1 files changed, 52 insertions, 0 deletions
diff --git a/src/mongo/db/s/migration_chunk_cloner_source_legacy_commands.cpp b/src/mongo/db/s/migration_chunk_cloner_source_legacy_commands.cpp
index 9e3e83774ee..d42c6bdaa99 100644
--- a/src/mongo/db/s/migration_chunk_cloner_source_legacy_commands.cpp
+++ b/src/mongo/db/s/migration_chunk_cloner_source_legacy_commands.cpp
@@ -216,5 +216,57 @@ public:
 
 } transferModsCommand;
 
+/**
+ * Command for extracting the oplog entries that needs to be migrated for the given migration
+ * session id.
+ * Note: this command is not stateless. Calling this command has a side-effect of gradually
+ * depleting the buffer that contains the oplog entries to be transfered.
+ */
+class MigrateSessionCommand : public BasicCommand {
+public:
+    MigrateSessionCommand() : BasicCommand("_getNextSessionMods") {}
+
+    void help(std::stringstream& h) const {
+        h << "internal";
+    }
+
+    virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
+        return false;
+    }
+
+    virtual bool slaveOk() const {
+        return false;
+    }
+
+    virtual bool adminOnly() const {
+        return true;
+    }
+
+    virtual void addRequiredPrivileges(const std::string& dbname,
+                                       const BSONObj& cmdObj,
+                                       std::vector<Privilege>* out) {
+        ActionSet actions;
+        actions.addAction(ActionType::internal);
+        out->push_back(Privilege(ResourcePattern::forClusterResource(), actions));
+    }
+
+    bool run(OperationContext* opCtx,
+             const std::string&,
+             const BSONObj& cmdObj,
+             BSONObjBuilder& result) {
+        const MigrationSessionId migrationSessionId(
+            uassertStatusOK(MigrationSessionId::extractFromBSON(cmdObj)));
+
+        BSONArrayBuilder arrBuilder;
+
+        AutoGetActiveCloner autoCloner(opCtx, migrationSessionId);
+        autoCloner.getCloner()->nextSessionMigrationBatch(opCtx, &arrBuilder);
+
+        result.appendArray("oplog", arrBuilder.arr());
+        return true;
+    }
+
+} migrateSessionCommand;
+
 }  // namespace
 }  // namespace mongo