It doesn't seem that there's a defined semantic convention for when an http instrumentation span should start and end. There's some ambiguity that would be worth clarifying, namely whether these measurements should also consider the duration of additional middleware layers.

As a start, I would argue we should declare that instrumentations should consider the full request/response cycle of a web application (include middlewares).

Reference for discussion origination: open-telemetry/opentelemetry-python#659

This is a more specific discussion of #330.