用tornado实现websocket

import tornado.web
import tornado.websocket
import tornado.httpserver
import tornado.ioloop
import tornado.options
from uuid import uuid4

class ShoppingCart(object):
    totalInventory = 10
    callbacks = []
    carts = {}

    def register(self, callback):
        self.callbacks.append(callback)

    def unregister(self, callback):
        self.callbacks.remove(callback)

    def moveItemToCart(self, session):
        if session in self.carts:
            return

        self.carts[session] = True
        self.notifyCallbacks()

    def removeItemFromCart(self, session):
        if session not in self.carts:
            return

        del(self.carts[session])
        self.notifyCallbacks()

    def notifyCallbacks(self):
        for callback in self.callbacks:
            callback(self.getInventoryCount())

    def getInventoryCount(self):
        return self.totalInventory - len(self.carts)

class DetailHandler(tornado.web.RequestHandler):
    def get(self):
        session = uuid4()
        count = self.application.shoppingCart.getInventoryCount()
        self.render("index.html", session=session, count=count)

class CartHandler(tornado.web.RequestHandler):
    def post(self):
        action = self.get_argument(‘action‘)
        session = self.get_argument(‘session‘)

        if not session:
            self.set_status(400)
            return

        if action == ‘add‘:
            self.application.shoppingCart.moveItemToCart(session)
        elif action == ‘remove‘:
            self.application.shoppingCart.removeItemFromCart(session)
        else:
            self.set_status(400)

class StatusHandler(tornado.websocket.WebSocketHandler):
    def open(self):
        self.application.shoppingCart.register(self.callback)

    def on_close(self):
        self.application.shoppingCart.unregister(self.callback)

    def on_message(self, message):
        pass

    def callback(self, count):
        self.write_message(‘{"inventoryCount":"%d"}‘ % count)

class Application(tornado.web.Application):
    def __init__(self):
        self.shoppingCart = ShoppingCart()

        handlers = [
            (r‘/‘, DetailHandler),
            (r‘/cart‘, CartHandler),
            (r‘/cart/status‘, StatusHandler)
        ]

        settings = {
            ‘template_path‘: ‘templates‘,
            ‘static_path‘: ‘static‘
        }

        tornado.web.Application.__init__(self, handlers, **settings)

if __name__ == ‘__main__‘:
    tornado.options.parse_command_line()

    app = Application()
    server = tornado.httpserver.HTTPServer(app)
    server.listen(8000)
    tornado.ioloop.IOLoop.instance().start()

Tornado在websocket模块中提供了一个WebSocketHandler类。这个类提供了和已连接的客户端通信的WebSocket事件和方法的钩子。当一个新的WebSocket连接打开时，open方法被调用，而on_message和on_close方法分别在连接接收到新的消息和客户端关闭时被调用。

此外，WebSocketHandler类还提供了write_message方法用于向客户端发送消息，close方法用于关闭连接。

class EchoHandler(tornado.websocket.WebSocketHandler):
    def open(self):
        self.write_message(‘connected!‘)

    def on_message(self, message):
        self.write_message(message)

正如你在我们的EchoHandler实现中所看到的，open方法只是使用WebSocketHandler基类提供的write_message方法向客户端发送字符串"connected!"。每次处理程序从客户端接收到一个新的消息时调用on_message方法，我们的实现中将客户端提供的消息原样返回给客户端