参数

server

An array containing the basic information about the server that was picked.

key	value
hash	server hash, example: localhost:27017;-;X;56052
type	Node type (primary/secondary/mongos/arbiter): 2
max_bson_size	The maximum BSON Size over the wire this node accepts: 16777216
max_message_size	The maximum Message Size over the wire this node accepts: 48000000
request_id	The request identifier for this message: 42

messageHeaders

key	value
length	integer, bytes, message reply length
request_id	integer, the server request identifier
response_id	integer, the driver request identifier this message is a response of
opcode	integer, the opcode id

operationHeaders

key	value
flags	integer, bitmask of protocol flags
cursor_id	integer, ID of the cursor created on the server (0 if none created, or its been exhausted)
start	The starting offset of this cursor
returned	integer, how many documents are returned in this trip