magic-wormhole/src/wormhole/_send.py

from zope.interface import implementer
from automat import MethodicalMachine
from . import _interfaces
from ._key import derive_phase_key, encrypt_data

@implementer(_interfaces.ISend)
class Send(object):
    m = MethodicalMachine()
    def __init__(self, side, timing):
        self._side = side
        self._timing = timing
    def wire(self, mailbox):
        self._M = _interfaces.IMailbox(mailbox)

    @m.state(initial=True)
    def S0_no_key(self): pass
    @m.state(terminal=True)
    def S1_verified_key(self): pass

    @m.input()
    def got_verified_key(self, key): pass
    @m.input()
    def send(self, phase, plaintext): pass

    @m.output()
    def queue(self, phase, plaintext):
        assert isinstance(phase, type("")), type(phase)
        assert isinstance(plaintext, type(b"")), type(plaintext)
        self._queue.append((phase, plaintext))
    @m.output()
    def record_key(self, key):
        self._key = key
    @m.output()
    def drain(self, key):
        del key
        for (phase, plaintext) in self._queue:
            self._encrypt_and_send(phase, plaintext)
        self._queue[:] = []
    @m.output()
    def deliver(self, phase, plaintext):
        assert isinstance(phase, type("")), type(phase)
        assert isinstance(plaintext, type(b"")), type(plaintext)
        self._encrypt_and_send(phase, plaintext)

    def _encrypt_and_send(self, phase, plaintext):
        data_key = derive_phase_key(self._side, phase)
        encrypted = encrypt_data(data_key, plaintext)
        self._M.add_message(phase, encrypted)

    S0_no_key.upon(send, enter=S0_no_key, outputs=[queue])
    S0_no_key.upon(got_verified_key, enter=S1_verified_key,
                   outputs=[record_key, drain])
    S1_verified_key.upon(send, enter=S1_verified_key, outputs=[deliver])