214 lines
8.4 KiB
Text
214 lines
8.4 KiB
Text
= nng_compat(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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nng_compat - compatibility with nanomsg 1.0
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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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#include <nanomsg/bus.h>
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#include <nanomsg/pair.h>
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#include <nanomsg/pipeline.h>
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#include <nanomsg/pubsub.h>
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#include <nanomsg/reqrep.h>
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#include <nanomsg/survey.h>
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#include <nanomsg/inproc.h>
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#include <nanomsg/ipc.h>
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#include <nanomsg/tcp.h>
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#include <nanomsg/ws.h>
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----
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== DESCRIPTION
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(((compatibility layer)))
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xref:nng.7.adoc[_NNG_] provides source-level compatibility for
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most _libnanomsg_ 1.0 applications.
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IMPORTANT: This is intended to facilitate converting ((legacy applications)) to
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use _NNG_.
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New applications should use the newer xref:nng.7.adoc[_NNG_] API instead.
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Applications making use of this must take care
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to link with xref:libnng.3.adoc[_libnng_] instead of _libnn_.
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TIP: While not recommended for long term use, the value returned by
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xref:nng_socket_id.3.adoc[`nng_socket_id()`] can be used with these functions
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just like a value returned by xref:nn_socket.3compat.adoc[`nn_socket()`].
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This can be way to facilitate incremental transition to the new API.
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NOTE: Some capabilities, protocols, and transports, will not be accessible
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using this API, as the compatible API has no provision for expression
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of certain concepts introduced in the new API.
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NOTE: While reasonable efforts have been made to provide for compatibility,
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some things may behave differently, and some less common parts of the
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_libnanomsg_ 1.0 API are not supported at this time, including certain
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options and the statistics API.
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See the <<Caveats>> section below.
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=== Compiling
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When compiling legacy _nanomsg_ applications, it will generally be
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necessary to change the include search path to add the `compat` subdirectory
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of the directory where headers were installed.
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For example, if _NNG_ is installed in `$prefix`, then header files will
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normally be located in `$prefix/include/nng`.
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In this case, to build legacy _nanomsg_ apps against _NNG_ you would
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add `$prefix/include/nng/compat` to your compiler's search path.
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Alternatively, you can change your source code so that `#include` statements
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referring to `<nanomsg>` instead refer to `<nng/compat/nanomsg>`.
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For example, instead of:
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[source,c]
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----
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#include <nanomsg/nn.h>
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#include <nanomsg/reqrep.h>
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----
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you would have this:
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[source,c]
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----
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#include <nng/compat/nanomsg/nn.h>
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#include <nng/compat/nanomsg/reqrep.h>
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----
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Legacy applications built using these methods should be linked against _libnng_
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instead of _libnn_, just like any other _NNG_ application.
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=== Functions
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The following functions are provided:
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// For PDF, we don't have horizontal lists, so we have to conditionalize
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// this and use tables there -- it looks ugly otherwise.
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ifndef::backend-pdf[]
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[horizontal]
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xref:nn_socket.3compat.adoc[`nn_socket()`]:: create socket
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xref:nn_getsockopt.3compat.adoc[`nn_getsockopt()`]:: get socket option
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xref:nn_setsockopt.3compat.adoc[`nn_setsockopt()`]:: set socket option
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xref:nn_bind.3compat.adoc[`nn_bind()`]:: accept connections from remote peers
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xref:nn_connect.3compat.adoc[`nn_connect()`]:: connect to remote peer
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xref:nn_send.3compat.adoc[`nn_send()`]:: send data
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xref:nn_recv.3compat.adoc[`nn_recv()`]:: receive data
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xref:nn_shutdown.3compat.adoc[`nn_shutdown()`]:: shut down endpoint
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xref:nn_close.3compat.adoc[`nn_close()`]:: close socket
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xref:nn_poll.3compat.adoc[`nn_poll()`]:: poll sockets
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xref:nn_device.3compat.adoc[`nn_device()`]:: create forwarding device
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xref:nn_recvmsg.3compat.adoc[`nn_recvmsg()`]:: receive message
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xref:nn_sendmsg.3compat.adoc[`nn_sendmsg()`]:: send message
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xref:nn_cmsg.3compat.adoc[`nn_cmsg()`]:: message control data
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xref:nn_get_statistic.3compat.adoc[`nn_get_statistic()`]:: get statistic (stub)
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xref:nn_allocmsg.3compat.adoc[`nn_allocmsg()`]:: allocate message
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xref:nn_reallocmsg.3compat.adoc[`nn_reallocmsg()`]:: reallocate message
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xref:nn_freemsg.3compat.adoc[`nn_freemsg()`]:: free message
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xref:nn_errno.3compat.adoc[`nn_errno()`]:: return most recent error
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xref:nn_strerror.3compat.adoc[`nn_strerror()`]:: return message for error
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xref:nn_term.3compat.adoc[`nn_term()`]:: terminate library
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endif::[]
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ifdef::backend-pdf[]
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// Add links for the following as they are written.
