properly close the connection with two chans: pty and ws chans

relay.go

@@ -7,6 +7,7 @@ import (
 	"net/url"
 	"os"
 	"os/exec"
+	"sync"
 	"time"
 
 	"github.com/creack/pty"
@@ -23,7 +24,9 @@ const (
 	pongWait = 10 * time.Second
 
 	// Maximum message size allowed from peer.
-	maxMessageSize = 8192
+	maxMessageSize  = 4096
+	readBufferSize  = 1024
+	WriteBufferSize = 1024
 
 	// Send pings to peer with this period. Must be less than pongWait.
 	pingPeriod = (pongWait * 9) / 10
@@ -32,6 +35,27 @@ const (
 	closeGracePeriod = 10 * time.Second
 )
 
+var host *string = nil
+
+var upgrader = websocket.Upgrader{
+	ReadBufferSize:  readBufferSize,
+	WriteBufferSize: WriteBufferSize,
+	CheckOrigin: func(r *http.Request) bool {
+		org := r.Header.Get("Origin")
+		h, err := url.Parse(org)
+
+		if err != nil {
+			return false
+		}
+
+		if (host == nil) || (*host != h.Host) {
+			log.Println("Failed origin check of ", org)
+		}
+
+		return (host != nil) && (*host == h.Host)
+	},
+}
+
 // TermConn represents the connected websocket and pty.
 // if isViewer is true
 type TermConn struct {
@@ -42,7 +66,8 @@ type TermConn struct {
 	ptmx     *os.File             // the pty that runs the command
 	cmd      *exec.Cmd            // represents the process, we need it to terminate the process
 	vchan    chan *websocket.Conn // channel to receive viewers
-	done  chan struct{}
+	ws_done  chan struct{}        // ws is closed, only close this chan in ws reader
+	pty_done chan struct{}        // pty is closed, close this chan in pty reader
 }
 
 func (tc *TermConn) createPty(cmdline []string) error {
@@ -71,31 +96,14 @@ func (tc *TermConn) createPty(cmdline []string) error {
 	return nil
 }
 
-var host *string = nil
-
-var upgrader = websocket.Upgrader{
-	ReadBufferSize:  4096,
-	WriteBufferSize: 4096,
-	CheckOrigin: func(r *http.Request) bool {
-		org := r.Header.Get("Origin")
-		h, err := url.Parse(org)
-
-		if err != nil {
-			return false
-		}
-
-		if (host == nil) || (*host != h.Host) {
-			log.Println("Failed origin check of ", org)
-		}
-
-		return (host != nil) && (*host == h.Host)
-	},
-}
-
 // Periodically send ping message to detect the status of the ws
-func (tc *TermConn) ping() {
+func (tc *TermConn) ping(wg *sync.WaitGroup) {
+	defer wg.Done()
+
 	ticker := time.NewTicker(pingPeriod)
 	defer ticker.Stop()
+
+out:
 	for {
 		select {
 		case <-ticker.C:
@@ -104,18 +112,25 @@ func (tc *TermConn) ping() {
 
 			if err != nil {
 				log.Println("Failed to write ping message:", err)
-				return
+				break out
+			}
+		case <-tc.pty_done:
+			log.Println("Exit ping routine as pty is going away")
+			break out
+
+		case <-tc.ws_done:
+			log.Println("Exit ping routine as ws is going away")
+			break out
+		}
 	}
 
-		case <-tc.done:
+	log.Println("Ping routine exited")
-			log.Println("Exit ping routine as pty/ws is going away")
-			return
-		}
-	}
 }
 
 // shovel data from websocket to pty stdin
-func (tc *TermConn) wsToPtyStdin() {
+func (tc *TermConn) wsToPtyStdin(wg *sync.WaitGroup) {
+	defer wg.Done()
+
 	tc.ws.SetReadLimit(maxMessageSize)
 
 	// set the readdeadline. The idea here is simple,
@@ -128,61 +143,94 @@ func (tc *TermConn) wsToPtyStdin() {
 		return nil
 	})
 
-	// we do not need to forward user input to viewers, only the stdout
+	bufChan := make(chan []byte)
+
+	go func() { //create a goroutine to read from ws
 		for {
 			_, buf, err := tc.ws.ReadMessage()
 
 			if err != nil {
 				log.Println("Failed to receive data from ws:", err)
+				close(bufChan) // close chan by producer
+				close(tc.ws_done)
 				break
 			}
 
-		_, err = tc.ptmx.Write(buf)
+			bufChan <- buf
+		}
+	}()
+	// we do not need to forward user input to viewers, only the stdout
+out:
+	for {
+		select {
+		case buf, ok := <-bufChan:
+			if !ok {
+				log.Println("Exit wsToPtyStdin routine pty stdin error")
+				break out
+			}
+			_, err := tc.ptmx.Write(buf)
 
 			if err != nil {
 				log.Println("Failed to send data to pty stdin: ", err)
-			break
+				break out
+			}
+		case <-tc.ws_done:
+			log.Println("Exit wsToPtyStdin routine as ws is going away")
+			break out
+		case <-tc.pty_done:
+			log.Println("Exit wsToPtyStdin routine as pty is going away")
+			break out
 		}
 	}
+
+	log.Println("wsToPtyStdin routine exited")
 }
 
