From 8e4e4aa5fdb45b8581ff29f77c87fe4e892a207b Mon Sep 17 00:00:00 2001
From: Simon McVittie <simon.mcvittie@collabora.co.uk>
Date: Fri, 23 Jan 2015 19:25:35 +0000
Subject: [PATCH 4/6] dbus-monitor: add support for using BecomeMonitor to be a
 read-only monitor

Move the dbus_connection_add_filter() call further up as a precaution,
because it isn't safe for a monitor to not have a filter that
swallows all messages.
---
 tools/Makefile.am    | 11 +++---
 tools/dbus-monitor.c | 95 ++++++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 84 insertions(+), 22 deletions(-)

diff --git a/tools/Makefile.am b/tools/Makefile.am
index 05d1dcb..821ad5c 100644
--- a/tools/Makefile.am
+++ b/tools/Makefile.am
@@ -31,10 +31,13 @@ dbus_send_SOURCES=				\
 	dbus-print-message.h			\
 	dbus-send.c
 
-dbus_monitor_SOURCES=				\
-	dbus-monitor.c				\
-	dbus-print-message.c			\
-	dbus-print-message.h
+dbus_monitor_SOURCES= \
+	dbus-monitor.c \
+	dbus-print-message.c \
+	dbus-print-message.h \
+	tool-common.c \
+	tool-common.h \
+	$(NULL)
 
 if DBUS_WIN
 dbus_launch_SOURCES=				\
diff --git a/tools/dbus-monitor.c b/tools/dbus-monitor.c
index ff8390d..23e0c17 100644
--- a/tools/dbus-monitor.c
+++ b/tools/dbus-monitor.c
@@ -34,6 +34,7 @@
 #include <time.h>
 
 #include "dbus-print-message.h"
+#include "tool-common.h"
 
 #define EAVESDROPPING_RULE "eavesdrop=true"
 
@@ -78,13 +79,6 @@ gettimeofday (struct timeval *__p,
 }
 #endif
 
-inline static void
-oom (const char *doing)
-{
-  fprintf (stderr, "OOM while %s\n", doing);
-  exit (1);
-}
-
 static DBusHandlerResult
 monitor_filter_func (DBusConnection     *connection,
 		     DBusMessage        *message,
@@ -96,10 +90,9 @@ monitor_filter_func (DBusConnection     *connection,
                               DBUS_INTERFACE_LOCAL,
                               "Disconnected"))
     exit (0);
-  
-  /* Conceptually we want this to be
-   * DBUS_HANDLER_RESULT_NOT_YET_HANDLED, but this raises
-   * some problems.  See bug 1719.
+
+  /* Monitors must not allow libdbus to reply to messages, so we eat
+   * the message. See bug 1719.
    */
   return DBUS_HANDLER_RESULT_HANDLED;
 }
@@ -242,6 +235,66 @@ only_one_type (dbus_bool_t *seen_bus_type,
     }
 }
 
+static dbus_bool_t
+become_monitor (DBusConnection *connection,
+    int numFilters,
+    char **filters)
+{
+  DBusError error = DBUS_ERROR_INIT;
+  DBusMessage *m;
+  DBusMessage *r;
+  int i;
+  dbus_uint32_t zero = 0;
+  DBusMessageIter appender, array_appender;
+
+  m = dbus_message_new_method_call (DBUS_SERVICE_DBUS,
+      DBUS_PATH_DBUS, DBUS_INTERFACE_MONITORING, "BecomeMonitor");
+
+  if (m == NULL)
+    tool_oom ("becoming a monitor");
+
+  dbus_message_iter_init_append (m, &appender);
+
+  if (!dbus_message_iter_open_container (&appender, DBUS_TYPE_ARRAY, "s",
+        &array_appender))
+    tool_oom ("opening string array");
+
+  for (i = 0; i < numFilters; i++)
+    {
+      if (!dbus_message_iter_append_basic (&array_appender, DBUS_TYPE_STRING,
+            &filters[i]))
+        tool_oom ("adding filter to array");
+    }
+
+  if (!dbus_message_iter_close_container (&appender, &array_appender) ||
+      !dbus_message_iter_append_basic (&appender, DBUS_TYPE_UINT32, &zero))
+    tool_oom ("finishing arguments");
+
+  r = dbus_connection_send_with_reply_and_block (connection, m, -1, &error);
+
+  if (r != NULL)
+    {
+      dbus_message_unref (r);
+    }
+  else if (dbus_error_has_name (&error, DBUS_ERROR_UNKNOWN_INTERFACE))
+    {
+      fprintf (stderr, "dbus-monitor: unable to enable new-style monitoring, "
+          "your dbus-daemon is too old. Falling back to eavesdropping.\n");
+      dbus_error_free (&error);
+    }
+  else
+    {
+      fprintf (stderr, "dbus-monitor: unable to enable new-style monitoring: "
+          "%s: \"%s\". Falling back to eavesdropping.\n",
+          error.name, error.message);
+      dbus_error_free (&error);
+    }
+
+  dbus_message_unref (m);
+
+  return (r != NULL);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -312,10 +365,10 @@ main (int argc, char *argv[])
 
           filters = (char **) realloc (filters, numFilters * sizeof (char *));
           if (filters == NULL)
-            oom ("adding a new filter slot");
+            tool_oom ("adding a new filter slot");
           filters[j] = (char *) malloc (filter_len);
           if (filters[j] == NULL)
-            oom ("adding a new filter");
+            tool_oom ("adding a new filter");
           snprintf (filters[j], filter_len, "%s,%s", EAVESDROPPING_RULE, arg);
           j++;
       }
@@ -365,7 +418,17 @@ main (int argc, char *argv[])
       exit (1);
     }
 
-  if (numFilters)
+  if (!dbus_connection_add_filter (connection, filter_func, NULL, NULL))
+    {
+      fprintf (stderr, "Couldn't add filter!\n");
+      exit (1);
+    }
+
+  if (become_monitor (connection, numFilters, filters))
+    {
+      /* no more preparation needed */
+    }
+  else if (numFilters)
     {
       size_t offset = 0;
       for (i = 0; i < j; i++)
@@ -408,10 +471,6 @@ main (int argc, char *argv[])
         }
     }
 
-  if (!dbus_connection_add_filter (connection, filter_func, NULL, NULL)) {
-    fprintf (stderr, "Couldn't add filter!\n");
-    exit (1);
-  }
 
   while (dbus_connection_read_write_dispatch(connection, -1))
     ;
-- 
2.1.4