SERVER-19057 avoid extra buffer copy when creating message in rpc builders

1 files changed, 10 insertions, 3 deletions

diff --git a/src/mongo/rpc/legacy_request_builder.cpp b/src/mongo/rpc/legacy_request_builder.cpp
index 05f1fe79ce3..db333dc4c6a 100644
--- a/src/mongo/rpc/legacy_request_builder.cpp
+++ b/src/mongo/rpc/legacy_request_builder.cpp
@@ -37,16 +37,19 @@
 #include "mongo/rpc/metadata.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/assert_util.h"
+#include "mongo/util/net/message.h"
 
 namespace mongo {
 namespace rpc {
 
-LegacyRequestBuilder::LegacyRequestBuilder() : _message{stdx::make_unique<Message>()} {}
+LegacyRequestBuilder::LegacyRequestBuilder() : LegacyRequestBuilder(stdx::make_unique<Message>()) {}
 
 LegacyRequestBuilder::~LegacyRequestBuilder() {}
 
 LegacyRequestBuilder::LegacyRequestBuilder(std::unique_ptr<Message> message)
-    : _message{std::move(message)} {}
+    : _message{std::move(message)} {
+    _builder.skip(mongo::MsgData::MsgDataHeaderSize);
+}
 
 LegacyRequestBuilder& LegacyRequestBuilder::setDatabase(StringData database) {
     invariant(_state == State::kDatabase);
@@ -110,7 +113,11 @@ Protocol LegacyRequestBuilder::getProtocol() const {
 
 std::unique_ptr<Message> LegacyRequestBuilder::done() {
     invariant(_state == State::kInputDocs);
-    _message->setData(dbQuery, _builder.buf(), _builder.len());
+    MsgData::View msg = _builder.buf();
+    msg.setLen(_builder.len());
+    msg.setOperation(dbQuery);
+    _builder.decouple();                      // release ownership from BufBuilder
+    _message->setData(msg.view2ptr(), true);  // transfer ownership to Message
     _state = State::kDone;
     return std::move(_message);
 }