traces_sampler receives always "generic ASGI request" as transaction name.

[antonpirker]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

1.11.1

Steps to Reproduce

I have manually instrumented traces_sampler counted on transaction name in sampling context. At some point with sentry-sdk version upgrade, it stopped work - there is always "generic ASGI request" in transaction name. But at the performance page, transaction has a proper name.

How we initiate sentry FastAPI integration:

sentry_sdk.init(
    dsn=SENTRY_DSN,
    environment="dev",
    traces_sampler=sentry_traces_sampler,
    integrations=[
        starlette.StarletteIntegration(transaction_style="endpoint"),
        fastapi.FastApiIntegration(transaction_style="endpoint"),`
    ]
)

The traces_sampler function:

def sentry_traces_sampler(sampling_context):
    transaction_sampling_mapper = {
        "app.api.api_v1.routers.users.some_name": 0.1,
        "app.api.api_v1.routers.messages.some_name_2": 0.5,
    }
    return transaction_sampling_mapper.get(
        sampling_context["transaction_context"]["name"], 1.0
    )

Expected Result

Actual Result

Possible solution: Give the plain URL of the request instead of "generic ASGI request" as the transaction name to traces_sampler.

[antonpirker]

Related to #1599

[antonpirker]

The problem here is, that we give the event to the traces_sampler as soon as possible. At this point in time the Starlette or FastAPI integrations have not yet set the transaction name to the route (because they have not yet run)

To give the traces_sampler something to work with, we will set the transaction name to the URL (which later will be overwritten by the Starlette/FastAPI integrations with the route. (because transaction names need to have low cardinality, we can not leave the URL as the name, because it will mess up grouping)

[antonpirker]

Oh, I just remembered that @polina-popova commented in this issue that it used to work at some point: #1599 (comment)