如何判断页面已完成加载？

Question

我正在使用Chromium的无头Web浏览器API。基于chrome_remote_shell源代码，我提出了以下代码：

#!/usr/bin/env python

import json
import requests
import pprint
import websocket

tablist = json.loads(requests.get("http://%s:%s/json" % ("localhost", 9222)).text)
print(tablist)
wsurl = tablist[0]['webSocketDebuggerUrl']
conn = websocket.create_connection(wsurl)
navcom = json.dumps({"id":0, "method":"Network.enable"})
conn.send(navcom)
navcom = json.dumps({"id":1, "method":"Page.navigate", "params":{"url":"https://news.ycombinator.com/"}})
conn.send(navcom)

while True:
    packet = json.loads(conn.recv())
    if 'method' in packet:
        print(packet['method'])
    else:
        print(packet)

这是示例输出：

[{u'description': u'', u'title': u'Hacker News', u'url': u'https://news.ycombinator.com/', u'webSocketDebuggerUrl': u'ws://localhost:9222/devtools/page/7d03a57d-77a9-4ceb-b645-3b85461de5be', u'type': u'page', u'id': u'7d03a57d-77a9-4ceb-b645-3b85461de5be', u'devtoolsFrontendUrl': u'/devtools/inspector.html?ws=localhost:9222/devtools/page/7d03a57d-77a9-4ceb-b645-3b85461de5be'}]
{u'id': 0, u'result': {}}
Network.requestWillBeSent
{u'id': 1, u'result': {u'frameId': u'21045.1'}}
Network.responseReceived
Network.dataReceived
Network.dataReceived
Network.loadingFinished
Network.requestWillBeSent
Network.requestWillBeSent
Network.requestServedFromCache
Network.responseReceived
Network.dataReceived
Network.loadingFinished
Network.requestWillBeSent
Network.requestServedFromCache
Network.responseReceived
Network.dataReceived
Network.loadingFinished
Network.requestWillBeSent
Network.requestServedFromCache
Network.responseReceived
Network.dataReceived
Network.loadingFinished
Network.responseReceived
Network.dataReceived
Network.loadingFinished
Network.requestWillBeSent
Network.requestServedFromCache
Network.responseReceived
Network.dataReceived
Network.loadingFinished

我注意到我收到了一长串消息，最后一条消息是Network.loadingFinished，但是我为多个requestIds收到了这条消息。如何修改脚本，使其在页面完全加载后终止，并且可以退出循环？

Answer 1

事实证明，我也应该通过Page.enable订阅页面事件：

#!/usr/bin/env python

import json
import requests
import pprint
import websocket
import sys

tablist = json.loads(requests.get("http://%s:%s/json" % ("localhost", 9222)).text)
print(tablist)
wsurl = tablist[0]['webSocketDebuggerUrl']
conn = websocket.create_connection(wsurl)
navcom = json.dumps({"id":0, "method":"Network.enable"})
conn.send(navcom)
navcom = json.dumps({"id":1, "method":"Page.enable"})
conn.send(navcom)
navcom = json.dumps({"id":2, "method":"Page.navigate", "params":{"url":sys.argv[1]}})
conn.send(navcom)

while True:
    s = conn.recv()
    packet = json.loads(s)
    if packet.get('method') == 'Page.loadEventFired':
        break
    print(s)