I am making a proxy application for a browser. It has to use only the standard libraries. So far, I've managed to create the server. When trying to access a web page from a client, i get the following information:
CONNECT gmail.com:443 HTTP/1.1 User-Agent: Mozilla/5.0 Firefox/49.0 Proxy-Connection: keep-alive Connection: keep-alive Host: gmail.com:443
My question is: what to use in order to handle the requests? How to handle a file download?
Once you get that CONNECT command, do what is asked: create the upstream connection, and return the appropriate success/failure response. If the upstream connection was successful, all you have to do now is copy bytes in both directions, simultaneously. The endpoints will take care of all SSL issues, uploads, downloads, etc. You have no further role to play.