man: add sd_bus_message_new_call(3)

man/print-unit-path.c

@@ -0,0 +1,64 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#include <systemd/sd-bus.h>
+#define _cleanup_(f) __attribute__((cleanup(f)))
+
+/* This is equivalent to:
+ * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
+ *       org.freedesktop.systemd1.Manager GetUnitByPID $$
+ *
+ * Compile with 'cc -lsystemd print-unit-path.c'
+ */
+
+#define DESTINATION "org.freedesktop.systemd1"
+#define PATH        "/org/freedesktop/systemd1"
+#define INTERFACE   "org.freedesktop.systemd1.Manager"
+#define MEMBER      "GetUnitByPID"
+
+static int log_error(int error, const char *message) {
+  fprintf(stderr, "%s: %s\n", message, strerror(-error));
+  return error;
+}
+
+static int print_unit_path(sd_bus *bus) {
+  _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
+  _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+  _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+  int r;
+
+  r = sd_bus_message_new_method_call(bus, &m,
+                                     DESTINATION, PATH, INTERFACE, MEMBER);
+  if (r < 0)
+    return log_error(r, "Failed to create bus message");
+
+  r = sd_bus_message_append(m, "u", (unsigned) getpid());
+  if (r < 0)
+    return log_error(r, "Failed to append to bus message");
+
+  r = sd_bus_call(bus, m, -1, &error, &reply);
+  if (r < 0)
+    return log_error(r, "Call failed");
+
+  const char *ans;
+  r = sd_bus_message_read(reply, "o", &ans);
+  if (r < 0)
+    return log_error(r, "Failed to read reply");
+
+  printf("Unit path is \"%s\".\n", ans);
+
+  return 0;
+}
+
+int main(int argc, char **argv) {
+  _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+  int r;
+
+  r = sd_bus_open_system(&bus);
+  if (r < 0)
+    return log_error(r, "Failed to acquire bus");
+
+  print_unit_path(bus);
+}

man/rules/meson.build

@@ -210,6 +210,7 @@ manpages = [
   '3',
   ['sd_bus_message_get_realtime_usec', 'sd_bus_message_get_seqnum'],
   ''],
+ ['sd_bus_message_new_method_call', '3', [], ''],
  ['sd_bus_message_new_method_error',
   '3',
   ['sd_bus_message_new_method_errno',

man/sd-bus.xml

@@ -60,6 +60,7 @@
 <citerefentry><refentrytitle>sd_bus_message_copy</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_get_cookie</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_get_monotonic_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+<citerefentry><refentrytitle>sd_bus_message_new_method_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_new_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_new_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_read_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

