Added mutex to avoid concurrent writes

app/app.go

@@ -14,6 +14,7 @@ import (
 	"os/exec"
 	"strconv"
 	"strings"
+	"sync"
 	"text/template"
 
 	"github.com/braintree/manners"
@@ -243,6 +244,7 @@ func (app *App) handleWS(w http.ResponseWriter, r *http.Request) {
 		connection: conn,
 		command:    cmd,
 		pty:        ptyIo,
+		writeMutex: &sync.Mutex{},
 	}
 
 	context.goHandleClient()

app/client_context.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"sync"
 	"syscall"
 	"unsafe"
 
@@ -20,6 +21,7 @@ type clientContext struct {
 	connection *websocket.Conn
 	command    *exec.Cmd
 	pty        *os.File
+	writeMutex *sync.Mutex
 }
 
 const (
@@ -96,19 +98,24 @@ func (context *clientContext) processSend() {
 
 	for {
 		size, err := context.pty.Read(buf)
-		safeMessage := base64.StdEncoding.EncodeToString([]byte(buf[:size]))
 		if err != nil {
 			log.Printf("Command exited for: %s", context.request.RemoteAddr)
 			return
 		}
-
-		err = context.connection.WriteMessage(websocket.TextMessage, append([]byte{Output}, []byte(safeMessage)...))
-		if err != nil {
+		safeMessage := base64.StdEncoding.EncodeToString([]byte(buf[:size]))
+		if err = context.write(append([]byte{Output}, []byte(safeMessage)...)); err != nil {
+			log.Printf(err.Error())
 			return
 		}
 	}
 }
 
+func (context *clientContext) write(data []byte) error {
+	context.writeMutex.Lock()
+	defer context.writeMutex.Unlock()
+	return context.connection.WriteMessage(websocket.TextMessage, data)
+}
+
 func (context *clientContext) sendInitialize() error {
 	hostname, _ := os.Hostname()
 	titleVars := ContextVars{
@@ -118,34 +125,34 @@ func (context *clientContext) sendInitialize() error {
 		RemoteAddr: context.request.RemoteAddr,
 	}
 
+	context.writeMutex.Lock()
 	writer, err := context.connection.NextWriter(websocket.TextMessage)
 	if err != nil {
+		context.writeMutex.Unlock()
 		return err
 	}
 	writer.Write([]byte{SetWindowTitle})
 	if err = context.app.titleTemplate.Execute(writer, titleVars); err != nil {
+		context.writeMutex.Unlock()
 		return err
 	}
 	writer.Close()
+	context.writeMutex.Unlock()
 
 	htermPrefs := make(map[string]interface{})
 	for key, value := range context.app.options.Preferences {
 		htermPrefs[strings.Replace(key, "_", "-", -1)] = value
 	}
 	prefs, _ := json.Marshal(htermPrefs)
-	context.connection.WriteMessage(
-		websocket.TextMessage,
-		append([]byte{SetPreferences}, prefs...),
-	)
-
+	if err := context.write(append([]byte{SetPreferences}, prefs...)); err != nil {
+		return err
+	}
 	if context.app.options.EnableReconnect {
 		reconnect, _ := json.Marshal(context.app.options.ReconnectTime)
-		context.connection.WriteMessage(
-			websocket.TextMessage,
-			append([]byte{SetReconnect}, reconnect...),
-		)
+		if err := context.write(append([]byte{SetReconnect}, reconnect...)); err != nil {
+			return err
+		}
 	}
-
 	return nil
 }
 
@@ -153,6 +160,11 @@ func (context *clientContext) processReceive() {
 	for {
 		_, data, err := context.connection.ReadMessage()
 		if err != nil {
+			log.Print(err.Error())
+			return
+		}
+		if len(data) == 0 {
+			log.Print("An error has occured")
 			return
 		}
 
@@ -168,7 +180,10 @@ func (context *clientContext) processReceive() {
 			}
 
 		case Ping:
-			context.connection.WriteMessage(websocket.TextMessage, []byte{Pong})
+			if err := context.write([]byte{Pong}); err != nil {
+				log.Print(err.Error())
+				return
+			}
 		case ResizeTerminal:
 			var args argResizeTerminal
 			err = json.Unmarshal(data[1:], &args)