|October 5th, 2015|
nc -lp 8070Now 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.  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.)
 Sniffing the traffic would have been ideal, but I wasn't in a position to get in between them.