Dialer: add optional method NetDialTLSContext (#746)

Fixes issue: https://github.com/gorilla/websocket/issues/745

With the previous interface, NetDial and NetDialContext were used for
both TLS and non-TLS TCP connections, and afterwards TLSClientConfig was
used to do the TLS handshake.

While this API works for most cases, it prevents from using more advance
authentication methods during the TLS handshake, as this is out of the
control of the user.

This commits introduces another a new dial method, NetDialTLSContext,
which is used when dialing for TLS/TCP. The code then assumes that the
handshake is done there and TLSClientConfig is not used.

This API change is fully backwards compatible and it better aligns with
net/http.Transport API, which has these two dial flavors. See:
https://pkg.go.dev/net/http#Transport

Signed-off-by: Lluis Campos <lluis.campos@northern.tech>

client.go

@@ -56,9 +56,15 @@ type Dialer struct {
 	NetDial func(network, addr string) (net.Conn, error)
 
 	// NetDialContext specifies the dial function for creating TCP connections. If
-	// NetDialContext is nil, net.DialContext is used.
+	// NetDialContext is nil, NetDial is used.
 	NetDialContext func(ctx context.Context, network, addr string) (net.Conn, error)
 
+	// NetDialTLSContext specifies the dial function for creating TLS/TCP connections. If
+	// NetDialTLSContext is nil, NetDialContext is used.
+	// If NetDialTLSContext is set, Dial assumes the TLS handshake is done there and
+	// TLSClientConfig is ignored.
+	NetDialTLSContext func(ctx context.Context, network, addr string) (net.Conn, error)
+
 	// Proxy specifies a function to return a proxy for a given
 	// Request. If the function returns a non-nil error, the
 	// request is aborted with the provided error.
@@ -67,6 +73,8 @@ type Dialer struct {
 
 	// TLSClientConfig specifies the TLS configuration to use with tls.Client.
 	// If nil, the default configuration is used.
+	// If either NetDialTLS or NetDialTLSContext are set, Dial assumes the TLS handshake
+	// is done there and TLSClientConfig is ignored.
 	TLSClientConfig *tls.Config
 
 	// HandshakeTimeout specifies the duration for the handshake to complete.
@@ -239,13 +247,32 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 	// Get network dial function.
 	var netDial func(network, add string) (net.Conn, error)
 
+	switch u.Scheme {
+	case "http":
 		if d.NetDialContext != nil {
 			netDial = func(network, addr string) (net.Conn, error) {
 				return d.NetDialContext(ctx, network, addr)
 			}
 		} else if d.NetDial != nil {
 			netDial = d.NetDial
-	} else {
+		}
+	case "https":
+		if d.NetDialTLSContext != nil {
+			netDial = func(network, addr string) (net.Conn, error) {
+				return d.NetDialTLSContext(ctx, network, addr)
+			}
+		} else if d.NetDialContext != nil {
+			netDial = func(network, addr string) (net.Conn, error) {
+				return d.NetDialContext(ctx, network, addr)
+			}
+		} else if d.NetDial != nil {
+			netDial = d.NetDial
+		}
+	default:
+		return nil, nil, errMalformedURL
+	}
+
+	if netDial == nil {
 		netDialer := &net.Dialer{}
 		netDial = func(network, addr string) (net.Conn, error) {
 			return netDialer.DialContext(ctx, network, addr)
@@ -306,7 +333,9 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		}
 	}()
 
-	if u.Scheme == "https" {
+	if u.Scheme == "https" && d.NetDialTLSContext == nil {
+		// If NetDialTLSContext is set, assume that the TLS handshake has already been done
+
 		cfg := cloneTLSConfig(d.TLSClientConfig)
 		if cfg.ServerName == "" {
 			cfg.ServerName = hostNoPort