 // shovel data from pty Stdout to WS
-func (tc *TermConn) ptyStdoutToWs() {
+func (tc *TermConn) ptyStdoutToWs(wg *sync.WaitGroup) {
 	var viewers []*websocket.Conn
-	readBuf := make([]byte, 4096)
-	closed := false
 
-out:
+	defer wg.Done()
+	bufChan := make(chan []byte)
+
+	go func() { //create a goroutine to read from pty
 		for {
+			readBuf := make([]byte, 1024) //pty reads in 1024 blocks
 			n, err := tc.ptmx.Read(readBuf)
 
 			if err != nil {
 				log.Println("Failed to read from pty stdout: ", err)
+				close(bufChan)
+				close(tc.pty_done)
 				break
 			}
 
+			readBuf = readBuf[:n] // slice the buffer so that it is exact the size of data read.
+			bufChan <- readBuf
+		}
+	}()
+
+out:
+	for {
 		// handle viewers, we want to use non-blocking receive
 		select {
-		case viewer := <-tc.vchan:
+		case buf, ok := <-bufChan:
-			log.Println("Received viewer")
+			if !ok {
-			viewers = append(viewers, viewer)
+				tc.ws.SetWriteDeadline(time.Now().Add(writeWait))
+				tc.ws.WriteMessage(websocket.CloseMessage,
+					websocket.FormatCloseMessage(websocket.CloseNormalClosure, "Pty closed"))
 
-		case <-tc.done:
-			log.Println("Websocket is closed by main goroutine")
-			closed = true
 				break out
-
-		default: // do not block on these two channels
 			}
-
 			// We could add ws to viewers as well (then we can use io.MultiWriter),
 			// but we want to handle errors differently
 			tc.ws.SetWriteDeadline(time.Now().Add(writeWait))
-		if err = tc.ws.WriteMessage(websocket.BinaryMessage, readBuf[0:n]); err != nil {
+			if err := tc.ws.WriteMessage(websocket.BinaryMessage, buf); err != nil {
 				log.Println("Failed to write message: ", err)
-			break
+				break out
 			}
 
+			//write to the viewer
 			for i, w := range viewers {
 				if w == nil {
 					continue
@@ -190,13 +238,27 @@ out:
 
 				// if the viewer exits, we will just ignore the error
 				w.SetWriteDeadline(time.Now().Add(viewWait))
-			if err = w.WriteMessage(websocket.BinaryMessage, readBuf[0:n]); err != nil {
+				if err := w.WriteMessage(websocket.BinaryMessage, buf); err != nil {
 					log.Println("Failed to write message to viewer: ", err)
 
 					viewers[i] = nil
 					w.Close() // we own the socket and need to close it
 				}
 			}
+
+		case viewer := <-tc.vchan:
+			log.Println("Received viewer")
+			viewers = append(viewers, viewer)
+
+		case <-tc.ws_done:
+			log.Println("Exit ptyStdoutToWs routine as ws is going away")
+			break out
+
+		case <-tc.pty_done:
+			log.Println("Exit ptyStdoutToWs routine as pty is going away")
+			break out // do not block on these two channels
+		}
+
 	}
 
 	// close the watcher
@@ -206,12 +268,7 @@ out:
 		}
 	}
 
-	if !closed { // If the error is caused by pty, try to close the socket
+	log.Println("ptyStdoutToWs routine exited")
-		tc.ws.SetWriteDeadline(time.Now().Add(writeWait))
-		tc.ws.WriteMessage(websocket.CloseMessage,
-			websocket.FormatCloseMessage(websocket.CloseNormalClosure, "Pty closed"))
-		time.Sleep(closeGracePeriod)
-	}
 }
 
 // this function should be executed by the main goroutine for the connection
@@ -247,7 +304,6 @@ func (tc *TermConn) release() {
 		}
 
 		close(tc.vchan)
-		close(tc.done)
 	}
 
 	tc.ws.Close()
@@ -270,24 +326,30 @@ func wsHandlePlayer(w http.ResponseWriter, r *http.Request) {
 	defer tc.release()
 	log.Println("\n\nCreated the websocket")
 
+	tc.ws_done = make(chan struct{})
+	tc.pty_done = make(chan struct{})
+	tc.vchan = make(chan *websocket.Conn)
+
 	if err := tc.createPty(cmdToExec); err != nil {
 		log.Println("Failed to create PTY: ", err)
 		return
 	}
 
-	tc.done = make(chan struct{})
-	tc.vchan = make(chan *websocket.Conn)
-
 	registry.addPlayer("main", &tc)
 
 	// main event loop to shovel data between ws and pty
 	// do not call ptyStdoutToWs in this goroutine, otherwise
 	// the websocket will not close. This is because ptyStdoutToWs
 	// is usually blocked in the pty.Read
-	go tc.ping()
+	var wg sync.WaitGroup
-	go tc.ptyStdoutToWs()
+	wg.Add(3)
 
-	tc.wsToPtyStdin()
+	go tc.ping(&wg)
+	go tc.ptyStdoutToWs(&wg)
+	go tc.wsToPtyStdin(&wg)
+
+	wg.Wait()
+	log.Println("Wait returned")
 }
 
 // handle websockets