对Chrome中的本地WSGI服务器的CORS AJAX请求的延迟过长

Question

对Chrome中的本地WSGI服务器的CORS AJAX请求的延迟过长

jpk*_*jpk 7 javascript python jquery wsgi http

建立

两个WSGI服务器在不同端口上本地运行.一台服务器返回一个包含javascript的html页面,该页面使用jQuery对另一个WSGI服务器执行跨源ajax请求.

origin_server.py提供HTML http://localhost:9010.

#!/usr/bin/env python

from wsgiref.simple_server import make_server


def origin_html(environ, start_response):
    status = '200 OK'
    response_headers = [('Content-Type', 'text/html')]
    start_response(status, response_headers)    

    f = open('./index.html', 'rb')
    return [f.read()]

httpd = make_server('localhost', 9010, origin_html)
httpd.serve_forever()

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cors_server.py 提供javascript将请求的跨源资源.

#!/usr/bin/env python

from wsgiref.simple_server import make_server
import json


def cors_json(environ, start_response):
    status = '200 OK'
    response_headers = [
        ('Content-Type', 'application/json'),
        ('Access-Control-Allow-Origin', '*')
    ]
    start_response(status, response_headers)

    return [json.dumps({'foo': 'bar'})]

httpd = make_server('localhost', 9011, cors_json)
httpd.serve_forever()

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index.html该页面由origin_sever.py.

<!DOCTYPE html>
<html>
    <head>
        <script
            type="text/javascript"
            src="https://code.jquery.com/jquery-2.1.3.min.js"
            >
        </script>

        <script type="text/javascript">
            $(document).ready(function () { 
                console.log('Doing the thing.');
                $.get('http://localhost:9011').done(function (data) {
                    console.log('Got the thing', data);
                });
            });
        </script>
    </head>
    <body>
        Beep boop.
    </body>
</html>

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github上面的代码在这里:https://github.com/thatjpk/local-wsgi-cors-ajax

供参考的东西版本:

2012年中期MacBook Pro,OS X 10.10
Python 2.7.6
wsgiref 0.1.2
Chrome 40.0.2214.93(已禁用扩展程序并重置设置以进行测试.)
Firefox 35.0.1

问题

Given the above I can open up two terminals, start origin_server.py in one, and cors_server.py in the other, then open a browser tab and point it to the origin server at http://localhost:9010/. This loads the page, and does the cross-origin request.

Ideally, the latencies should all be very low because it's all local. However, I'm consistently seeing latencies for the cross-origin request of well over ten seconds. What's bizzarre is I've only ever seen this in Chrome in a non-incognito window. Firefox, curl, httpie, and Chrome incognito tabs on the same machine all complete the cross-origin request in sub-10ms, while non-incognito Chrome tabs take three orders of magnitude longer.

如果我将CORS从等式中删除,并且只是放入http://localhost:9011Chrome地址栏,则json会立即加载到视图中.这显然只发生在来自javascript的请求时.

如果cors_server.py在Chrome中的请求处于"待处理"状态时尝试发出其他请求,则第二个请求将一直等到第一个请求完成.这意味着在执行到达处理程序之前,第一个请求以某种方式将wsgi服务器占用了很长时间cors_server.py.

当请求永远完成时,肯定会有更多的事情发生.我收集了以下内容tcpdump -i lo0 dst port 9011 or src port 9011.

这是来自httpie(http get localhost:9011)的请求,可以快速完成.

