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296 lines
11 KiB
296 lines
11 KiB
"""
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# Wire
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Handles on-the-wire communication with a host computer. The communication is:
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- Request / response.
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- Protobuf-encoded, see `protobuf.py`.
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- Wrapped in a simple envelope format, see `trezor/wire/codec_v1.py` or `trezor/wire/thp_v1.py`.
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- Transferred over USB interface, or UDP in case of Unix emulation.
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This module:
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1. Runs workflows, also called `handlers`, to process the message.
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2. Creates and passes the `Context` object to the handlers. This provides an interface to
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wait, read, write etc. on the wire.
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## Session handler
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When the `wire.setup` is called the `handle_session` coroutine is scheduled. The
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`handle_session` waits for some messages to be received on some particular interface and
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reads the message's header. When the message type is known the first handler is called. This way the
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`handle_session` goes through all the workflows.
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"""
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from apps import workflow_handlers
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from micropython import const
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from typing import TYPE_CHECKING
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from storage.cache_codec import InvalidSessionError
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from trezor import log, loop, protobuf, utils, workflow
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from trezor.enums import FailureType
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from trezor.messages import Failure
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from trezor.wire import codec_v1, context, protocol_common
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from trezor.wire.errors import ActionCancelled, DataError, Error
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import trezor.enums.MessageType as MT
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# Import all errors into namespace, so that `wire.Error` is available from
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# other packages.
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from trezor.wire.errors import * # isort:skip # noqa: F401,F403
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if TYPE_CHECKING:
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from trezorio import WireInterface
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from typing import Any, Callable, Container, Coroutine, TypeVar
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Msg = TypeVar("Msg", bound=protobuf.MessageType)
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HandlerTask = Coroutine[Any, Any, protobuf.MessageType]
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Handler = Callable[[Msg], HandlerTask]
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LoadedMessageType = TypeVar("LoadedMessageType", bound=protobuf.MessageType)
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# If set to False protobuf messages marked with "experimental_message" option are rejected.
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EXPERIMENTAL_ENABLED = False
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def setup(iface: WireInterface, is_debug_session: bool = False) -> None:
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"""Initialize the wire stack on passed USB interface."""
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loop.schedule(
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handle_session(iface, codec_v1.SESSION_ID.to_bytes(4, "big"), is_debug_session)
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)
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def wrap_protobuf_load(
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buffer: bytes,
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expected_type: type[LoadedMessageType],
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) -> LoadedMessageType:
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try:
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msg = protobuf.decode(buffer, expected_type, EXPERIMENTAL_ENABLED)
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if __debug__ and utils.EMULATOR:
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log.debug(
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__name__, "received message contents:\n%s", utils.dump_protobuf(msg)
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)
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return msg
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except Exception as e:
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if __debug__:
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log.exception(__name__, e)
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if e.args:
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raise DataError("Failed to decode message: " + " ".join(e.args))
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else:
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raise DataError("Failed to decode message")
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_PROTOBUF_BUFFER_SIZE = const(8192)
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WIRE_BUFFER = bytearray(_PROTOBUF_BUFFER_SIZE)
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if __debug__:
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PROTOBUF_BUFFER_SIZE_DEBUG = 1024
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WIRE_BUFFER_DEBUG = bytearray(PROTOBUF_BUFFER_SIZE_DEBUG)
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async def _handle_single_message(
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ctx: context.Context, msg: protocol_common.Message, use_workflow: bool
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) -> protocol_common.Message | None:
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"""Handle a message that was loaded from USB by the caller.
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Find the appropriate handler, run it and write its result on the wire. In case
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a problem is encountered at any point, write the appropriate error on the wire.
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If the workflow finished normally or with an error, the return value is None.
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If an unexpected message had arrived on the wire while the workflow was processing,
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the workflow is shut down with an `UnexpectedMessage` exception. This is not
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considered an "error condition" to return over the wire -- instead the message
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is processed as if starting a new workflow.
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In such case, the `UnexpectedMessage` is caught and the message is returned
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to the caller. It will then be processed in the next iteration of the message loop.
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"""
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if __debug__:
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try:
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msg_type = protobuf.type_for_wire(msg.type).MESSAGE_NAME
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except Exception:
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msg_type = f"{msg.type} - unknown message type"
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log.debug(
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__name__,
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"%s:%x receive: <%s>",
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ctx.iface.iface_num(),
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int.from_bytes(ctx.session_id, "big"),
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msg_type,
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)
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res_msg: protobuf.MessageType | None = None
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# We need to find a handler for this message type. Should not raise.
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handler = find_handler(ctx.iface, msg.type) # pylint: disable=assignment-from-none
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if handler is None:
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# If no handler is found, we can skip decoding and directly
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# respond with failure.
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await ctx.write(unexpected_message())
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return None
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if msg.type in workflow.ALLOW_WHILE_LOCKED:
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workflow.autolock_interrupts_workflow = False
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# Here we make sure we always respond with a Failure response
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# in case of any errors.
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try:
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# Find a protobuf.MessageType subclass that describes this
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# message. Raises if the type is not found.
