From 76a1c8fa1d1bf97d93fc84b44b6d5bff6270c7cb Mon Sep 17 00:00:00 2001
From: Radon Rosborough <radon.neon@gmail.com>
Date: Sun, 7 Jun 2020 16:24:45 -0600
Subject: [PATCH] Automatic reconnect to server with exp backoff

---
 frontend/src/app.ts | 109 +++++++++++++++++++++++++-------------------
 1 file changed, 63 insertions(+), 46 deletions(-)

diff --git a/frontend/src/app.ts b/frontend/src/app.ts
index b4c693e..206180b 100644
--- a/frontend/src/app.ts
+++ b/frontend/src/app.ts
@@ -14,56 +14,73 @@ term.open(document.getElementById("terminal"));
 fitAddon.fit();
 window.addEventListener("resize", () => fitAddon.fit());
 
-const socket = new WebSocket(
-  (document.location.protocol === "http:" ? "ws://" : "wss://") +
-    document.location.host +
-    `/api/v1/ws?lang=${lang}`
-);
+const initialRetryDelayMs = 200;
+let retryDelayMs = initialRetryDelayMs;
 
-socket.addEventListener("open", () =>
-  console.log("Successfully connected to server")
-);
-socket.addEventListener("message", (event) => {
-  let message: any;
-  try {
-    message = JSON.parse(event.data);
-  } catch (err) {
-    console.error("Malformed message from server:", event.data);
-    return;
-  }
-  switch (message?.event) {
-    case "terminalClear":
-      term.reset();
+function tryConnect() {
+  console.log("Connecting to server...");
+  socket = new WebSocket(
+    (document.location.protocol === "http:" ? "ws://" : "wss://") +
+      document.location.host +
+      `/api/v1/ws?lang=${lang}`
+  );
+  socket.addEventListener("open", () => {
+    retryDelayMs = initialRetryDelayMs;
+    console.log("Successfully connected to server");
+  });
+  socket.addEventListener("message", (event: MessageEvent) => {
+    let message: any;
+    try {
+      message = JSON.parse(event.data);
+    } catch (err) {
+      console.error("Malformed message from server:", event.data);
       return;
-    case "terminalOutput":
-      if (typeof message.output !== "string") {
+    }
+    switch (message?.event) {
+      case "terminalClear":
+        term.reset();
+        return;
+      case "terminalOutput":
+        if (typeof message.output !== "string") {
+          console.error("Unexpected message from server:", message);
+          return;
+        }
+        term.write(message.output);
+        return;
+      case "setMonacoLanguage":
+        if (typeof message.monacoLanguage !== "string") {
+          console.error("Unexpected message from server:", message);
+          return;
+        }
+        monaco.editor.setModelLanguage(
+          editor.getModel(),
+          message.monacoLanguage
+        );
+        return;
+      default:
         console.error("Unexpected message from server:", message);
         return;
-      }
-      term.write(message.output);
-      return;
-    case "setMonacoLanguage":
-      if (typeof message.monacoLanguage !== "string") {
-        console.error("Unexpected message from server:", message);
-        return;
-      }
-      monaco.editor.setModelLanguage(editor.getModel(), message.monacoLanguage);
-      return;
-    default:
-      console.error("Unexpected message from server:", message);
-      return;
-  }
-});
-socket.addEventListener("close", (event) => {
-  if (event.wasClean) {
-    console.log("Connection closed cleanly");
-  } else {
-    console.error("Connection died");
-  }
-});
-socket.addEventListener("onerror", (event) =>
-  console.error("Connection error:", event)
-);
+    }
+  });
+  socket.addEventListener("close", (event: CloseEvent) => {
+    if (event.wasClean) {
+      console.log("Connection closed cleanly");
+    } else {
+      console.error("Connection died");
+    }
+    scheduleConnect();
+  });
+}
+
+function scheduleConnect() {
+  const delay = retryDelayMs * Math.random();
+  console.log(`Trying to reconnect in ${Math.floor(delay)}ms`);
+  setTimeout(tryConnect, delay);
+  retryDelayMs *= 2;
+}
+
+let socket = null;
+tryConnect();
 
 term.onData((data) =>
   socket.send(JSON.stringify({ event: "terminalInput", input: data }))