Handle Trailers-Only OK responses in streaming calls without exception handling

[michaelmccord]

Summary

• Avoid expensive TaskCanceledException in server streaming calls when the server returns a Trailers-Only response with OK status by setting HttpResponseTcs with TrySetResult before Cleanup runs
• Add fallback in GetResponseStatus to read grpc-status from response headers when not found in trailers (Trailers-Only responses per gRPC spec)
• Handle null HttpResponseMessage.Content on .NET Framework in HttpContentClientStreamReader.MoveNextCore
• Remove await CallTask from GetResponseHeadersCoreAsync to prevent deadlock when ResponseHeadersAsync is awaited before MoveNext on streaming calls with status in headers

Fixes #2696

Test plan

• AsyncServerStreamingCall_TrailersOnly_TrailersReturnedWithHeaders passes on all TFMs (net8.0, net9.0, net10.0, net462)
• AsyncServerStreamingCall_NoMessagesSuccess_SuccussCommitLogged passes on all TFMs including net462
• Full Grpc.Net.Client.Tests suite passes with 0 failures across all TFMs
• No regressions in Grpc.AspNetCore.Server.Tests

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: JamesNK / name: James Newton-King (cdfb654, cfaaa4c)
• ✅ login: michaelmccord / name: Michael McCord (b86a5d6)

[JamesNK]

Why have lots of people immediately thumbs up this?

Do you know if there are existing unit tests for this scenario?

[michaelmccord]

Why have lots of people immediately thumbs up this?

Do you know if there are existing unit tests for this scenario?

1. I messaged a few people that knew I had been trying to track this problem down for a few days so that it would get attention.
2. The tests I'm aware of are below (the ones which failed originally due to my inital changes and I subsequently fixed with additional code changes):

• AsyncServerStreamingCallTests.AsyncServerStreamingCall_TrailersOnly_TrailersReturnedWithHeaders — test/Grpc.Net.Client.Tests/AsyncServerStreamingCallTests.cs
• RetryTests.AsyncServerStreamingCall_NoMessagesSuccess_SuccussCommitLogged — test/Grpc.Net.Client.Tests/Retry/RetryTests.cs

One piece that I'm not entirely sure of is the removal of the await from GetResponseHeadersCoreAsync. It seemed to me that given my changes this was no longer necessary and it was causing a deadlock, but I wasn't 100% sure.

[michaelmccord]

@JamesNK -- any thoughts on this?

[JamesNK]

@michaelmccord I've made some changes and added tests. I think it is ready to merge. Can you take a look at my updates and double check they're ok.

[michaelmccord]

@michaelmccord I've made some changes and added tests. I think it is ready to merge. Can you take a look at my updates and double check they're ok.

Seems okay to me.