::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact

See Raw Headers with Netcat

October 5th, 2015
tech  [html]

Getting response headers is easy: run curl -D- -o/dev/null -sS [url] or load the site in a browser with the networking tab open. Getting request headers is harder, because webservers don't have a way to dump this exactly as they received it. Yes, you can set them to log specific headers, but logging all headers exactly as they came over the wire isn't something I see in nginx or apache. Netcat can help here. Start it up on some unused port:
    nc -lp 8070
Now make the thing you're debugging visit yoursite:8070. Netcat will print out what headers you got:
    GET / HTTP/1.1
    Host: www.jefftk.com:8070
    Referer: http://www.jefftk.com/...
    Accept-Encoding: gzip,deflate
    Cache-Control: no-store, no-cache
    Accept-Language: en-US
    Connection: Keep-alive
    Accept: */*
    Accept-Encoding: gzip,deflate
    ...
See the duplicate Accept-Encoding header? It turned out that A was adding an extra encoding header which then made B disable gzip. [1] Once I had the raw headers as sent it was pretty clear what the problem was.

(Because the problem was a duplicated header I'm glad I didn't go with a higher level tool that might have masked that problem by storing headers in hashtable or something.)


[1] Sniffing the traffic would have been ideal, but I wasn't in a position to get in between them.

Comment via: google plus, facebook

Recent posts on blogs I like:

How Fast New York Regional Rail Could Be Part 2

In my last post about New York regional rail schedules, I covered the New Haven and Harlem Lines of Metro-North and the Main Line and Hempstead Branch of the LIRR. I was hoping to cover more lines tonight, but due to time constraints only the Hudson Line …

via Pedestrian Observations October 17, 2019

Strong stances

I. The question of confidence Should one hold strong opinions? Some say yes. Some say that while it’s hard to tell, it tentatively seems pretty bad (probably). There are many pragmatically great upsides, and a couple of arguably unconscionable downsides. …

via Meteuphoric October 15, 2019

What do executives do, anyway?

An executive with 8,000 indirect reports and 2000 hours of work in a year can afford to spend, at most, 15 minutes per year per person in their reporting hierarchy... even if they work on nothing else. That job seems impossible. How can anyone make any im…

via apenwarr September 29, 2019

more     (via openring)

More Posts:


  ::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact