Expose gettext() to client-side JS

This exposes the function set by webhelper.set_gettext() to the client-
side Javascript as a gettext() function, defined on the global window
object. This allows apps to translate messages that are generated
at runtime, not just messages in static HTML.

Some often-used JavaScriptCore operations can be turned into separate
functions, which we can put in a separate source file. This is in
anticipation of the next commit where we will define another function
property of the global object.

[endlessm/eos-sdk#291]

3 files changed, 179 insertions, 0 deletions

diff --git a/webhelper/webextensions/wh2extension.c b/webhelper/webextensions/wh2extension.c
index c51171e..48ea9aa 100644
--- a/webhelper/webextensions/wh2extension.c
+++ b/webhelper/webextensions/wh2extension.c
@@ -5,9 +5,13 @@
 #include <string.h>
 
 #include <glib.h>
+#include <JavaScriptCore/JavaScript.h>
 #include <webkit2/webkit-web-extension.h>
 #include <webkitdom/webkitdom.h>
 
+#include "wh2jscutil.h"
+
+#define PRIVATE_NAME "_webhelper_private"
 #define WH2_DBUS_INTERFACE_NAME "com.endlessm.WebHelper2.Translation"
 #define MAIN_PROGRAM_OBJECT_PATH "/com/endlessm/gettext"
 #define MAIN_PROGRAM_INTERFACE_NAME "com.endlessm.WebHelper2.Gettext"
@@ -74,6 +78,51 @@ translation_function (const gchar *message,
   return retval;
 }
 
+static JSValueRef
+gettext_shim (JSContextRef     js,
+              JSObjectRef      function,
+              JSObjectRef      this_object,
+              size_t           n_args,
+              const JSValueRef args[],
+              JSValueRef      *exception)
+{
+  if (n_args != 1)
+    {
+      gchar *errmsg = g_strdup_printf ("Expected one argument to gettext(),"
+                                       "but got %d.", n_args);
+      *exception = throw_exception (js, errmsg);
+      g_free (errmsg);
+      return NULL;
+    }
+  if (!JSValueIsString (js, args[0]))
+    {
+      *exception = throw_exception (js,
+                                    "Expected a string argument to gettext().");
+      return NULL;
+    }
+
+  JSObjectRef window = JSContextGetGlobalObject (js);
+  JSStringRef private_name = JSStringCreateWithUTF8CString (PRIVATE_NAME);
+  JSValueRef private_data = JSObjectGetProperty (js, window, private_name,
+                                                 exception);
+  if (JSValueIsUndefined (js, private_data))
+    return NULL;  /* propagate exception */
+  Context *ctxt = (Context *) JSObjectGetPrivate ((JSObjectRef) private_data);
+
+  JSStringRef message_ref = JSValueToStringCopy (js, args[0], exception);
+  if (message_ref == NULL)
+    return NULL;  /* propagate exception */
+  gchar *message = string_ref_to_string (message_ref);
+  JSStringRelease (message_ref);
+
+  gchar *translation = translation_function (message, ctxt);
+  g_free (message);
+
+  JSValueRef retval = string_to_value_ref (js, translation);
+  g_free (translation);
+  return retval;
+}
+
 static void
 translate_html (WebKitDOMDocument *dom,
                 Context           *ctxt)
@@ -216,6 +265,41 @@ on_page_created (WebKitWebExtension *extension,
                    pctxt, NULL);
 }
 
+/* window-object-cleared is the best time to define properties on the page's
+window object, according to the documentation. */
+static void
+on_window_object_cleared (WebKitScriptWorld *script_world,
+                          WebKitWebPage     *page,
+                          WebKitFrame       *frame,
+                          Context           *ctxt)
+{
+  JSGlobalContextRef js =
+    webkit_frame_get_javascript_context_for_script_world (frame, script_world);
+  JSObjectRef window = JSContextGetGlobalObject (js);
+
+  /* First we need to create a custom class for a private data object to store
+  our context in, because you can't pass callback data to JavaScriptCore
+  callbacks. You also can't set private data on a Javascript object if it's not
+  of a custom class, because the built-in classes don't allocate space for a
+  private pointer. */
+  JSClassDefinition class_def = {
+    .className = "PrivateContextObject"
+  };
+  JSClassRef klass = JSClassCreate (&class_def);
+  JSObjectRef private_data = JSObjectMake (js, klass, ctxt);
+  JSClassRelease (klass);
+
+  if (!set_object_property (js, window, PRIVATE_NAME, (JSValueRef) private_data,
+                            kJSPropertyAttributeReadOnly | kJSPropertyAttributeDontEnum | kJSPropertyAttributeDontDelete))
+    return;
+
+  JSObjectRef gettext_func =
+    JSObjectMakeFunctionWithCallback (js, NULL, gettext_shim);
+  if (!set_object_property (js, window, "gettext", (JSValueRef) gettext_func,
+                            kJSPropertyAttributeNone))
+    return;
+}
+
 static void
 on_bus_acquired (GDBusConnection *connection,
                  const gchar     *name,
@@ -225,6 +309,11 @@ on_bus_acquired (GDBusConnection *connection,
 
   ctxt->connection = connection;
 
