SYNOPSIS
#include <nanomsg/nn.h>
struct nn_cmsghdr *NN_CMSG_FIRSTHDR(struct nn_msghdr *hdr);
struct nn_cmsghdr *NN_CMSG_NXTHDR(struct nn_msghdr *hdr, struct nn_cmsghdr *cmsg);
unsigned char *NN_CMSG_DATA(struct nn_cmsghdr *cmsg);
size_t NN_CMSG_SPACE(size_t len);
size_t NN_CMSG_LEN(size_t len);
DESCRIPTION
These functions can be used to iterate over ancillary data attached to a message.
Structure nn_cmsghdr represents a single ancillary property and contains following members:
size_t cmsg_len; int cmsg_level; int cmsg_type;
cmsg_len is the size of the property data, including the preceding nn_cmsghdr structure. cmsg_level is the level of the property; same values can be used as with nn_getsockopt(3) and nn_setsockopt(3). cmsg_type is the name of the property. These names are specific for each level.
NN_CMSG_FIRSTHDR returns a pointer to the first nn_cmsghdr in the control buffer in the supplied nn_msghdr structure.
NN_CMSG_NXTHDR returns the next nn_cmsghdr after the supplied nn_cmsghdr. Returns NULL if there isn’t enough space in the buffer.
NN_CMSG_DATA returns a pointer to the data associated with supplied nn_cmsghdr.
NN_CMSG_SPACE returns the number of bytes occupied by nn_cmsghdr with payload of the specified length.
NN_CMSG_LEN returns the value to store in the cmsg_len member of the cmsghdr structure, taking into account any necessary alignment.
EXAMPLE
Iterating over ancillary properties:
struct nn_cmsghdr *hdr = NN_CMSG_FIRSTHDR (&msg);
while (hdr != NULL) {
size_t len = hdr->cmsg_len - sizeof (nn_cmsghdr);
printf ("level: %d property: %d length: %dB data: ",
(int) hdr->cmsg_level,
(int) hdr->cmsg_type,
(int) len);
unsigned char *data = NN_CMSG_DATA(hdr);
while (len) {
printf ("%02X", *data);
++data;
--len;
}
printf ("\n");
hdr = NN_CMSG_NXTHDR (&msg, hdr);
}