net/http/httptest: make Server.CloseClientConnections wait for conns to close

httptest.Server was rewritten during Go 1.6, but
CloseClientConnections was accidentally made async in the rewrite and
not caught due to lack of tests.

Restore the Go 1.5 behavior and add tests.

Fixes #14290
Updates #14291

Change-Id: I14f01849066785053ccca2373931bc82d78c0a13
Reviewed-on: https://go-review.googlesource.com/19432
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/net/http/httptest/server.go

@@ -202,10 +202,31 @@ func (s *Server) logCloseHangDebugInfo() {
 
 // CloseClientConnections closes any open HTTP connections to the test Server.
 func (s *Server) CloseClientConnections() {
+	var conns int
+	ch := make(chan bool)
+
 	s.mu.Lock()
-	defer s.mu.Unlock()
 	for c := range s.conns {
-		s.closeConn(c)
+		conns++
+		s.closeConnChan(c, ch)
+	}
+	s.mu.Unlock()
+
+	// Wait for outstanding closes to finish.
+	//
+	// Out of paranoia for making a late change in Go 1.6, we
+	// bound how long this can wait, since golang.org/issue/14291
+	// isn't fully understood yet. At least this should only be used
+	// in tests.
+	timer := time.NewTimer(5 * time.Second)
+	defer timer.Stop()
+	for i := 0; i < conns; i++ {
+		select {
+		case <-ch:
+		case <-timer.C:
+			// Too slow. Give up.
+			return
+		}
 	}
 }
 
@@ -267,9 +288,13 @@ func (s *Server) wrap() {
 	}
 }
 
-// closeConn closes c. Except on plan9, which is special. See comment below.
+// closeConn closes c.
 // s.mu must be held.
-func (s *Server) closeConn(c net.Conn) {
+func (s *Server) closeConn(c net.Conn) { s.closeConnChan(c, nil) }
+
+// closeConnChan is like closeConn, but takes an optional channel to receive a value
+// when the goroutine closing c is done.
+func (s *Server) closeConnChan(c net.Conn, done chan<- bool) {
 	if runtime.GOOS == "plan9" {
 		// Go's Plan 9 net package isn't great at unblocking reads when
 		// their underlying TCP connections are closed.  Don't trust
@@ -278,7 +303,21 @@ func (s *Server) closeConn(c net.Conn) {
 		// resources if the syscall doesn't end up returning. Oh well.
 		s.forgetConn(c)
 	}
-	go c.Close()
+
+	// Somewhere in the chaos of https://golang.org/cl/15151 we found that
+	// some types of conns were blocking in Close too long (or deadlocking?)
+	// and we had to call Close in a goroutine. I (bradfitz) forget what
+	// that was at this point, but I suspect it was *tls.Conns, which
+	// were later fixed in https://golang.org/cl/18572, so this goroutine
+	// is _probably_ unnecessary now. But it's too late in Go 1.6 too remove
+	// it with confidence.
+	// TODO(bradfitz): try to remove it for Go 1.7. (golang.org/issue/14291)
+	go func() {
+		c.Close()
+		if done != nil {
+			done <- true
+		}
+	}()
 }
 
 // forgetConn removes c from the set of tracked conns and decrements it from the

src/net/http/httptest/server_test.go

@@ -84,3 +84,17 @@ func TestServerCloseBlocking(t *testing.T) {
 
 	ts.Close() // test we don't hang here forever.
 }
+
+// Issue 14290
+func TestServerCloseClientConnections(t *testing.T) {
+	var s *Server
+	s = NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		s.CloseClientConnections()
+	}))
+	defer s.Close()
+	res, err := http.Get(s.URL)
+	if err == nil {
+		res.Body.Close()
+		t.Fatal("Unexpected response: %#v", res)
+	}
+}