response_size_histogram for ASGI instrumention

[imanshafiei540]

Describe the solution you'd like
Can we have response_size_histogram inside the opentelemetry-instrumentation-asgi logic?
Currently, we do have access to content-length header from the response inside the OpenTelemetryMiddleware, so it would be beneficial that we can have the ability to record response_size like duration.

Describe alternatives you've considered
Currently, I'm thinking about disable the FastAPI auto instrumentation and implement both response size and duration.

Additional context
The only instrumentator I could find that have the ability to record response_size is opentelemetry-instrumentation-tornado (HTTP_SERVER_RESPONSE_SIZE).

Let me know if that makes sense.
Thanks.

[shalevr]

According to the specification it seems possible to add http.server.response.size if there is access to this attribute.
This metric is optional, so maybe it's the reason it's not implemented.
Do you want to work on this issue?

[imanshafiei540]

Hello @shalevr , Thank you for your response. I'm happy working on it.
I'll create a pull request.