positive fixint / uint8 / uint16 / uint32 / uint64	Length of Payload
...	Payload

Handshake

TODO: Magic word, features as map

Request
4 bytes	Magic number 49 47 4E 49, or "IGNI". Helps identifying misconfigured SSL or other apps probing the port.
fixint / uint	Payload length
positive fixint	Version major
positive fixint	Version minor
positive fixint	Version patch
positive fixint	Client code (1 for JDBC, 2 for general-purpose client)
bin	Features (bitmask)
map (int → any)	Extensions (auth, attributes, etc). Server can skip unknown extension data (when client is newer).

Response
4 bytes	Magic number 49 47 4E 49, or "IGNI". Helps identifying misconfigured SSL or different server on the port.
fixint / uint	Payload length
positive fixint	Server version major
positive fixint	Server version minor
positive fixint	Server version patch
boolean	Success flag
string	When success flag is false: Error message
bin	When success flag is true: Server features (bitmask)
map (int → any)	When success flag is true: Extensions (auth, attributes, etc). Client can skip unknown extension data (when server is newer).

Risks and Assumptions

TODO

...