SERVER-112036 Fix overly permissive check for $v:1 oplog entries in change stream event generation (#42262)

GitOrigin-RevId: c13e4b5c3e5063706b874c4beda43b804c14b16a

docs/change_streams.md

@@ -77,7 +77,8 @@ _mongosh_, the "jstest shell" (_mongo_) and many drivers provide simpler "watch"
 
 ### Opening a Collection-Level Change Stream
 
-To open a collection-level change stream on a specific collection (e.g., `testDB.testCollection`):
+To open a collection-level change stream on a specific collection (e.g., `testDB.testCollection`),
+the following _mongosh_ command can be used:
 
 ```js
 db.getSiblingDB("testDB").runCommand({
@@ -93,7 +94,8 @@ db.getSiblingDB("testDB").runCommand({
 
 ### Opening a Database-Level Change Stream
 
-To open a database-level change stream on a specific database (e.g., `testDB`), use
+To open a database-level change stream on a specific database (e.g., `testDB`), use the following
+command in _mongosh_:
 
 ```js
 db.getSiblingDB("testDB").runCommand({
@@ -115,7 +117,8 @@ The internal namespace that is used by database-level change streams is `<dbName
 ### Opening an All-Cluster Change Stream
 
 All-cluster change streams can only be opened on the `admin` database and also need the
-`allChangesForCluster` flag to be set to `true` in order to work:
+`allChangesForCluster` flag to be set to `true` in order to work. The following _mongosh_ command
+can be used to open an all-cluster change stream:
 
 ```js
 db.adminCommand({
@@ -188,6 +191,10 @@ class. The resume token internal data is stored in [ResumeTokenData](https://git
 
 Resume tokens are versioned. Currently only version 2 is supported.
 
+Future versions may introduce new resume token versions. Client applications should treat resume
+tokens as opaque identifiers and should not make any assumptions about the format or internals
+or resume tokens, nor should they rely on the internal implementation details of resume tokens.
+
 ### Change Stream Cursors
 
 When opening a change stream on a replica set, a cursor will be established on the targeted replica

src/mongo/db/pipeline/change_stream_event_transform.cpp

@@ -345,24 +345,22 @@ Document ChangeStreamDefaultEventTransformation::applyTransformation(const Docum
             // Check that the oplog entry format is as expected:
             // - if there is an '_id' field, it is a replace.
             // - if there is no '_id' field and the '$v' is 2, it is a delta (diff) update.
-            // - if there is no '_id' field and the '$v' is not 2, it is a modifier update.
+            // If there is no '_id' field and the '$v' is not 2, it is an old-style modifier
-            uassert(6741200,
+            // update. This is unsupported.
-                    str::stream() << "Expected _id field, or $v field missing, or $v equal to "
-                                  << static_cast<int>(UpdateOplogEntryVersion::kUpdateNodeV1)
-                                  << " (kUpdateNodeV1) or "
-                                  << static_cast<int>(UpdateOplogEntryVersion::kDeltaV2)
-                                  << " (kDeltaV2), but got oplog version $v: "
-                                  << oplogVersion.toString(),
-                    !id.missing() || oplogVersion.missing() ||
-                        oplogVersion.getInt() ==
-                            static_cast<int>(UpdateOplogEntryVersion::kUpdateNodeV1) ||
-                        oplogVersion.getInt() ==
-                            static_cast<int>(UpdateOplogEntryVersion::kDeltaV2));
-
             // It is important to check for '_id' field first, because a replacement style update
             // can still have a '$v' field in the object.
-            if (id.missing() && !oplogVersion.missing() &&
+            const bool isUpdateEntry = id.missing();
-                oplogVersion.getInt() == static_cast<int>(UpdateOplogEntryVersion::kDeltaV2)) {
+            uassert(
+                6741200,
+                str::stream() << "Expected _id field, or $v field missing, or $v equal to "
+                              << static_cast<int>(UpdateOplogEntryVersion::kDeltaV2)
+                              << " (kDeltaV2), but got oplog version $v: "
+                              << oplogVersion.toString(),
+                !isUpdateEntry ||
+                    (!oplogVersion.missing() && oplogVersion.getType() == BSONType::numberInt &&
+                     oplogVersion.getInt() == static_cast<int>(UpdateOplogEntryVersion::kDeltaV2)));
+
+            if (isUpdateEntry) {
                 // Parsing the delta oplog entry.
                 operationType = DocumentSourceChangeStream::kUpdateOpType;
                 Value diffObj = input[repl::OplogEntry::kObjectFieldName]
@@ -395,6 +393,7 @@ Document ChangeStreamDefaultEventTransformation::applyTransformation(const Docum
