mitmproxy puts entire URL into GET

[Tillerino]

I'm sure I'm doing something completely wrong here.

1. backend is a simple echo server running on localhost:8081: npm install http-echo-server; PORT=8081 npx http-echo-server.

2. a reverse-proxy to this backend on port 5001: mitmdump -p 5001 --mode reverse:http://127.0.0.1:8081

3. a simple request: curl -x http://localhost:5001 http://example.com/hello

I would have expected to see a request for /hello on the backend, but instead I see a request for http://example.com/hello (output of 1):

[server] event: listening (port: 8081)
[server] event: connection (socket#1)
[socket#1] event: resume
[socket#1] event: data
--> GET http://example.com/hello HTTP/1.1
--> Host: 127.0.0.1:8081
--> User-Agent: curl/8.4.0
--> Accept: */*
--> Proxy-Connection: Keep-Alive

This is very strange, since GET doesn't usually contain the schema or host. Whereas mitm logs something entirely different (output of 2):

[16:43:30.257] reverse proxy to http://127.0.0.1:8081 listening at *:5001.
[16:43:33.014][[::1]:40476] client connect
[16:43:33.015][[::1]:40476] server connect 127.0.0.1:8081
[::1]:40476: GET http://127.0.0.1:8081/hello
          << 200 OK 130b
[16:43:35.022][[::1]:40476] server disconnect 127.0.0.1:8081
[16:43:35.022][[::1]:40476] client disconnect

Now this is no quirk of the frontend or backend. I've tried Firefox as a frontend instead of curl, and I've used a different backend (which is where I started) - all with the same result. What's going wrong here? Am I missing a configuration?

[mhils]

You are using reverse proxy mode (which is typically invisible to the client), but you are also configuring a proxy on the client side. As a result, your client sends an absolute-form request (intended for a proxy) to mitmproxy, which forwards it unmodified to the target server. You can either:

1. Not use a proxy, i.e. run curl http://localhost:5001/hello
2. Run mitmproxy in regular mode, i.e. mitmdump -p 5001

If you want to run a regular proxy but change where the request is going, check out https://docs.mitmproxy.org/stable/overview-features/#map-remote.

[Tillerino]

Ah yes, I see. So what I wanted to do here was something along the lines of:

mitmdump -p 5001 --map-remote "|~m GET|//.+/|//localhost:8081/"

Thanks for the quick response!