17:33:57.176028 IP localhost.64723 > localhost.9011: Flags [S], seq 2244357563, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910553864 ecr 0,sackOK,eol], length 0
17:33:57.176089 IP localhost.9011 > localhost.64723: Flags [S.], seq 1494086712, ack 2244357564, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910553864 ecr 910553864,sackOK,eol], length 0
17:33:57.176103 IP localhost.64723 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176113 IP localhost.9011 > localhost.64723: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176145 IP localhost.64723 > localhost.9011: Flags [P.], seq 1:136, ack 1, win 12759, options [nop,nop,TS val 910553864 ecr 910553864], length 135
17:33:57.176158 IP localhost.9011 > localhost.64723: Flags [.], ack 136, win 12755, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176760 IP localhost.9011 > localhost.64723: Flags [P.], seq 1:18, ack 136, win 12755, options [nop,nop,TS val 910553864 ecr 910553864], length 17
17:33:57.176781 IP localhost.64723 > localhost.9011: Flags [.], ack 18, win 12758, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176811 IP localhost.9011 > localhost.64723: Flags [P.], seq 18:55, ack 136, win 12755, options [nop,nop,TS val 910553864 ecr 910553864], length 37
17:33:57.176823 IP localhost.64723 > localhost.9011: Flags [.], ack 55, win 12757, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176834 IP localhost.9011 > localhost.64723: Flags [P.], seq 55:92, ack 136, win 12755, options [nop,nop,TS val 910553864 ecr 910553864], length 37
17:33:57.176844 IP localhost.64723 > localhost.9011: Flags [.], ack 92, win 12756, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176857 IP localhost.9011 > localhost.64723: Flags [P.], seq 92:178, ack 136, win 12755, options [nop,nop,TS val 910553864 ecr 910553864], length 86
17:33:57.176866 IP localhost.64723 > localhost.9011: Flags [.], ack 178, win 12753, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176878 IP localhost.9011 > localhost.64723: Flags [P.], seq 178:192, ack 136, win 12755, options [nop,nop,TS val 910553864 ecr 910553864], length 14
17:33:57.176886 IP localhost.64723 > localhost.9011: Flags [.], ack 192, win 12753, options [nop,nop,TS val 910553864 ecr 910553864], length 0
17:33:57.176961 IP localhost.9011 > localhost.64723: Flags [F.], seq 192, ack 136, win 12755, options [nop,nop,TS val 910553865 ecr 910553864], length 0
17:33:57.176975 IP localhost.64723 > localhost.9011: Flags [.], ack 193, win 12753, options [nop,nop,TS val 910553865 ecr 910553865], length 0
17:33:57.176980 IP localhost.9011 > localhost.64723: Flags [.], ack 136, win 12755, options [nop,nop,TS val 910553865 ecr 910553865], length 0
17:33:57.182034 IP localhost.64723 > localhost.9011: Flags [F.], seq 136, ack 193, win 12753, options [nop,nop,TS val 910553870 ecr 910553865], length 0
17:33:57.182095 IP localhost.9011 > localhost.64723: Flags [.], ack 137, win 12755, options [nop,nop,TS val 910553870 ecr 910553870], length 0

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这是来自Firefox的请求,可以快速完成.

18:12:57.416741 IP localhost.65089 > localhost.9011: Flags [S], seq 2202457533, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 912890306 ecr 0,sackOK,eol], length 0
18:12:57.416794 IP localhost.9011 > localhost.65089: Flags [S.], seq 1807873905, ack 2202457534, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 912890306 ecr 912890306,sackOK,eol], length 0
18:12:57.416806 IP localhost.65089 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.416818 IP localhost.9011 > localhost.65089: Flags [.], ack 1, win 12759, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.416883 IP localhost.65089 > localhost.9011: Flags [P.], seq 1:346, ack 1, win 12759, options [nop,nop,TS val 912890306 ecr 912890306], length 345
18:12:57.416899 IP localhost.9011 > localhost.65089: Flags [.], ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417478 IP localhost.9011 > localhost.65089: Flags [P.], seq 1:18, ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 17
18:12:57.417492 IP localhost.65089 > localhost.9011: Flags [.], ack 18, win 12758, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417516 IP localhost.9011 > localhost.65089: Flags [P.], seq 18:55, ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 37
18:12:57.417538 IP localhost.65089 > localhost.9011: Flags [.], ack 55, win 12757, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417548 IP localhost.9011 > localhost.65089: Flags [P.], seq 55:92, ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 37
18:12:57.417555 IP localhost.65089 > localhost.9011: Flags [.], ack 92, win 12756, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417562 IP localhost.9011 > localhost.65089: Flags [P.], seq 92:192, ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 100
18:12:57.417569 IP localhost.65089 > localhost.9011: Flags [.], ack 192, win 12753, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417618 IP localhost.9011 > localhost.65089: Flags [F.], seq 192, ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417629 IP localhost.65089 > localhost.9011: Flags [.], ack 193, win 12753, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417634 IP localhost.9011 > localhost.65089: Flags [.], ack 346, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417638 IP localhost.65089 > localhost.9011: Flags [F.], seq 346, ack 193, win 12753, options [nop,nop,TS val 912890306 ecr 912890306], length 0
18:12:57.417647 IP localhost.9011 > localhost.65089: Flags [.], ack 347, win 12748, options [nop,nop,TS val 912890306 ecr 912890306], length 0

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这是来自Chrome隐身标签的请求,可以快速完成.

