Fill in the `Pattern` field on an `http.Request`. This field is filled
out by the standard library's `http.ServeMux` but is not filled in by
`gorilla/mux`. It is used to identify the matching route pattern and is
primarily used for traces and metrics to reduce cardinality on paths
that have variables in the routes so they can be recorded to traces.
The primary result of this change is that HTTP request traces will now
have the name `{method} {route}` rather than only `{method}` so an
invocation of `docker ps` will show up as `GET /containers/json` instead
of just `GET`.
Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>
Jonathan A. Sternberg
48d9ab2412