Fix Ping data-race

While testing some code under `-race` flag, the race detector flagged a
data race on `spdystream.Ping` code path.

```
==================
WARNING: DATA RACE
Read at 0x00c012a966a8 by goroutine 483923:
  github.com/moby/spdystream.(*Connection).handlePingFrame()
      /go/pkg/mod/github.com/moby/spdystream@v0.2.0/connection.go:615 +0x3e
  github.com/moby/spdystream.(*Connection).frameHandler()
      /go/pkg/mod/github.com/moby/spdystream@v0.2.0/connection.go:432 +0x144
  github.com/moby/spdystream.(*Connection).Serve.func2()
      /go/pkg/mod/github.com/moby/spdystream@v0.2.0/connection.go:331 +0xa6
  github.com/moby/spdystream.(*Connection).Serve.func4()
      /go/pkg/mod/github.com/moby/spdystream@v0.2.0/connection.go:332 +0x47

Previous write at 0x00c012a966a8 by goroutine 483918:
  github.com/moby/spdystream.(*Connection).Ping()
      /go/pkg/mod/github.com/moby/spdystream@v0.2.0/connection.go:281 +0x117
  github.com/moby/spdystream.(*Connection).Ping-fm()
      <autogenerated>:1 +0x39
  k8s.io/apimachinery/pkg/util/httpstream/spdy.(*connection).sendPings()
      /go/pkg/mod/k8s.io/apimachinery@v0.26.3/pkg/util/httpstream/spdy/connection.go:197 +0x1b6
  k8s.io/apimachinery/pkg/util/httpstream/spdy.newConnection.func2()
      /go/pkg/mod/k8s.io/apimachinery@v0.26.3/pkg/util/httpstream/spdy/connection.go:96 +0x47

Goroutine 483923 (running) created at:
  github.com/moby/spdystream.(*Connection).Serve()
      /go/pkg/mod/github.com/moby/spdystream@v0.2.0/connection.go:327 +0x9e
  k8s.io/apimachinery/pkg/util/httpstream/spdy.newConnection.func1()
      /go/pkg/mod/k8s.io/apimachinery@v0.26.3/pkg/util/httpstream/spdy/connection.go:94 +0x47

Goroutine 483918 (running) created at:
  k8s.io/apimachinery/pkg/util/httpstream/spdy.newConnection()
      /go/pkg/mod/k8s.io/apimachinery@v0.26.3/pkg/util/httpstream/spdy/connection.go:96 +0x34d
  k8s.io/apimachinery/pkg/util/httpstream/spdy.NewClientConnectionWithPings()
      /go/pkg/mod/k8s.io/apimachinery@v0.26.3/pkg/util/httpstream/spdy/connection.go:57 +0x224
  k8s.io/apimachinery/pkg/util/httpstream/spdy.(*SpdyRoundTripper).NewConnection()
      /go/pkg/mod/k8s.io/apimachinery@v0.26.3/pkg/util/httpstream/spdy/roundtripper.go:357 +0x644
  k8s.io/client-go/transport/spdy.Negotiate()
      /go/pkg/mod/k8s.io/client-go@v0.26.3/transport/spdy/spdy.go:98 +0x42d
  k8s.io/client-go/tools/remotecommand.(*streamExecutor).newConnectionAndStream()
      /go/pkg/mod/k8s.io/client-go@v0.26.3/tools/remotecommand/remotecommand.go:125 +0x2d7
  k8s.io/client-go/tools/remotecommand.(*streamExecutor).StreamWithContext()
      /go/pkg/mod/k8s.io/client-go@v0.26.3/tools/remotecommand/remotecommand.go:157 +0xbc
==================
```

This PR aims to fix the present data race and enables the race detector
for tests.

Signed-off-by: Tiago Silva <tiago.silva@goteleport.com>

.github/workflows/ci.yaml

@@ -29,4 +29,4 @@ jobs:
         go install github.com/kunalkushwaha/ltag@latest \
         && ./scripts/validate/fileheader
     - name: Test
-      run: go test -v ./...
+      run: go test -v -race ./...

connection.go

@@ -208,9 +208,10 @@ type Connection struct {
 	nextStreamId     spdy.StreamId
 	receivedStreamId spdy.StreamId
 
-	pingIdLock sync.Mutex
-	pingId     uint32
-	pingChans  map[uint32]chan error
+	// pingLock protects pingChans and pingId
+	pingLock  sync.Mutex
+	pingId    uint32
+	pingChans map[uint32]chan error
 
 	shutdownLock sync.Mutex
 	shutdownChan chan error
@@ -274,16 +275,20 @@ func NewConnection(conn net.Conn, server bool) (*Connection, error) {
 // returns the response time
 func (s *Connection) Ping() (time.Duration, error) {
 	pid := s.pingId
-	s.pingIdLock.Lock()
+	s.pingLock.Lock()
 	if s.pingId > 0x7ffffffe {
 		s.pingId = s.pingId - 0x7ffffffe
 	} else {
 		s.pingId = s.pingId + 2
 	}
-	s.pingIdLock.Unlock()
 	pingChan := make(chan error)
 	s.pingChans[pid] = pingChan
-	defer delete(s.pingChans, pid)
+	s.pingLock.Unlock()
+	defer func() {
+		s.pingLock.Lock()
+		delete(s.pingChans, pid)
+		s.pingLock.Unlock()
+	}()
 
 	frame := &spdy.PingFrame{Id: pid}
 	startTime := time.Now()
@@ -612,10 +617,14 @@ func (s *Connection) handleDataFrame(frame *spdy.DataFrame) error {
 }
 
 func (s *Connection) handlePingFrame(frame *spdy.PingFrame) error {
-	if s.pingId&0x01 != frame.Id&0x01 {
+	s.pingLock.Lock()
+	pingId := s.pingId
+	pingChan, pingOk := s.pingChans[frame.Id]
+	s.pingLock.Unlock()
+
+	if pingId&0x01 != frame.Id&0x01 {
 		return s.framer.WriteFrame(frame)
 	}
-	pingChan, pingOk := s.pingChans[frame.Id]
 	if pingOk {
 		close(pingChan)
 	}