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req_type = protobuf.type_for_wire(msg.type)
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# Try to decode the message according to schema from
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# `req_type`. Raises if the message is malformed.
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req_msg = wrap_protobuf_load(msg.data, req_type)
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# Create the handler task.
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task = handler(req_msg)
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# Run the workflow task. Workflow can do more on-the-wire
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# communication inside, but it should eventually return a
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# response message, or raise an exception (a rather common
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# thing to do). Exceptions are handled in the code below.
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if use_workflow:
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# Spawn a workflow around the task. This ensures that concurrent
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# workflows are shut down.
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res_msg = await workflow.spawn(context.with_context(ctx, task))
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else:
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# For debug messages, ignore workflow processing and just await
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# results of the handler.
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res_msg = await task
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except context.UnexpectedMessage as exc:
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# Workflow was trying to read a message from the wire, and
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# something unexpected came in. See Context.read() for
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# example, which expects some particular message and raises
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# UnexpectedMessage if another one comes in.
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# In order not to lose the message, we return it to the caller.
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# TODO:
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# We might handle only the few common cases here, like
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# Initialize and Cancel.
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return exc.msg
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except BaseException as exc:
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# Either:
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# - the message had a type that has a registered handler, but does not have
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# a protobuf class
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# - the message was not valid protobuf
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# - workflow raised some kind of an exception while running
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# - something canceled the workflow from the outside
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if __debug__:
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if isinstance(exc, ActionCancelled):
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log.debug(__name__, "cancelled: %s", exc.message)
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elif isinstance(exc, loop.TaskClosed):
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log.debug(__name__, "cancelled: loop task was closed")
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else:
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log.exception(__name__, exc)
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res_msg = failure(exc)
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if res_msg is not None:
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# perform the write outside the big try-except block, so that usb write
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# problem bubbles up
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await ctx.write(res_msg)
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return None
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async def handle_session(
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iface: WireInterface, session_id: bytes, is_debug_session: bool = False
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) -> None:
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if __debug__ and is_debug_session:
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ctx_buffer = WIRE_BUFFER_DEBUG
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else:
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ctx_buffer = WIRE_BUFFER
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ctx = context.Context(iface, ctx_buffer, session_id)
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next_msg: protocol_common.Message | None = None
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if __debug__ and is_debug_session:
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import apps.debug
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apps.debug.DEBUG_CONTEXT = ctx
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# Take a mark of modules that are imported at this point, so we can
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# roll back and un-import any others.
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modules = utils.unimport_begin()
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while True:
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try:
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if next_msg is None:
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# If the previous run did not keep an unprocessed message for us,
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# wait for a new one coming from the wire.
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try:
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msg = await ctx.read_from_wire()
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except protocol_common.WireError as exc:
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if __debug__:
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log.exception(__name__, exc)
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await ctx.write(failure(exc))
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continue
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else:
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# Process the message from previous run.
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msg = next_msg
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next_msg = None
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# Set ctx.session_id to the value msg.session_id
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ctx.session_id = msg.session_id
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try:
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next_msg = await _handle_single_message(
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ctx, msg, use_workflow=not is_debug_session
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)
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except Exception as exc:
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# Log and ignore. The session handler can only exit explicitly in the
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# following finally block.
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if __debug__:
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log.exception(__name__, exc)
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finally:
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if not __debug__ or not is_debug_session:
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# Unload modules imported by the workflow. Should not raise.
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# This is not done for the debug session because the snapshot taken
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# in a debug session would clear modules which are in use by the
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# workflow running on wire.
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utils.unimport_end(modules)
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if next_msg is None and msg.type not in AVOID_RESTARTING_FOR:
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# Shut down the loop if there is no next message waiting.
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# Let the session be restarted from `main`.
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loop.clear()
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return # pylint: disable=lost-exception
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except Exception as exc:
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# Log and try again. The session handler can only exit explicitly via
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# loop.clear() above.
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if __debug__:
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log.exception(__name__, exc)
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def _find_handler_placeholder(iface: WireInterface, msg_type: int) -> Handler | None:
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"""Placeholder handler lookup before a proper one is registered."""
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return None
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find_handler = _find_handler_placeholder
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AVOID_RESTARTING_FOR: Container[int] = ()
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def failure(exc: BaseException) -> Failure:
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if isinstance(exc, Error):
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return Failure(code=exc.code, message=exc.message)
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elif isinstance(exc, loop.TaskClosed):
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return Failure(code=FailureType.ActionCancelled, message="Cancelled")
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elif isinstance(exc, InvalidSessionError):
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return Failure(code=FailureType.InvalidSession, message="Invalid session")
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else:
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# NOTE: when receiving generic `FirmwareError` on non-debug build,
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# change the `if __debug__` to `if True` to get the full error message.
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if __debug__:
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message = str(exc)
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else:
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message = "Firmware error"
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return Failure(code=FailureType.FirmwareError, message=message)
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def unexpected_message() -> Failure:
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return Failure(code=FailureType.UnexpectedMessage, message="Unexpected message")
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