Add hook to set custom span name in requests instrumentation

[lzchen]

Similar to wsgi, accept a callback function in RequestsInstrumentor().instrument to be able to pass custom span name.

The specs say "MAY" for this feature, but we should be consistent across our instrumentations.

Part of open-telemetry/opentelemetry-python#1297

[srikanthccv]

Hi @lzchen, I would like to work on this. I have one question here. Should this span name call back function for requests accept any arguments such as http method or url etc...

[lzchen]

@lonewolf3739
Apologies, I've already started work on this. May I suggest working on this instead?

To address your question, yes, I think we can pass in anything that is relevant to the http call.

[srikanthccv]

Ok.

[danielbraun89]

The currently implemented requests name_callback does not accept neither method nor url as inputs. The user dont have any info to generate the name from.

[lzchen]

@danielbraun89
Shouldn't the user always have access to method and url? They can simply use those within the callback itself, they don't need to be passed in.

[srikanthccv]

@lzchen I don't think user would know the method and url with requests instrumentation. We had discussion on whether to pass environ with flask name_callback. With Flask flask.request is accessible to user always.

[lzchen]

Oh that is true, I misunderstood the question. I will create a fix for it.