client_server_test.go

@@ -11,6 +11,7 @@ import (
 	"crypto/x509"
 	"encoding/base64"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -920,3 +921,180 @@ func TestEmptyTracingDialWithContext(t *testing.T) {
 	defer ws.Close()
 	sendRecv(t, ws)
 }
+
+// TestNetDialConnect tests selection of dial method between NetDial, NetDialContext, NetDialTLS or NetDialTLSContext
+func TestNetDialConnect(t *testing.T) {
+
+	upgrader := Upgrader{}
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if IsWebSocketUpgrade(r) {
+			c, err := upgrader.Upgrade(w, r, http.Header{"X-Test-Host": {r.Host}})
+			if err != nil {
+				t.Fatal(err)
+			}
+			c.Close()
+		} else {
+			w.Header().Set("X-Test-Host", r.Host)
+		}
+	})
+
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	tlsServer := httptest.NewTLSServer(handler)
+	defer tlsServer.Close()
+
+	testUrls := map[*httptest.Server]string{
+		server:    "ws://" + server.Listener.Addr().String() + "/",
+		tlsServer: "wss://" + tlsServer.Listener.Addr().String() + "/",
+	}
+
+	cas := rootCAs(t, tlsServer)
+	tlsConfig := &tls.Config{
+		RootCAs:            cas,
+		ServerName:         "example.com",
+		InsecureSkipVerify: false,
+	}
+
+	tests := []struct {
+		name              string
+		server            *httptest.Server // server to use
+		netDial           func(network, addr string) (net.Conn, error)
+		netDialContext    func(ctx context.Context, network, addr string) (net.Conn, error)
+		netDialTLSContext func(ctx context.Context, network, addr string) (net.Conn, error)
+		tlsClientConfig   *tls.Config
+	}{
+
+		{
+			name:   "HTTP server, all NetDial* defined, shall use NetDialContext",
+			server: server,
+			netDial: func(network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDial should not be called")
+			},
+			netDialContext: func(_ context.Context, network, addr string) (net.Conn, error) {
+				return net.Dial(network, addr)
+			},
+			netDialTLSContext: func(_ context.Context, network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDialTLSContext should not be called")
+			},
+			tlsClientConfig: nil,
+		},
+		{
+			name:              "HTTP server, all NetDial* undefined",
+			server:            server,
+			netDial:           nil,
+			netDialContext:    nil,
+			netDialTLSContext: nil,
+			tlsClientConfig:   nil,
+		},
+		{
+			name:   "HTTP server, NetDialContext undefined, shall fallback to NetDial",
+			server: server,
+			netDial: func(network, addr string) (net.Conn, error) {
+				return net.Dial(network, addr)
+			},
+			netDialContext: nil,
+			netDialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDialTLSContext should not be called")
+			},
+			tlsClientConfig: nil,
+		},
+		{
+			name:   "HTTPS server, all NetDial* defined, shall use NetDialTLSContext",
+			server: tlsServer,
+			netDial: func(network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDial should not be called")
+			},
+			netDialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDialContext should not be called")
+			},
+			netDialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+				netConn, err := net.Dial(network, addr)
+				if err != nil {
+					return nil, err
+				}
+				tlsConn := tls.Client(netConn, tlsConfig)
+				err = tlsConn.Handshake()
+				if err != nil {
+					return nil, err
+				}
+				return tlsConn, nil
+			},
+			tlsClientConfig: nil,
+		},
+		{
+			name:   "HTTPS server, NetDialTLSContext undefined, shall fallback to NetDialContext and do handshake",
+			server: tlsServer,
+			netDial: func(network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDial should not be called")
+			},
+			netDialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+				return net.Dial(network, addr)
+			},
+			netDialTLSContext: nil,
+			tlsClientConfig:   tlsConfig,
+		},
+		{
+			name:   "HTTPS server, NetDialTLSContext and NetDialContext undefined, shall fallback to NetDial and do handshake",
+			server: tlsServer,
+			netDial: func(network, addr string) (net.Conn, error) {
+				return net.Dial(network, addr)
+			},
+			netDialContext:    nil,
+			netDialTLSContext: nil,
+			tlsClientConfig:   tlsConfig,
+		},
+		{
+			name:              "HTTPS server, all NetDial* undefined",
+			server:            tlsServer,
+			netDial:           nil,
+			netDialContext:    nil,
+			netDialTLSContext: nil,
+			tlsClientConfig:   tlsConfig,
+		},
+		{
+			name:   "HTTPS server, all NetDialTLSContext defined, dummy TlsClientConfig defined, shall not do handshake",
+			server: tlsServer,
+			netDial: func(network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDial should not be called")
+			},
+			netDialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+				return nil, errors.New("NetDialContext should not be called")
+			},
+			netDialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+				netConn, err := net.Dial(network, addr)
+				if err != nil {
+					return nil, err
+				}
+				tlsConn := tls.Client(netConn, tlsConfig)
+				err = tlsConn.Handshake()
+				if err != nil {
+					return nil, err
+				}
+				return tlsConn, nil
+			},
+			tlsClientConfig: &tls.Config{
+				RootCAs:            nil,
+				ServerName:         "badserver.com",
+				InsecureSkipVerify: false,
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		dialer := Dialer{
+			NetDial:           tc.netDial,
+			NetDialContext:    tc.netDialContext,
+			NetDialTLSContext: tc.netDialTLSContext,
+			TLSClientConfig:   tc.tlsClientConfig,
+		}
+
+		// Test websocket dial
+		c, _, err := dialer.Dial(testUrls[tc.server], nil)
+		if err != nil {
+			t.Errorf("FAILED %s, err: %s", tc.name, err.Error())
+		} else {
+			c.Close()
+		}
+	}
+}