add option to delete board if the last user left

resolves Delete Board as the last user leaves lovasoa#199

README.md

@@ -86,6 +86,7 @@ You can see a list of these variables in [`configuration.js`](./server/configura
 Some important environment variables are :
  - `WBO_HISTORY_DIR` : configures the directory where the boards are saved. Defaults to `./server-data/`.
  - `WBO_MAX_EMIT_COUNT` : the maximum number of messages that a client can send per unit of time. Increase this value if you want smoother drawings, at the expense of being susceptible to denial of service attacks if your server does not have enough processing power. By default, the units of this quantity are messages per 4 seconds, and the default value is `192`.
+- `DELETE_ON_LEAVE` : (default: `false` / `true`) whether the board gets deleted if the last user leaves or not
 
 ## Troubleshooting
 

client-data/js/board.js

@@ -48,6 +48,7 @@ Tools.drawingEvent = true;
 Tools.showMarker = true;
 Tools.showOtherCursors = true;
 Tools.showMyCursor = true;
+Tools.metadata = {users: 1};
 
 Tools.isIE = /MSIE|Trident/.test(window.navigator.userAgent);
 
@@ -78,6 +79,14 @@ Tools.connect = function () {
 		});
 	});
 
+    //Receive metadata about the board from server
+	this.socket.on("metadata", function (msg) {
+        if (!message.users) {
+            console.error("Received a badly formatted message (no users). ", message);
+        }
+        Object.assign(Tools.metadata, message)
+	});
+
 	this.socket.on("reconnect", function onReconnection() {
 		Tools.socket.emit('joinboard', Tools.boardName);
 	});
@@ -704,4 +713,15 @@ Tools.svg.height.baseVal.value = document.body.clientHeight;
 	document.removeEventListener("mouseup", menu_mouseup);
     }
     menu.addEventListener("mousedown", menu_mousedown);
+    // Ask to save before leave 
+    if(Tools.server_config.DELETE_ON_LEAVE){
+        window.onbeforeunload = function() {
+            if(Tools.metadata.users === 1) {
+            // TODO: Add config from other PR
+            // if(Tools.metadata.saved === true) {
+                return 'The board will be deleted after you leave, make sure you saved the content!';
+            }
+            return undefined;
+        }
+    }
 })()

server/boardData.js

@@ -261,6 +261,13 @@ class BoardData {
     }
   }
 
+  /** Deletes the board from storage
+   */
+   deleteBoard() {
+       this.board = {}
+       this.save()
+  }
+
   /** Load the data in the board from a file.
    * @param {string} name - name of the board
    */

server/client_configuration.js

@@ -7,4 +7,5 @@ module.exports = {
   MAX_EMIT_COUNT_PERIOD: config.MAX_EMIT_COUNT_PERIOD,
   BLOCKED_TOOLS: config.BLOCKED_TOOLS,
   AUTO_FINGER_WHITEOUT: config.AUTO_FINGER_WHITEOUT,
+  DELETE_ON_LEAVE: config.DELETE_ON_LEAVE,
 };

server/configuration.js

@@ -45,4 +45,6 @@ module.exports = {
   /** Automatically switch to White-out on finger touch after drawing
       with Pencil using a stylus. Only supported on iPad with Apple Pencil. */
   AUTO_FINGER_WHITEOUT: process.env['AUTO_FINGER_WHITEOUT'] !== "disabled",
-};
+  /** Automatically delete boards as soon as the last user leaves the board */
+  DELETE_ON_LEAVE: process.env['DELETE_ON_LEAVE'] === "true",
+};

server/sockets.js

@@ -63,6 +63,7 @@ function socketConnection(socket) {
 
     var board = await getBoard(name);
     board.users.add(socket.id);
+    broadcastMetaData(socket, board.name, { users: board.users.size })
     log("board joined", { board: board.name, users: board.users.size });
     return board;
   }
@@ -141,15 +142,24 @@ function socketConnection(socket) {
         board.users.delete(socket.id);
         var userCount = board.users.size;
         log("disconnection", { board: board.name, users: board.users.size });
+        broadcastMetaData(socket, board.name, { users: board.users.size })
         if (userCount === 0) {
-          board.save();
+            if(config.DELETE_ON_LEAVE){
+                board.deleteBoard()
+            } else {
+                board.save();
+            }
           delete boards[room];
         }
       }
     });
   });
 }
 
+function broadcastMetaData(socket, boardName, metaData) {
+    socket.broadcast.to(boardName).emit("metadata", metaData);
+}
+
 function handleMessage(boardName, message, socket) {
   if (message.tool === "Cursor") {
     message.socket = socket.id;