Add server interceptor acting as a middleware

[ThHareau]

Fix for #591

Example of usage:

class SentryInstrumenterInterceptor extends $grpc.ServerInterceptor {
  @override
  Stream<R> interceptStreaming<Q, R>(
      $grpc.ServiceCall call,
      $grpc.ServiceMethod<Q, R> method,
      Stream<Q> requests,
      $grpc.ServerStreamingInvoker<Q, R> invoker) async* {
    final name = method.name;
    final transaction = Sentry.startTransaction(method.name, 'grpc');
    print('Before $name');

    yield* super.interceptStreaming(call, method, requests, invoker);

    print('After $name');
    transaction.finish();
  }
}

---

I did not check if this PR solves #611, anyway if it does not it would probably be nice to open a second PR, this one is complex enough

[linux-foundation-easycla]

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• ✅ login: ThHareau / name: Thomas Hareau (1bacbe6, 66feb5d)

[ThHareau]

The goal here is to be close to the Client implementation. As the handler is a Stream, I did not add unary. It is probably doable tho.

[github-actions]

PR Health

Changelog Entry ❗

Package	Changed Files
package:grpc	lib/grpc.dart lib/src/server/handler.dart lib/src/server/interceptor.dart lib/src/server/server.dart lib/src/server/service.dart

Changes to files need to be accounted for in their respective changelogs.

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Coverage ⚠️

File	Coverage
lib/grpc.dart	💔 Not covered
lib/src/server/handler.dart	💚 96 %
lib/src/server/interceptor.dart	💚 100 %
lib/src/server/server.dart	💚 82 % ⬆️ 0 %
lib/src/server/service.dart	💚 97 % ⬆️ 1 %

This check for test coverage is informational (issues shown here will not fail the PR).

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API leaks ⚠️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols
grpc	Any $1.Duration

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[ThHareau]

Should I do anything about the changelog health check?

[mosuem]

Should I do anything about the changelog health check?

No, the breaking change should not be regarded as breaking and is from a different PR (note to self: the check should show that the breakage was introduced elsewhere..). The version is probably fine.

I'll take a closer look at this once I get to it, quite busy ATM unfortunately. But thanks a lot already for the contribution!

[ThHareau]

Should I do anything about the changelog health check?

No, the breaking change should not be regarded as breaking and is from a different PR (note to self: the check should show that the breakage was introduced elsewhere..). The version is probably fine.

I'll take a closer look at this once I get to it, quite busy ATM unfortunately. But thanks a lot already for the contribution!

No worries, it can wait a bit 🙂 Just fyi, I'll be away from the 12th to end of march, so I won't be able to answer during this period. But I'll reply afterward.

[ThHareau]

CI should pass now :)

[ThHareau]

@mosuem Is the changelog failure something I can act on?