17:28:10.096905 IP6 localhost.64691 > localhost.9011: Flags [S], seq 2861078667, win 65535, options [mss 16324,nop,wscale 5,nop,nop,TS val 910207638 ecr 0,sackOK,eol], length 0
17:28:10.096926 IP6 localhost.9011 > localhost.64691: Flags [R.], seq 0, ack 2861078668, win 0, length 0
17:28:10.097010 IP localhost.64692 > localhost.9011: Flags [S], seq 3615577823, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910207638 ecr 0,sackOK,eol], length 0
17:28:10.097056 IP localhost.9011 > localhost.64692: Flags [S.], seq 3533709271, ack 3615577824, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910207638 ecr 910207638,sackOK,eol], length 0
17:28:10.097066 IP localhost.64692 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910207638 ecr 910207638], length 0
17:28:10.097075 IP localhost.9011 > localhost.64692: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910207638 ecr 910207638], length 0
17:28:10.097274 IP localhost.64692 > localhost.9011: Flags [P.], seq 1:373, ack 1, win 12759, options [nop,nop,TS val 910207638 ecr 910207638], length 372
17:28:10.097293 IP localhost.9011 > localhost.64692: Flags [.], ack 373, win 12747, options [nop,nop,TS val 910207638 ecr 910207638], length 0
17:28:10.098108 IP localhost.9011 > localhost.64692: Flags [P.], seq 1:18, ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207638], length 17
17:28:10.098131 IP localhost.64692 > localhost.9011: Flags [.], ack 18, win 12758, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098166 IP localhost.9011 > localhost.64692: Flags [P.], seq 18:55, ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207639], length 37
17:28:10.098184 IP localhost.64692 > localhost.9011: Flags [.], ack 55, win 12757, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098212 IP localhost.9011 > localhost.64692: Flags [P.], seq 55:92, ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207639], length 37
17:28:10.098232 IP localhost.64692 > localhost.9011: Flags [.], ack 92, win 12756, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098246 IP localhost.9011 > localhost.64692: Flags [P.], seq 92:178, ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207639], length 86
17:28:10.098267 IP localhost.64692 > localhost.9011: Flags [.], ack 178, win 12753, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098277 IP localhost.9011 > localhost.64692: Flags [P.], seq 178:192, ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207639], length 14
17:28:10.098283 IP localhost.64692 > localhost.9011: Flags [.], ack 192, win 12753, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098352 IP localhost.9011 > localhost.64692: Flags [F.], seq 192, ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098369 IP localhost.64692 > localhost.9011: Flags [.], ack 193, win 12753, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.098380 IP localhost.9011 > localhost.64692: Flags [.], ack 373, win 12747, options [nop,nop,TS val 910207639 ecr 910207639], length 0
17:28:10.099183 IP localhost.64692 > localhost.9011: Flags [F.], seq 373, ack 193, win 12753, options [nop,nop,TS val 910207640 ecr 910207639], length 0
17:28:10.099217 IP localhost.9011 > localhost.64692: Flags [.], ack 374, win 12747, options [nop,nop,TS val 910207640 ecr 910207640], length 0

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这是来自常规Chrome标签的请求,耗时约18秒.

