LBYL on GSettings

net/proxy/proxy_config_service_linux.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/proxy/proxy_config_service_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #if defined(USE_GCONF)
 #include <gconf/gconf-client.h>
@@ skipping 504 matching lines @@
     }
     DCHECK(!client_);
 #if defined(DLOPEN_GSETTINGS)
     if (gio_handle_) {
       dlclose(gio_handle_);
       gio_handle_ = NULL;
     }
 #endif
   }
 
+  bool SchemaExists(const char* schema_name) {
+    const gchar* const* schemas = g_settings_list_schemas();
+    while (*schemas) {
+      if (strcmp(schema_name, reinterpret_cast<const char*>(schemas)) == 0)
+        return true;
+      schemas++;
+    }
+    return false;
+  }
+
   // LoadAndCheckVersion() must be called *before* Init()!
   bool LoadAndCheckVersion(base::Environment* env);
 
   virtual bool Init(MessageLoop* glib_default_loop,
                     MessageLoopForIO* file_loop) {
     DCHECK(MessageLoop::current() == glib_default_loop);
     DCHECK(!client_);
     DCHECK(!loop_);
-    client_ = g_settings_new("org.gnome.system.proxy");
-    if (!client_) {
+
+    if (!SchemaExists("org.gnome.system.proxy") ||
+        !(client_ = g_settings_new("org.gnome.system.proxy"))) {
       // It's not clear whether/when this can return NULL.
       LOG(ERROR) << "Unable to create a gsettings client";
       return false;
     }
     loop_ = glib_default_loop;
     // We assume these all work if the above call worked.
     http_client_ = g_settings_get_child(client_, "http");
     https_client_ = g_settings_get_child(client_, "https");
     ftp_client_ = g_settings_get_child(client_, "ftp");
     socks_client_ = g_settings_get_child(client_, "socks");
@@ skipping 125 matching lines @@
   // conflict both because they are identical and also due to scoping. The
   // scoping will also ensure that these get used instead of the global ones.
   struct _GSettings;
   typedef struct _GSettings GSettings;
   GSettings* (*g_settings_new)(const gchar* schema);
   GSettings* (*g_settings_get_child)(GSettings* settings, const gchar* name);
   gboolean (*g_settings_get_boolean)(GSettings* settings, const gchar* key);
   gchar* (*g_settings_get_string)(GSettings* settings, const gchar* key);
   gint (*g_settings_get_int)(GSettings* settings, const gchar* key);
   gchar** (*g_settings_get_strv)(GSettings* settings, const gchar* key);
+  const gchar* const* (*g_settings_list_schemas)();
 
   // The library handle.
   void* gio_handle_;
 
   // Load a symbol from |gio_handle_| and store it into |*func_ptr|.
   bool LoadSymbol(const char* name, void** func_ptr) {
     dlerror();
     *func_ptr = dlsym(gio_handle_, name);
     const char* error = dlerror();
     if (error) {
@@ skipping 108 matching lines @@
                   reinterpret_cast<void**>(&g_settings_new)) ||
       !LoadSymbol("g_settings_get_child",
                   reinterpret_cast<void**>(&g_settings_get_child)) ||
       !LoadSymbol("g_settings_get_string",
                   reinterpret_cast<void**>(&g_settings_get_string)) ||
       !LoadSymbol("g_settings_get_boolean",
                   reinterpret_cast<void**>(&g_settings_get_boolean)) ||
       !LoadSymbol("g_settings_get_int",
                   reinterpret_cast<void**>(&g_settings_get_int)) ||
       !LoadSymbol("g_settings_get_strv",
-                  reinterpret_cast<void**>(&g_settings_get_strv))) {
+                  reinterpret_cast<void**>(&g_settings_get_strv)) ||
+      !LoadSymbol("g_settings_list_schemas",
+                  reinterpret_cast<void**>(&g_settings_list_schemas))) {
     VLOG(1) << "Cannot load gsettings API. Will fall back to gconf.";
     dlclose(gio_handle_);
     gio_handle_ = NULL;
     return false;
   }
 #endif
 
-  GSettings* client = g_settings_new("org.gnome.system.proxy");
-  if (!client) {
+  GSettings* client;
+  if (!SchemaExists("org.gnome.system.proxy") ||
+      !(client = g_settings_new("org.gnome.system.proxy"))) {
     VLOG(1) << "Cannot create gsettings client. Will fall back to gconf.";
     return false;
   }
   g_object_unref(client);
 
   std::string path;
   if (!env->GetVar("PATH", &path)) {
     LOG(ERROR) << "No $PATH variable. Assuming no gnome-network-properties.";
   } else {
     // Yes, we're on the UI thread. Yes, we're accessing the file system.
@@ skipping 913 matching lines @@
 void ProxyConfigServiceLinux::RemoveObserver(Observer* observer) {
   delegate_->RemoveObserver(observer);
 }
 
 ProxyConfigService::ConfigAvailability
     ProxyConfigServiceLinux::GetLatestProxyConfig(ProxyConfig* config) {
   return delegate_->GetLatestProxyConfig(config);
 }
 
 }  // namespace net