added option for dialer to follow redirects

dialer.go

@@ -129,6 +129,10 @@ type Dialer struct {
 	// Note that for debugging purposes of an http handshake (e.g. sent request
 	// and received response), there is an wsutil.DebugDialer struct.
 	WrapConn func(conn net.Conn) net.Conn
+
+	// FollowRedirects is a boolean specifying if to follow redirects
+	// Redirects are any 3xx responses coming from the server
+	FollowRedirects bool
 }
 
 // Dial connects to the url host and upgrades connection to WebSocket.
@@ -188,7 +192,10 @@ func (d Dialer) Dial(ctx context.Context, urlstr string) (conn net.Conn, br *buf
 	}
 
 	br, hs, err = d.Upgrade(conn, u)
-
+
+	if e, ok := err.(RedirectError); ok {
+		return d.Dial(ctx, string(e))
+	}
 	return
 }
 
@@ -332,19 +339,24 @@ func (d Dialer) Upgrade(conn io.ReadWriter, u *url.URL) (br *bufio.Reader, hs Ha
 		err = ErrHandshakeBadProtocol
 		return
 	}
+	var isRedirect bool
 	if resp.status != 101 {
-		err = StatusError(resp.status)
-		if onStatusError := d.OnStatusError; onStatusError != nil {
-			// Invoke callback with multireader of status-line bytes br.
-			onStatusError(resp.status, resp.reason,
-				io.MultiReader(
-					bytes.NewReader(sl),
-					strings.NewReader(crlf),
-					br,
-				),
-			)
+		if resp.status >= 300 && resp.status < 400 && d.FollowRedirects {
+			isRedirect = true // Cant return, need to process Location header
+		} else {
+			err = StatusError(resp.status)
+			if onStatusError := d.OnStatusError; onStatusError != nil {
+				// Invoke callback with multireader of status-line bytes br.
+				onStatusError(resp.status, resp.reason,
+					io.MultiReader(
+						bytes.NewReader(sl),
+						strings.NewReader(crlf),
+						br,
+					),
+				)
+			}
+			return
 		}
-		return
 	}
 	// If response status is 101 then we expect all technical headers to be
 	// valid. If not, then we stop processing response without giving user
@@ -369,6 +381,12 @@ func (d Dialer) Upgrade(conn io.ReadWriter, u *url.URL) (br *bufio.Reader, hs Ha
 		}
 
 		switch btsToString(k) {
+		case headerLocationCanonical:
+			if d.FollowRedirects && isRedirect {
+				err = RedirectError(string(v))
+				return
+			}
+
 		case headerUpgradeCanonical:
 			headerSeen |= headerSeenUpgrade
 			if !bytes.Equal(v, specHeaderValueUpgrade) && !bytes.EqualFold(v, specHeaderValueUpgrade) {
@@ -457,6 +475,12 @@ func (s StatusError) Error() string {
 	return "unexpected HTTP response status: " + strconv.Itoa(int(s))
 }
 
+type RedirectError string
+
+func (r RedirectError) Error() string {
+	return "received redirect from server to: " + string(r)
+}
+
 func isTimeoutError(err error) bool {
 	t, ok := err.(net.Error)
 	return ok && t.Timeout()

http.go

@@ -42,6 +42,7 @@ var (
 	headerHost          = "Host"
 	headerUpgrade       = "Upgrade"
 	headerConnection    = "Connection"
+	headerLocation      = "Location"
 	headerSecVersion    = "Sec-WebSocket-Version"
 	headerSecProtocol   = "Sec-WebSocket-Protocol"
 	headerSecExtensions = "Sec-WebSocket-Extensions"
@@ -51,6 +52,7 @@ var (
 	headerHostCanonical          = textproto.CanonicalMIMEHeaderKey(headerHost)
 	headerUpgradeCanonical       = textproto.CanonicalMIMEHeaderKey(headerUpgrade)
 	headerConnectionCanonical    = textproto.CanonicalMIMEHeaderKey(headerConnection)
+	headerLocationCanonical      = textproto.CanonicalMIMEHeaderKey(headerLocation)
 	headerSecVersionCanonical    = textproto.CanonicalMIMEHeaderKey(headerSecVersion)
 	headerSecProtocolCanonical   = textproto.CanonicalMIMEHeaderKey(headerSecProtocol)
 	headerSecExtensionsCanonical = textproto.CanonicalMIMEHeaderKey(headerSecExtensions)