printing: Don't show duplicate printers

Check UUID for printers obtained via DNSSD whether
they are already installed on local CUPS server.
Don't show such printers.

Not all printers published via DNSSD have UUID entry though.

https://bugzilla.gnome.org/show_bug.cgi?id=786794

modules/printbackends/cups/gtkprintbackendcups.c

@@ -1899,7 +1899,8 @@ static const char * const printer_attrs[] =
     "ipp-versions-supported",
     "multiple-document-handling-supported",
     "copies-supported",
-    "number-up-supported"
+    "number-up-supported",
+    "device-uri"
   };
 
 /* Attributes we're interested in for printers without PPD */
@@ -1996,11 +1997,13 @@ typedef struct
   int       number_of_covers;
   gchar    *output_bin_default;
   GList    *output_bin_supported;
+  gchar    *original_device_uri;
 } PrinterSetupInfo;
 
 static void
 printer_setup_info_free (PrinterSetupInfo *info)
 {
+  g_free (info->original_device_uri);
   g_free (info->state_msg);
   g_strfreev (info->covers);
   g_slice_free (PrinterSetupInfo, info);
@@ -2376,6 +2379,10 @@ cups_printer_handle_attribute (GtkPrintBackendCups *cups_backend,
 
       info->output_bin_supported = g_list_reverse (info->output_bin_supported);
     }
+  else if (g_strcmp0 (ippGetName (attr), "device-uri") == 0)
+    {
+      info->original_device_uri = g_strdup (ippGetString (attr, 0, NULL));
+    }
   else
     {
       GTK_NOTE (PRINTING,
@@ -2464,6 +2471,7 @@ cups_create_printer (GtkPrintBackendCups *cups_backend,
 
   cups_printer->default_cover_before = g_strdup (info->default_cover_before);
   cups_printer->default_cover_after = g_strdup (info->default_cover_after);
+  cups_printer->original_device_uri = g_strdup (info->original_device_uri);
 
   if (info->default_number_up > 0)
     cups_printer->default_number_up = info->default_number_up;
@@ -2830,9 +2838,54 @@ typedef struct
   guint                printer_state;
   gchar               *type;
   gchar               *domain;
+  gchar               *UUID;
   GtkPrintBackendCups *backend;
 } AvahiConnectionTestData;
 
+static GtkPrinter *
+find_printer_by_uuid (GtkPrintBackendCups *backend,
+                      const gchar         *UUID)
+{
+  GtkPrinterCups *printer;
+  GtkPrinter     *result = NULL;
+  GList          *printers;
+  GList          *iter;
+  gchar          *printer_uuid;
+
+  printers = gtk_print_backend_get_printer_list (GTK_PRINT_BACKEND (backend));
+  for (iter = printers; iter != NULL; iter = iter->next)
+    {
+      printer = GTK_PRINTER_CUPS (iter->data);
+      if (printer->original_device_uri != NULL)
+        {
+          printer_uuid = g_strrstr (printer->original_device_uri, "uuid=");
+          if (printer_uuid != NULL && strlen (printer_uuid) >= 41)
+            {
+              printer_uuid += 5;
+              printer_uuid = g_strndup (printer_uuid, 36);
+
+#if GLIB_CHECK_VERSION(2, 52, 0)
+              if (g_uuid_string_is_valid (printer_uuid))
+#endif
+                {
+                  if (g_strcmp0 (printer_uuid, UUID) == 0)
+                    {
+                      result = GTK_PRINTER (printer);
+                      g_free (printer_uuid);
+                      break;
+                    }
+                }
+
+              g_free (printer_uuid);
+            }
+        }
+    }
+
+  g_list_free (printers);
+
+  return result;
+}
+
 /*
  *  Create new GtkPrinter from informations included in TXT records.
  */
@@ -2878,6 +2931,10 @@ create_cups_printer_from_avahi_data (AvahiConnectionTestData *data)
   set_info_state_message (info);
 
   printer = gtk_print_backend_find_printer (GTK_PRINT_BACKEND (data->backend), data->printer_name);
+
+  if (printer == NULL && data->UUID != NULL)
+    printer = find_printer_by_uuid (data->backend, data->UUID);
+
   if (printer == NULL)
     {
       printer = cups_create_printer (data->backend, info);
@@ -3080,6 +3137,11 @@ avahi_service_resolver_cb (GObject      *source_object,
                   if (data->printer_state != 0 || endptr != value)
                     data->got_printer_state = TRUE;
                 }
+              else if (g_strcmp0 (key, "UUID") == 0)
+                {
+                  if (*value != '\0')
+                    data->UUID = g_strdup (value);
+                }
 
               g_clear_pointer (&key, g_free);
               g_clear_pointer (&value, g_free);

modules/printbackends/cups/gtkprintercups.c

@@ -100,6 +100,7 @@ static void
 gtk_printer_cups_init (GtkPrinterCups *printer)
 {
   printer->device_uri = NULL;
+  printer->original_device_uri = NULL;
   printer->printer_uri = NULL;
   printer->state = 0;
   printer->hostname = NULL;
@@ -151,6 +152,7 @@ gtk_printer_cups_finalize (GObject *object)
   printer = GTK_PRINTER_CUPS (object);
 
   g_free (printer->device_uri);
+  g_free (printer->original_device_uri);
   g_free (printer->printer_uri);
   g_free (printer->hostname);
   g_free (printer->ppd_name);

modules/printbackends/cups/gtkprintercups.h

@@ -48,6 +48,7 @@ struct _GtkPrinterCups
   GtkPrinter parent_instance;
 
   gchar *device_uri;
+  gchar *original_device_uri;
   gchar *printer_uri;
   gchar *hostname;
   gint port;