How to write a module to process http response message body?

[xinghua_hi]

I am a nginx development novice.Now i need to process the http response 
message body.For example , get all numbers in the response html,then
every number times two and use new number instead of the original
number. Do I need to write a new http module or use the existing module?
Which existing module can I imitate?Which function should i foucs on ?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,191422,191422#msg-191422