OpMsgRequest upconvertRequest(StringData db, BSONObj cmdObj, int queryFlags) {
cmdObj = cmdObj.getOwned(); // Usually this is a no-op since it is already owned.
auto readPrefContainer = BSONObj();
const StringData firstFieldName = cmdObj.firstElementFieldName();
if (firstFieldName == "$query" || firstFieldName == "query") {
// Commands sent over OP_QUERY specify read preference by putting it at the top level and
// putting the command in a nested field called either query or $query.
// Check if legacyCommand has an invalid $maxTimeMS option.
uassert(ErrorCodes::InvalidOptions,
"cannot use $maxTimeMS query option with commands; use maxTimeMS command option "
"instead",
!cmdObj.hasField("$maxTimeMS"));
if (auto readPref = cmdObj["$readPreference"])
readPrefContainer = readPref.wrap();
cmdObj = cmdObj.firstElement().Obj().shareOwnershipWith(cmdObj);
} else if (auto queryOptions = cmdObj["$queryOptions"]) {
// Mongos rewrites commands with $readPreference to put it in a field nested inside of
// $queryOptions. Its command implementations often forward commands in that format to
// shards. This function is responsible for rewriting it to a format that the shards
// understand.
readPrefContainer = queryOptions.Obj().shareOwnershipWith(cmdObj);
cmdObj = cmdObj.removeField("$queryOptions");
}
if (!readPrefContainer.isEmpty()) {
cmdObj = BSONObjBuilder(std::move(cmdObj)).appendElements(readPrefContainer).obj();
} else if (!cmdObj.hasField("$readPreference") && (queryFlags & QueryOption_SlaveOk)) {
BSONObjBuilder bodyBuilder(std::move(cmdObj));
ReadPreferenceSetting(ReadPreference::SecondaryPreferred).toContainingBSON(&bodyBuilder);
cmdObj = bodyBuilder.obj();
}
// Try to move supported array fields into document sequences.
auto docSequenceIt = docSequenceFieldsForCommands.find(cmdObj.firstElementFieldName());
auto docSequenceElem = docSequenceIt == docSequenceFieldsForCommands.end()
? BSONElement()
: cmdObj[docSequenceIt->second];
if (!isArrayOfObjects(docSequenceElem))
return OpMsgRequest::fromDBAndBody(db, std::move(cmdObj));
auto docSequenceName = docSequenceElem.fieldNameStringData();
// Note: removing field before adding "$db" to avoid the need to copy the potentially large
// array.
auto out = OpMsgRequest::fromDBAndBody(db, cmdObj.removeField(docSequenceName));
out.sequences.push_back({docSequenceName.toString()});
for (auto elem : docSequenceElem.Obj()) {
out.sequences[0].objs.push_back(elem.Obj().shareOwnershipWith(cmdObj));
}
return out;
}
Message opCommandRequestFromOpMsgRequest(const OpMsgRequest& request) {
const auto commandName = request.getCommandName();
BufBuilder builder;
builder.skip(mongo::MsgData::MsgDataHeaderSize); // Leave room for message header.
builder.appendStr(request.getDatabase());
builder.appendStr(commandName);
// OP_COMMAND is only used when communicating with 3.4 nodes and they serialize their metadata
// fields differently. In addition to field-level differences, some generic arguments are pulled
// out to a metadata object, separate from the body. We do all down-conversion here so that the
// rest of the code only has to deal with the current format.
BSONObjBuilder metadataBuilder; // Will be appended to the message after we finish the body.
{
BSONObjBuilder bodyBuilder(builder);
for (auto elem : request.body) {
const auto fieldName = elem.fieldNameStringData();
if (fieldName == "$configServerState") {
metadataBuilder.appendAs(elem, "configsvr");
} else if (fieldName == "$readPreference") {
BSONObjBuilder ssmBuilder(metadataBuilder.subobjStart("$ssm"));
ssmBuilder.append(elem);
ssmBuilder.append("$secondaryOk",
uassertStatusOK(ReadPreferenceSetting::fromInnerBSON(elem))
.canRunOnSecondary());
} else if (fieldName == "$db") {
// skip
} else if (fieldGoesInMetadata(commandName, fieldName)) {
metadataBuilder.append(elem);
} else {
bodyBuilder.append(elem);
}
}
for (auto&& seq : request.sequences) {
invariant(seq.name.find('.') == std::string::npos); // Only support top-level for now.
dassert(!bodyBuilder.asTempObj().hasField(seq.name));
bodyBuilder.append(seq.name, seq.objs);
}
}
metadataBuilder.obj().appendSelfToBufBuilder(builder);
MsgData::View msg = builder.buf();
msg.setLen(builder.len());
msg.setOperation(dbCommand);
return Message(builder.release());
}