SERVER-37982 Distinguish use cases for collecting document key fields

1 files changed, 13 insertions, 2 deletions

diff --git a/src/mongo/db/pipeline/process_interface_shardsvr.h b/src/mongo/db/pipeline/process_interface_shardsvr.h
index ddafac24cdb..fba537a2e1a 100644
--- a/src/mongo/db/pipeline/process_interface_shardsvr.h
+++ b/src/mongo/db/pipeline/process_interface_shardsvr.h
@@ -43,8 +43,19 @@ class MongoInterfaceShardServer final : public MongoInterfaceStandalone {
 public:
     using MongoInterfaceStandalone::MongoInterfaceStandalone;
 
-    std::pair<std::vector<FieldPath>, bool> collectDocumentKeyFields(
-        OperationContext* opCtx, NamespaceStringOrUUID nssOrUUID) const final;
+    std::pair<std::vector<FieldPath>, bool> collectDocumentKeyFieldsForHostedCollection(
+        OperationContext* opCtx, const NamespaceString&, UUID) const final;
+
+    std::vector<FieldPath> collectDocumentKeyFieldsActingAsRouter(
+        OperationContext*, const NamespaceString&) const final {
+        // We don't expect anyone to use this method on the shard itself (yet). This is currently
+        // only used for $out. For $out in a sharded cluster, the mongos is responsible for
+        // collecting the document key fields before serializing them and sending them to the
+        // shards. This is logically a MONGO_UNREACHABLE, but a malicious user could construct a
+        // request to send directly to the shards which does not include the uniqueKey, so we must
+        // be prepared to gracefully error.
+        uasserted(50997, "Unexpected attempt to consult catalog cache on a shard server");
+    }
 
     /**
      * Inserts the documents 'objs' into the namespace 'ns' using the ClusterWriter for locking,