net: close connection in localServer teardown

The transponder sets up a deferred close on accepted connections which
is fine after the client reads all data. However there are no mutexes
nor channels to block the transponder from closing. If the scheduler
runs close before the client read, it will cause an EOF failure.

Fixes #42720

Change-Id: Ic21b476c5efc9265a80a2c6f8484efdb5af66405
Reviewed-on: https://go-review.googlesource.com/c/go/+/273672
Run-TryBot: Meng Zhuo <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Trust: Meng Zhuo <[email protected]>
Reviewed-by: Damien Neil <[email protected]>

src/net/conn_test.go

@@ -32,7 +32,7 @@ func TestConnAndListener(t *testing.T) {
 		}
 		defer ls.teardown()
 		ch := make(chan error, 1)
-		handler := func(ls *localServer, ln Listener) { transponder(ln, ch) }
+		handler := func(ls *localServer, ln Listener) { ls.transponder(ln, ch) }
 		if err := ls.buildup(handler); err != nil {
 			t.Fatal(err)
 		}

src/net/mockserver_test.go

@@ -87,6 +87,7 @@ type localServer struct {
 	lnmu sync.RWMutex
 	Listener
 	done chan bool // signal that indicates server stopped
+	cl   []Conn    // accepted connection list
 }
 
 func (ls *localServer) buildup(handler func(*localServer, Listener)) error {
@@ -99,18 +100,23 @@ func (ls *localServer) buildup(handler func(*localServer, Listener)) error {
 
 func (ls *localServer) teardown() error {
 	ls.lnmu.Lock()
+	defer ls.lnmu.Unlock()
 	if ls.Listener != nil {
 		network := ls.Listener.Addr().Network()
 		address := ls.Listener.Addr().String()
 		ls.Listener.Close()
+		for _, c := range ls.cl {
+			if err := c.Close(); err != nil {
+				return err
+			}
+		}
 		<-ls.done
 		ls.Listener = nil
 		switch network {
 		case "unix", "unixpacket":
 			os.Remove(address)
 		}
 	}
-	ls.lnmu.Unlock()
 	return nil
 }
 
@@ -203,7 +209,7 @@ func newDualStackServer() (*dualStackServer, error) {
 	}, nil
 }
 
-func transponder(ln Listener, ch chan<- error) {
+func (ls *localServer) transponder(ln Listener, ch chan<- error) {
 	defer close(ch)
 
 	switch ln := ln.(type) {
@@ -220,7 +226,7 @@ func transponder(ln Listener, ch chan<- error) {
 		ch <- err
 		return
 	}
-	defer c.Close()
+	ls.cl = append(ls.cl, c)
 
 	network := ln.Addr().Network()
 	if c.LocalAddr().Network() != network || c.RemoteAddr().Network() != network {

src/net/protoconn_test.go

@@ -72,7 +72,7 @@ func TestTCPConnSpecificMethods(t *testing.T) {
 		t.Fatal(err)
 	}
 	ch := make(chan error, 1)
-	handler := func(ls *localServer, ln Listener) { transponder(ls.Listener, ch) }
+	handler := func(ls *localServer, ln Listener) { ls.transponder(ls.Listener, ch) }
 	ls, err := (&streamListener{Listener: ln}).newLocalServer()
 	if err != nil {
 		t.Fatal(err)

src/net/server_test.go

@@ -86,7 +86,7 @@ func TestTCPServer(t *testing.T) {
 			}
 			for i := 0; i < N; i++ {
 				ch := tpchs[i]
-				handler := func(ls *localServer, ln Listener) { transponder(ln, ch) }
+				handler := func(ls *localServer, ln Listener) { ls.transponder(ln, ch) }
 				if err := lss[i].buildup(handler); err != nil {
 					t.Fatal(err)
 				}
@@ -178,7 +178,7 @@ func TestUnixAndUnixpacketServer(t *testing.T) {
 		}
 		for i := 0; i < N; i++ {
 			ch := tpchs[i]
-			handler := func(ls *localServer, ln Listener) { transponder(ln, ch) }
+			handler := func(ls *localServer, ln Listener) { ls.transponder(ln, ch) }
 			if err := lss[i].buildup(handler); err != nil {
 				t.Fatal(err)
 			}

src/net/tcpsock_test.go

@@ -393,7 +393,7 @@ func TestIPv6LinkLocalUnicastTCP(t *testing.T) {
 		}
 		defer ls.teardown()
 		ch := make(chan error, 1)
-		handler := func(ls *localServer, ln Listener) { transponder(ln, ch) }
+		handler := func(ls *localServer, ln Listener) { ls.transponder(ln, ch) }
 		if err := ls.buildup(handler); err != nil {
 			t.Fatal(err)
 		}