3 files changed, 74 insertions, 5 deletions

diff --git a/src/net/http/export_test.go b/src/net/http/export_test.go
index e5bc02afa..a6980b538 100644
--- a/src/net/http/export_test.go
+++ b/src/net/http/export_test.go
@@ -57,6 +57,26 @@ func (t *Transport) IdleConnChMapSizeForTesting() int {
 	return len(t.idleConnCh)
 }
 
+func (t *Transport) IsIdleForTesting() bool {
+	t.idleMu.Lock()
+	defer t.idleMu.Unlock()
+	return t.wantIdle
+}
+
+func (t *Transport) RequestIdleConnChForTesting() {
+	t.getIdleConnCh(connectMethod{nil, "http", "example.com"})
+}
+
+func (t *Transport) PutIdleTestConn() bool {
+	c, _ := net.Pipe()
+	return t.putIdleConn(&persistConn{
+		t:        t,
+		conn:     c,                   // dummy
+		closech:  make(chan struct{}), // so it can be closed
+		cacheKey: connectMethodKey{"", "http", "example.com"},
+	})
+}
+
 func NewTestTimeoutHandler(handler Handler, ch <-chan time.Time) Handler {
 	f := func() <-chan time.Time {
 		return ch
diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index f1a683752..70e574fc8 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -47,13 +47,16 @@ const DefaultMaxIdleConnsPerHost = 2
 // HTTPS, and HTTP proxies (for either HTTP or HTTPS with CONNECT).
 // Transport can also cache connections for future re-use.
 type Transport struct {
-	idleMu      sync.Mutex
-	idleConn    map[connectMethodKey][]*persistConn
-	idleConnCh  map[connectMethodKey]chan *persistConn
+	idleMu     sync.Mutex
+	wantIdle   bool // user has requested to close all idle conns
+	idleConn   map[connectMethodKey][]*persistConn
+	idleConnCh map[connectMethodKey]chan *persistConn
+
 	reqMu       sync.Mutex
 	reqCanceler map[*Request]func()
-	altMu       sync.RWMutex
-	altProto    map[string]RoundTripper // nil or map of URI scheme => RoundTripper
+
+	altMu    sync.RWMutex
+	altProto map[string]RoundTripper // nil or map of URI scheme => RoundTripper
 
 	// Proxy specifies a function to return a proxy for a given
 	// Request. If the function returns a non-nil error, the
@@ -262,6 +265,7 @@ func (t *Transport) CloseIdleConnections() {
 	m := t.idleConn
 	t.idleConn = nil
 	t.idleConnCh = nil
+	t.wantIdle = true
 	t.idleMu.Unlock()
 	for _, conns := range m {
 		for _, pconn := range conns {
@@ -385,6 +389,11 @@ func (t *Transport) putIdleConn(pconn *persistConn) bool {
 			delete(t.idleConnCh, key)
 		}
 	}
+	if t.wantIdle {
+		t.idleMu.Unlock()
+		pconn.close()
+		return false
+	}
 	if t.idleConn == nil {
 		t.idleConn = make(map[connectMethodKey][]*persistConn)
 	}
@@ -413,6 +422,7 @@ func (t *Transport) getIdleConnCh(cm connectMethod) chan *persistConn {
 	key := cm.key()
 	t.idleMu.Lock()
 	defer t.idleMu.Unlock()
+	t.wantIdle = false
 	if t.idleConnCh == nil {
 		t.idleConnCh = make(map[connectMethodKey]chan *persistConn)
 	}
diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index 2ffd35979..66fcc3c7d 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -2177,6 +2177,45 @@ func TestRoundTripReturnsProxyError(t *testing.T) {
 	}
 }
 
+// tests that putting an idle conn after a call to CloseIdleConns does return it
+func TestTransportCloseIdleConnsThenReturn(t *testing.T) {
+	tr := &Transport{}
+	wantIdle := func(when string, n int) bool {
+		got := tr.IdleConnCountForTesting("|http|example.com") // key used by PutIdleTestConn
+		if got == n {
+			return true
+		}
+		t.Errorf("%s: idle conns = %d; want %d", when, got, n)
+		return false
+	}
+	wantIdle("start", 0)
+	if !tr.PutIdleTestConn() {
+		t.Fatal("put failed")
+	}
+	if !tr.PutIdleTestConn() {
+		t.Fatal("second put failed")
+	}
+	wantIdle("after put", 2)
+	tr.CloseIdleConnections()
+	if !tr.IsIdleForTesting() {
+		t.Error("should be idle after CloseIdleConnections")
+	}
+	wantIdle("after close idle", 0)
+	if tr.PutIdleTestConn() {
+		t.Fatal("put didn't fail")
+	}
+	wantIdle("after second put", 0)
+
+	tr.RequestIdleConnChForTesting() // should toggle the transport out of idle mode
+	if tr.IsIdleForTesting() {
+		t.Error("shouldn't be idle after RequestIdleConnChForTesting")
+	}
+	if !tr.PutIdleTestConn() {
+		t.Fatal("after re-activation")
+	}
+	wantIdle("after final put", 1)
+}
+
 func wantBody(res *http.Response, err error, want string) error {
 	if err != nil {
 		return err