net/http: make Transport.CancelRequest work for requests blocked in a dial

Fixes #6951

LGTM=josharian
R=golang-codereviews, josharian
CC=golang-codereviews
https://golang.org/cl/69280043

src/pkg/net/http/export_test.go

@@ -21,7 +21,7 @@ var ExportAppendTime = appendTime
 func (t *Transport) NumPendingRequestsForTesting() int {
 	t.reqMu.Lock()
 	defer t.reqMu.Unlock()
-	return len(t.reqConn)
+	return len(t.reqCanceler)
 }
 
 func (t *Transport) IdleConnKeysForTesting() (keys []string) {

src/pkg/net/http/transport.go

@@ -51,7 +51,7 @@ type Transport struct {
 	idleConn    map[connectMethodKey][]*persistConn
 	idleConnCh  map[connectMethodKey]chan *persistConn
 	reqMu       sync.Mutex
-	reqConn    map[*Request]*persistConn
+	reqCanceler map[*Request]func()
 	altMu       sync.RWMutex
 	altProto    map[string]RoundTripper // nil or map of URI scheme => RoundTripper
 
@@ -190,8 +190,9 @@ func (t *Transport) RoundTrip(req *Request) (resp *Response, err error) {
 	// host (for http or https), the http proxy, or the http proxy
 	// pre-CONNECTed to https server.  In any case, we'll be ready
 	// to send it requests.
-	pconn, err := t.getConn(cm)
+	pconn, err := t.getConn(req, cm)
 	if err != nil {
+		t.setReqCanceler(req, nil)
 		return nil, err
 	}
 
@@ -243,10 +244,10 @@ func (t *Transport) CloseIdleConnections() {
 // connection.
 func (t *Transport) CancelRequest(req *Request) {
 	t.reqMu.Lock()
-	pc := t.reqConn[req]
+	cancel := t.reqCanceler[req]
 	t.reqMu.Unlock()
-	if pc != nil {
-		pc.conn.Close()
+	if cancel != nil {
+		cancel()
 	}
 }
 
@@ -417,16 +418,16 @@ func (t *Transport) getIdleConn(cm connectMethod) (pconn *persistConn) {
 	}
 }
 
-func (t *Transport) setReqConn(r *Request, pc *persistConn) {
+func (t *Transport) setReqCanceler(r *Request, fn func()) {
 	t.reqMu.Lock()
 	defer t.reqMu.Unlock()
-	if t.reqConn == nil {
-		t.reqConn = make(map[*Request]*persistConn)
+	if t.reqCanceler == nil {
+		t.reqCanceler = make(map[*Request]func())
 	}
-	if pc != nil {
-		t.reqConn[r] = pc
+	if fn != nil {
+		t.reqCanceler[r] = fn
 	} else {
-		delete(t.reqConn, r)
+		delete(t.reqCanceler, r)
 	}
 }
 
@@ -441,7 +442,7 @@ func (t *Transport) dial(network, addr string) (c net.Conn, err error) {
 // specified in the connectMethod.  This includes doing a proxy CONNECT
 // and/or setting up TLS.  If this doesn't return an error, the persistConn
 // is ready to write requests to.
-func (t *Transport) getConn(cm connectMethod) (*persistConn, error) {
+func (t *Transport) getConn(req *Request, cm connectMethod) (*persistConn, error) {
 	if pc := t.getIdleConn(cm); pc != nil {
 		return pc, nil
 	}
@@ -451,6 +452,16 @@ func (t *Transport) getConn(cm connectMethod) (*persistConn, error) {
 		err error
 	}
 	dialc := make(chan dialRes)
+
+	handlePendingDial := func() {
+		if v := <-dialc; v.err == nil {
+			t.putIdleConn(v.pc)
+		}
+	}
+
+	cancelc := make(chan struct{})
+	t.setReqCanceler(req, func() { close(cancelc) })
+
 	go func() {
 		pc, err := t.dialConn(cm)
 		dialc <- dialRes{pc, err}
@@ -467,12 +478,11 @@ func (t *Transport) getConn(cm connectMethod) (*persistConn, error) {
 		// else's dial that they didn't use.
 		// But our dial is still going, so give it away
 		// when it finishes:
-		go func() {
-			if v := <-dialc; v.err == nil {
-				t.putIdleConn(v.pc)
-			}
-		}()
+		go handlePendingDial()
 		return pc, nil
+	case <-cancelc:
+		go handlePendingDial()
+		return nil, errors.New("net/http: request canceled while waiting for connection")
 	}
 }
 
