Is there a proxy server script that has the ability to manipulate traffic?

Question

proxy

A question.
There is an application on android that communicates via web sockets with the server.
There is a task to start up the data through a proxy, namely to specify the proxy address instead of the original.
On this proxy, specify the address of the main server.
You will need to view the data and, under certain conditions / matches, send your command to the main server.
Does such an engine / script actually exist so that it can be organized in it by making some settings or by prescribing some macros / plugins in it?

Answer 1

squid.
But, in principle, you can do this through iptables.

Answer 2

mitmproxy.org
is now politically correct debugging MITM
like "[neighbor's] WiFi unblocker"