native_client_sdk/src/getting_started/part1/hello_tutorial.cc

// Copyright (c) 2013 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.

/// @file hello_tutorial.cc
/// This example demonstrates loading, running and scripting a very simple NaCl
/// module.  To load the NaCl module, the browser first looks for the
/// CreateModule() factory method (at the end of this file).  It calls
/// CreateModule() once to load the module code.  After the code is loaded,
/// CreateModule() is not called again.
///
/// Once the code is loaded, the browser calls the CreateInstance()
/// method on the object returned by CreateModule().  It calls CreateInstance()
/// each time it encounters an <embed> tag that references your NaCl module.
///
/// The browser can talk to your NaCl module via the postMessage() Javascript
/// function.  When you call postMessage() on your NaCl module from the browser,
/// this becomes a call to the HandleMessage() method of your pp::Instance
/// subclass.  You can send messages back to the browser by calling the
/// PostMessage() method on your pp::Instance.  Note that these two methods
/// (postMessage() in Javascript and PostMessage() in C++) are asynchronous.
/// This means they return immediately - there is no waiting for the message
/// to be handled.  This has implications in your program design, particularly
/// when mutating property values that are exposed to both the browser and the
/// NaCl module.

#include "ppapi/cpp/instance.h"
#include "ppapi/cpp/module.h"
#include "ppapi/cpp/var.h"

/// The Instance class.  One of these exists for each instance of your NaCl
/// module on the web page.  The browser will ask the Module object to create
/// a new Instance for each occurrence of the <embed> tag that has these
/// attributes:
///     src="hello_tutorial.nmf"
///     type="application/x-pnacl"
/// To communicate with the browser, you must override HandleMessage() to
/// receive messages from the browser, and use PostMessage() to send messages
/// back to the browser.  Note that this interface is asynchronous.
class HelloTutorialInstance : public pp::Instance {
 public:
  /// The constructor creates the plugin-side instance.
  /// @param[in] instance the handle to the browser-side plugin instance.
  explicit HelloTutorialInstance(PP_Instance instance) : pp::Instance(instance)
  {}
  virtual ~HelloTutorialInstance() {}

  /// Handler for messages coming in from the browser via postMessage().  The
  /// @a var_message can contain be any pp:Var type; for example int, string
  /// Array or Dictinary. Please see the pp:Var documentation for more details.
  /// @param[in] var_message The message posted by the browser.
  virtual void HandleMessage(const pp::Var& var_message) {
    // TODO(sdk_user): 1. Make this function handle the incoming message.
  }
};

/// The Module class.  The browser calls the CreateInstance() method to create
/// an instance of your NaCl module on the web page.  The browser creates a new
/// instance for each <embed> tag with type="application/x-pnacl".
class HelloTutorialModule : public pp::Module {
 public:
  HelloTutorialModule() : pp::Module() {}
  virtual ~HelloTutorialModule() {}

  /// Create and return a HelloTutorialInstance object.
  /// @param[in] instance The browser-side instance.
  /// @return the plugin-side instance.
  virtual pp::Instance* CreateInstance(PP_Instance instance) {
    return new HelloTutorialInstance(instance);
  }
};

namespace pp {
/// Factory function called by the browser when the module is first loaded.
/// The browser keeps a singleton of this module.  It calls the
/// CreateInstance() method on the object you return to make instances.  There
/// is one instance per <embed> tag on the page.  This is the main binding
/// point for your NaCl module with the browser.
Module* CreateModule() {
  return new HelloTutorialModule();
}
}  // namespace pp