Fix thundering herd problem with debouncer

changelog.d/1230.bugfix

@@ -0,0 +1 @@
+Fix an issue where the QuitDebouncer would reprocess old QUITs, and process QUITs too early during the debouncing process.

spec/unit/IrcServer.spec.js

@@ -2,6 +2,23 @@
 const { IrcServer } = require("../../lib/irc/IrcServer");
 const extend = require("extend");
 describe("IrcServer", function() {
+    describe("getQuitDebounceDelay", () => {
+        it("should get a random period between min and max", () => {
+            const delayMinMs = 5;
+            const delayMaxMs = 10;
+            const server = new IrcServer("irc.foobar",
+                extend(true, IrcServer.DEFAULT_CONFIG, {
+                    quitDebounce: {
+                        delayMinMs,
+                        delayMaxMs,
+                    }
+                })
+            );
+            const delay = server.getQuitDebounceDelay();
+            expect(delay).toBeGreaterThan(delayMinMs);
+            expect(delay).toBeLessThan(delayMaxMs);
+        });
+    })
     describe("getNick", function() {
         it("should get a nick from a userid", function() {
             const server = new IrcServer("irc.foobar",

src/bridge/QuitDebouncer.ts

@@ -61,7 +61,7 @@ export class QuitDebouncer {
             // Nobody to debounce, yay.
             return;
         }
-        const delay = Math.max(server.getQuitDebounceDelayMinMs(), server.getQuitDebounceDelayMaxMs() * Math.random());
+        const delay = server.getQuitDebounceDelay();
         log.info(`Will attempt to reconnect users for ${channel} after ${delay}ms`)
         setTimeout(() => {
             // Clear our existing sets, we're about to operate on the channel.

src/irc/IrcServer.ts

@@ -95,23 +95,14 @@ export class IrcServer {
     }
 
     /**
-     * Get the minimum number of ms to debounce before bridging a QUIT to Matrix
-     * during a detected net-split. If the user rejoins a channel before bridging
-     * the quit to a leave, the leave will not be sent.
-     * @return {number}
-     */
-    public getQuitDebounceDelayMinMs() {
-        return this.config.quitDebounce.delayMinMs;
-    }
-
-    /**
-     * Get the maximum number of ms to debounce before bridging a QUIT to Matrix
-     * during a detected net-split. If a leave is bridged, it will occur at a
-     * random time between delayMinMs (see above) delayMaxMs.
-     * @return {number}
+     * Get a random interval to delay a quits for when debouncing. Will be between
+     * `delayMinMs` and `delayMaxMs`
      */
-    public getQuitDebounceDelayMaxMs() {
-        return this.config.quitDebounce.delayMaxMs;
+    public getQuitDebounceDelay(): number {
+        const { delayMaxMs, delayMinMs } = this.config.quitDebounce;
+        return delayMinMs + (
+            delayMaxMs - delayMinMs
+        ) * Math.random();
     }
 
     /**