GDBus: Add `return' debug option

This prints all GDBusMethodInvocation API usage and is normally used
with the `incoming' option. Example:

 # G_DBUS_DEBUG=incoming,return ./polkitd --replace
 Entering main event loop
 Connected to the system bus
 Registering null backend at priority -10
 [...]
 Acquired the name org.freedesktop.PolicyKit1
 [...]

 ========================================================================
 GDBus-debug:Incoming:
  <<<< METHOD INVOCATION org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
       on object /org/freedesktop/PolicyKit1/Authority
       invoked by name :1.26
       serial 299
 ========================================================================
 GDBus-debug:Return:
  >>>> METHOD ERROR org.freedesktop.PolicyKit1.Error.Failed
       message `Cannot determine session the caller is in'
       in response to org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
       on object /org/freedesktop/PolicyKit1/Authority
       to name :1.26
       reply-serial 299

 [...]

 ========================================================================
 GDBus-debug:Incoming:
  <<<< METHOD INVOCATION org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
       on object /org/freedesktop/PolicyKit1/Authority
       invoked by name :1.2402
       serial 25
 ========================================================================
 GDBus-debug:Return:
  >>>> METHOD RETURN
       in response to org.freedesktop.PolicyKit1.Authority.RegisterAuthenticationAgent()
       on object /org/freedesktop/PolicyKit1/Authority
       to name :1.2402
       reply-serial 25

Signed-off-by: David Zeuthen <davidz@redhat.com>

docs/reference/gio/overview.xml

@@ -359,6 +359,10 @@
              <term>incoming</term>
              <listitem><para>Show when an incoming D-Bus method call is received</para></listitem>
            </varlistentry>
+           <varlistentry>
+             <term>return</term>
+             <listitem><para>Show when a reply is returned via the #GDBusMethodInvocation API</para></listitem>
+           </varlistentry>
            <varlistentry>
              <term>emission</term>
              <listitem><para>Trace g_dbus_connection_emit_signal() API usage</para></listitem>
@@ -372,8 +376,10 @@
              <listitem><para>Show information about D-Bus address lookups and autolaunching</para></listitem>
            </varlistentry>
          </variablelist>
-         The special value <literal>all</literal> can be used to turn on
+         The special value <literal>all</literal> can be used to turn
-         all debug options.
+         on all debug options. The special value
+         <literal>help</literal> can be used to print a list of
+         supported options to standard output.
       </para>
    </formalpara>
 

gio/gdbusconnection.c

@@ -5883,10 +5883,12 @@ distribute_method_call (GDBusConnection *connection,
                "GDBus-debug:Incoming:\n"
                " <<<< METHOD INVOCATION %s.%s()\n"
                "      on object %s\n"
-               "      invoked by name %s\n",
+               "      invoked by name %s\n"
+               "      serial %d\n",
                interface_name, member,
                path,
-               g_dbus_message_get_sender (message) != NULL ? g_dbus_message_get_sender (message) : "(none)");
+               g_dbus_message_get_sender (message) != NULL ? g_dbus_message_get_sender (message) : "(none)",
+               g_dbus_message_get_serial (message));
       _g_dbus_debug_print_unlock ();
     }
 

gio/gdbusmethodinvocation.c

@@ -381,6 +381,23 @@ g_dbus_method_invocation_return_value (GDBusMethodInvocation *invocation,
       g_variant_type_free (type);
     }
 
+  if (G_UNLIKELY (_g_dbus_debug_return ()))
+    {
+      _g_dbus_debug_print_lock ();
+      g_print ("========================================================================\n"
+               "GDBus-debug:Return:\n"
+               " >>>> METHOD RETURN\n"
+               "      in response to %s.%s()\n"
+               "      on object %s\n"
+               "      to name %s\n"
+               "      reply-serial %d\n",
+               invocation->interface_name, invocation->method_name,
+               invocation->object_path,
+               invocation->sender,
+               g_dbus_message_get_serial (invocation->message));
+      _g_dbus_debug_print_unlock ();
+    }
+
   reply = g_dbus_message_new_method_reply (invocation->message);
   g_dbus_message_set_body (reply, parameters);
   error = NULL;
@@ -560,6 +577,26 @@ g_dbus_method_invocation_return_dbus_error (GDBusMethodInvocation *invocation,
   g_return_if_fail (error_name != NULL && g_dbus_is_name (error_name));
   g_return_if_fail (error_message != NULL);
 
+  if (G_UNLIKELY (_g_dbus_debug_return ()))
+    {
+      _g_dbus_debug_print_lock ();
+      g_print ("========================================================================\n"
+               "GDBus-debug:Return:\n"
+               " >>>> METHOD ERROR %s\n"
+               "      message `%s'\n"
+               "      in response to %s.%s()\n"
+               "      on object %s\n"
+               "      to name %s\n"
+               "      reply-serial %d\n",
+               error_name,
+               error_message,
+               invocation->interface_name, invocation->method_name,
+               invocation->object_path,
+               invocation->sender,
+               g_dbus_message_get_serial (invocation->message));
+      _g_dbus_debug_print_unlock ();
+    }
+
   reply = g_dbus_message_new_method_error_literal (invocation->message,
                                                    error_name,
                                                    error_message);

gio/gdbusprivate.c

@@ -1178,8 +1178,9 @@ _g_dbus_worker_flush_sync (GDBusWorker    *worker,
 #define G_DBUS_DEBUG_CALL           (1<<3)
 #define G_DBUS_DEBUG_SIGNAL         (1<<4)
 #define G_DBUS_DEBUG_INCOMING       (1<<5)
-#define G_DBUS_DEBUG_EMISSION       (1<<6)
+#define G_DBUS_DEBUG_RETURN         (1<<6)
-#define G_DBUS_DEBUG_ADDRESS        (1<<7)
+#define G_DBUS_DEBUG_EMISSION       (1<<7)
+#define G_DBUS_DEBUG_ADDRESS        (1<<8)
 
 static gint _gdbus_debug_flags = 0;
 
@@ -1225,6 +1226,13 @@ _g_dbus_debug_incoming (void)
   return (_gdbus_debug_flags & G_DBUS_DEBUG_INCOMING) != 0;
 }
 
+gboolean
+_g_dbus_debug_return (void)
+{
+  _g_dbus_initialize ();
+  return (_gdbus_debug_flags & G_DBUS_DEBUG_RETURN) != 0;
+}
+
 gboolean
 _g_dbus_debug_emission (void)
 {
@@ -1283,6 +1291,7 @@ _g_dbus_initialize (void)
             { "call",           G_DBUS_DEBUG_CALL           },
             { "signal",         G_DBUS_DEBUG_SIGNAL         },
             { "incoming",       G_DBUS_DEBUG_INCOMING       },
+            { "return",         G_DBUS_DEBUG_RETURN         },
             { "emission",       G_DBUS_DEBUG_EMISSION       },
             { "address",        G_DBUS_DEBUG_ADDRESS        }
           };

gio/gdbusprivate.h

@@ -85,6 +85,7 @@ gboolean _g_dbus_debug_payload (void);
 gboolean _g_dbus_debug_call    (void);
 gboolean _g_dbus_debug_signal  (void);
 gboolean _g_dbus_debug_incoming (void);
+gboolean _g_dbus_debug_return (void);
 gboolean _g_dbus_debug_emission (void);
 gboolean _g_dbus_debug_address (void);