@@ -732,6 +742,10 @@ func (pc *persistConn) isBroken() bool {
 	return b
 }
 
+func (pc *persistConn) cancelRequest() {
+	pc.conn.Close()
+}
+
 var remoteSideClosedFunc func(error) bool // or nil to use default
 
 func remoteSideClosed(err error) bool {
@@ -843,7 +857,7 @@ func (pc *persistConn) readLoop() {
 			alive = <-waitForBodyRead
 		}
 
-		pc.t.setReqConn(rc.req, nil)
+		pc.t.setReqCanceler(rc.req, nil)
 
 		if !alive {
 			pc.close()
@@ -910,7 +924,7 @@ var errTimeout error = &httpError{err: "net/http: timeout awaiting response head
 var errClosed error = &httpError{err: "net/http: transport closed before response was received"}
 
 func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
-	pc.t.setReqConn(req.Request, pc)
+	pc.t.setReqCanceler(req.Request, pc.cancelRequest)
 	pc.lk.Lock()
 	pc.numExpectedResponses++
 	headerFn := pc.mutateHeaderFunc
@@ -995,7 +1009,7 @@ WaitResponse:
 	pc.lk.Unlock()
 
 	if re.err != nil {
-		pc.t.setReqConn(req.Request, nil)
+		pc.t.setReqCanceler(req.Request, nil)
 	}
 	return re.res, re.err
 }

src/pkg/net/http/transport_test.go

@@ -11,9 +11,11 @@ import (
 	"bytes"
 	"compress/gzip"
 	"crypto/rand"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
+	"log"
 	"net"
 	"net/http"
 	. "net/http"
@@ -1321,6 +1323,61 @@ func TestTransportCancelRequest(t *testing.T) {
 	}
 }
 
+func TestTransportCancelRequestInDial(t *testing.T) {
+	defer afterTest(t)
+	if testing.Short() {
+		t.Skip("skipping test in -short mode")
+	}
+	var logbuf bytes.Buffer
+	eventLog := log.New(&logbuf, "", 0)
+
+	unblockDial := make(chan bool)
+	defer close(unblockDial)
+
+	inDial := make(chan bool)
+	tr := &Transport{
+		Dial: func(network, addr string) (net.Conn, error) {
+			eventLog.Println("dial: blocking")
+			inDial <- true
+			<-unblockDial
+			return nil, errors.New("nope")
+		},
+	}
+	cl := &Client{Transport: tr}
+	gotres := make(chan bool)
+	req, _ := NewRequest("GET", "http://something.no-network.tld/", nil)
+	go func() {
+		_, err := cl.Do(req)
+		eventLog.Printf("Get = %v", err)
+		gotres <- true
+	}()
+
+	select {
+	case <-inDial:
+	case <-time.After(5 * time.Second):
+		t.Fatal("timeout; never saw blocking dial")
+	}
+
+	eventLog.Printf("canceling")
+	tr.CancelRequest(req)
+
+	select {
+	case <-gotres:
+	case <-time.After(5 * time.Second):
+		panic("hang. events are: " + logbuf.String())
+		t.Fatal("timeout; cancel didn't work?")
+	}
+
+	got := logbuf.String()
+	want := `dial: blocking
+canceling
+Get = Get http://something.no-network.tld/: net/http: request canceled while waiting for connection
+`
+	if got != want {
+		t.Errorf("Got events:\n%s\nWant:\n%s", got, want)
+	}
+}
+
 // golang.org/issue/3672 -- Client can't close HTTP stream
 // Calling Close on a Response.Body used to just read until EOF.
 // Now it actually closes the TCP connection.