From f674c8bf879f1dedf0ec31ee2ab6b9679f74befe Mon Sep 17 00:00:00 2001
From: Daniel <daniel-blyth@live.com.au>
Date: Sun, 5 Jul 2026 01:55:06 +1000
Subject: [PATCH] fix: Server fails to start with IndexKeySpecsConflict on
 _Idempotency TTL index on MongoDB 8.0

---
 spec/MongoStorageAdapter.spec.js              | 28 +++++++++++++++++++
 .../Storage/Mongo/MongoStorageAdapter.js      | 17 ++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/spec/MongoStorageAdapter.spec.js b/spec/MongoStorageAdapter.spec.js
index facf1b2c41..daf9596b50 100644
--- a/spec/MongoStorageAdapter.spec.js
+++ b/spec/MongoStorageAdapter.spec.js
@@ -5,6 +5,7 @@ const { MongoClient, Collection } = require('mongodb');
 const databaseURI = 'mongodb://localhost:27017/parseServerMongoAdapterTestDatabase';
 const request = require('../lib/request');
 const Config = require('../lib/Config');
+const SchemaController = require('../lib/Controllers/SchemaController');
 const TestUtils = require('../lib/TestUtils');
 const Utils = require('../lib/Utils');
 const { randomUUID: uuidv4 } = require('crypto');
@@ -900,6 +901,33 @@ describe_only_db('mongo')('MongoStorageAdapter', () => {
       expect(userIndexes.find(idx => idx.name === '_perishable_token' || idx.name === '_perishable_token_1')).toBeDefined();
       expect(roleIndexes.find(idx => idx.name === 'name_1')).toBeDefined();
     });
+
+    it('ensureIndex tolerates an existing conflicting index instead of crashing startup (#10431)', async () => {
+      await reconfigureServer({ databaseAdapter: undefined, databaseURI, databaseOptions: {} });
+      const adapter = Config.get(Parse.applicationId).database.adapter;
+      const collection = await adapter._adaptiveCollection('_Idempotency');
+      // Simulate a pre-existing `ttl` index created by an older Parse Server / driver whose stored
+      // spec conflicts with the one requested on startup (same name + key, different options). This
+      // produces IndexKeySpecsConflict (code 86) — the same failure MongoDB 8.0 triggers via its
+      // internal `enableOrderedIndex` field, which previously aborted server startup.
+      await collection._mongoCollection.dropIndex('ttl').catch(() => {});
+      await collection._mongoCollection.createIndex(
+        { expire: 1 },
+        { name: 'ttl', expireAfterSeconds: 100, sparse: true }
+      );
+      const schema = {
+        fields: {
+          ...SchemaController.defaultColumns._Default,
+          ...SchemaController.defaultColumns._Idempotency,
+        },
+      };
+      // Mirrors DatabaseController.performInitialization's TTL-index call, which previously threw.
+      await expectAsync(
+        adapter.ensureIndex('_Idempotency', schema, ['expire'], 'ttl', false, { ttl: 0 })
+      ).toBeResolved();
+      const indexes = await getIndexes('_Idempotency');
+      expect(indexes.find(idx => idx.name === 'ttl')).toBeDefined();
+    });
   });
 
   describe('logClientEvents', () => {
diff --git a/src/Adapters/Storage/Mongo/MongoStorageAdapter.js b/src/Adapters/Storage/Mongo/MongoStorageAdapter.js
index 9c17b2a18b..4bd83c57f8 100644
--- a/src/Adapters/Storage/Mongo/MongoStorageAdapter.js
+++ b/src/Adapters/Storage/Mongo/MongoStorageAdapter.js
@@ -818,7 +818,22 @@ export class MongoStorageAdapter implements StorageAdapter {
       .then(collection =>
         collection._mongoCollection.createIndex(indexCreationRequest, indexOptions)
       )
-      .catch(err => this.handleError(err));
+      .catch(error => {
+        // MongoDB 8.0 enriches stored index specs with internal fields (e.g. `enableOrderedIndex`)
+        // that Parse Server never sets. Re-issuing an otherwise-identical createIndex on startup
+        // then fails with IndexKeySpecsConflict (86) / IndexOptionsConflict (85) even though a
+        // functionally-equivalent index already exists — which aborts server startup. Treat that
+        // as success (the existing index already serves its purpose), mirroring
+        // ensureAuthDataUniqueness. Logged so a genuine conflict is still visible. (#10431)
+        if (error.code === 85 || error.code === 86) {
+          logger.warn(
+            `Index "${indexName || ''}" on ${className} already exists with a conflicting ` +
+              `specification; keeping the existing index. (code ${error.code})`
+          );
+          return;
+        }
+        return this.handleError(error);
+      });
   }
 
   // Create a unique index. Unique indexes on nullable fields are not allowed. Since we don't