Automatically exclude tunnel request from backend transactions

[timfish]

Problem Statement

When setting up the tunnel option, users will often follow the docs and add a local API route to forward those envelopes.

These POST requests will usually get auto-instrumented on the backend and will potentially result in a transaction for every frontend envelope.

Solution Brainstorm

Filter these out in some way?

If the tunnel option is set in the frontend, we could automatically set the Content-Type as application/x-sentry-envelope. This can be picked up in the http instrumentation and used to ignore these requests.

• Adding the Content-Type header will also fix a Svelte issue Feedback widget with screenshot via tunnelling not working #16112

[Lms24]

added this as a sub issue of https://github.com/getsentry/projects/issues/385 (which I guess we still have to port to Linear) but fully agree, this sounds like a good approach!