= nng_recvmsg(3)
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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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nng_recvmsg - recv message
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== SYNOPSIS
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[source, c]
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----
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#include <nng/nng.h>
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int nng_recvmsg(nng_socket s, nng_msg **msgp, int flags);
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----
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== DESCRIPTION
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The `nng_recvmsg()` receives a message on socket _s_, storing the
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received message at the location pointed to by _msgp_.
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TIP: Using this function gives access to the message structure, and thus may
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offer more functionality than the simpler xref:nng_recv.3.adoc[`nng_recv()`] function.
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The _flags_ may contain the following value:
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`NNG_FLAG_NONBLOCK`::
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The function returns immediately, even if no message is available.
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Without this flag, the function will wait until a message is received
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by the socket _s_, or any configured timer expires.
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NOTE: The semantics of what receiving a message means vary from protocol to
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protocol, so examination of the protocol documentation is encouraged.
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(For example, with an xref:nng_req.7.adoc[_req_] socket a message may only be received
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after a request has been sent, and an xref:nng_sub.7.adoc[_sub_] socket
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may only receive messages corresponding to topics to which it has subscribed.)
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Furthermore, some protocols may not support receiving data at all, such as
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xref:nng_pub.7.adoc[_pub_].
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== RETURN VALUES
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This function returns 0 on success, and non-zero otherwise.
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== ERRORS
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[horizontal]
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`NNG_EAGAIN`:: The operation would block, but `NNG_FLAG_NONBLOCK` was specified.
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`NNG_ECLOSED`:: The socket _s_ is not open.
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`NNG_EINVAL`:: An invalid set of _flags_ was specified.
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`NNG_ENOMEM`:: Insufficient memory is available.
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`NNG_ENOTSUP`:: The protocol for socket _s_ does not support receiving.
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`NNG_ESTATE`:: The socket _s_ cannot receive data in this state.
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`NNG_ETIMEDOUT`:: The operation timed out.
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== SEE ALSO
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[.text-left]
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xref:nng_msg_free.3.adoc[nng_msg_free(3)],
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xref:nng_recv.3.adoc[nng_recv(3)],
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xref:nng_sendmsg.3.adoc[nng_sendmsg(3)],
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xref:nng_strerror.3.adoc[nng_strerror(3)],
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xref:nng.7.adoc[nng(7)]
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