3a3a557efe
git-subtree-dir: external/nng git-subtree-split: c5e9d8acfc226418dedcf2e34a617bffae043ff6
99 lines
3 KiB
Text
99 lines
3 KiB
Text
= nn_recvmsg(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_recvmsg - receive message (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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int nn_recvmsg(int sock, struct nn_msghdr *hdr, int flags);
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----
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== DESCRIPTION
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The `nn_recvmsg()` function receives a message into the header described by
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_hdr_ using the socket _sock_.
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NOTE: This function is 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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The _flags_ field may contain the special flag `NN_DONTWAIT`.
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In this case, if no message is ready for receiving on _sock_,
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the operation shall not block, but instead will fail with the error `EAGAIN`.
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The _hdr_ points to a structure of type `struct nn_msghdr`, which has the
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following definition:
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[source, c]
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----
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struct nn_iovec {
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void * iov_base;
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size_t iov_len;
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};
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struct nn_msghdr {
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struct nn_iovec *msg_iov;
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int msg_iovlen;
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void * msg_control;
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size_t msg_controllen;
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};
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----
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The `msg_iov` is an array of scatter items, permitting the message
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to be spread into different memory blocks.
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There are `msg_iovlen` elements in this array, each of which
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has the base address (`iov_base`) and length (`iov_len`) indicated.
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The last member of this array may have the `iov_len` field set to `NN_MSG`,
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in which case the function shall allocate a message buffer, and store the
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pointer to it at the address indicated by `iov_base`.
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This can help save an extra copy operation.
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The buffer should be deallocated by xref:nn_freemsg.3compat.adoc[`nn_freemsg()`]
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or similar when it is no longer needed.
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The values of `msg_control` and `msg_controllen` describe a buffer
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of ancillary data associated with the message.
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This is currently only useful to obtain the message headers
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used with xref:nng.7.adoc#raw_mode[raw mode] sockets.
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In all other circumstances these fields should be zero.
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Details about this structure are covered in
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xref:nn_cmsg.3compat.adoc[`nn_cmsg(3compat)`].
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== RETURN VALUES
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This function returns the number of bytes received on success, and -1 on error.
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== ERRORS
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[horizontal]
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`EAGAIN`:: The operation would block.
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`EBADF`:: The socket _sock_ is not open.
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`EFSM`:: The socket cannot receive in this state.
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`EINVAL`:: The _hdr_ is invalid.
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`ENOTSUP`:: This protocol cannot receive.
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`ETIMEDOUT`:: Operation timed out.
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== SEE ALSO
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[.text-left]
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xref:nn_cmsg.3compat.adoc[nn_cmsg(3compat)],
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xref:nn_errno.3compat.adoc[nn_errno(3compat)],
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xref:nn_recv.3compat.adoc[nn_recv(3compat)],
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xref:nn_send.3compat.adoc[nn_send(3compat)],
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xref:nn_socket.3compat.adoc[nn_socket(3compat)],
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xref:nng_compat.3compat.adoc[nn_compat(3compat)],
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xref:nng.7.adoc[nng(7)]
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