feat(pubsub): include subscription name in StreamingPull header

[haphungw]

Fix #4470

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.02%. Comparing base (76753ba) to head (a06c971).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4585      +/-   ##
==========================================
+ Coverage   95.01%   95.02%   +0.01%     
==========================================
  Files         195      195              
  Lines        7456     7459       +3     
==========================================
+ Hits         7084     7088       +4     
+ Misses        372      371       -1     

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[dbolduc]

How can we test this so the code doesn't regress?

I have an idea (SPOILERS)

We have a mock Pub/Sub service ...

google-cloud-rust/src/pubsub/grpc-mock/src/mocks.rs

Line 29 in 7191e09

request: tonic::Request<mpsc::Receiver<tonic::Result<v1::StreamingPullRequest>>>,

... which we use in the session.rs unit tests. Maybe we can add a new unit test where we extract the metadata from the incoming tonic::Request and check that it has the header we just set?

https://docs.rs/tonic/0.14.2/tonic/struct.Request.html#method.metadata

[dbolduc]

comment: This works, and I am ok with it.

Some background: this is a handwritten interface for a bidirectional gRPC stream added onto a fully generated struct.

We have not come up with a generic solution for bidirectional streams yet that we can generate.

So subscription works but it won't help us solve the general problem. (Which might look like accepting an initial request? (although I don't think in general that is even known. Ugh. It is a hard problem that probably @coryan will have to tackle next quarter)).

[dbolduc]

Consider accepting the whole x_goog_request_params