                     }
                 }
             } else {
+                // Replace.
                 operationType = DocumentSourceChangeStream::kReplaceOpType;
                 fullDocument = input[repl::OplogEntry::kObjectFieldName];
             }
@@ -630,7 +629,7 @@ Document ChangeStreamDefaultEventTransformation::applyTransformation(const Docum
 boost::optional<std::pair<StringData, Value>>
 ChangeStreamDefaultEventTransformation::handleSupportedEvent(const Document& o2Field) const {
     for (auto&& supportedEvent : _supportedEvents) {
-        if (auto lookup = o2Field[supportedEvent]; !o2Field[supportedEvent].missing()) {
+        if (auto lookup = o2Field[supportedEvent]; !lookup.missing()) {
             // Known event.
             return std::make_pair(supportedEvent,
                                   Value{copyDocExceptFields(o2Field, {supportedEvent})});

src/mongo/db/pipeline/document_source_change_stream_test.cpp

@@ -4507,9 +4507,9 @@ TEST_F(ChangeStreamStageDBTest, TransformsEntriesForLegalClientCollectionsWithSy
     }
 }
 
-TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsVMissing) {
+TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsVMissingWithId) {
-    // A missing $v field in the update oplog entry implies $v:1, which is no longer supported.
+    // An _id field in the update oplog entry implies a replace.
-    BSONObj o = BSON("$set" << BSON("y" << 1));
+    BSONObj o = BSON("_id" << 1 << "$set" << BSON("y" << 1));
     BSONObj o2 = BSON("_id" << 1 << "x" << 2);
     auto replace = makeOplogEntry(OpTypeEnum::kUpdate, nss, o, testUuid(), boost::none, o2);
 
@@ -4519,7 +4519,7 @@ TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsVMissing) {
         {DSChangeStream::kOperationTypeField, DSChangeStream::kReplaceOpType},
         {DSChangeStream::kClusterTimeField, kDefaultTs},
         {DSChangeStream::kWallTimeField, Date_t()},
-        {DSChangeStream::kFullDocumentField, D{{"$set", D{{"y", 1}}}}},
+        {DSChangeStream::kFullDocumentField, D{{"_id", 1}, {"$set", D{{"y", 1}}}}},
         {DSChangeStream::kNamespaceField, D{{"db", nss.db_forTest()}, {"coll", nss.coll()}}},
         {DSChangeStream::kDocumentKeyField, D{{"_id", 1}, {"x", 2}}},
     };
@@ -4527,6 +4527,23 @@ TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsVMissing) {
     checkTransformation(replace, expectedReplace);
 }
 
+TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsVMissingWithoutId) {
+    // A missing _id field and a missing $v field in the update oplog entry implies a $v:1 update
+    // oplog entry, which is no longer supported.
+    BSONObj o = BSON("$set" << BSON("y" << 1));
+    BSONObj o2 = BSON("_id" << 1 << "x" << 2);
+    auto updateField = makeOplogEntry(OpTypeEnum::kUpdate, nss, o, testUuid(), boost::none, o2);
+    checkTransformation(updateField, boost::none, kDefaultSpec, {}, {}, {}, 6741200);
+}
+
+TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsInvalidV) {
+    // A $v field in the update oplog entry without an _id field requires '$v:2'.
+    BSONObj o = BSON("$v" << "ABC" << "diff" << BSON("i" << BSON("v" << 5)));
+    BSONObj o2 = BSON("_id" << 1 << "x" << 2);
+    auto updateField = makeOplogEntry(OpTypeEnum::kUpdate, nss, o, testUuid(), boost::none, o2);
+    checkTransformation(updateField, boost::none, kDefaultSpec, {}, {}, {}, 6741200);
+}
+
 TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsDeltaUpdateNonV2NotSupported) {
     BSONObj diff = BSON("u" << BSON("y" << 1));
     BSONObj o = BSON("diff" << diff << "$v" << 3);
@@ -4554,20 +4571,8 @@ TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsDeltaUpdate) {
 TEST_F(ChangeStreamStageDBTest, TransformUpdateFieldsModifierUpdate) {
     BSONObj o = BSON("x" << 2 << "y" << 1);
     BSONObj o2 = BSON("_id" << 1);
-    auto replace = makeOplogEntry(OpTypeEnum::kUpdate, nss, o, testUuid(), boost::none, o2);
+    auto updateField = makeOplogEntry(OpTypeEnum::kUpdate, nss, o, testUuid(), boost::none, o2);
-
+    checkTransformation(updateField, boost::none, kDefaultSpec, {}, {}, {}, 6741200);
-    Document expectedReplace{
-        {DSChangeStream::kIdField,
-         makeResumeToken(kDefaultTs, testUuid(), o2, DSChangeStream::kReplaceOpType)},
-        {DSChangeStream::kOperationTypeField, DSChangeStream::kReplaceOpType},
-        {DSChangeStream::kClusterTimeField, kDefaultTs},
-        {DSChangeStream::kWallTimeField, Date_t()},
-        {DSChangeStream::kFullDocumentField, D{{"x", 2}, {"y", 1}}},
-        {DSChangeStream::kNamespaceField, D{{"db", nss.db_forTest()}, {"coll", nss.coll()}}},
-        {DSChangeStream::kDocumentKeyField, D{{"_id", 1}}},
-    };
-
-    checkTransformation(replace, expectedReplace);
 }
 
 TEST_F(ChangeStreamStageDBTest, TransformRemoveFields) {