feat(ssh): simplify web terminal flow by control messages as JSON requests

All control messages are now sent as JSON requests, including a new
message type exclusively for error reporting. WebSocket binary data is
now reserved for terminal output, simplifying the protocol and improving
separation of concerns.

Author: henrybarreto

ssh/web/conn.go

@@ -90,6 +90,22 @@ func (c *Conn) WriteMessage(message *Message) (int, error) {
 	return wrote, nil
 }
 
+func (c *Conn) WriteBinary(data []byte) (int, error) {
+	socket := c.Socket.(*websocket.Conn)
+
+	frame, err := socket.NewFrameWriter(websocket.BinaryFrame)
+	if err != nil {
+		return 0, errors.Join(ErrConnWriteMessageFailedFrame, err)
+	}
+
+	wrote, err := frame.Write(data)
+	if err != nil {
+		return wrote, errors.Join(ErrConnReadMessageSocketWrite, err)
+	}
+
+	return wrote, nil
+}
+
 func (c *Conn) Read(buffer []byte) (int, error) {
 	return c.Socket.Read(buffer)
 }

ssh/web/errors.go

@@ -36,10 +36,11 @@ var (
 )
 
 var (
-	ErrConnReadMessageSocketRead  = errors.New("failed to read the message from socket")
-	ErrConnReadMessageSocketWrite = errors.New("failed to write the message's data to socket")
-	ErrConnReadMessageJSONInvalid = errors.New("failed to parse the message from json")
-	ErrConnReadMessageKindInvalid = errors.New("this kind of message is invalid")
+	ErrConnReadMessageSocketRead   = errors.New("failed to read the message from socket")
+	ErrConnReadMessageSocketWrite  = errors.New("failed to write the message's data to socket")
+	ErrConnReadMessageJSONInvalid  = errors.New("failed to parse the message from json")
+	ErrConnReadMessageKindInvalid  = errors.New("this kind of message is invalid")
+	ErrConnWriteMessageFailedFrame = errors.New("failed to create frame")
 )
 
 var (

ssh/web/messages.go

@@ -11,6 +11,9 @@ const (
 	// messageKindSignature is the identifier to a signature message. This kind of message contains the data to be
 	// signed by the user's private key.
 	messageKindSignature
+	// messageKindError is the identifier to output an erro rmessage. This kind of message contains data to be show
+	// in terminal for information propose.
+	messageKindError
 )
 
 type Message struct {

ssh/web/session.go

@@ -264,7 +264,7 @@ func newSession(ctx context.Context, cache cache.Cache, conn *Conn, creds *Crede
 	return nil
 }
 
-func redirToWs(rd io.Reader, ws io.ReadWriter) error {
+func redirToWs(rd io.Reader, ws *Conn) error {
 	var buf [32 * 1024]byte
 	var start, end, buflen int
 
@@ -292,7 +292,7 @@ func redirToWs(rd io.Reader, ws io.ReadWriter) error {
 			}
 		}
 
-		if _, err = ws.Write([]byte(string(bytes.Runes(buf[0:end])))); err != nil {
+		if _, err = ws.WriteBinary([]byte(string(bytes.Runes(buf[0:end])))); err != nil {
 			return err
 		}
 

ssh/web/web.go

@@ -9,6 +9,7 @@ import (
 	"github.com/shellhub-io/shellhub/pkg/cache"
 	"github.com/shellhub-io/shellhub/ssh/pkg/magickey"
 	"github.com/shellhub-io/shellhub/ssh/web/pkg/token"
+	log "github.com/sirupsen/logrus"
 	"golang.org/x/net/websocket"
 )
 
@@ -69,7 +70,14 @@ func NewSSHServerBridge(router *echo.Echo, cache cache.Cache) {
 
 		// exit sends the error's message to the client on the browser.
 		exit := func(wsconn *websocket.Conn, err error) {
-			wsconn.Write([]byte(err.Error())) //nolint:errcheck
+			buffer, err := json.Marshal(Message{
+				Kind: messageKindError,
+				Data: err.Error(),
+			})
+
+			log.WithError(err).Error("failed to parsing the error message on web terminal")
+
+			wsconn.Write(buffer) //nolint:errcheck
 		}
 
 		token, err := getToken(wsconn.Request())