add getter for session transport protocol

This is useful when diagnosing issues with SockJS that may be related to what
kind of protocol a connection is using.

sockjs/session.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"io"
 	"net/http"
+	"path"
 	"sync"
 	"time"
 )
@@ -222,6 +223,11 @@ func (s *session) Send(msg string) error {
 
 func (s *session) ID() string { return s.id }
 
+func (s *session) Protocol() string {
+	protocol := path.Base(s.req.URL.Path)
+	return protocol
+}
+
 func (s *session) GetSessionState() SessionState {
 	s.RLock()
 	defer s.RUnlock()

sockjs/sockjs.go

@@ -6,6 +6,8 @@ import "net/http"
 type Session interface {
 	// Id returns a session id
 	ID() string
+	// Protocol used for the transport
+	Protocol() string
 	// Request returns the first http request
 	Request() *http.Request
 	// Recv reads one text frame from session