From ec35b353a7f64819760579506dc7d4ae4f017fef Mon Sep 17 00:00:00 2001
From: Rafael dos Santos Silva <xfalcox@gmail.com>
Date: Thu, 29 Oct 2020 21:59:02 -0300
Subject: [PATCH] FEATURE: Add a CSS class to the HTML element on background
 connection error (#10991)

This is a way to detect that Discourse isn't able to receive online updates from
the server, and will be used to trigger an UI warning to the user that the session
is working on offline mode.

Meta request https://meta.discourse.org/t/offline-indicator/123000?u=falco
---
 .../discourse/app/initializers/message-bus.js          | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/app/assets/javascripts/discourse/app/initializers/message-bus.js b/app/assets/javascripts/discourse/app/initializers/message-bus.js
index f5dcf26563e..5f44db12731 100644
--- a/app/assets/javascripts/discourse/app/initializers/message-bus.js
+++ b/app/assets/javascripts/discourse/app/initializers/message-bus.js
@@ -5,6 +5,15 @@ import { handleLogoff } from "discourse/lib/ajax";
 import { isProduction, isTesting } from "discourse-common/config/environment";
 
 const LONG_POLL_AFTER_UNSEEN_TIME = 1200000; // 20 minutes
+const CONNECTIVITY_ERROR_CLASS = "message-bus-offline";
+
+function updateConnectivityIndicator(stat) {
+  if (stat === "error") {
+    document.documentElement.classList.add(CONNECTIVITY_ERROR_CLASS);
+  } else {
+    document.documentElement.classList.remove(CONNECTIVITY_ERROR_CLASS);
+  }
+}
 
 function ajax(opts) {
   if (opts.complete) {
@@ -12,6 +21,7 @@ function ajax(opts) {
     opts.complete = function (xhr, stat) {
       handleLogoff(xhr);
       oldComplete(xhr, stat);
+      updateConnectivityIndicator(stat);
     };
   } else {
     opts.complete = handleLogoff;