class Handler
def initialize(first_msg)
@type, @seq, @limit = msg.type, msg.seq, msg.limit
first_msg.ack!
end

def upto(limit)
if limit > @limit
raise BadMessage, "Message sequence too short"
end

loop do
msg = Message.get

if msg.type != @type ||
msg.limit != @limit ||
msg.seq > limit
raise BadMessage, "Invalid message continuation"
end

yield msg
end
end

def dispatch
raise NotImplementedError
end
end

class Protocol
def initialize(handlers)
@handlers = handlers
end

def dispatch
loop { dispatch_one }
end

def dispatch_one
msg = Message.get
return unless msg.seq == 0

@handlers.find do |handler|
handler.accept?(msg)
end.new(msg).dispatch
rescue e
# nothing;
# or: debug_trace(e)
end
end

class FirmwareFlashHandler
UNLOCK_KEY = ByteArray("\x00" * 64)

def initialize(first_msg)
unless first_msg.payload == UNLOCK_KEY
raise BadMessage, "Invalid unlock key"
end

super
end

def dispatch
flasher = FirmwareFlasher.new

upto(@limit - 1) do |msg|
flasher.process(msg.payload)
msg.ack!
end

upto(@limit) do |msg|
flasher.verify_hash(msg.payload)
msg.ack!
end
end
end

Protocol.new([
FirmwareFlashHandler
]).dispatch