As I know, squid would send a 504 gateway timeout when request timeout. But what if the client has already received a response header 200 ok. I mean when the response data is sent back in chunked encoding. 
For example: header "200 ok" body part "a" body part "b" body part "c". After receiving "200 ok" and "a", request timeout happen, what would squid do this time, would it send a 504 gateway timeout back to the client ? If so, can the client received this header "504 gateway timeout" since it has already received a header "200 ok"