SERVER-42507 Add internal javascript emit aggregation expression

1 files changed, 67 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/javascript_execution.h b/src/mongo/db/pipeline/javascript_execution.h
new file mode 100644
index 00000000000..2b326eb5c30
--- /dev/null
+++ b/src/mongo/db/pipeline/javascript_execution.h
@@ -0,0 +1,67 @@
+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/client.h"
+#include "mongo/db/pipeline/value.h"
+#include "mongo/scripting/engine.h"
+
+namespace mongo {
+/*
+ * This class provides a more sensible interface with JavaScript Scope objects. It helps with
+ * boilerplate related to calling JS functions from C++ code, and extracting BSON objects from the
+ * JS engine.
+ */
+class JsExecution {
+public:
+    /**
+     * Construct with a thread-local scope.
+     */
+    JsExecution() : _scope(nullptr) {
+        _scope.reset(getGlobalScriptEngine()->newScopeForCurrentThread());
+    }
+
+    void callFunctionWithoutReturn(ScriptingFunction func,
+                                   const BSONObj& params,
+                                   const BSONObj& thisObj) {
+        _scope->registerOperation(Client::getCurrent()->getOperationContext());
+        const auto guard = makeGuard([&] { _scope->unregisterOperation(); });
+
+        _scope->invoke(func, &params, &thisObj, 0, true);
+    }
+
+    Scope* getScope() {
+        return _scope.get();
+    }
+
+private:
+    std::unique_ptr<Scope> _scope;
+};
+}  // namespace mongo