fix malformed chunked encoding

[tarunKoyalwar]

Proposed Changes

• As mentioned in Chunked responses length is not calculated correctly proxify#135 . chunked encoding is corrupted (content length mismatch) which causes sites like portswigger.net to not load at all

POC

• setup proxy and send a curl request

$ curl -v https://portswigger.net -x http://127.0.0.1:8080    

./proxify -ha "127.0.0.1:8080" -v 

                       _ ___    
   ___  _______ __ __ (_) _/_ __
  / _ \/ __/ _ \\ \ // / _/ // /
 / .__/_/  \___/_\_\/_/_/ \_, / 
/_/                      /___/

		projectdiscovery.io

[INF] Current proxify version 0.0.9 (latest)
[INF] HTTP Proxy Listening on 127.0.0.1:8080
[INF] Socks5 Proxy Listening on 127.0.0.1:10080
[INF] Saving proxify traffic to logs
2023/03/30 01:27:29 ERROR: martian: got error while writing response back to client: malformed chunked encoding

• same is observed with browser traffic

Investigate/ Review

$ curl -v https://projectdiscovery.io -x http://127.0.0.1:8080  
> CONNECT projectdiscovery.io:443 HTTP/1.1
> Host: projectdiscovery.io:443
> User-Agent: curl/7.86.0
> Proxy-Connection: Keep-Alive
> 
< HTTP/1.1 200 OK
< Content-Length: 0
* Ignoring Content-Length in CONNECT 200 response

• ^ martian by default send content-length header even if there is no body . It probably shouldn't do that (at least for CONNECT responses )

[tarunKoyalwar]

Looks like Content Length is added whenres.Write is used even if we set Content-Length = -1 . since this is not a error we probably can skip this