| # Copyright 2021 The Pigweed Authors |
| # |
| # Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| # use this file except in compliance with the License. You may obtain a copy of |
| # the License at |
| # |
| # https://www.apache.org/licenses/LICENSE-2.0 |
| # |
| # Unless required by applicable law or agreed to in writing, software |
| # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| # License for the specific language governing permissions and limitations under |
| # the License. |
| """Provides a simple interface for transferring bulk data over pw_rpc.""" |
| |
| import abc |
| import asyncio |
| import logging |
| import threading |
| from typing import Any, Callable, Dict, Optional |
| |
| from pw_rpc.callback_client import BidirectionalStream |
| from pw_status import Status |
| from pw_transfer.transfer_pb2 import Chunk |
| |
| _LOG = logging.getLogger(__name__) |
| |
| |
| class _Timer: |
| """A timer which invokes a callback after a certain timeout.""" |
| def __init__(self, callback: Callable[[], Any]): |
| self._callback = callback |
| self._task: Optional[asyncio.Task[Any]] = None |
| |
| def start(self, timeout_s: float): |
| """Starts a new timer. |
| |
| If a timer is already running, it is stopped and a new timer started. |
| This can be used to implement watchdog-like behavior, where a callback |
| is invoked after some time without a kick. |
| """ |
| self.stop() |
| self._task = asyncio.create_task(self._run(timeout_s)) |
| |
| def stop(self): |
| """Terminates a running timer.""" |
| if self._task is not None: |
| self._task.cancel() |
| self._task = None |
| |
| async def _run(self, timeout_s: float): |
| await asyncio.sleep(timeout_s) |
| self._callback() |
| self._task = None |
| |
| |
| class _Transfer(abc.ABC): |
| """A client-side data transfer through a Manager. |
| |
| Subclasses are responsible for implementing all of the logic for their type |
| of transfer, receiving messages from the server and sending the appropriate |
| messages in response. |
| """ |
| def __init__(self, transfer_id: int, data: bytes, |
| send_chunk: Callable[[Chunk], None], |
| end_transfer: Callable[['_Transfer', Status], None]): |
| self.id = transfer_id |
| self.status = Status.OK |
| self.data = data |
| self.done = threading.Event() |
| self._send_chunk = send_chunk |
| self._end_transfer = end_transfer |
| |
| @abc.abstractmethod |
| async def begin(self) -> None: |
| """Sends the initial chunk to notify the sever of the transfer.""" |
| |
| @abc.abstractmethod |
| async def handle_chunk(self, chunk: Chunk) -> bool: |
| """Processes an incoming chunk from the server. |
| |
| Returns True if the transfer is complete or False otherwise. |
| |
| Only called for non-terminating chunks (i.e. those without a status). |
| """ |
| |
| def _send_error(self, error: Status) -> None: |
| """Sends an error chunk to the server. Should only be called once.""" |
| self.status = error |
| self._send_chunk(Chunk(transfer_id=self.id, status=error.value)) |
| |
| |
| class _WriteTransfer(_Transfer): |
| """A client -> server write transfer.""" |
| def __init__( |
| self, |
| transfer_id: int, |
| data: bytes, |
| send_chunk: Callable[[Chunk], None], |
| end_transfer: Callable[[_Transfer, Status], None], |
| response_timeout_s: float, |
| ): |
| super().__init__(transfer_id, data, send_chunk, end_transfer) |
| self._offset = 0 |
| self._response_timeout_s = response_timeout_s |
| self._response_timer = _Timer( |
| lambda: self._end_transfer(self, Status.DEADLINE_EXCEEDED)) |
| |
| self._max_bytes_to_send = 0 |
| self._max_chunk_size = 0 |
| self._chunk_delay_us: Optional[int] = None |
| |
| async def begin(self) -> None: |
| """Sends the transfer ID, notifying the server that we want to write.""" |
| self._send_chunk(Chunk(transfer_id=self.id)) |
| self._response_timer.start(self._response_timeout_s) |
| |
| async def handle_chunk(self, chunk: Chunk) -> bool: |
| """Processes an incoming chunk from the server. |
| |
| In a write transfer, the server only sends transfer parameter updates |
| to the client. When a message is received, update local parameters and |
| send data accordingly. |
| """ |
| |
| self._response_timer.stop() |
| |
| # Check whether the client has sent a previous data offset, which |
