.
The caller is responsible for checking the type of the returned #GVariant matches what is expected.