92 lines
3 KiB
Text
92 lines
3 KiB
Text
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= nng_respondent(7)
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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_respondent - respondent protocol
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== SYNOPSIS
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[source,c]
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----
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#include <nng/protocol/survey0/respond.h>
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----
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== DESCRIPTION
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(((protocol, _respondent_)))
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The ((_respondent_ protocol)) is one half of a ((survey pattern)).
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In this pattern, a surveyor sends a survey, which is broadcast to all
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peer respondents.
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The respondents then have a chance to reply (but are not obliged to reply).
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The survey itself is a timed event, so that responses
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received after the survey has finished are discarded.
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TIP: This protocol is useful in solving voting problems, such as leader
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election in cluster configurations, as well as certain kinds of service
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discovery problems.
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The _respondent_ protocol is the respondent side, and the
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xref:nng_surveyor.7.adoc[_surveyor_] protocol is the surveyor side.
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=== Socket Operations
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The xref:nng_respondent_open.3.adoc[`nng_respondent0_open()`] functions create a
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respondent socket.
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This socket may be used to receive messages, and then to send replies.
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A reply can only be sent after receiving a survey, and generally the
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reply will be sent to surveyor from whom the last survey was received.
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Respondents may discard a survey by simply not replying to it.
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Raw mode sockets (set with xref:nng_options.5.adoc#NNG_OPT_RAW[`NNG_OPT_RAW`])
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ignore all these restrictions.
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=== Context Operations
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This protocol supports the creation of xref:nng_ctx.5.adoc[contexts] for concurrent
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use cases using xref:nng_ctx_open.3.adoc[`nng_ctx_open()`].
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Incoming surveys will be routed to and received by only one context.
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Additional surveys may be received by other contexts in parallel.
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Replies made using a context will be returned to the the surveyor that
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issued the survey most recently received by that context.
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The restrictions for order of operations with sockets apply equally
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well for contexts, except that each context will be treated as if it were
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a separate socket.
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=== Protocol Versions
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Only version 0 of this protocol is supported.
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(At the time of writing, no other versions of this protocol have been defined.
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An earlier and incompatible version of the protocol was used in older
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pre-releases of http://nanomsg.org[nanomsg], but was not released in any
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production version.)
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=== Protocol Options
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The _respondent_ protocol has no protocol-specific options.
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=== Protocol Headers
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(((backtrace)))
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The _respondent_ protocol uses a _backtrace_ in the header.
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This is more fully documented in the xref:nng_surveyor.7.adoc[_surveyor_] manual.
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// TODO: Insert reference to RFC.
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== SEE ALSO
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[.text-left]
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xref:nng_respondent_open.3.adoc[nng_respondent_open(3)],
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xref:nng_surveyor.7.adoc[nng_surveyor(7)],
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xref:nng.7.adoc[nng(7)]
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