| # indicates that some chunks were lost in transmission. |
| if chunk.offset < self._offset: |
| _LOG.debug('Write transfer %d rolling back to offset %d from %d', |
| self.id, chunk.offset, self._offset) |
| |
| self._offset = chunk.offset |
| |
| if self._offset > len(self.data): |
| # Bad offset; terminate the transfer. |
| _LOG.error( |
| 'Transfer %d: server requested invalid offset %d (size %d)', |
| self.id, self._offset, len(self.data)) |
| |
| self._send_error(Status.OUT_OF_RANGE) |
| return True |
| |
| self._max_bytes_to_send = min(chunk.pending_bytes, |
| len(self.data) - self._offset) |
| |
| if chunk.HasField('max_chunk_size_bytes'): |
| self._max_chunk_size = chunk.max_chunk_size_bytes |
| if chunk.HasField('min_delay_microseconds'): |
| self._chunk_delay_us = chunk.min_delay_microseconds |
| |
| while self._max_bytes_to_send > 0: |
| write_chunk = self._next_chunk() |
| self._offset += len(write_chunk.data) |
| self._max_bytes_to_send -= len(write_chunk.data) |
| |
| self._send_chunk(write_chunk) |
| |
| if self._chunk_delay_us: |
| await asyncio.sleep(self._chunk_delay_us / 1e6) |
| |
| self._response_timer.start(self._response_timeout_s) |
| return False |
| |
| def _next_chunk(self) -> Chunk: |
| """Returns the next Chunk message to send in the data transfer.""" |
| chunk = Chunk(transfer_id=self.id, offset=self._offset) |
| |
| if len(self.data) - self._offset <= self._max_chunk_size: |
| # Final chunk of the transfer. |
| chunk.data = self.data[self._offset:] |
| chunk.remaining_bytes = 0 |
| else: |
| chunk.data = self.data[self._offset:self._offset + |
| self._max_chunk_size] |
| |
| return chunk |
| |
| |
| class _ReadTransfer(_Transfer): |
| """A client <- server read transfer. |
| |
| Although Python can effectively handle an unlimited transfer window, this |
| client sets a conservative window and chunk size to avoid overloading the |
| device. These are configurable in the constructor. |
| """ |
| def __init__(self, |
| transfer_id: int, |
| send_chunk: Callable[[Chunk], None], |
| end_transfer: Callable[[_Transfer, Status], None], |
| response_timeout_s: float, |
| max_retries: int = 3, |
| max_bytes_to_receive: int = 8192, |
| max_chunk_size: int = 1024, |
| chunk_delay_us: int = None): |
| super().__init__(transfer_id, bytes(), send_chunk, end_transfer) |
| |
| self._response_timeout_s = response_timeout_s |
| self._response_timer = _Timer(self._on_timeout) |
| self._chunk_timeout_count = 0 |
| self._max_retries = max_retries |
| |
| self._max_bytes_to_receive = max_bytes_to_receive |
| self._max_chunk_size = max_chunk_size |
| self._chunk_delay_us = chunk_delay_us |
| |
| self._remaining_transfer_size: Optional[int] = None |
| self._offset = 0 |
| self._pending_bytes = max_bytes_to_receive |
| |
| async def begin(self) -> None: |
| """Sends the initial transfer parameters for the read transfer.""" |
| self._send_transfer_parameters() |
| |
| async def handle_chunk(self, chunk: Chunk) -> bool: |
| """Processes an incoming chunk from the server. |
| |
| In a read transfer, the client receives data chunks from the server. |
| Once all pending data is received, the transfer parameters are updated. |
| """ |
| |
| self._response_timer.stop() |
| self._chunk_timeout_count = 0 |
| |
| if chunk.offset != self._offset: |
| # Initially, the transfer service only supports in-order transfers. |
| # If data is received out of order, request that the server |
| # retransmit from the previous offset. |
| self._pending_bytes = 0 |
| self._send_transfer_parameters() |
| return False |
| |
| self.data += chunk.data |
| self._pending_bytes -= len(chunk.data) |
| self._offset += len(chunk.data) |
| |
| if chunk.HasField('remaining_bytes'): |
| if chunk.remaining_bytes == 0: |
| # No more data to read. Acknowledge receipt and finish. |
| self._send_chunk( |
| Chunk(transfer_id=self.id, status=Status.OK.value)) |
| return True |
| |
| # The server may optionally indicate that it has a known size of |
| # data available. This is not yet used. |
| self._remaining_transfer_size = chunk.remaining_bytes |
| |
| if self._pending_bytes == 0: |
| # All pending data was received. Send out a new parameters chunk for |
| # the next block. |
| # _send_transfer_parameters starts the response timer. |
