agent: add 1 buffer to errc to prevent goroutine leak

[lzhfromustc]

Description
In function (*Server).runEtcd(), if select at line 150 chooses case <-time.After(time.Minute):, then the goroutine created at line 125 will be blocked forever, because there is no receive to synchronize with errc <- srv.startProxy() at line 129

etcd/functional/agent/handler.go

Lines 123 to 158 in 84e2788

	func (srv *Server) runEtcd() error {
	errc := make(chan error)
	go func() {
	time.Sleep(5 * time.Second)
	// server advertise client/peer listener had to start first
	// before setting up proxy listener
	errc <- srv.startProxy()
	}()
	if srv.etcdCmd != nil {
	srv.lg.Info(
	"starting etcd command",
	zap.String("command-path", srv.etcdCmd.Path),
	)
	err := srv.etcdCmd.Start()
	perr := <-errc
	srv.lg.Info(
	"started etcd command",
	zap.String("command-path", srv.etcdCmd.Path),
	zap.Errors("errors", []error{err, perr}),
	)
	if err != nil {
	return err
	}
	return perr
	}
	select {
	case <-srv.etcdServer.Server.ReadyNotify():
	srv.lg.Info("embedded etcd is ready")
	case <-time.After(time.Minute):
	srv.etcdServer.Close()
	return fmt.Errorf("took too long to start %v", <-srv.etcdServer.Err())
	}
	return <-errc
	}

How it is fixed
This patch is similar to line 210 in file lease/leasehttp/http.go of #7015
We add 1 buffer to the channel errc, and then the send errc <- srv.startProxy() will not be blocked and no goroutine will be leaked, but all receives will still be waiting for sent. So this patch is very safe.

[codecov-io]

Codecov Report

Merging #11302 into master will increase coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #11302      +/-   ##
==========================================
+ Coverage   64.05%   64.35%   +0.29%     
==========================================
  Files         403      403              
  Lines       37953    37953              
==========================================
+ Hits        24312    24424     +112     
+ Misses      11980    11888      -92     
+ Partials     1661     1641      -20

Impacted Files	Coverage Δ
pkg/netutil/netutil.go	63.11% <0%> (-6.56%)	⬇️
pkg/logutil/zap_grpc.go	47.61% <0%> (-4.77%)	⬇️
clientv3/retry_interceptor.go	65% <0%> (-4.5%)	⬇️
clientv3/leasing/util.go	95% <0%> (-3.34%)	⬇️
auth/store.go	65.9% <0%> (-2.43%)	⬇️
etcdserver/api/v3rpc/lease.go	67.04% <0%> (-2.28%)	⬇️
clientv3/op.go	72.08% <0%> (-1.25%)	⬇️
embed/serve.go	36.48% <0%> (-0.91%)	⬇️
etcdserver/cluster_util.go	56.52% <0%> (-0.8%)	⬇️
clientv3/leasing/cache.go	87.22% <0%> (-0.56%)	⬇️
... and 20 more

---

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[spzala]

lgtm thanks!

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 21 days if no further activity occurs. Thank you for your contributions.