From 4b51940f6e36878261dc18b8867c27f44c4975a9 Mon Sep 17 00:00:00 2001
From: Moustafa Maher <m.maher@10gen.com>
Date: Fri, 15 Jan 2021 01:52:57 +0000
Subject: SERVER-52547 Avoid reparsing the command object multiple times

---
 src/mongo/db/commands.h | 49 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 9 deletions(-)

(limited to 'src/mongo/db/commands.h')

diff --git a/src/mongo/db/commands.h b/src/mongo/db/commands.h
index dc1a53f2e8f..5dcd2d94b77 100644
--- a/src/mongo/db/commands.h
+++ b/src/mongo/db/commands.h
@@ -958,10 +958,11 @@ public:
  *
  */
 template <typename Derived>
-class BasicCommandWithRequestParser : public BasicCommand {
-public:
+class BasicCommandWithRequestParser : public BasicCommandWithReplyBuilderInterface {
+protected:
     // Commands that only have a single name don't need to define any constructors.
-    BasicCommandWithRequestParser() : BasicCommand(Derived::Request::kCommandName) {}
+    BasicCommandWithRequestParser()
+        : BasicCommandWithReplyBuilderInterface(Derived::Request::kCommandName) {}
 
     bool runWithReplyBuilder(OperationContext* opCtx,
                              const std::string& db,
@@ -970,21 +971,51 @@ public:
         auto result = replyBuilder->getBodyBuilder();
 
         // To enforce API versioning
-        using RequestType = typename Derived::Request;
-        auto request = RequestType::parse(
-            IDLParserErrorContext(Derived::Request::kCommandName,
-                                  APIParameters::get(opCtx).getAPIStrict().value_or(false)),
-            cmdObj);
+        auto requestParser = RequestParser(opCtx, cmdObj);
 
-        auto cmdDone = run(opCtx, db, request.toBSON(cmdObj), result);
+        auto cmdDone = runWithRequestParser(opCtx, db, cmdObj, requestParser, result);
         validateResult(result.asTempObj());
         return cmdDone;
     }
 
+    class RequestParser;
+
+    /**
+     * Runs the given command. Returns true upon success.
+     */
+    virtual bool runWithRequestParser(OperationContext* opCtx,
+                                      const std::string& db,
+                                      const BSONObj& cmdObj,
+                                      const RequestParser& requestParser,
+                                      BSONObjBuilder& result) = 0;
+
     // Custom logic to validate results to enforce API versioning.
     virtual void validateResult(const BSONObj& resultObj) = 0;
 };
 
+template <typename Derived>
+class BasicCommandWithRequestParser<Derived>::RequestParser {
+public:
+    using RequestType = typename Derived::Request;
+
+    RequestParser(OperationContext* opCtx, const BSONObj& cmdObj)
+        : _request{_parseRequest(opCtx, cmdObj)} {}
+
+    const RequestType& request() const {
+        return _request;
+    }
+
+private:
+    static RequestType _parseRequest(OperationContext* opCtx, const BSONObj& cmdObj) {
+        return RequestType::parse(
+            IDLParserErrorContext(RequestType::kCommandName,
+                                  APIParameters::get(opCtx).getAPIStrict().value_or(false)),
+            cmdObj);
+    }
+
+    RequestType _request;
+};
+
 /**
  * Deprecated. Do not add new subclasses.
  */
-- 
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