if I want to modify squid's source code , where should to start?
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I have read squid source code for some time.

In common circumstances , if squid forward a request which is requesting a resource need to be fragmented , squid will read the reply , process it ,cache it and send it back to client as soon as possible.

But I want to make squid not send back reply immediately . I want to make squid read all of data from original server ,and  then do some process (i.e encoding or decoding) before send any byte of the reply back to client . 

I wonder if I can do this , and where should I start?