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[.hdlist,width=90%, grid=rows,cols="1,2", align="center"]
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|===
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|xref:nn_socket.3compat.adoc[`nn_socket()`]|create socket
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|xref:nn_getsockopt.3compat.adoc[`nn_getsockopt()`]|get socket option
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|xref:nn_setsockopt.3compat.adoc[`nn_setsockopt()`]|set socket option
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|xref:nn_bind.3compat.adoc[`nn_bind()`]|accept connections from remote peers
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|xref:nn_connect.3compat.adoc[`nn_connect()`]|connect to remote peer
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|xref:nn_send.3compat.adoc[`nn_send()`]|send data
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|xref:nn_recv.3compat.adoc[`nn_recv()`]|receive data
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|xref:nn_shutdown.3compat.adoc[`nn_shutdown()`]|shut down endpoint
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|xref:nn_close.3compat.adoc[`nn_close()`]|close socket
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|xref:nn_poll.3compat.adoc[`nn_poll()`]|poll sockets
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|xref:nn_device.3compat.adoc[`nn_device()`]|create forwarding device
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|xref:nn_recvmsg.3compat.adoc[`nn_recvmsg()`]|receive message
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|xref:nn_sendmsg.3compat.adoc[`nn_sendmsg()`]|send message
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|xref:nn_cmsg.3compat.adoc[`nn_cmsg()`]|message control data
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|xref:nn_get_statistic.3compat.adoc[`nn_get_statistic()`]|get statistic (stub)
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|xref:nn_allocmsg.3compat.adoc[`nn_allocmsg()`]|allocate message
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|xref:nn_reallocmsg.3compat.adoc[`nn_reallocmsg()`]|reallocate message
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|xref:nn_freemsg.3compat.adoc[`nn_freemsg()`]|free message
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|xref:nn_errno.3compat.adoc[`nn_errno()`]|return most recent error
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|xref:nn_strerror.3compat.adoc[`nn_strerror()`]|return message for error
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|xref:nn_term.3compat.adoc[`nn_term()`]|terminate library
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|===
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endif::[]
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=== Caveats
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The following caveats apply when using the legacy API with _NNG_.
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* Socket numbers can be quite large.
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The legacy _libnanomsg_ attempted to reuse socket numbers, like
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file descriptors in UNIX systems.
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_NNG_ avoids this to prevent accidental reuse or
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collision after a descriptor is closed.
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Consequently, socket numbers can become quite large, and should
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probably not be used for array indices.
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* The following options (`nn_getsockopt`) are unsupported:
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`NN_SNDPRIO`, `NN_RCVPRIO`, `NN_IPV4ONLY`.
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The priority options may be supported in the future, when
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the underlying capability is present in _NNG_.
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* Access to statistics using this legacy API
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(xref:nn_get_statistic.3compat.adoc[`nn_get_statistic()`]) is unsupported.
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* Some transports can support longer URLs than legacy _libnanomsg_ can.
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It is a good idea to use short pathnames in URLs if interoperability
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is a concern.
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* Only absolute paths are supported in `ipc://` URLs.
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For example, `ipc:///tmp/mysocket` is acceptable, but `ipc://mysocket` is not.
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* The WebSocket transport in this implementation (`ws://` URLs)
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only supports BINARY frames.
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* Some newer transports are unusable from this mode.
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In particular, this legacy API offers no way to configure
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TLS or ZeroTier parameters that may be required for use.
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* ABI versioning of the compatibility layer is not supported,
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and the `NN_VERSION_` macros are not present.
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* Runtime symbol information is not implemented.
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Specifically, there is no `nn_symbol()` function yet.
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(This may be addressed later if there is a need.)
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* The TCP transport (`tcp://` URLs) does not support specifying the local
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address or interface when binding. (This could be fixed in the future,
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but most likely this will be available only using the new API.)
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* The values of `NN_RCVMAXSIZE` are constrained.
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Specifically, values set larger than 2GB using the new API will be reported
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as unlimited (`-1`) in the new API, and the value `0` will disable any
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enforcement, just like `-1`.
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(There is no practical reason to ever want to limit the receive size to
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zero.)
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* This implementation counts buffers in terms of messages rather than bytes.
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As a result, the buffer sizes accessed with `NN_SNDBUF` and `NN_RCVBUF` are
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rounded up to a whole number of kilobytes, then divided by 1024, in order
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to approximate buffering assuming 1 KB messages.
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Few applications should need to adjust the default values.
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== SEE ALSO
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[.text-left]
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xref:libnng.3.adoc[libnng(3)],
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xref:nng.7.adoc[nng(7)]
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