man/sd_bus_message_new_method_call.xml

@@ -0,0 +1,134 @@
+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
+
+<refentry id="sd_bus_message_new_method_call"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_bus_message_new_method_call</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_bus_message_new_method_call</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_bus_message_new_method_call</refname>
+
+    <refpurpose>Create a method call message</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>int sd_bus_message_new_method_call</funcdef>
+        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
+        <paramdef>sd_bus_message **<parameter>m</parameter></paramdef>
+        <paramdef>const char *<parameter>destination</parameter></paramdef>
+        <paramdef>const char *<parameter>path</parameter></paramdef>
+        <paramdef>const char *<parameter>interface</parameter></paramdef>
+        <paramdef>const char *<parameter>member</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>The <function>sd_bus_message_new_method_call()</function> function creates a new bus
+    message object that encapsulates a D-Bus method call, and returns it in the
+    <parameter>m</parameter> output parameter. The call will be made on the destination
+    <parameter>destination</parameter>, path <parameter>path</parameter>, on the interface
+    <parameter>interface</parameter>, member <parameter>member</parameter>.</para>
+
+    <para>Briefly, the <emphasis>destination</emphasis> is a dot-separated name that identifies a
+    service connected to the bus. The <emphasis>path</emphasis> is a slash-separated identifier of
+    an object within the destination that resembles a file system path. The meaning of this path is
+    defined by the destination. The <emphasis>interface</emphasis> is a dot-separated name that
+    resembles a Java interface name that identifies a group of methods and signals supported by the
+    object identified by path. Methods and signals are collectively called
+    <emphasis>members</emphasis> and are identified by a simple name composed of ASCII letters,
+    numbers, and underscores. See the <ulink
+    url="https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts">D-Bus Tutorial</ulink> for an
+    in-depth explanation.</para>
+
+    <para>The <parameter>destination</parameter> parameter may be <constant>NULL</constant>. The
+    <parameter>interface</parameter> parameter may be <constant>NULL</constant>, if the destination
+    has only a single member with the given name and there is no ambiguity if the interface name is
+    omitted.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>This function returns 0 if the message object was successfully created, and a negative
+    errno-style error code otherwise.</para>
+  </refsect1>
+
+  <refsect1 id='errors'>
+    <title>Errors</title>
+
+    <para>Returned errors may indicate the following problems:</para>
+
+    <variablelist>
+      <varlistentry>
+        <term><constant>-EINVAL</constant></term>
+
+        <listitem><para>The output parameter <parameter>m</parameter> is
+        <constant>NULL</constant>.</para>
+
+        <para>The <parameter>destination</parameter> parameter is non-null and is not a valid D-Bus
+        service name (<literal>org.somewhere.Something</literal>), the <parameter>path</parameter>
+        parameter is not a valid D-Bus path (<literal>/an/object/path</literal>), the
+        <parameter>interface</parameter> parameter is non-null and is not a valid D-Bus interface
+        name (<literal>an.interface.name</literal>), or the <parameter>member</parameter> parameter
+        is not a valid D-Bus member (<literal>Name</literal>).</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-ENOTCONN</constant></term>
+
+        <listitem><para>The bus parameter <parameter>bus</parameter> is <constant>NULL</constant> or
+        the bus is not connected.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-ENOMEM</constant></term>
+
+        <listitem><para>Memory allocation failed.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <xi:include href="libsystemd-pkgconfig.xml" />
+
+  <refsect1>
+    <title>Examples</title>
+
+    <example>
+      <title>Make a call to a D-Bus method that takes a single parameter</title>
+
+      <programlisting><xi:include href="print-unit-path.c" parse="text" /></programlisting>
+      <para>This defines a minimally useful program that will open a connection to the bus, create a
+      message object, send it, wait for the reply, and finally extract and print the answer. It does
+      error handling and proper memory management.</para>
+    </example>
+  </refsect1>
+
+  <refsect1>
+    <title>See Also</title>
+
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_path_encode</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>

man/sd_bus_message_new_signal.xml

@@ -44,7 +44,11 @@
     object that encapsulates a D-Bus signal, and returns it in the <parameter>m</parameter> output
     parameter. The signal will be sent to path <parameter>path</parameter>, on the interface
     <parameter>interface</parameter>, member <parameter>member</parameter>. When this message is
-    sent, no reply is expected.</para>
+    sent, no reply is expected. See
+    <citerefentry><refentrytitle>sd_bus_message_new_call</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    for a short description of the meaning of the <parameter>path</parameter>,
+    <parameter>interface</parameter>, and <parameter>member</parameter> parameters.
+    </para>
   </refsect1>
 
   <refsect1>

man/sd_bus_path_encode.xml

@@ -80,7 +80,7 @@
     always be <constant>NUL</constant>-terminated. The returned string
     will be the concatenation of the bus path prefix plus an escaped
     version of the external identifier string. This operation may be
-    reversed with <function>sd_bus_decode()</function>. It is
+    reversed with <function>sd_bus_path_decode()</function>. It is
     recommended to only use external identifiers that generally
     require little escaping to be turned into valid bus path
     identifiers (for example, by sticking to a 7-bit ASCII character