Weird ISP Issue
Apr 12, 2018
2 minute read

I was trying to lookup the documentation for Click and I got redirected to a page showing Werkzeug’s documentation. I’d assumed it was a broken configuration on the server, because other subdomains like Armin’s blog also sent me to the same page. I got in touch with Armin and he asked me if I was using https everywhere, and that wasn’t supported by the server. But, I wasn’t. The next thing to try was to switch my ISP and check, and viola it worked!

I did some debugging and figured out that in some responses the HTTP status line was not being sent, and the first line in the response contained Date. Also, the response seems to be correct, when I hit a hard refresh on the browser, which sets the Cache-Control header to no-cache. So, it looks like some cache in between me and the server is going nuts with this specific request.

$ nc click.pocoo.org 80 < input.txt
Date: Thu, 12 Apr 2018 05:17:14 GMT
Last-Modified: Mon, 07 Apr 2014 18:35:36 GMT
Connection: Keep-Alive

And the input.txt file looks like this.

HEAD / HTTP/1.1
Host: click.pocoo.org
User-Agent: Mozilla/6.0 (X11; Ubuntu; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/59.0
Accept: */*
Accept-Encoding: deflate, gzip

Adding the line Cache-Control: no-cache to this input causes the problem to go away.

$ nc click.pocoo.org 80 < input.txt
HTTP/1.1 301 Moved Permanently
Server: nginx
Date: Thu, 12 Apr 2018 05:30:56 GMT
Content-Type: text/html
Content-Length: 178
Connection: keep-alive
Location: http://sphinx-doc.org/

Also, I’m able to reproduce this with all the subdomains on pocoo.org - click, sphinx, lucumr, … I’m not sure if it has something to do with the server, or if it is entirely independent of that. But, the problem does go away when I switch to a different network.

I’m not sure what I can do next to narrow down the problem, even more. Any hints/tips appreciated.



comments powered by Disqus