chat: Move message deletion to `padRemove` hook

src/ep.json

@@ -28,6 +28,7 @@
         "padCheck": "ep_etherpad-lite/node/chat",
         "padCopy": "ep_etherpad-lite/node/chat",
         "padLoad": "ep_etherpad-lite/node/chat",
+        "padRemove": "ep_etherpad-lite/node/chat",
         "socketio": "ep_etherpad-lite/node/chat"
       }
     },

src/node/chat.js

@@ -173,6 +173,14 @@ exports.padLoad = async (hookName, {pad}) => {
   if (!('chatHead' in pad)) pad.chatHead = -1;
 };
 
+exports.padRemove = async (hookName, {pad}) => {
+  const ops = (function* () {
+    const {chatHead = -1} = pad;
+    for (let i = 0; i <= chatHead; ++i) yield pad.db.remove(`pad:${pad.id}:chat:${i}`);
+  })();
+  for (const op of new Stream(ops).batch(100).buffer(99)) await op;
+};
+
 exports.socketio = (hookName, {io}) => {
   socketio = io;
 };

src/node/db/Pad.js

@@ -530,11 +530,6 @@ class Pad {
     }));
     p.push(db.remove(`pad2readonly:${padID}`));
 
-    // delete all chat messages
-    p.push(promises.timesLimit(this.chatHead + 1, 500, async (i) => {
-      await this.db.remove(`pad:${this.id}:chat:${i}`, null);
-    }));
-
     // delete all revisions
     p.push(promises.timesLimit(this.head + 1, 500, async (i) => {
       await this.db.remove(`pad:${this.id}:revs:${i}`, null);