fix proxy deprecated post

[bhardwajparth51]

Closes #12121

Technical

Modified deprecated_handler.py to proxy POST requests to the fast_web
container (http://fast_web:8080) instead of using a 303 redirect in the
local dev environment. GET requests continue to use the existing redirect
behavior. A new proxy_to_fastapi() function handles forwarding all headers,
cookies, and request body, and returns the response via delegate.RawText
to bypass the web.py layout processor.

Testing

1. Start the local dev environment:

   make git && docker compose up -d

2. Test POST proxying:

   curl -i -X POST http://localhost:8080/reading-goal.json \
     -d '{"year":2024}' \
     -H "Content-Type: application/json"

Expected: 200 OK with x-served-by: FastAPI in the headers.

3. Test GET redirect still works:

   curl -i http://localhost:8080/reading-goal.json

Expected: 303 See Other with Location: http://localhost:18080/reading-goal.json

Screenshot

GET request (redirected to :18080):

POST request (proxied to FastAPI):

Stakeholders

@RayBB

[bhardwajparth51]

Hey @RayBB , PR is ready for review whenever you have bandwidth!

[RayBB]

Looks like a great start. Let's use httpx instead of requests. Also, please add a video of the reading goals setting working in the local app. It's great to see screenshots of the request but it's better to see the actual GUI working.

Thanks!

[RayBB]

Also, I think we'll want to set a different x served by header to indicate that it's a proxy for the fastapi server.

[bhardwajparth51]

Hey @RayBB, I've addressed your feedback:

1. Switched from requests to httpx using httpx.Client
2. Added x-served-by: FastAPI-Proxy header to distinguish proxied responses from direct FastAPI responses
3. Recorded a video showing the reading goal being set successfully in the local GUI:
   Screencast from 19-03-26 11:40:00 PM IST.webm

Let me know if anything else needs to be changed!

[RayBB]

Mostly looking good. Two small things to fix. Seems to work locally!

[RayBB]

Tested locally, it's working excellently.

Fixes a very annoying issue we were having locally around redirects.

Appreciate your help here!

[bhardwajparth51]

Happy to help! looking forward to the next one :)