How to parse USER-AGENT field in http header using regex?

Question

I want to parse some information from the User-Agent: HTTP header. The problem is that I'm getting two User-Agent: HTTP headers in the same HTTP Request:

CONNECT www.facebook.com:443 HTTP/1.1
Host: www.facebook.com
Proxy-Connection: keep-alive
User-Agent: Mozilla/5.0 (http://iim.com/a.jph) AppleWebKit/536.6 (KHTML, like Gecko) Chrome/20.0.1092.
CONNECT www.facebook.com:443 HTTP/1.1
Host: www.facebook.com
Proxy-Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.6 (KHTML, like Gecko) Chrome/20.0.1092.
CONNECT www.facebook.com:443 HTTP/1.1

I want the regex to match the non-http portion e.g Windows NT 6.1; WOW64. The flow analyzer software I'm using java regex engine.

My attempts

User-Agent:\s+.*?\((.*?)\)

Its matching both; I want to skip http portion of it.

Jerry · Accepted Answer · 2013-09-26 19:53:29Z

2

Use a negative lookahead to prevent the match of http:

User-Agent:\s+.*?\((?!http)(.*?)\)

Though you might want to change the .*? to negated classes:

User-Agent:[^(]+\((?!http)([^)]+)\)

edited Sep 26, 2013 at 19:53

answered Sep 26, 2013 at 19:46

Jerry

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3 Comments

asontu Over a year ago

The \s+ becomes unnecessary if you do [^(]+, which is indeed what I would also advice rather than .*?

asontu Over a year ago

I'm wondering if a user agent ever has the OS like Linux (Ubuntu) 12.10, where you wanna catch what's after the first )...

Jerry Over a year ago

@funkwurm If you're curious, you can try: User-Agent:[^(]+\((?!http)((?:[^)]|\((?1)\))+)\)

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