File receiver

Async file-receiving transport pairing offers, acknowledgments, and TransitReceiver.

from attr import attrib, attrs
from attr.validators import instance_of
from automat import MethodicalMachine
from zope.interface import implementer

from . import _interfaces
from ._key import CryptoError, decrypt_data, derive_key, derive_phase_key
from .util import provides


@attrs
@implementer(_interfaces.IReceive)
class Receive:
    _side = attrib(validator=instance_of(str))
    _timing = attrib(validator=provides(_interfaces.ITiming))
    m = MethodicalMachine()
    set_trace = getattr(m, "_setTrace",
                        lambda self, f: None)  # pragma: no cover

    def __attrs_post_init__(self):
        self._key = None

    def wire(self, boss, send):
        self._B = _interfaces.IBoss(boss)
        self._S = _interfaces.ISend(send)

    @m.state(initial=True)
    def S0_unkno

... (truncated -- full source via MCP)