net/http: fix memory leak in Transport

Fixes #5794

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/10747044

src/pkg/net/http/export_test.go

@@ -48,6 +48,12 @@ func (t *Transport) IdleConnCountForTesting(cacheKey string) int {
 	return len(conns)
 }
 
+func (t *Transport) IdleConnChMapSizeForTesting() int {
+	t.idleMu.Lock()
+	defer t.idleMu.Unlock()
+	return len(t.idleConnCh)
+}
+
 func NewTestTimeoutHandler(handler Handler, ch <-chan time.Time) Handler {
 	f := func() <-chan time.Time {
 		return ch

src/pkg/net/http/transport.go

@@ -217,6 +217,7 @@ func (t *Transport) CloseIdleConnections() {
 	t.idleMu.Lock()
 	m := t.idleConn
 	t.idleConn = nil
+	t.idleConnCh = nil
 	t.idleMu.Unlock()
 	if m == nil {
 		return
@@ -295,8 +296,10 @@ func (t *Transport) putIdleConn(pconn *persistConn) bool {
 		max = DefaultMaxIdleConnsPerHost
 	}
 	t.idleMu.Lock()
+
+	waitingDialer := t.idleConnCh[key]
 	select {
-	case t.idleConnCh[key] <- pconn:
+	case waitingDialer <- pconn:
 		// We're done with this pconn and somebody else is
 		// currently waiting for a conn of this type (they're
 		// actively dialing, but this conn is ready
@@ -305,6 +308,11 @@ func (t *Transport) putIdleConn(pconn *persistConn) bool {
 		t.idleMu.Unlock()
 		return true
 	default:
+		if waitingDialer != nil {
+			// They had populated this, but their dial won
+			// first, so we can clean up this map entry.
+			delete(t.idleConnCh, key)
+		}
 	}
 	if t.idleConn == nil {
 		t.idleConn = make(map[string][]*persistConn)
@@ -324,7 +332,13 @@ func (t *Transport) putIdleConn(pconn *persistConn) bool {
 	return true
 }
 
+// getIdleConnCh returns a channel to receive and return idle
+// persistent connection for the given connectMethod.
+// It may return nil, if persistent connections are not being used.
 func (t *Transport) getIdleConnCh(cm *connectMethod) chan *persistConn {
+	if t.DisableKeepAlives {
+		return nil
+	}
 	key := cm.key()
 	t.idleMu.Lock()
 	defer t.idleMu.Unlock()

src/pkg/net/http/transport_test.go

@@ -1575,6 +1575,41 @@ func TestProxyFromEnvironment(t *testing.T) {
 	}
 }
 
+func TestIdleConnChannelLeak(t *testing.T) {
+	var mu sync.Mutex
+	var n int
+
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		mu.Lock()
+		n++
+		mu.Unlock()
+	}))
+	defer ts.Close()
+
+	tr := &Transport{
+		Dial: func(netw, addr string) (net.Conn, error) {
+			return net.Dial(netw, ts.Listener.Addr().String())
+		},
+	}
+	defer tr.CloseIdleConnections()
+
+	c := &Client{Transport: tr}
+
+	// First, without keep-alives.
+	for _, disableKeep := range []bool{true, false} {
+		tr.DisableKeepAlives = disableKeep
+		for i := 0; i < 5; i++ {
+			_, err := c.Get(fmt.Sprintf("http://foo-host-%d.tld/", i))
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+		if got := tr.IdleConnChMapSizeForTesting(); got != 0 {
+			t.Fatalf("ForDisableKeepAlives = %v, map size = %d; want 0", disableKeep, got)
+		}
+	}
+}
+
 // rgz is a gzip quine that uncompresses to itself.
 var rgz = []byte{
 	0x1f, 0x8b, 0x08, 0x08, 0x00, 0x00, 0x00, 0x00,