Raft::StateMachine(T)

Abstract base for application state machines. Subclasses implement apply, snapshot, and restore.

The generic parameter T is the application's command type. It must implement three methods that together form the on-disk/wire serialization contract for log entries:

• def to_io(io : IO, format : IO::ByteFormat) : Nil — write self to io
• def self.from_io(io : IO, format : IO::ByteFormat) : T — read from io
• def bytesize : Int32 — number of bytes to_io will write

bytesize must return exactly the byte count to_io writes. The library uses bytesize to:

• predict serialized size for segment-rotation decisions in Log#append
• emit the size prefix in LogEntry#to_io without an intermediate buffer

A bytesize that disagrees with to_io will silently corrupt the log: offsets drift from actual byte positions, and subsequent reads return garbage or fail.