17:28:27.147218 IP6 localhost.64699 > localhost.9011: Flags [S], seq 1481186887, win 65535, options [mss 16324,nop,wscale 5,nop,nop,TS val 910224643 ecr 0,sackOK,eol], length 0
17:28:27.147230 IP6 localhost.9011 > localhost.64699: Flags [R.], seq 0, ack 1481186888, win 0, length 0
17:28:27.147277 IP6 localhost.64700 > localhost.9011: Flags [S], seq 1928824698, win 65535, options [mss 16324,nop,wscale 5,nop,nop,TS val 910224643 ecr 0,sackOK,eol], length 0
17:28:27.147287 IP6 localhost.9011 > localhost.64700: Flags [R.], seq 0, ack 1928824699, win 0, length 0
17:28:27.147331 IP6 localhost.64701 > localhost.9011: Flags [S], seq 63463797, win 65535, options [mss 16324,nop,wscale 5,nop,nop,TS val 910224643 ecr 0,sackOK,eol], length 0
17:28:27.147340 IP6 localhost.9011 > localhost.64701: Flags [R.], seq 0, ack 63463798, win 0, length 0
17:28:27.147578 IP localhost.64704 > localhost.9011: Flags [S], seq 2185396531, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224643 ecr 0,sackOK,eol], length 0
17:28:27.147602 IP localhost.64705 > localhost.9011: Flags [S], seq 2307844059, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224643 ecr 0,sackOK,eol], length 0
17:28:27.147617 IP localhost.9011 > localhost.64704: Flags [S.], seq 4199967470, ack 2185396532, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224643 ecr 910224643,sackOK,eol], length 0
17:28:27.147627 IP localhost.64706 > localhost.9011: Flags [S], seq 324888549, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224643 ecr 0,sackOK,eol], length 0
17:28:27.147638 IP localhost.9011 > localhost.64705: Flags [S.], seq 1097272416, ack 2307844060, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224643 ecr 910224643,sackOK,eol], length 0
17:28:27.147643 IP localhost.64704 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224643 ecr 910224643], length 0
17:28:27.147665 IP localhost.9011 > localhost.64706: Flags [S.], seq 837656804, ack 324888550, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224643 ecr 910224643,sackOK,eol], length 0
17:28:27.147669 IP localhost.64705 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224643 ecr 910224643], length 0
17:28:27.147675 IP localhost.9011 > localhost.64704: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224643 ecr 910224643], length 0
17:28:27.147681 IP localhost.64706 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224643 ecr 910224643], length 0
17:28:27.147686 IP localhost.9011 > localhost.64705: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224643 ecr 910224643], length 0
17:28:27.147691 IP localhost.9011 > localhost.64706: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224643 ecr 910224643], length 0
17:28:27.243730 IP6 localhost.64708 > localhost.9011: Flags [S], seq 4213763930, win 65535, options [mss 16324,nop,wscale 5,nop,nop,TS val 910224733 ecr 0,sackOK,eol], length 0
17:28:27.243748 IP6 localhost.9011 > localhost.64708: Flags [R.], seq 0, ack 4213763931, win 0, length 0
17:28:27.243855 IP localhost.64709 > localhost.9011: Flags [S], seq 1721904940, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224733 ecr 0,sackOK,eol], length 0
17:28:27.243910 IP localhost.9011 > localhost.64709: Flags [S.], seq 2521348026, ack 1721904941, win 65535, options [mss 16344,nop,wscale 5,nop,nop,TS val 910224733 ecr 910224733,sackOK,eol], length 0
17:28:27.243925 IP localhost.64709 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224733 ecr 910224733], length 0
17:28:27.243934 IP localhost.9011 > localhost.64709: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910224733 ecr 910224733], length 0
17:28:27.244093 IP localhost.64709 > localhost.9011: Flags [P.], seq 1:390, ack 1, win 12759, options [nop,nop,TS val 910224733 ecr 910224733], length 389
17:28:27.244108 IP localhost.9011 > localhost.64709: Flags [.], ack 390, win 12747, options [nop,nop,TS val 910224733 ecr 910224733], length 0
17:28:45.693569 IP localhost.64704 > localhost.9011: Flags [F.], seq 1, ack 1, win 12759, options [nop,nop,TS val 910243145 ecr 910224643], length 0
17:28:45.693596 IP localhost.64705 > localhost.9011: Flags [F.], seq 1, ack 1, win 12759, options [nop,nop,TS val 910243145 ecr 910224643], length 0
17:28:45.693605 IP localhost.64706 > localhost.9011: Flags [F.], seq 1, ack 1, win 12759, options [nop,nop,TS val 910243145 ecr 910224643], length 0
17:28:45.693627 IP localhost.9011 > localhost.64704: Flags [.], ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693636 IP localhost.9011 > localhost.64705: Flags [.], ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693645 IP localhost.9011 > localhost.64706: Flags [.], ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693655 IP localhost.64704 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693661 IP localhost.64705 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693666 IP localhost.64706 > localhost.9011: Flags [.], ack 1, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693737 IP localhost.9011 > localhost.64704: Flags [F.], seq 1, ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693766 IP localhost.64704 > localhost.9011: Flags [.], ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693862 IP localhost.9011 > localhost.64705: Flags [F.], seq 1, ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693909 IP localhost.64705 > localhost.9011: Flags [.], ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693935 IP localhost.9011 > localhost.64706: Flags [F.], seq 1, ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.693949 IP localhost.64706 > localhost.9011: Flags [.], ack 2, win 12759, options [nop,nop,TS val 910243145 ecr 910243145], length 0
17:28:45.694861 IP localhost.9011 > localhost.64709: Flags [P.], seq 1:18, ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910224733], length 17
17:28:45.694886 IP localhost.64709 > localhost.9011: Flags [.], ack 18, win 12758, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.694937 IP localhost.9011 > localhost.64709: Flags [P.], seq 18:55, ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910243146], length 37
17:28:45.694958 IP localhost.64709 > localhost.9011: Flags [.], ack 55, win 12757, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.694971 IP localhost.9011 > localhost.64709: Flags [P.], seq 55:92, ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910243146], length 37
17:28:45.694982 IP localhost.64709 > localhost.9011: Flags [.], ack 92, win 12756, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.694997 IP localhost.9011 > localhost.64709: Flags [P.], seq 92:178, ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910243146], length 86
17:28:45.695009 IP localhost.64709 > localhost.9011: Flags [.], ack 178, win 12753, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.695016 IP localhost.9011 > localhost.64709: Flags [P.], seq 178:192, ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910243146], length 14
17:28:45.695020 IP localhost.64709 > localhost.9011: Flags [.], ack 192, win 12753, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.695087 IP localhost.9011 > localhost.64709: Flags [F.], seq 192, ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.695111 IP localhost.64709 > localhost.9011: Flags [.], ack 193, win 12753, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.695120 IP localhost.9011 > localhost.64709: Flags [.], ack 390, win 12747, options [nop,nop,TS val 910243146 ecr 910243146], length 0
17:28:45.696046 IP localhost.64709 > localhost.9011: Flags [F.], seq 390, ack 193, win 12753, options [nop,nop,TS val 910243147 ecr 910243146], length 0
17:28:45.696069 IP localhost.9011 > localhost.64709: Flags [.], ack 391, win 12747, options [nop,nop,TS val 910243147 ecr 910243147], length 0

