= 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)]
|
