如何在 Web 套接字中从服务器向客户端发送消息

Posted 2023-02-16

【中文标题】如何在 Web 套接字中从服务器向客户端发送消息

【英文标题】：How to send a message from the server to the client in a web socket

【发布时间】：2020-08-18 00:37:45

【问题描述】：

我正在做一个小程序，旨在在rabbitmq上接收消息并发送到连接到具有相同索引的websocket的客户端，但是在发送到客户端时遇到问题，我重用了一个必须工作的代码在 3.6 .9 中，我不记得龙卷风（我使用的 websocket 库）的版本，但我改变了电脑，我可以再次安装它，现在我有了最新版本的库和 python。

我将发布我的旧代码，因为 msm 错误更容易理解

import tornado.websocket
import tornado.ioloop
import threading
import pika
import json

def verificar_novo(se):
    for i in range(0,len(conexao_lista)):
        if se == conexao_lista[i]["endereco"]:
            return 0
    return 1

def excluir_conexao(endereco):
    for i in range(0,len(conexao_lista)):
        if conexao_lista[i]["endereco"] == endereco:
            del(conexao_lista[i])
            break

""" Função para procurar mensagens no rabbit e retornar para os clientes"""
def callback(ch, method, properties, body):
    menssagem_rabbit = json.loads(body)
    threading.Lock()
    for i in range(0, len(conexao_lista)):
        if (conexao_lista[i]["configuracao"]["ras_eve_id_indice"]) == (menssagem_rabbit["ras_eve_id_indice"]):
            conexao_lista[i]["endereco"].write_message(menssagem_rabbit)
            break
    threading.RLock()



""" Classe de conexao com cliente"""
class WebSocketHandler(tornado.websocket.WebSocketHandler):
    def open(self):
        print("Novo cliente conectado")


    def on_close(self):
        print("Cliente desconectado")
        excluir_conexao(self)

    def on_message(self, message):

        n = verificar_novo(self)
        if n == 0:
            self.write_message(u"Sua menssagem: " + message)
        else:
            dados_json = json.loads(message)
            conexao_dicionario["endereco"] = self
            conexao_dicionario["configuracao"] = dados_json
            conexao_lista.append(conexao_dicionario.copy())
            self.write_message(u"Usuario conectado " + dados_json["id_usuario"])


    def check_origin(self, origin):
        return True

"""Função que a thread ficara rodando para consumir as mensagem em segundo plano"""
def procurar_mensagens():
    connection = pika.BlockingConnection(pika.ConnectionParameters(host='localhost'))
    channel = connection.channel()
    channel.basic_consume(queue='testerenan', on_message_callback=callback, auto_ack=True)
    channel.start_consuming()

"""Variaveis"""
conexao_lista = []
conexao_dicionario = "endereco": "","configuracao":""


"""Chamando a Thread"""
threading.Thread(target=procurar_mensagens, args=()).start()

"""Conexão do WebSocket"""
application = tornado.web.Application([(r"/", WebSocketHandler),])


if __name__ == "__main__":
    application.listen(8888)
    tornado.ioloop.IOLoop.instance().start()

出现的错误：

Exception in thread Thread-1: 
Traceback (most recent call last):
  File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run() 
  File "/usr/lib/python3.8/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs) 
  File "/home/renan/Área de Trabalho/Projeto-WebSocket/Servidor.py", line 63, in procurar_mensagens
    channel.start_consuming()
  File "/usr/local/lib/python3.8/dist-packages/pika/adapters/blocking_connection.py", line 1866, in start_consuming
    self._process_data_events(time_limit=None) 
  File "/usr/local/lib/python3.8/dist-packages/pika/adapters/blocking_connection.py", line 2027, in _process_data_events
    self.connection.process_data_events(time_limit=time_limit)
  File "/usr/local/lib/python3.8/dist-packages/pika/adapters/blocking_connection.py", line 834, in process_data_events
    self._dispatch_channel_events()
  File "/usr/local/lib/python3.8/dist-packages/pika/adapters/blocking_connection.py", line 566, in _dispatch_channel_events
    impl_channel._get_cookie()._dispatch_events() 
  File "/usr/local/lib/python3.8/dist-packages/pika/adapters/blocking_connection.py", line 1493, in _dispatch_events
    consumer_info.on_message_callback(self, evt.method, 
  File "/home/renan/Área de Trabalho/Projeto-WebSocket/Servidor.py", line 26, in callback
    conexao_lista[i]["endereco"].write_message(menssagem_rabbit) 
  File "/home/renan/.local/lib/python3.8/site-packages/tornado/websocket.py", line 342, in write_message
    return self.ws_connection.write_message(message, binary=binary)
  File "/home/renan/.local/lib/python3.8/site-packages/tornado/websocket.py", line 1098, in write_message
    fut = self._write_frame(True, opcode, message, flags=flags) 
  File "/home/renan/.local/lib/python3.8/site-packages/tornado/websocket.py", line 1075, in _write_frame
    return self.stream.write(frame)
  File "/home/renan/.local/lib/python3.8/site-packages/tornado/iostream.py", line 555, in write
    future = Future() # type: Future[None] 
  File "/usr/lib/python3.8/asyncio/events.py", line 639, in get_event_loop
    raise RuntimeError('There is no current event loop in thread %r.' 
RuntimeError: There is no current event loop in thread 'Thread-1'.

如果有人想看，我会留下项目以供下载： https://github.com/Renan-Sacca/Projeto-WebSocket

【参考方案1】：

一般来说，混合线程和 Tornado 时必须非常小心 - 不能从其他线程调用大多数 tornado 方法（这一直是正确的，但库在 Tornado 5.0 中对强制执行它更加严格）。特别是这包括write_message。所以在callback 中，您必须让IOLoop 为您调用，而不是调用write_message。

在主块中，执行global main_io_loop; main_io_loop = IOLoop.current() 保存主线程的IOLoop，以便以后参考。然后在callback 中将write_message 的调用替换为

main_io_loop.add_callback(conexao_lista[i]["endereco"].write_message, menssagem_rabbit)