mirror of
https://github.com/morgan9e/systemd
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48c64813ec
When varlink parameters are empty, omit the "parameters" field entirely
rather than sending "parameters":{}. This reduces message size and
follows varlink specification which allows parameters to be omitted.
The implementation supports three equivalent representations for empty
parameters: field omission, JSON null, and empty object {}. All three
are accepted on input for backward compatibility.
Fixes: #38474
72 lines
3.2 KiB
XML
72 lines
3.2 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd-varlink"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd-varlink</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd-varlink</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd-varlink</refname>
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<refpurpose>APIs for Varlink IPC</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-varlink.h></funcsynopsisinfo>
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</funcsynopsis>
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<cmdsynopsis>
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<command>pkg-config --cflags --libs libsystemd</command>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>sd-varlink.h</filename> is part of
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<citerefentry><refentrytitle>libsystemd</refentrytitle><manvolnum>3</manvolnum></citerefentry> and
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provides APIs for implementing Varlink IPC clients and services. See <ulink url="https://varlink.org/"/>
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for more information about Varlink IPC.</para>
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<para>Varlink IPC uses <ulink url="https://json.org/">JSON</ulink> as marshalling format. The sd-varlink
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API relies on the
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<citerefentry><refentrytitle>sd-json</refentrytitle><manvolnum>3</manvolnum></citerefentry> API for JSON
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serialization, deserialization and manipulation.</para>
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<para>Canonical encoding rules: sd-varlink omits the <literal>"parameters"</literal> member on the wire in replies,
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errors, and notifications when there are no parameters to transmit. This reduces message size and
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avoids ambiguity. Receivers must be tolerant and accept any of the following encodings for the
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absence of parameters: an omitted <literal>"parameters"</literal> key (preferred), a JSON <literal>null</literal>
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value, or an empty object <literal>{}</literal>. When decoding, sd-varlink treats JSON <literal>null</literal>
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as if the member was omitted.</para>
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<para>The <citerefentry><refentrytitle>varlinkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool
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makes the functionality implemented by sd-varlink available from the command line.</para>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para><simplelist type="inline">
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<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-json</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>varlinkctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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<member><citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
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<member><citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
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</simplelist></para>
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</refsect1>
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</refentry>
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