Expose tls connection state in http response

client.go

@@ -317,6 +317,7 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		}
 	}()
 
+	var tlsState *tls.ConnectionState
 	if u.Scheme == "https" && d.NetDialTLSContext == nil {
 		// If NetDialTLSContext is set, assume that the TLS handshake has already been done
 
@@ -330,13 +331,18 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		if trace != nil && trace.TLSHandshakeStart != nil {
 			trace.TLSHandshakeStart()
 		}
-		err := doHandshake(ctx, tlsConn, cfg)
-		if trace != nil && trace.TLSHandshakeDone != nil {
-			trace.TLSHandshakeDone(tlsConn.ConnectionState(), err)
-		}
 
-		if err != nil {
+		if err := doHandshake(ctx, tlsConn, cfg); err != nil {
+			if trace != nil && trace.TLSHandshakeDone != nil {
+				trace.TLSHandshakeDone(tls.ConnectionState{}, err)
+			}
 			return nil, nil, err
+		} else {
+			cs := tlsConn.ConnectionState()
+			if trace != nil && trace.TLSHandshakeDone != nil {
+				trace.TLSHandshakeDone(cs, nil)
+			}
+			tlsState = &cs
 		}
 	}
 
@@ -374,6 +380,10 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		}
 	}
 
+	if resp.TLS == nil && tlsState != nil {
+		resp.TLS = tlsState
+	}
+
 	if resp.StatusCode != 101 ||
 		!tokenListContainsValue(resp.Header, "Upgrade", "websocket") ||
 		!tokenListContainsValue(resp.Header, "Connection", "upgrade") ||

client_server_test.go

@@ -330,6 +330,25 @@ func TestDialTLS(t *testing.T) {
 	sendRecv(t, ws)
 }
 
+func TestDialTLSConnState(t *testing.T) {
+	s := newTLSServer(t)
+	defer s.Close()
+
+	d := cstDialer
+	d.TLSClientConfig = &tls.Config{RootCAs: rootCAs(t, s.Server)}
+	ws, resp, err := d.Dial(s.URL, nil)
+	if err != nil {
+		t.Fatalf("Dial: %v", err)
+	}
+	if resp.TLS == nil {
+		t.Errorf("http response tls is nil")
+	} else if len(resp.TLS.PeerCertificates) == 0 {
+		t.Errorf("http response PeerCertificates count is 0")
+	}
+	defer ws.Close()
+	sendRecv(t, ws)
+}
+
 func TestDialTimeout(t *testing.T) {
 	s := newServer(t)
 	defer s.Close()