struct MsgHeader {
int32 *messageLength*; // total message size, including this
int32 requestID; // identifier for this message
int32 responseTo; // requestID from the original request
int32 *opCode*; // request type - see table below for details
}?
~Opcode Name Value Comment~
*OP_REPLY 1 Reply to a client request. responseTo is set.*
|999999|OP_UPDATE 2001 Update document.|
|999999|OP_INSERT 2002 Insert new document.|
|999999|RESERVED 2003 Formerly used for OP_GET_BY_OID.|
*OP_QUERY 2004 Query a collection.*
|999999|OP_GET_MORE 2005 Get more data from a query. See Cursors.|
|999999|OP_DELETE 2006 Delete documents.|
|999999|OP_KILL_CURSORS 2007 Notify database that the client has finished with the cursor.|
|999999|OP_COMMAND 2010 Cluster internal protocol representing a command request.|
|999999|OP_COMMANDREPLY 2011 Cluster internal protocol representing a reply to an OP_COMMAND.|
*OP_MSG 2013 Send a message using the format introduced in MongoDB 3.6.*