Proxy with FastAPI

Two async FastAPI routes relay the script and events with httpx.

Set it up

1. Install httpx

   terminal

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   pip install httpx

2. Add the routes to your app

   metricraven_proxy.py

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   # metricraven_proxy.py · FastAPI with httpx
   import httpx
   from fastapi import FastAPI, Request, Response
   
   app = FastAPI()
   client = httpx.AsyncClient(timeout=15)
   
   
   async def relay(request: Request, url: str, cache_control: str) -> Response:
       headers = {
           name: request.headers[name]
           for name in ("content-type", "origin", "user-agent")
           if name in request.headers
       }
       if request.client:
           headers["x-visitor-ip"] = request.client.host
       try:
           upstream = await client.request(
               request.method,
               url,
               headers=headers,
               content=await request.body() if request.method == "POST" else None,
           )
       except httpx.HTTPError:
           return Response(status_code=502)
       return Response(
           upstream.content,
           status_code=upstream.status_code,
           headers={
               "Content-Type": upstream.headers.get("content-type", "application/octet-stream"),
               "Cache-Control": cache_control,
           },
       )
   
   
   @app.get("/a/script")
   async def metricraven_script(request: Request):
       return await relay(request, "https://metricraven.com/js/script.js", "public, max-age=3600")
   
   
   @app.post("/a/event")
   async def metricraven_event(request: Request):
       return await relay(request, "https://metricraven.com/api/v1/collect", "no-store")

3. Pass the visitor IP through Uvicorn

   Behind a load balancer, start Uvicorn with --proxy-headers and set --forwarded-allow-ips to your proxy's address, so request.client.host is the visitor.

4. Point your script tag at your own paths

   Replace your MetricRaven tag with this one. src loads the tracker from your domain and data-api sends its events there too.

   Your website's shared layout

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   <script defer src="/a/script" data-api="/a/event" data-site-id="YOUR_SITE_ID"></script>

Notes

• If a CDN or load balancer sits in front of this server, the connecting address is that proxy, not the visitor. Use the visitor IP header it sets (and only one it overwrites, so visitors can't fake it).

How the proxy works and which headers it must send: Use your own domain.