crypto/tls: replace errClosed with net.ErrClosed

CL 250357 exported net.ErrClosed to allow more reliable detection
of closed network connection errors.  Use that error in crypto/tls
as well.

The error message is changed from "tls: use of closed connection"
to "use of closed network connection", so the code that detected such
errors by looking for that text in the error message will need to be
updated to use errors.Is(err, net.ErrClosed) instead.

Fixes #41066

Change-Id: Ic05c0ed6a4f57af2a0302d53b00851a59200be2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/256897
Reviewed-by: Katie Hockman <[email protected]>
Trust: Katie Hockman <[email protected]>
Trust: Ian Lance Taylor <[email protected]>
Run-TryBot: Katie Hockman <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: ainar-g

src/crypto/tls/conn.go

@@ -1070,7 +1070,6 @@ func (c *Conn) readHandshake() (interface{}, error) {
 }
 
 var (
-	errClosed   = errors.New("tls: use of closed connection")
 	errShutdown = errors.New("tls: protocol is shutdown")
 )
 
@@ -1080,7 +1079,7 @@ func (c *Conn) Write(b []byte) (int, error) {
 	for {
 		x := atomic.LoadInt32(&c.activeCall)
 		if x&1 != 0 {
-			return 0, errClosed
+			return 0, net.ErrClosed
 		}
 		if atomic.CompareAndSwapInt32(&c.activeCall, x, x+2) {
 			break
@@ -1285,7 +1284,7 @@ func (c *Conn) Close() error {
 	for {
 		x = atomic.LoadInt32(&c.activeCall)
 		if x&1 != 0 {
-			return errClosed
+			return net.ErrClosed
 		}
 		if atomic.CompareAndSwapInt32(&c.activeCall, x, x|1) {
 			break

src/crypto/tls/tls_test.go

@@ -569,8 +569,8 @@ func TestConnCloseBreakingWrite(t *testing.T) {
 	}
 
 	<-closeReturned
-	if err := tconn.Close(); err != errClosed {
-		t.Errorf("Close error = %v; want errClosed", err)
+	if err := tconn.Close(); err != net.ErrClosed {
+		t.Errorf("Close error = %v; want net.ErrClosed", err)
 	}
 }