From d9b32262f89fe397e34c071d0f2ded2b91909766 Mon Sep 17 00:00:00 2001
From: Johan Vosloo <johan@headspacetech.com>
Date: Sat, 14 Feb 2026 20:51:54 +0200
Subject: [PATCH] Fix eventsource reconnection: proper backoff and close()
 behavior

Fixes three bugs in the EventSource plugin reconnection logic:

1. XOR instead of exponentiation: 2 ^ retryCount uses JavaScript
   bitwise XOR, not exponentiation. This produces erratic delays
   (e.g. 2 ^ 2 = 0, giving 0ms delay). Fixed to Math.pow(2, n).

2. Backoff only triggers on CLOSED state: The error handler only
   reconnected when readyState == EventSource.CLOSED, but browsers
   keep readyState = CONNECTING on connection-refused errors and
   auto-retry every ~3 seconds -- bypassing the backoff entirely.
   Fixed by closing the EventSource on error to stop the browser
   native auto-reconnect, then managing retry with proper backoff.

3. close() does not stop reconnection: Calling close() in a user
   on error handler sets readyState to CLOSED, which immediately
   triggers the plugin own error handler to call open() -- making
   the problem worse. Fixed by tracking a closed flag that is set
   in close() and checked before scheduling reconnection.

Fixes #259
---
 src/eventsource.js | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/src/eventsource.js b/src/eventsource.js
index 75217794e..eb51e3bed 100644
--- a/src/eventsource.js
+++ b/src/eventsource.js
@@ -47,6 +47,8 @@
 					eventSource: null,
 					listeners: [],
 					retryCount: 0,
+					closed: false,
+					reconnectTimeout: null,
 					open: function (url) {
 						// calculate default values for URL argument.
 						if (url == undefined) {
@@ -68,6 +70,9 @@
 							}
 						}
 
+						// Mark as not explicitly closed (allow reconnection)
+						stub.closed = false;
+
 						// Open the EventSource and get ready to populate event handlers
 						stub.eventSource = new EventSource(url, {
 							withCredentials: withCredentials,
@@ -78,13 +83,17 @@
 							stub.retryCount = 0;
 						});
 
-						// On connection error, use exponential backoff to retry (random values from 1 second to 2^7 (128) seconds
+						// On connection error, use exponential backoff to retry
 						stub.eventSource.addEventListener("error", function (event) {
-							// If the EventSource is closed, then try to reopen
-							if (stub.eventSource.readyState == EventSource.CLOSED) {
+							// Close the EventSource to prevent the browser's native auto-reconnect,
+							// which does not use backoff and can cause rapid-fire retries.
+							stub.eventSource.close();
+
+							// Only reconnect if the user has not explicitly called close()
+							if (!stub.closed) {
 								stub.retryCount = Math.min(7, stub.retryCount + 1);
-								var timeout = Math.random() * (2 ^ stub.retryCount) * 500;
-								window.setTimeout(stub.open, timeout);
+								var timeout = Math.random() * Math.pow(2, stub.retryCount) * 500;
+								stub.reconnectTimeout = window.setTimeout(stub.open, timeout);
 							}
 						});
 
@@ -95,6 +104,11 @@
 						}
 					},
 					close: function () {
+						stub.closed = true;
+						if (stub.reconnectTimeout != null) {
+							window.clearTimeout(stub.reconnectTimeout);
+							stub.reconnectTimeout = null;
+						}
 						if (stub.eventSource != undefined) {
 							stub.eventSource.close();
 						}