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