These helper functions manipulate socket ancillary data. They deal with msg_control and msg_conrollen member of msghdr and leave the rest of the structure alone.
/* Allocate buffer for control data. The buffer will be of size zero, however,
to minimise number of (re)allocations you should specify the capacity in
such a way as o fit all the ancillary data. Returns 0 in case of success,
-1 if the buffer cannot be allocated. */
void msg_control_init (struct msghdr *hdr, size_t capacity);
/* Deallocate control data. */
void msg_control_term (struct msghdr *hdr);
/* Return property specified by level and type. If the size of the property
is known in advance, 'size' may be set to NULL. Returns 0 in case of success,
-1 if the property in question is not present. */
int msg_control_get (struct msghdr *hdr,
int level, int type, void **data, size_t *size);
/* Add the property specified by level and type to the buffer. Returns 0 in case
of success, -1 if additional space in the buffer cannot be allocated. */
int msg_control_set (struct msghdr *hdr,
int level, int type, void *data, size_t size);
/* Remove the property specified by level and type from the buffer. Returns 0
in case of success, -1 if the property in question is not present. */
int msg_control_rm (struct msghdr *hdr, int level, int type);
/* Use this function instead of sendmsg(2). */
ssize_t msg_control_send (int fd, struct msghdr *hdr, int flags);
/* Use this function instead of recvmsg(2). */
ssize_t msg_control_recv (int fd, struct msghdr *hdr, int *flags);
This project is licensed under MIT/X11 license.