Prior to this commit, using the tracing support could result in an
NullPointerException since the instrumentation expected the tracing
propagation information to be always available from the request
extensions.
This commit improves the strategy for extracing the inbound propagation
information.
First, the instrumentation now looks up the propagation information in
the GraphQL context first, then in the request extensions as a fallback.
We ensure that no NPE can be raised if the information is missing.
Some clients might change the propagation information in the request
extensions, but in the HTTP world, most clients will send those as HTTP
headers. We are adding a new `PropagationWebGraphQlInterceptor` that can
be configured on the application to copy the relevant HTTP headers from
the HTTP request to the GraphQL context. For other transports, we
currently advise the request extensions - both WebSocket and RSocket
multiplex over the same transport message, making this approach
impossible.
Fixes gh-547
a43c92854f