SERVER-28663 rename config server metadata from configsvr to $configsvr

This is prep for OP_MSG where "configsvr" conflicts with a field of the same
name in the reply to isMaster. OP_COMMAND will continue to use the old name
since it will only be used to communicate with older nodes.

6 files changed, 52 insertions, 7 deletions

diff --git a/src/mongo/rpc/command_reply.cpp b/src/mongo/rpc/command_reply.cpp
index c5ff1b9ab78..884a63fae61 100644
--- a/src/mongo/rpc/command_reply.cpp
+++ b/src/mongo/rpc/command_reply.cpp
@@ -55,8 +55,21 @@ CommandReply::CommandReply(const Message* message) : _message(message) {
 
     _commandReply = uassertStatusOK(cur.readAndAdvance<Validated<BSONObj>>()).val;
     _commandReply.shareOwnershipWith(message->sharedBuffer());
-    _metadata = uassertStatusOK(cur.readAndAdvance<Validated<BSONObj>>()).val;
-    _metadata.shareOwnershipWith(message->sharedBuffer());
+
+    // OP_COMMAND is only used when communicating with 3.4 nodes and they serialize their metadata
+    // fields differently. We do all up- and down-conversion here so that the rest of the code only
+    // has to deal with the current format.
+    auto rawMetadata = uassertStatusOK(cur.readAndAdvance<Validated<BSONObj>>()).val;
+    BSONObjBuilder metadataBuilder;
+    for (auto elem : rawMetadata) {
+        if (elem.fieldNameStringData() == "configsvr") {
+            metadataBuilder.appendAs(elem, "$configServerState");
+        } else {
+            metadataBuilder.append(elem);
+        }
+    }
+    _metadata = metadataBuilder.obj();
+
     uassert(40420, "OP_COMMAND reply contains trailing bytes following metadata", cur.empty());
 }
 
diff --git a/src/mongo/rpc/command_reply_builder.cpp b/src/mongo/rpc/command_reply_builder.cpp
index b47b0545c80..001522163ce 100644
--- a/src/mongo/rpc/command_reply_builder.cpp
+++ b/src/mongo/rpc/command_reply_builder.cpp
@@ -65,7 +65,17 @@ BSONObjBuilder CommandReplyBuilder::getInPlaceReplyBuilder(std::size_t reserveBy
 
 CommandReplyBuilder& CommandReplyBuilder::setMetadata(const BSONObj& metadata) {
     invariant(_state == State::kMetadata);
-    metadata.appendSelfToBufBuilder(_builder);
+    // OP_COMMAND is only used when communicating with 3.4 nodes and they serialize their metadata
+    // fields differently. We do all up- and down-conversion here so that the rest of the code only
+    // has to deal with the current format.
+    BSONObjBuilder bob(_builder);
+    for (auto elem : metadata) {
+        if (elem.fieldNameStringData() == "$configServerState") {
+            bob.appendAs(elem, "configsvr");
+        } else {
+            bob.append(elem);
+        }
+    }
     _state = State::kOutputDocs;
     return *this;
 }
diff --git a/src/mongo/rpc/command_request.cpp b/src/mongo/rpc/command_request.cpp
index 024b8ebe9c1..98df6c3ed84 100644
--- a/src/mongo/rpc/command_request.cpp
+++ b/src/mongo/rpc/command_request.cpp
@@ -110,8 +110,20 @@ CommandRequest::CommandRequest(const Message* message) : _message(message) {
                           << '\'',
             _commandArgs.firstElementFieldName() == _commandName);
 
+    // OP_COMMAND is only used when communicating with 3.4 nodes and they serialize their metadata
+    // fields differently. We do all up- and down-conversion here so that the rest of the code only
+    // has to deal with the current format.
     uassertStatusOK(cur.readAndAdvance<>(&obj));
-    _metadata = std::move(obj.val);
+    BSONObjBuilder metadataBuilder;
+    for (auto elem : obj.val) {
+        if (elem.fieldNameStringData() == "configsvr") {
+            metadataBuilder.appendAs(elem, "$configServerState");
+        } else {
+            metadataBuilder.append(elem);
+        }
+    }
+    _metadata = metadataBuilder.obj();
+
     uassert(40419, "OP_COMMAND request contains trailing bytes following metadata", cur.empty());
 }
 
diff --git a/src/mongo/rpc/command_request_builder.cpp b/src/mongo/rpc/command_request_builder.cpp
index 11b25beef6e..34f6daa0888 100644
--- a/src/mongo/rpc/command_request_builder.cpp
+++ b/src/mongo/rpc/command_request_builder.cpp
@@ -70,7 +70,17 @@ CommandRequestBuilder& CommandRequestBuilder::setCommandArgs(BSONObj commandArgs
 
 CommandRequestBuilder& CommandRequestBuilder::setMetadata(BSONObj metadata) {
     invariant(_state == State::kMetadata);
-    metadata.appendSelfToBufBuilder(_builder);
+    // OP_COMMAND is only used when communicating with 3.4 nodes and they serialize their metadata
+    // fields differently. We do all up- and down-conversion here so that the rest of the code only
+    // has to deal with the current format.
+    BSONObjBuilder bob(_builder);
+    for (auto elem : metadata) {
+        if (elem.fieldNameStringData() == "$configServerState") {
+            bob.appendAs(elem, "configsvr");
+        } else {
+            bob.append(elem);
+        }
+    }
     _state = State::kInputDocs;
     return *this;
 }
diff --git a/src/mongo/rpc/metadata/config_server_metadata.h b/src/mongo/rpc/metadata/config_server_metadata.h
index 7865281ad26..9369f6d949e 100644
--- a/src/mongo/rpc/metadata/config_server_metadata.h
+++ b/src/mongo/rpc/metadata/config_server_metadata.h
@@ -83,7 +83,7 @@ public:
     }
 
     static StringData fieldName() {
-        return "configsvr";
+        return "$configServerState";
     }
 
 private:
diff --git a/src/mongo/rpc/metadata/config_server_metadata_test.cpp b/src/mongo/rpc/metadata/config_server_metadata_test.cpp
index 6d8749ac495..0b2d649e52d 100644
--- a/src/mongo/rpc/metadata/config_server_metadata_test.cpp
+++ b/src/mongo/rpc/metadata/config_server_metadata_test.cpp
@@ -48,7 +48,7 @@ TEST(ConfigSvrMetadataTest, Roundtrip) {
     metadata.writeToMetadata(&builder);
 
     BSONObj expectedObj(
-        BSON("configsvr" << BSON(
+        BSON("$configServerState" << BSON(
                  "opTime" << BSON("ts" << opTime.getTimestamp() << "t" << opTime.getTerm()))));
 
     BSONObj serializedObj = builder.obj();