app.py

import os
from fastapi import FastAPI, Request, HTTPException, Depends, Query
from fastapi.responses import HTMLResponse, PlainTextResponse
import httpx
import uvicorn

# --- Security Dependency ---

ACCESS_KEY = os.environ.get("AK")

async def verify_access_key(ak: str = Query(..., alias="AK")):
    """
    Dependency to secure endpoints by verifying the 'AK' query parameter
    against the secret key stored in the environment.
    """
    if not ACCESS_KEY:
        # Server-side configuration error if the secret is not set
        raise HTTPException(
            status_code=500,
            detail="Access key is not configured on the server."
        )
    if ak != ACCESS_KEY:
        # Client-side error for an invalid access key
        raise HTTPException(
            status_code=401,
            detail="Unauthorized: Invalid access key provided."
        )

# --- FastAPI Application ---

app = FastAPI(
    title="URL Fetcher API",
    description="A simple API to fetch URL content, with a protected endpoint."
)


# --- MODIFIED: Root Endpoint ---
@app.get("/", response_class=PlainTextResponse)
async def root():
    """
    Root endpoint for health checks. Returns a simple 'OK' response.
    """
    return "OK"


@app.get("/ping", response_class=PlainTextResponse)
async def ping():
    """
    An unprotected endpoint to check if the service is running.
    Returns a simple 'pong' response.
    """
    return "pong"


@app.get("/fetch_url", response_class=HTMLResponse, dependencies=[Depends(verify_access_key)])
async def fetch_url_content(request: Request):
    """
    Fetches the HTML content of a URL from the 'url' query parameter.
    This endpoint is protected and requires a valid 'AK' (access key).
    """
    target_url = request.query_params.get('url')

    if not target_url:
        raise HTTPException(
            status_code=400,
            detail="The 'url' query parameter is required."
        )

    async with httpx.AsyncClient(follow_redirects=True) as client:
        try:
            headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36'}
            response = await client.get(target_url, headers=headers)
            response.raise_for_status()  # Raise an exception for bad status codes (4xx or 5xx)
            return HTMLResponse(content=response.text, status_code=response.status_code)

        except httpx.RequestError as exc:
            raise HTTPException(status_code=400, detail=f"An error occurred while requesting {exc.request.url!r}: {exc}")
        except httpx.HTTPStatusError as exc:
            raise HTTPException(status_code=exc.response.status_code, detail=f"Error response {exc.response.status_code} while requesting {exc.request.url!r}.")