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看起来Chrome首先尝试IPv6,而wsgiref不喜欢.所以连接重置服务器发送有意义.

对于非隐身Chrome浏览器,似乎客户端会进行多次连接尝试.服务器重置前几次尝试,然后接受一些,然后只使用其中一个连接,客户端实际发送请求.我假设因为wsgiref.simple_server是单线程,以前的连接必须超时才能使实际请求得到处理; 因此延迟.

It's interesting to note that even incognito Chrome still experiences a reset, but only it's only retried once, and then works as expected. Firefox and httpie both only establish a single connection that works smoothly.

Questions

Why does Chrome try to open so many connections for a single request?
What about Chrome's incognito mode causes it to behave more agreeably, here?
Is this... a bug? (In either Chrome or wsgiref?)

Answer 1

jpk*_*jpk 6

tl; dr:Chrome进行了过于激进的优化.新闻11.

事实证明这是因为Chrome的"优化"可以加快页面加载,API交互等.

Chrome有一个名为"预测网络操作以提高网页加载效果"的设置.(在高级设置中它处于隐私状态.)启用此选项后,即使在客户端代码到达执行点之前,Chrome也会抢先打开与承载页面资源的服务器的TCP连接,这将告诉浏览器发出HTTP请求.

在这种情况下,Chrome发现我将向CORS服务器发出一个AJAX请求并打开与服务器的多个TCP连接,以便为我稍后可能提出的其他HTTP请求做准备(即使我的javascript只会发出一个请求)到服务器).它显然在连接之前打开这些额外的连接,实际上将携带javascript将发出的一个HTTP请求.这意味着对于单线程服务器,这些附加连接必须超时才能提供承载请求的连接.这是延迟的来源.

默认情况下启用"预测网络操作以提高页面加载性能"设置,并且在隐身时处于非活动状态(可能是因为它将用户的行为泄露给可能或可能实际上不会获得请求的服务器).在此方案中,禁用它可防止打开这些额外连接,Chrome的行为与Firefox完全相同.

这让我想知道Chrome在互联网上的生产服务器上打开了多少TCP连接,这些连接在发送请求之前未使用或保持打开状态超过一段时间.未使用的连接甚至不会显示在访问日志中,因为没有发出HTTP请求,因此很难估计Chrome用户创建了多少额外负载.在我看来,这种行为是有害的.首先,因为它试图提高客户端性能(这是令人钦佩的),但这样做是以服务器运营商为代价的(不是).第二,因为(隐姓埋名被禁用)可以产生负面的隐私影响.

谢谢!我不敢相信我浪费了多少时间.是时候找到一个新的浏览器来开发:(几周前我注意到Chrome对我的开发服务器做了一些奇怪的事情(发出请求,取消它们,只是再次制作它们).而现在这个!一直在敲打这个延迟在Chrome 44.0.2403.130中,此设置现在标记为"预取资源以更快地加载页面". (3认同)

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