Improve isTLSAlready checkv1.40.0

All conn implementations having a Handshake() error method are now seen
as a TLS conn and aren't wrapped in another tls.Client.

1 files changed, 5 insertions, 1 deletions

diff --git a/client.go b/client.go
index 0ded492..7af216c 100644
--- a/client.go
+++ b/client.go
@@ -1976,7 +1976,11 @@ func dialAddr(addr string, dial DialFunc, dialDualStack, isTLS bool, tlsConfig *
 	if conn == nil {
 		panic("BUG: DialFunc returned (nil, nil)")
 	}
-	_, isTLSAlready := conn.(*tls.Conn)
+
+	// We assume that any conn that has the Handshake() method is a TLS conn already.
+	// This doesn't cover just tls.Conn but also other TLS implementations.
+	_, isTLSAlready := conn.(interface{ Handshake() error })
+
 	if isTLS && !isTLSAlready {
 		if timeout == 0 {
 			return tls.Client(conn, tlsConfig), nil