From a8c6b97354ea8aaf2bc285ab03e733923b0a6fde Mon Sep 17 00:00:00 2001
From: Neil Fraser <fraser@google.com>
Date: Wed, 3 Mar 2021 10:46:16 -0800
Subject: [PATCH] Drop telnet connection when client closes (#447)

---
 connect/connectServer     | 45 ++++++++++++++++++++++++++-------------
 static/connect/connect.js | 21 ++++++++++++++++--
 2 files changed, 49 insertions(+), 17 deletions(-)

diff --git a/connect/connectServer b/connect/connectServer
index 66beb212..260131e9 100755
--- a/connect/connectServer
+++ b/connect/connectServer
@@ -61,6 +61,10 @@ const DEFAULT_CFG = {
 var Queue = function (id) {
   // Save 'this' for closures below.
   var thisQueue = this;
+  /**
+   * ID of this queue in queueList.
+   */
+  this.id = id;
   /**
    * Time that this queue was pinged by a user.  Abandoned queues are deleted.
    */
@@ -91,12 +95,7 @@ var Queue = function (id) {
    */
   this.client = new net.Socket();
 
-  this.client.on('close', function() {
-    if (queueList[id]) {
-      delete queueList[id];
-      console.log('Code City closed session ' + id);
-    }
-  });
+  this.client.on('close', this.destroy.bind(this, 'Code City closed session'));
 
   this.client.on('error', function(error) {
     console.log('TCP error for session ' + id, error);
@@ -155,6 +154,18 @@ var Queue = function (id) {
   this.client.connect(CFG.remotePort, CFG.remoteHost);
 };
 
+/**
+ * Close this queue and deregister it.
+ * @param {string} msg Console message to print (with ID appended).
+ */
+Queue.prototype.destroy = function(msg) {
+  if (queueList[this.id]) {
+    delete queueList[this.id];
+  }
+  this.client.end();
+  console.log(msg + ' ' + this.id);
+};
+
 /**
  * Load a file from disk, add substitutions, and serve to the web.
  * @param {!Object} response HTTP server response object.
@@ -278,7 +289,7 @@ function handleRequest(request, response) {
       try {
         var receivedJson = JSON.parse(requestBody);
         if (!receivedJson['q']) {
-          throw 'no queue';
+          throw Error('No queue');
         }
       } catch (e) {
         console.error('Illegal JSON');
@@ -300,6 +311,7 @@ function ping(receivedJson, response) {
   var ackMemoNum = receivedJson['ackMemoNum'];
   var cmdNum = receivedJson['cmdNum'];
   var cmds = receivedJson['cmds'];
+  var logout = receivedJson['logout'];
 
   var queue = queueList[q];
   if (!queue) {
@@ -343,11 +355,16 @@ function ping(receivedJson, response) {
     var ackCmdNextPing = false;
   }
 
-  // Wait a fifth of a second for each command,
-  // but don't wait for more than a second.
-  var delay = Math.min(delay, 1000);
-  var replyFunc = pong.bind(null, queue, response, ackCmdNextPing);
-  setTimeout(replyFunc, delay);
+  if (logout) {
+    pong(queue, response, ackCmdNextPing);
+    queue.destroy('Client disconnected');
+  } else {
+    // Wait a fifth of a second for each command,
+    // but don't wait for more than a second.
+    var delay = Math.min(delay, 1000);
+    var replyFunc = pong.bind(null, queue, response, ackCmdNextPing);
+    setTimeout(replyFunc, delay);
+  }
 }
 
 function pong(queue, response, ackCmdNextPing) {
@@ -396,9 +413,7 @@ function cleanup() {
   for (var id in queueList) {
     var queue = queueList[id];
     if (queue.lastPingTime < bestBefore) {
-      queue.client.end();
-      delete queueList[id];
-      console.log('Timeout of session ' + id);
+      queue.destroy('Timeout of session');
     }
   }
 }
diff --git a/static/connect/connect.js b/static/connect/connect.js
index d3f5ce84..d9583092 100644
--- a/static/connect/connect.js
+++ b/static/connect/connect.js
@@ -180,6 +180,17 @@ CCC.init = function() {
   CCC.displayCell = document.getElementById('displayCell');
   CCC.commandTextarea = document.getElementById('commandTextarea');
 
+  // When the user closes the tab/window, tell connect server to logout.
+  window.addEventListener('unload', function() {
+    CCC.abortPing();
+    clearTimeout(CCC.nextPingPid);
+    var sendingJson = {
+      'q': CCC.queueId_,
+      'logout': true
+    };
+    navigator.sendBeacon(CCC.PING_URL, JSON.stringify(sendingJson));
+  }, false);
+
   // When focus returns to this frame from an iframe, go to the command area.
   // This happens whenever a command link is clicked in an iframe.
   window.addEventListener('focus', function() {
@@ -411,12 +422,18 @@ CCC.sendCommand = function(commands, echo) {
   sessionStorage.setItem('commandHistory', JSON.stringify(CCC.commandHistory));
   // User is sending command, reset the ping to be frequent.
   CCC.pingInterval = CCC.MIN_PING_INTERVAL;
-  // Interrupt any in-flight ping.
+  CCC.abortPing();
+  CCC.doPing();
+};
+
+/**
+ * Interrupt any in-flight ping.
+ */
+CCC.abortPing = function() {
   if (CCC.xhrObject) {
     CCC.xhrObject.abort();
     CCC.xhrObject = null;
   }
-  CCC.doPing();
 };
 
 /**