A simple reverse-proxy server in Sanic using HTTPX streaming responses

proxy.py

#!/bin/python3
#
"""Example Sanic Reverse Proxy"""

from urllib.parse import urlsplit, urlunsplit
from sanic import Sanic, Request
from sanic.response import stream, HTTPResponse
import httpx

env = {"hostname-from": "localhost", "port-from": 8000, "port-to": 8080}

host = Sanic("host")

@host.before_server_start
def setup(app, loop):
    app.ctx.remote = f"http://{env['hostname-from']}:{env['port-from']}"
    app.ctx.client = httpx.AsyncClient()

@host.route("/<path>", methods=("GET", "HEAD", "OPTIONS"))
async def proxy(request: Request, path):
    app_ctx = request.app.ctx
    to = "/".join((app_ctx.remote, path))
    headers = [(k, v) for k, v in request.headers.items() if k != "host"]
    headers.append(("x-forwarded-for", request.conn_info.client))
    resp_ctx = app_ctx.client.stream(request.method, to, headers=headers, allow_redirects=False)
    httpx_resp = await resp_ctx.__aenter__()
    try:
        if httpx_resp.status_code in (201, 301, 302, 303, 307, 308):
            loc = httpx_resp.headers.get("location", "").split(",")[0]
            if loc and "://" not in loc:
                split_result = urlsplit(loc)
                scheme, netloc, url, query, fragment = split_result
                split_loc = netloc.split(":", 1)
                if split_loc[0] == env['hostname-from'] and \
                        (len(split_loc) < 2 or split_loc[1] == str(env['port-from'])):
                    if len(split_loc) < 2:
                        if (scheme in ("https", "wss") and env['port-to'] != 443) or env['port-to'] != 80:
                            netloc = ":".join(request.host, str(env['port-to']))
                        else:
                            netloc = request.host
                    elif (scheme in ("https", "wss") and env['port-to'] == 443) or env['port-to'] == 80:
                        netloc = request.host
                    else:
                        netloc = ":".join(request.host, str(env['port-to']))
                    loc = urlunsplit((scheme, netloc, url, query, None))
                    del httpx_resp.headers["location"]
                    httpx_resp.headers["location"] = loc
        resp_headers = httpx_resp.headers.multi_items()
    except Exception:
        await resp_ctx.__aexit__(None, None, None)
        raise
    if request.method in ("HEAD", "OPTIONS") or httpx_resp.status_code in (301, 302, 303, 307, 308):
        await httpx_resp.aclose()
        return HTTPResponse(None, status=httpx_resp.status_code, headers=resp_headers)
    async def passthrough(response):
        async for chunk in httpx_resp.aiter_raw():
            await response.stream.send(chunk, end_stream=False)
        await httpx_resp.aclose()
    return stream(passthrough, status=httpx_resp.status_code, headers=resp_headers)

@host.route("/", methods=("GET", "HEAD", "OPTIONS"))
async def index(request):
    return await proxy(request, "")

host.run(host="0.0.0.0", port=env['port-to'])