Adjusted comms fix to be independent of latency

Previously, the comms fix depended on the connected user handshaking
on the endCall message, which gives a tiny window where another user
could potentially reconnect and send out the joinRoom message before
cleanup of the previous call is finished.

This change places the room leaving algo before the endCall message
within the same hook as the disconnecting message, which should help
mitigate this latency window issue by preventing messages from
propagating to the frontend while its still performing its cleanup.

Author: WZWren

comms/server.js

@@ -15,9 +15,30 @@ const io = require("socket.io")(server, {
 io.on("connection", (socket) => {
   // emit endCall to the room it was in.
   socket.on("disconnecting", () => {
-    socket.to(Array.from(socket.rooms))
-      .except(socket.id)
-      .emit("endCall");
+    // for each room in the disconnecting socket...
+    socket.rooms.forEach((target) => {
+      // ignoring the room matching its own id...
+      if (target === socket.id) {
+        return;
+      }
+      // get the user ids within the room...
+      io.sockets.adapter.rooms
+          .get(target)
+          .forEach(
+            (id) => {
+              // and for each user id in the room not matching
+              // its own id...
+              if (id === socket.id) {
+                return;
+              }
+              // leave the target room...
+              io.sockets.sockets.get(id).leave(target);
+              console.log(id + " leaves " + target);
+              // then tell the user id to endCall.
+              io.to(id).emit("endCall");
+            }
+          );
+    });
   });
 
   // join a room and inform the peer that the other person has joined
@@ -27,11 +48,6 @@ io.on("connection", (socket) => {
     socket.to(data.target).emit("peerConnected");
   });
 
-  // leave the room - this is performed as part of a cleanup function.
-  socket.on("leaveRoom", (data) => {
-    socket.leave(data.target);
-  });
-
   // propagate the socket events for starting and handshaking a call forward.
   socket.on("startCall", (data) => {
     console.log(socket.id + " is starting call in "+ data.target);

peerprep/components/questionpage/CommsPanel.tsx

@@ -139,9 +139,6 @@ function CommsPanel({ className, roomId }: Props) {
 }
 
 function destroyCallListeners(roomId: string) {
-  socket.emit("leaveRoom", {
-    target: roomId,
-  });
   socket.removeAllListeners("startCall");
   socket.removeAllListeners("peerConnected");
   socket.removeAllListeners("handshakeCall");