struct OP_MSG { MsgHeader header; // standard message header uint32 flagBits; // message flags Sections[] sections; // data sections optional<uint32> checksum; // optional CRC-32C checksum } Flags Bit Name Description 0 checksumPresent The message ends with 4 bytes containing a CRC-32C. 1 moreToCome 16 exhaustAllowed Sections Kind byte indicating its type, followed by: Kind 0: Body — single BSON doc Kind 1: Document Sequence