| self._send_transfer_parameters() |
| else: |
| # Wait for the next pending chunk. |
| self._response_timer.start(self._response_timeout_s) |
| |
| return False |
| |
| def _send_transfer_parameters(self): |
| """Sends an updated transfer parameters chunk to the server.""" |
| |
| self._pending_bytes = self._max_bytes_to_receive |
| |
| chunk = Chunk(transfer_id=self.id, |
| pending_bytes=self._pending_bytes, |
| max_chunk_size_bytes=self._max_chunk_size, |
| offset=self._offset) |
| |
| if self._chunk_delay_us: |
| chunk.min_delay_microseconds = self._chunk_delay_us |
| |
| self._send_chunk(chunk) |
| |
| # Start the timeout for the server to send a read chunk. |
| self._response_timer.start(self._response_timeout_s) |
| |
| def _on_timeout(self) -> None: |
| """Handles a timeout while waiting for a chunk. |
| |
| In a read transfer, if a chunk is not received by the timeout, the |
| receiver resends the latest transfer parameters to prompt the server |
| for more data. This is done several times, up to a specified number of |
| retries, after which the transfer is terminated. |
| """ |
| self._chunk_timeout_count += 1 |
| |
| if self._chunk_timeout_count > self._max_retries: |
| self._end_transfer(self, Status.DEADLINE_EXCEEDED) |
| else: |
| self._send_transfer_parameters() |
| |
| |
| _TransferDict = Dict[int, _Transfer] |
| |
| |
| class Manager: # pylint: disable=too-many-instance-attributes |
| """A manager for transmitting data through an RPC TransferService. |
| |
| This should be initialized with an active Manager over an RPC channel. Only |
| one instance of this class should exist for a configured RPC TransferService |
| -- the Manager supports multiple simultaneous transfers. |
| |
| When created, a Manager starts a separate thread in which transfer |
| communications and events are handled. |
| """ |
| def __init__(self, |
| rpc_transfer_service, |
| default_response_timeout_s: float = 2.0): |
| """Initializes a Manager on top of a TransferService.""" |
| self._service: Any = rpc_transfer_service |
| self._default_response_timeout_s = default_response_timeout_s |
| |
| # Ongoing transfers in the service by ID. |
| self._read_transfers: _TransferDict = {} |
| self._write_transfers: _TransferDict = {} |
| |
| # RPC streams for read and write transfers. These are shareable by |
| # multiple transfers of the same type. |
| self._read_stream: Optional[BidirectionalStream] = None |
| self._write_stream: Optional[BidirectionalStream] = None |
| |
| self._loop = asyncio.new_event_loop() |
| |
| # Queues are used for communication between the Manager context and the |
| # dedicated asyncio transfer thread. |
| self._new_transfer_queue: asyncio.Queue = asyncio.Queue() |
| self._read_chunk_queue: asyncio.Queue = asyncio.Queue() |
| self._write_chunk_queue: asyncio.Queue = asyncio.Queue() |
| self._quit_event = asyncio.Event() |
| |
| self._thread = threading.Thread(target=self._start_event_loop_thread, |
| daemon=True) |
| |
| self._thread.start() |
| |
| def __del__(self): |
| # Notify the thread that the transfer manager is being destroyed and |
| # wait for it to exit. |
| if self._thread.is_alive(): |
| self._loop.call_soon_threadsafe(self._quit_event.set) |
| self._thread.join() |
| |
| def read(self, transfer_id: int) -> bytes: |
| """Receives ("downloads") data from the server. |
| |
| Raises: |
| Error: the transfer failed to complete |
| """ |
| |
| if transfer_id in self._read_transfers: |
| raise ValueError(f'Read transfer {transfer_id} already exists') |
| |
| transfer = _ReadTransfer(transfer_id, self._send_read_chunk, |
| self._end_read_transfer, |
| self._default_response_timeout_s) |
| self._start_read_transfer(transfer) |
| |
| transfer.done.wait() |
| |
| if not transfer.status.ok(): |
| raise Error(transfer.id, transfer.status) |
| |
| return transfer.data |
| |
| def write(self, transfer_id: int, data: bytes) -> None: |
| """Transmits ("uploads") data to the server. |
| |
| Raises: |
| Error: the transfer failed to complete |
| """ |
| |
| if transfer_id in self._write_transfers: |
| raise ValueError(f'Write transfer {transfer_id} already exists') |
| |
| transfer = _WriteTransfer(transfer_id, data, self._send_write_chunk, |
| self._end_write_transfer, |
