SERVER-29564 BSONObjBuilder can now be seeded with a BSONObj prefix

This will avoid copying whenever it is safe.

6 files changed, 20 insertions, 27 deletions

diff --git a/src/mongo/s/commands/cluster_aggregate.cpp b/src/mongo/s/commands/cluster_aggregate.cpp
index 72a860f1517..0453bfa1880 100644
--- a/src/mongo/s/commands/cluster_aggregate.cpp
+++ b/src/mongo/s/commands/cluster_aggregate.cpp
@@ -468,7 +468,8 @@ Status ClusterAggregate::aggPassthrough(OperationContext* opCtx,
         opCtx,
         ReadPreferenceSetting::get(opCtx),
         namespaces.executionNss.db().toString(),
-        !shard->isConfig() ? appendShardVersion(cmdObj, ChunkVersion::UNSHARDED()) : cmdObj,
+        !shard->isConfig() ? appendShardVersion(std::move(cmdObj), ChunkVersion::UNSHARDED())
+                           : std::move(cmdObj),
         Shard::RetryPolicy::kNoRetry));
 
     if (ErrorCodes::isStaleShardingError(cmdResponse.commandStatus.code())) {
diff --git a/src/mongo/s/commands/cluster_commands_helpers.cpp b/src/mongo/s/commands/cluster_commands_helpers.cpp
index b7311ac4dbe..a8d44e4017a 100644
--- a/src/mongo/s/commands/cluster_commands_helpers.cpp
+++ b/src/mongo/s/commands/cluster_commands_helpers.cpp
@@ -213,9 +213,8 @@ StatusWith<std::vector<AsyncRequestsSender::Response>> gatherResponses(
 
 }  // namespace
 
-BSONObj appendShardVersion(const BSONObj& cmdObj, ChunkVersion version) {
-    BSONObjBuilder cmdWithVersionBob;
-    cmdWithVersionBob.appendElements(cmdObj);
+BSONObj appendShardVersion(BSONObj cmdObj, ChunkVersion version) {
+    BSONObjBuilder cmdWithVersionBob(std::move(cmdObj));
     version.appendForCommands(&cmdWithVersionBob);
     return cmdWithVersionBob.obj();
 }
diff --git a/src/mongo/s/commands/cluster_commands_helpers.h b/src/mongo/s/commands/cluster_commands_helpers.h
index 184be2d6063..9445063e7e1 100644
--- a/src/mongo/s/commands/cluster_commands_helpers.h
+++ b/src/mongo/s/commands/cluster_commands_helpers.h
@@ -62,7 +62,7 @@ void appendWriteConcernErrorToCmdResponse(const ShardId& shardID,
 /**
  * Returns a copy of 'cmdObj' with 'version' appended.
  */
-BSONObj appendShardVersion(const BSONObj& cmdObj, ChunkVersion version);
+BSONObj appendShardVersion(BSONObj cmdObj, ChunkVersion version);
 
 /**
  * Generic function for dispatching commands to the cluster.
diff --git a/src/mongo/s/commands/commands_public.cpp b/src/mongo/s/commands/commands_public.cpp
index a3cadb1ddb7..398aa6f3123 100644
--- a/src/mongo/s/commands/commands_public.cpp
+++ b/src/mongo/s/commands/commands_public.cpp
@@ -1296,8 +1296,7 @@ public:
                 // long as we keep getting more chunks. The end condition is when we go to
                 // look for chunk n and it doesn't exist. This means that the file's last
                 // chunk is n-1, so we return the computed md5 results.
-                BSONObjBuilder bb;
-                bb.appendElements(filterCommandRequestForPassthrough(cmdObj));
+                BSONObjBuilder bb(filterCommandRequestForPassthrough(cmdObj));
                 bb.appendBool("partialOk", true);
                 bb.append("startAt", n);
                 if (!lastResult.isEmpty()) {
diff --git a/src/mongo/s/commands/strategy.cpp b/src/mongo/s/commands/strategy.cpp
index c6e69ee1bdd..afa4f04e55a 100644
--- a/src/mongo/s/commands/strategy.cpp
+++ b/src/mongo/s/commands/strategy.cpp
@@ -473,8 +473,7 @@ DbResponse Strategy::clientOpQueryCommand(OperationContext* opCtx,
             // If the slaveOK bit is set, behave as-if read preference secondary-preferred was
             // specified.
             const auto readPref = ReadPreferenceSetting(ReadPreference::SecondaryPreferred);
-            BSONObjBuilder finalCmdObjBuilder;
-            finalCmdObjBuilder.appendElements(cmdObj);
+            BSONObjBuilder finalCmdObjBuilder(std::move(cmdObj));
             readPref.toContainingBSON(&finalCmdObjBuilder);
             cmdObj = finalCmdObjBuilder.obj();
         }
@@ -662,11 +661,9 @@ void Strategy::writeOp(OperationContext* opCtx, DbMessage* dbm) {
             // Adjust namespace for command
             const NamespaceString& fullNS(commandRequest->getNS());
 
-            BSONObj commandBSON = commandRequest->toBSON();
-
             BSONObjBuilder builder;
             runAgainstRegistered(
-                opCtx, OpMsgRequest::fromDBAndBody(fullNS.db(), commandBSON), builder);
+                opCtx, OpMsgRequest::fromDBAndBody(fullNS.db(), commandRequest->toBSON()), builder);
 
             bool parsed = commandResponse.parseBSON(builder.done(), nullptr);
             (void)parsed;  // for compile
diff --git a/src/mongo/s/write_ops/batched_command_request.cpp b/src/mongo/s/write_ops/batched_command_request.cpp
index e4811ffe763..48c77723db3 100644
--- a/src/mongo/s/write_ops/batched_command_request.cpp
+++ b/src/mongo/s/write_ops/batched_command_request.cpp
@@ -138,21 +138,18 @@ bool BatchedCommandRequest::isValid(std::string* errMsg) const {
 }
 
 BSONObj BatchedCommandRequest::toBSON() const {
-    BSONObjBuilder builder;
-
-    switch (getBatchType()) {
-        case BatchedCommandRequest::BatchType_Insert:
-            builder.appendElements(_insertReq->toBSON());
-            break;
-        case BatchedCommandRequest::BatchType_Update:
-            builder.appendElements(_updateReq->toBSON());
-            break;
-        case BatchedCommandRequest::BatchType_Delete:
-            builder.appendElements(_deleteReq->toBSON());
-            break;
-        default:
-            MONGO_UNREACHABLE;
-    }
+    BSONObjBuilder builder([&] {
+        switch (getBatchType()) {
+            case BatchedCommandRequest::BatchType_Insert:
+                return _insertReq->toBSON();
+            case BatchedCommandRequest::BatchType_Update:
+                return _updateReq->toBSON();
+            case BatchedCommandRequest::BatchType_Delete:
+                return _deleteReq->toBSON();
+            default:
+                MONGO_UNREACHABLE;
+        }
+    }());
 
     // Append the shard version
     if (_shardVersion) {