Michael Vogt
b5f8725989
When sd_varlink_connect_url() gets an unknown URL we now
check if there is a `$LIBEXECDIR/varlink-bridges/$scheme`
binary and execute it (with the url as the first arguments).
This makes varlink more flexible as it provides a way to
dynamically add "bridges" in LIBEXECDIR/varlink-bridges/. This is
conceptually similar to the libvarlink `varlink --bridge` command
and allows to e.g. call varlink over http{,s} via e.g. the new
varlink-http-bridge.
With a running varlink-http-bridge [0] one can do:
```console
$ varlinkctl call http://localhost:8080/ws/sockets/io.systemd.Hostname \
io.systemd.Hostname.Describe {}
{
"Hostname" : "top",
...
```
Closes: https://github.com/systemd/systemd/issues/40640
[0] https://github.com/mvo5/varlink-http-bridge/pull/1
95 lines
4.2 KiB
XML
95 lines
4.2 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>Directories</title>
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<variablelist>
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<varlistentry>
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<term><filename>/usr/lib/systemd/varlink-bridges/</filename></term>
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<listitem>
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<para>When <function>sd_varlink_connect_url()</function> encounters a URL with a scheme that is not
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natively supported, it looks for a bridge helper binary named after the URL scheme in this
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directory. The binary is invoked the same way as <literal>exec:</literal> binaries but with the full
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URL passed as the first command line argument.</para>
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<para>For example, if
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<command>varlinkctl introspect https://example.com/ws/sockets/io.systemd.Hostname</command>
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is called, <command>varlinkctl</command> will look for an executable
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<filename>/usr/lib/systemd/varlink-bridges/https</filename> and invoke it with
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<literal>https://example.com/ws/sockets/io.systemd.Hostname</literal> as its only
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argument.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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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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