[glib] gmessages: Rebase g_log() on g_log_structured()

[Matthias Clasen <matthiasc src gnome org>]

commit fce7cfaf40b6e1e50c9140aa0397f5b8c8f821fb
Author: Philip Withnall <philip withnall collabora co uk>
Date:   Mon Jun 13 18:21:44 2016 +0100

    gmessages: Rebase g_log() on g_log_structured()
    
    Replace the underlying write_string() call which is the ultimate result
    of calling g_log() with a call to g_log_structured(). This means that
    all g_log() calls will pass through the structured log handling code
    path, as long as they are not already modified or dropped by the g_log()
    code (fatal masks, aborts, etc.).
    
    In the case that the default structured log writer is in use, this will
    result in the same format of log output to stdout or stderr, as
    previously happened. If a non-default writer is in use, it handles the
    message as it sees fit.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=744456

 glib/gmessages.c |   85 ++++++++++++++++++------------------------------------
 1 files changed, 28 insertions(+), 57 deletions(-)
---
diff --git a/glib/gmessages.c b/glib/gmessages.c
index a20f1dc..90b77b4 100644
--- a/glib/gmessages.c
+++ b/glib/gmessages.c
@@ -1865,6 +1865,25 @@ g_log_writer_standard_streams (GLogLevelFlags   log_level,
   return G_LOG_WRITER_HANDLED;
 }
 
+/* The old g_log() API is implemented in terms of the new structured log API.
+ * However, some of the checks do not line up between the two APIs: the
+ * structured API only handles fatalness of messages for log levels; the old API
+ * handles it per-domain as well. Consequently, we need to disable fatalness
+ * handling in the structured log API when called from the old g_log() API.
+ *
+ * We can guarantee that g_log_default_handler() will pass GLIB_OLD_LOG_API as
+ * the first field to g_log_structured(), if that is the case. This results in
+ * it appearing as the fourth field in g_log_structured_array().
+ */
+static gboolean
+log_is_old_api (const GLogField *fields,
+                gsize            n_fields)
+{
+  return (n_fields >= 4 &&
+          g_strcmp0 (fields[3].key, "GLIB_OLD_LOG_API") == 0 &&
+          g_strcmp0 (fields[3].value, "1") == 0);
+}
+
 /**
  * g_log_writer_default:
  * @log_level: log level, either from #GLogLevelFlags, or a user-defined
@@ -1927,7 +1946,7 @@ g_log_writer_default (GLogLevelFlags   log_level,
   /* Mark messages as fatal if they have a level set in
    * g_log_set_always_fatal().
    */
-  if (log_level & g_log_always_fatal)
+  if ((log_level & g_log_always_fatal) && !log_is_old_api (fields, n_fields))
     log_level |= G_LOG_FLAG_FATAL;
 
   /* Try logging to the systemd journal as first choice. */
@@ -2334,9 +2353,6 @@ g_log_default_handler (const gchar   *log_domain,
                       const gchar   *message,
                       gpointer       unused_data)
 {
-  gchar level_prefix[STRING_BUFFER_SIZE], *string;
-  GString *gstring;
-  FILE *stream;
   const gchar *domains;
 
   if ((log_level & DEFAULT_LEVELS) || (log_level >> G_LOG_LEVEL_USER_SHIFT))
@@ -2356,59 +2372,14 @@ g_log_default_handler (const gchar   *log_domain,
       return;
     }
 
-  stream = mklevel_prefix (level_prefix, log_level, FALSE);
-
-  gstring = g_string_new (NULL);
-  if (log_level & ALERT_LEVELS)
-    g_string_append (gstring, "\n");
-  if (!log_domain)
-    g_string_append (gstring, "** ");
-
-  if ((g_log_msg_prefix & (log_level & G_LOG_LEVEL_MASK)) == (log_level & G_LOG_LEVEL_MASK))
-    {
-      const gchar *prg_name = g_get_prgname ();
-
-      if (!prg_name)
-       g_string_append_printf (gstring, "(process:%lu): ", (gulong)getpid ());
-      else
-       g_string_append_printf (gstring, "(%s:%lu): ", prg_name, (gulong)getpid ());
-    }
-
-  if (log_domain)
-    {
-      g_string_append (gstring, log_domain);
-      g_string_append_c (gstring, '-');
-    }
-  g_string_append (gstring, level_prefix);
-
-  g_string_append (gstring, ": ");
-  if (!message)
-    g_string_append (gstring, "(NULL) message");
-  else
-    {
-      GString *msg;
-      const gchar *charset;
-
-      msg = g_string_new (message);
-      escape_string (msg);
-
-      if (g_get_charset (&charset))
-       g_string_append (gstring, msg->str);    /* charset is UTF-8 already */
-      else
-       {
-         string = strdup_convert (msg->str, charset);
-         g_string_append (gstring, string);
-         g_free (string);
-       }
-
-      g_string_free (msg, TRUE);
-    }
-  g_string_append (gstring, "\n");
-
-  string = g_string_free (gstring, FALSE);
-
-  write_string (stream, string);
-  g_free (string);
+  /* Print out via the structured log API, but drop any fatal flags since we
+   * have already handled them. The fatal handling in the structured logging
+   * API is more coarse-grained than in the old g_log() API, so we don't want
+   * to use it here.
+   */
+  g_log_structured (log_domain, log_level & ~G_LOG_FLAG_FATAL, "%s", message,
+                    "GLIB_OLD_LOG_API", "1",
+                    NULL);
 }
 
 /**