Why doesn’t aread() in a custom Transport set response.elapsed?

[thurse93]

We are trying to implement a custom LogTransport which logs both successful (e.g. there's a response) and unsuccesful (HTTPError) request attempts:

class AsyncLogTransport(httpx.AsyncBaseTransport):
    def __init__(self, **kwargs) -> None:
        self._wrapper = httpx.AsyncHTTPTransport(**kwargs)

    async def handle_async_request(
        self,
        request: Request,
    ) -> Response:
        try:
            response = await self._wrapper.handle_async_request(request)
        except HTTPError as exc:
            logging.error(
                "Request: %s %s -> %s",
                request.method,
                request.url,
                str(exc.__class__.__name__),
                extra={
                    "status": str(exc.__class__.__name__),
                    "method": request.method,
                    "path": str(request.url),
                },
            )
            raise
        await response.aread()
        logging.info(
            "Request: %s %s -> %s %s",
            request.method,
            request.url,
            response.status_code,
            response.reason_phrase,
            extra={
                "code": response.status_code,
                "status": f"{response.status_code} {response.reason_phrase}",
                "duration": response.elapsed.total_seconds(),
                "method": request.method,
                "path": str(request.url),
            },
        )
        return response

    async def aclose(self) -> None:
        await self._wrapper.aclose()

The code in the happy path - with minor adjustments - is taken from our response event hook and works perfectly there. However, when we try to access the .elapsed Field in the Transport we get the following error:

'.elapsed' may only be accessed after the response has been read or closed.

Can somebody explain why that is? We examined the code a bit but couldn't quite figure out why. When the byte stream is closed via Response.aclose() we thought that this should also set the elapsed attribute.

[thurse93]

Ok it seems I got a bit confused there, because it's quite obvious: elapsed gets set on closing BoundSyncStream or BoundAsyncStream, which are both constructed in the respective clients after the transports are getting invoked. I think I got lost in the streams... ^^ and the error message set me on the wrong track.

I guess that leaves us with only one option: Using the event hook for logging the regular reponses and using our custom transport for logging the errors.