PadMessageHandler: Accept retransmissions of USER_CHANGES

src/node/handler/PadMessageHandler.js

@@ -615,19 +615,15 @@ const handleUserChanges = async (socket, message) => {
     // Update the changeset so that it can be applied to the latest revision.
     while (r < pad.getHeadRevisionNumber()) {
       r++;
-
-      const c = await pad.getRevisionChangeset(r);
-
+      const {changeset: c, meta: {author: authorId}} = await pad.getRevision(r);
+      if (changeset === c && thisSession.author === authorId) {
+        // Assume this is a retransmission of an already applied changeset.
+        rebasedChangeset = Changeset.identity(Changeset.unpack(changeset).oldLen);
+      }
       // At this point, both "c" (from the pad) and "changeset" (from the
       // client) are relative to revision r - 1. The follow function
       // rebases "changeset" so that it is relative to revision r
       // and can be applied after "c".
-
-      // a changeset can be based on an old revision with the same changes in it
-      // prevent eplite from accepting it TODO: better send the client a NEW_CHANGES
-      // of that revision
-      if (baseRev + 1 === r && c === changeset) throw new Error('Changeset already accepted');
-
       rebasedChangeset = Changeset.follow(c, rebasedChangeset, false, pad.pool);
     }
 

src/static/js/collab_client.js

@@ -208,8 +208,9 @@ const getCollabClient = (ace2editor, serverVars, initialUserInfo, options, _pad)
     } else if (msg.type === 'ACCEPT_COMMIT') {
       serverMessageTaskQueue.enqueue(() => {
         const {newRev} = msg;
-        // newRev will equal rev if the changeset has no net effect (identity changeset, or removing
-        // and re-adding the same characters with the same attributes).
+        // newRev will equal rev if the changeset has no net effect (identity changeset, removing
+        // and re-adding the same characters with the same attributes, or retransmission of an
+        // already applied changeset).
         if (![rev, rev + 1].includes(newRev)) {
           window.console.warn(`bad message revision on ACCEPT_COMMIT: ${newRev} not ${rev + 1}`);
           // setChannelState("DISCONNECTED", "badmessage_acceptcommit");

src/tests/backend/specs/messages.js

@@ -75,12 +75,12 @@ describe(__filename, function () {
       await assertRejected();
     });
 
-    it('retransmission is rejected', async function () {
+    it('retransmission is accepted, has no effect', async function () {
       sendUserChanges('Z:1>5+5$hello');
       await assertAccepted(rev + 1);
       --rev;
       sendUserChanges('Z:1>5+5$hello');
-      await assertRejected();
+      await assertAccepted(rev + 1);
       assert.equal(pad.text(), 'hello\n');
     });