= nn_cmsg(3compat) // // Copyright 2018 Staysail Systems, Inc. <info@staysail.tech> // Copyright 2018 Capitar IT Group BV <info@capitar.com> // // This document is supplied under the terms of the MIT License, a // copy of which should be located in the distribution where this // file was obtained (LICENSE.txt). A copy of the license may also be // found online at https://opensource.org/licenses/MIT. // == NAME nn_cmsg - message control data (compatible API) == SYNOPSIS [source,c] ---- #include <nanomsg/nn.h> struct nn_cmsghdr { size_t cmsg_len; int cmsg_level; int cmsg_type; }; ---- == DESCRIPTION The `nn_cmsghdr` structure describes a block of control data that is associated with a message either sent by xref:nn_sendmsg.3compat.adoc[`nn_sendmsg()`] or received by xref:nn_recvmsg.3compat.adoc[`nn_recvmsg()`]. NOTE: This structure and supporting macros are provided for API xref:nng_compat.3compat.adoc[compatibility] with legacy _libnanomsg_. Consider using the relevant xref:libnng.3.adoc[modern API] instead. Each header is followed by `cmsg_len` bytes of data, plus any padding required to align the structure. The only defined ancillary data at this time is the protocol headers used by the protocols. This uses `cmsg_level` set to `PROTO_SP` and the `cmsg_type` set to `SP_HDR`. The actual data for this will vary from depending on the protocol used. Convenience macros are provided to make working with these fields easier. `struct nn_cmsghdr *NN_CMSG_FIRSTHDR(struct nn_msghdr *__hdr__)`:: This macro returns the first `struct nn_cmsghdr` header in _hdr_. `struct nn_cmsghdr *NN_CMSG_NXTHDR(struct nn_msghdr *__hdr__, struct nn_cmsghdr *__ch__)`:: This macro returns a pointer to the next `struct nn_cmsghdr` in _hdr_ after _ch_. `void *NN_CMSG_DATA(struct nn_cmsghdr *__ch__)`:: This macro returns a pointer to the header-specific data for _ch_. `size_t NN_CMSG_ALIGN(size_t __len__)`:: This macro returns the length specified by _len_, plus any padding required to provide the necessary alignment for another structure. `size_t NN_CMSG_SPACE(size_t __len__)`:: This macro returns the amount of space required for a header, with _len_ bytes of following data, and any necessary padding. `size_t NN_CMSG_LEN(size_t __len__)`:: This macro evaluates to the length of the header (including alignment), and the associated data of length _len_, but without any trailing padding to align for another header. == SEE ALSO [.text-left] xref:nn_recvmsg.3compat.adoc[nn_recvmsg(3compat)], xref:nn_sendmsg.3compat.adoc[nn_sendmsg(3compat)], xref:nng_compat.3compat.adoc[nng_compat(3compat)], xref:nng.7.adoc[nng(7)]