SERVER-47125 Don't trust OplogQueryMetadata.primaryIndex

2 files changed, 16 insertions, 5 deletions

diff --git a/src/mongo/rpc/metadata/oplog_query_metadata.h b/src/mongo/rpc/metadata/oplog_query_metadata.h
index 92ce4e24827..205569a4f31 100644
--- a/src/mongo/rpc/metadata/oplog_query_metadata.h
+++ b/src/mongo/rpc/metadata/oplog_query_metadata.h
@@ -88,11 +88,13 @@ public:
     }
 
     /**
-     * Returns the index of the current primary from the perspective of the sender.
-     * Returns kNoPrimary if there is no primary.
+     * True if the sender thinks there is a primary.
+     *
+     * Note: the $oplogQueryData's primaryIndex isn't safe to use, we don't know which config
+     * version it's from. All we can safely say is whether the sender thinks there's a primary.
      */
-    int getPrimaryIndex() const {
-        return _currentPrimaryIndex;
+    bool hasPrimaryIndex() const {
+        return _currentPrimaryIndex != kNoPrimary;
     }
 
     /**
diff --git a/src/mongo/rpc/metadata/oplog_query_metadata_test.cpp b/src/mongo/rpc/metadata/oplog_query_metadata_test.cpp
index bb267ccac59..6d7218e83fc 100644
--- a/src/mongo/rpc/metadata/oplog_query_metadata_test.cpp
+++ b/src/mongo/rpc/metadata/oplog_query_metadata_test.cpp
@@ -48,6 +48,7 @@ TEST(ReplResponseMetadataTest, OplogQueryMetadataRoundtrip) {
     ASSERT_EQ(opTime1, metadata.getLastOpCommitted().opTime);
     ASSERT_EQ(committedWall, metadata.getLastOpCommitted().wallTime);
     ASSERT_EQ(opTime2, metadata.getLastOpApplied());
+    ASSERT_TRUE(metadata.hasPrimaryIndex());
 
     BSONObjBuilder builder;
     metadata.writeToMetadata(&builder).transitional_ignore();
@@ -75,8 +76,8 @@ TEST(ReplResponseMetadataTest, OplogQueryMetadataRoundtrip) {
     ASSERT_EQ(opTime2, clonedMetadata.getLastOpApplied());
     ASSERT_EQ(committedWall, clonedMetadata.getLastOpCommitted().wallTime);
     ASSERT_EQ(metadata.getRBID(), clonedMetadata.getRBID());
-    ASSERT_EQ(metadata.getPrimaryIndex(), clonedMetadata.getPrimaryIndex());
     ASSERT_EQ(metadata.getSyncSourceIndex(), clonedMetadata.getSyncSourceIndex());
+    ASSERT_TRUE(clonedMetadata.hasPrimaryIndex());
 
     BSONObjBuilder clonedBuilder;
     clonedMetadata.writeToMetadata(&clonedBuilder).transitional_ignore();
@@ -85,6 +86,14 @@ TEST(ReplResponseMetadataTest, OplogQueryMetadataRoundtrip) {
     ASSERT_BSONOBJ_EQ(expectedObj, clonedSerializedObj);
 }
 
+TEST(ReplResponseMetadataTest, OplogQueryMetadataHasPrimaryIndex) {
+    for (auto [currentPrimaryIndex, hasPrimaryIndex] :
+         std::vector<std::pair<int, bool>>{{-1, false}, {0, true}, {1, true}}) {
+        OplogQueryMetadata oqm({OpTime(), Date_t()}, OpTime(), 1, currentPrimaryIndex, -1);
+        ASSERT_EQUALS(hasPrimaryIndex, oqm.hasPrimaryIndex());
+    }
+}
+
 }  // unnamed namespace
 }  // namespace rpc
 }  // namespace mongo