net/http: unflake TestTimeoutHandlerSuperfluousLogs

Uses 2 channels to synchronize that test, because
relying on sleeps creates flaky behavior, thus:

a) 1 buffered channel to send back the last spurious line
without having to reason about "happens before" behavior
a) 1 buffered channel at the end of the handler; it'll
be controlled by whether we expect to timeout or not,
but will always be closed when the test ends

Fixes #35051

Change-Id: Iff735aa8d1ed9de8d92b792374ec161cc0a72798
Reviewed-on: https://go-review.googlesource.com/c/go/+/208477
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>

src/net/http/serve_test.go

@@ -6306,6 +6306,10 @@ func testContentEncodingNoSniffing(t *testing.T, h2 bool) {
 // Issue 30803: ensure that TimeoutHandler logs spurious
 // WriteHeader calls, for consistency with other Handlers.
 func TestTimeoutHandlerSuperfluousLogs(t *testing.T) {
+ if testing.Short() {
+ t.Skip("skipping in short mode")
+ }
+
  setParallel(t)
  defer afterTest(t)
 
@@ -6314,44 +6318,54 @@ func TestTimeoutHandlerSuperfluousLogs(t *testing.T) {
  testFuncName := runtime.FuncForPC(pc).Name()
 
  timeoutMsg := "timed out here!"
- maxTimeout := 200 * time.Millisecond
 
  tests := []struct {
- name string
- sleepTime time.Duration
- wantResp string
+ name  string
+ mustTimeout bool
+ wantResp  string
  }{
  {
- name: "return before timeout",
- sleepTime: 0,
- wantResp: "HTTP/1.1 404 Not Found\r\nContent-Length: 0\r\n\r\n",
+ name: "return before timeout",
+ wantResp: "HTTP/1.1 404 Not Found\r\nContent-Length: 0\r\n\r\n",
  },
  {
- name: "return after timeout",
- sleepTime: maxTimeout * 2,
+ name:  "return after timeout",
+ mustTimeout: true,
  wantResp: fmt.Sprintf("HTTP/1.1 503 Service Unavailable\r\nContent-Length: %d\r\n\r\n%s",
  len(timeoutMsg), timeoutMsg),
  },
  }
 
  for _, tt := range tests {
+ tt := tt
  t.Run(tt.name, func(t *testing.T) {
- var lastSpuriousLine int32
+ exitHandler := make(chan bool, 1)
+ defer close(exitHandler)
+ lastLine := make(chan int, 1)
 
  sh := HandlerFunc(func(w ResponseWriter, r *Request) {
  w.WriteHeader(404)
  w.WriteHeader(404)
  w.WriteHeader(404)
  w.WriteHeader(404)
  _, _, line, _ := runtime.Caller(0)
- atomic.StoreInt32(&lastSpuriousLine, int32(line))
-
- <-time.After(tt.sleepTime)
+ lastLine <- line
+ <-exitHandler
  })
 
+ if !tt.mustTimeout {
+ exitHandler <- true
+ }
+
  logBuf := new(bytes.Buffer)
  srvLog := log.New(logBuf, "", 0)
- th := TimeoutHandler(sh, maxTimeout, timeoutMsg)
+ // When expecting to timeout, we'll keep the duration short.
+ dur := 20 * time.Millisecond
+ if !tt.mustTimeout {
+ // Otherwise, make it arbitrarily long to reduce the risk of flakes.
+ dur = 10 * time.Second
+ }
+ th := TimeoutHandler(sh, dur, timeoutMsg)
  cst := newClientServerTest(t, h1Mode /* the test is protocol-agnostic */, th, optWithServerLog(srvLog))
  defer cst.close()
 
@@ -6379,10 +6393,12 @@ func TestTimeoutHandlerSuperfluousLogs(t *testing.T) {
  t.Fatalf("Server logs count mismatch\ngot %d, want %d\n\nGot\n%s\n", g, w, blob)
  }
 
+ lastSpuriousLine := <-lastLine
+ firstSpuriousLine := lastSpuriousLine - 3
  // Now ensure that the regexes match exactly.
  // "http: superfluous response.WriteHeader call from <fn>.func\d.\d (<curFile>:lastSpuriousLine-[1, 3]"
  for i, logEntry := range logEntries {
- wantLine := atomic.LoadInt32(&lastSpuriousLine) - 3 + int32(i)
+ wantLine := firstSpuriousLine + i
  pat := fmt.Sprintf("^http: superfluous response.WriteHeader call from %s.func\\d+.\\d+ \\(%s:%d\\)$",
  testFuncName, curFileBaseName, wantLine)
  re := regexp.MustCompile(pat)