webkit/glue/cpp_bound_class.h

// 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.

/*
  CppBoundClass class:
  This base class serves as a parent for C++ classes designed to be bound to
  JavaScript objects.

  Subclasses should define the constructor to build the property and method
  lists needed to bind this class to a JS object.  They should also declare
  and define member variables and methods to be exposed to JS through
  that object.

  See cpp_binding_example.{h|cc} for an example.
*/

#ifndef WEBKIT_GLUE_CPP_BOUNDCLASS_H__
#define WEBKIT_GLUE_CPP_BOUNDCLASS_H__

#include <map>
#include <vector>

#include "webkit/glue/cpp_variant.h"

#include "base/callback_old.h"
#include "base/memory/scoped_ptr.h"

namespace WebKit {
class WebFrame;
}

typedef std::vector<CppVariant> CppArgumentList;

// CppBoundClass lets you map Javascript method calls and property accesses
// directly to C++ method calls and CppVariant* variable access.
class CppBoundClass {
 public:
  class PropertyCallback {
   public:
    virtual ~PropertyCallback() { }

    // Sets |value| to the value of the property. Returns false in case of
    // failure. |value| is always non-NULL.
    virtual bool GetValue(CppVariant* value) = 0;

    // sets the property value to |value|. Returns false in case of failure.
    virtual bool SetValue(const CppVariant& value) = 0;
  };

  // The constructor should call BindMethod, BindProperty, and
  // SetFallbackMethod as needed to set up the methods, properties, and
  // fallback method.
  CppBoundClass();
  virtual ~CppBoundClass();

  // Return a CppVariant representing this class, for use with BindProperty().
  // The variant type is guaranteed to be NPVariantType_Object.
  CppVariant* GetAsCppVariant();

  // Given a WebFrame, BindToJavascript builds the NPObject that will represent
  // this CppBoundClass object and binds it to the frame's window under the
  // given name.  This should generally be called from the WebView delegate's
  // WindowObjectCleared(). This CppBoundClass object will be accessible to
  // JavaScript as window.<classname>. The owner of this CppBoundClass object is
  // responsible for keeping it around while the frame is alive, and for
  // destroying it afterwards.
  void BindToJavascript(WebKit::WebFrame* frame, const std::string& classname);

  // The type of callbacks.
  typedef Callback2<const CppArgumentList&, CppVariant*>::Type Callback;
  typedef Callback1<CppVariant*>::Type GetterCallback;

  // Used by a test.  Returns true if a method with name |name| exists,
  // regardless of whether a fallback is registered.
  bool IsMethodRegistered(const std::string& name) const;

 protected:
  // Bind the Javascript method called |name| to the C++ callback |callback|.
  void BindCallback(const std::string& name, Callback* callback);

  // A wrapper for BindCallback, to simplify the common case of binding a
  // method on the current object.  Though not verified here, |method|
  // must be a method of this CppBoundClass subclass.
  template<typename T>
  void BindMethod(const std::string& name,
      void (T::*method)(const CppArgumentList&, CppVariant*)) {
    Callback* callback =
        NewCallback<T, const CppArgumentList&, CppVariant*>(
            static_cast<T*>(this), method);
    BindCallback(name, callback);
  }

  // Bind Javascript property |name| to the C++ getter callback |callback|.
  // This can be used to create read-only properties.
  void BindGetterCallback(const std::string& name, GetterCallback* callback);

  // A wrapper for BindGetterCallback, to simplify the common case of binding a
  // property on the current object.  Though not verified here, |method|
  // must be a method of this CppBoundClass subclass.
  template<typename T>
  void BindProperty(const std::string& name, void (T::*method)(CppVariant*)) {
    GetterCallback* callback =
        NewCallback<T, CppVariant*>(static_cast<T*>(this), method);
    BindGetterCallback(name, callback);
  }

  // Bind the Javascript property called |name| to a CppVariant |prop|.
  void BindProperty(const std::string& name, CppVariant* prop);

  // Bind Javascript property called |name| to a PropertyCallback |callback|.
  // CppBoundClass assumes control over the life time of the |callback|.
  void BindProperty(const std::string& name, PropertyCallback* callback);

  // Set the fallback callback, which is called when when a callback is
  // invoked that isn't bound.
  // If it is NULL (its default value), a JavaScript exception is thrown in
  // that case (as normally expected). If non NULL, the fallback method is
  // invoked and the script continues its execution.
  // Passing NULL for |callback| clears out any existing binding.
  // It is used for tests and should probably only be used in such cases
  // as it may cause unexpected behaviors (a JavaScript object with a
  // fallback always returns true when checked for a method's
  // existence).
  void BindFallbackCallback(Callback* fallback_callback) {
    fallback_callback_.reset(fallback_callback);
  }

  // A wrapper for BindFallbackCallback, to simplify the common case of
  // binding a method on the current object.  Though not verified here,
  // |method| must be a method of this CppBoundClass subclass.
  // Passing NULL for |method| clears out any existing binding.
  template<typename T>
  void BindFallbackMethod(
      void (T::*method)(const CppArgumentList&, CppVariant*)) {
    if (method) {
      Callback* callback =
          NewCallback<T, const CppArgumentList&, CppVariant*>(
              static_cast<T*>(this), method);
      BindFallbackCallback(callback);
    } else {
      BindFallbackCallback(NULL);
    }
  }

  // Some fields are protected because some tests depend on accessing them,
  // but otherwise they should be considered private.

  typedef std::map<NPIdentifier, PropertyCallback*> PropertyList;
  typedef std::map<NPIdentifier, Callback*> MethodList;
  // These maps associate names with property and method pointers to be
  // exposed to JavaScript.
  PropertyList properties_;
  MethodList methods_;

  // The callback gets invoked when a call is made to an nonexistent method.
  scoped_ptr<Callback> fallback_callback_;

 private:
  // NPObject callbacks.
  friend struct CppNPObject;
  bool HasMethod(NPIdentifier ident) const;
  bool Invoke(NPIdentifier ident, const NPVariant* args, size_t arg_count,
              NPVariant* result);
  bool HasProperty(NPIdentifier ident) const;
  bool GetProperty(NPIdentifier ident, NPVariant* result) const;
  bool SetProperty(NPIdentifier ident, const NPVariant* value);

  // A lazily-initialized CppVariant representing this class.  We retain 1
  // reference to this object, and it is released on deletion.
  CppVariant self_variant_;

  // True if our np_object has been bound to a WebFrame, in which case it must
  // be unregistered with V8 when we delete it.
  bool bound_to_frame_;

  DISALLOW_COPY_AND_ASSIGN(CppBoundClass);
};

#endif  // CPP_BOUNDCLASS_H__