+  /* Get a notification when Javascript is ready */
+  WebKitScriptWorld *script_world = webkit_script_world_get_default ();
+  g_signal_connect (script_world, "window-object-cleared",
+                    G_CALLBACK (on_window_object_cleared), ctxt);
+
   /* Export our interface on the bus */
   ctxt->node = g_dbus_node_info_new_for_xml (introspection_xml, &error);
   if (ctxt->node == NULL)
diff --git a/webhelper/webextensions/wh2jscutil.c b/webhelper/webextensions/wh2jscutil.c
new file mode 100644
index 0000000..34f325f
--- /dev/null
+++ b/webhelper/webextensions/wh2jscutil.c
@@ -0,0 +1,65 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/* Copyright 2015 Endless Mobile, Inc. */
+
+#include <glib.h>
+#include <JavaScriptCore/JavaScript.h>
+
+#include "wh2jscutil.h"
+
+G_GNUC_INTERNAL
+gboolean
+set_object_property  (JSContextRef         js,
+                      JSObjectRef          object,
+                      const gchar         *property_name,
+                      JSValueRef           property_value,
+                      JSPropertyAttributes flags)
+{
+  JSValueRef exception = NULL;
+  JSStringRef property_name_ref = JSStringCreateWithUTF8CString (property_name);
+  JSObjectSetProperty (js, object, property_name_ref, property_value, flags,
+                       &exception);
+  JSStringRelease (property_name_ref);
+  if (exception != NULL)
+    {
+      g_critical ("There was a problem setting the property '%s'.",
+                  property_name);
+      return FALSE;
+    }
+  return TRUE;
+}
+
+/* Returns a newly allocated string. */
+G_GNUC_INTERNAL
+gchar *
+string_ref_to_string (JSStringRef string_ref)
+{
+  size_t bufsize = JSStringGetMaximumUTF8CStringSize (string_ref);
+  gchar *string = g_new0 (gchar, bufsize);
+  JSStringGetUTF8CString (string_ref, string, bufsize);
+  return string;
+}
+
+G_GNUC_INTERNAL
+JSValueRef
+string_to_value_ref (JSContextRef js,
+                     const gchar *string)
+{
+  JSStringRef string_ref = JSStringCreateWithUTF8CString (string);
+  JSValueRef value_ref = JSValueMakeString (js, string_ref);
+  /* value_ref owns string_ref now */
+  return value_ref;
+}
+
+G_GNUC_INTERNAL
+JSValueRef
+throw_exception (JSContextRef js,
+                 const gchar  *message)
+{
+  JSValueRef msgval = string_to_value_ref (js, message);
+  JSValueRef inner_error = NULL;
+  JSObjectRef exception = JSObjectMakeError (js, 1, &msgval, &inner_error);
+  if (inner_error != NULL)
+    return inner_error;
+  return (JSValueRef) exception;
+}
diff --git a/webhelper/webextensions/wh2jscutil.h b/webhelper/webextensions/wh2jscutil.h
new file mode 100644
index 0000000..af800e5
--- /dev/null
+++ b/webhelper/webextensions/wh2jscutil.h
@@ -0,0 +1,25 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/* Copyright 2015 Endless Mobile, Inc. */
+
+#ifndef WH2_JSC_UTIL_H
+#define WH2_JSC_UTIL_H
+
+#include <glib.h>
+#include <JavaScriptCore/JavaScript.h>
+
+gboolean   set_object_property  (JSContextRef         js,
+                                 JSObjectRef          object,
+                                 const gchar         *property_name,
+                                 JSValueRef           property_value,
+                                 JSPropertyAttributes flags);
+
+gchar     *string_ref_to_string (JSStringRef          string_ref);
+
+JSValueRef string_to_value_ref  (JSContextRef         js,
+                                 const gchar         *string);
+
+JSValueRef throw_exception      (JSContextRef         js,
+                                 const gchar         *message);
+
+#endif /* WH2_JSC_UTIL_H */