server: replace cmux with native HTTP/2 multiplexing

[kairosci]

Remove the unmaintained cmux dependency in favor of h2c for
cleartext gRPC and TLS ALPN for encrypted connections.
Fixes #18032

[k8s-ci-robot]

Hi @kairosci. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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[kairosci]

/assign @ahrtr
/cc @ahrtr

[serathius]

/ok-to-test

[serathius]

cc @aojea is the idea sound at all?

[codecov]

Codecov Report

❌ Patch coverage is 23.12500% with 123 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.97%. Comparing base (dde11c0) to head (476fc51).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
server/embed/serve.go	25.78%	92 Missing and 3 partials ⚠️
server/etcdmain/grpc_proxy.go	0.00%	22 Missing ⚠️
server/embed/apply/buffered_conn.go	0.00%	6 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
server/embed/etcd.go	74.08% <100.00%> (-2.09%)	⬇️
server/embed/apply/buffered_conn.go	0.00% <0.00%> (ø)
server/etcdmain/grpc_proxy.go	14.13% <0.00%> (+0.03%)	⬆️
server/embed/serve.go	47.04% <25.78%> (-12.35%)	⬇️

... and 29 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #21801      +/-   ##
==========================================
- Coverage   70.08%   69.97%   -0.11%     
==========================================
  Files         426      427       +1     
  Lines       35245    35337      +92     
==========================================
+ Hits        24701    24727      +26     
- Misses       9157     9212      +55     
- Partials     1387     1398      +11     

---

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: kairosci
Once this PR has been reviewed and has the lgtm label, please ask for approval from ahrtr. For more information see the Code Review Process.

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[kairosci]

/retest

[k8s-ci-robot]

@kairosci: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-etcd-verify	476fc51	link	true	/test pull-etcd-verify
pull-etcd-e2e-arm64	476fc51	link	true	/test pull-etcd-e2e-arm64
pull-etcd-e2e-amd64	476fc51	link	true	/test pull-etcd-e2e-amd64
pull-etcd-e2e-386	476fc51	link	true	/test pull-etcd-e2e-386

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[serathius]

@kairosci previously this task was assumed to be impossible due to how HTTP/2 works. But it's yours AI tokens.

[aojea]

cc @aojea is the idea sound at all?

after a quick look this PR is implementing the same logic as cmux, a read ahead buffer and a dispatcher ... I do not see the benefit of absorbing the problem in tree, the cmux package is pretty stable and battle tested ... unless there is a very big benefit I advice to be conservative, touching in this area can open a lot of subtle bugs and regressions

[ahrtr]

@kairosci thank you for the PR.

I suggest to look at this change after we release etcd v3.7, as we don't want to introduce any new feature or major change to etcd at current stage.