| self._default_response_timeout_s) |
| self._start_write_transfer(transfer) |
| |
| transfer.done.wait() |
| |
| if not transfer.status.ok(): |
| raise Error(transfer.id, transfer.status) |
| |
| def _send_read_chunk(self, chunk: Chunk) -> None: |
| assert self._read_stream is not None |
| self._read_stream.send(chunk) |
| |
| def _send_write_chunk(self, chunk: Chunk) -> None: |
| assert self._write_stream is not None |
| self._write_stream.send(chunk) |
| |
| def _start_event_loop_thread(self): |
| """Entry point for event loop thread that starts an asyncio context.""" |
| asyncio.set_event_loop(self._loop) |
| |
| # Recreate the async communication channels in the context of the |
| # running event loop. |
| self._new_transfer_queue = asyncio.Queue() |
| self._read_chunk_queue = asyncio.Queue() |
| self._write_chunk_queue = asyncio.Queue() |
| self._quit_event = asyncio.Event() |
| |
| self._loop.create_task(self._transfer_event_loop()) |
| self._loop.run_forever() |
| |
| async def _transfer_event_loop(self): |
| """Main async event loop.""" |
| exit_thread = self._loop.create_task(self._quit_event.wait()) |
| new_transfer = self._loop.create_task(self._new_transfer_queue.get()) |
| read_chunk = self._loop.create_task(self._read_chunk_queue.get()) |
| write_chunk = self._loop.create_task(self._write_chunk_queue.get()) |
| |
| while not self._quit_event.is_set(): |
| # Perform a select(2)-like wait for one of several events to occur. |
| done, _ = await asyncio.wait( |
| (exit_thread, new_transfer, read_chunk, write_chunk), |
| return_when=asyncio.FIRST_COMPLETED) |
| |
| if exit_thread in done: |
| break |
| |
| if new_transfer in done: |
| await new_transfer.result().begin() |
| new_transfer = self._loop.create_task( |
| self._new_transfer_queue.get()) |
| |
| if read_chunk in done: |
| self._loop.create_task( |
| self._handle_chunk(self._read_transfers, |
| self._end_read_transfer, |
| read_chunk.result())) |
| read_chunk = self._loop.create_task( |
| self._read_chunk_queue.get()) |
| |
| if write_chunk in done: |
| self._loop.create_task( |
| self._handle_chunk(self._write_transfers, |
| self._end_write_transfer, |
| write_chunk.result())) |
| write_chunk = self._loop.create_task( |
| self._write_chunk_queue.get()) |
| |
| self._loop.stop() |
| |
| @staticmethod |
| async def _handle_chunk( |
| transfers: _TransferDict, |
| completion: Callable[[_Transfer, Status], None], |
| chunk: Chunk, |
| ) -> None: |
| """Processes an incoming chunk from a stream. |
| |
| The chunk is dispatched to an active transfer based on its ID. If the |
| transfer indicates that it is complete, the provided completion callback |
| is invoked. |
| """ |
| |
| try: |
| transfer = transfers[chunk.transfer_id] |
| except KeyError: |
| _LOG.error( |
| 'TransferManager received chunk for unknown transfer %d', |
| chunk.transfer_id) |
| # TODO(frolv): What should be done here, if anything? |
| return |
| |
| should_exit = False |
| |
| # Status chunks are only used to terminate a transfer. They do not |
| # contain any data that requires processing. |
| if not chunk.HasField('status'): |
| should_exit = await transfer.handle_chunk(chunk) |
| |
| if should_exit or chunk.HasField('status'): |
| completion(transfer, Status(chunk.status)) |
| |
| def _start_read_transfer(self, transfer: _Transfer) -> None: |
| """Begins a new read transfer, opening the stream if it isn't.""" |
| |
| self._read_transfers[transfer.id] = transfer |
| |
| if not self._read_stream: |
| self._read_stream = self._service.Read( |
| lambda _, chunk: self._loop.call_soon_threadsafe( |
| self._read_chunk_queue.put_nowait, chunk)) |
| |
| _LOG.debug('Starting new read transfer %d', transfer.id) |
| self._loop.call_soon_threadsafe(self._new_transfer_queue.put_nowait, |
| transfer) |
| |
| def _end_read_transfer(self, transfer: _Transfer, status: Status) -> None: |
| """Completes a read transfer.""" |
| del self._read_transfers[transfer.id] |
| |
| if not status.ok(): |
| _LOG.error('Read transfer %d terminated with status %s', |
| transfer.id, status) |
| transfer.status = status |
| |
| # If no more transfers are using the read stream, close it. |
| if not self._read_transfers and self._read_stream: |
| self._read_stream.cancel() |
| self._read_stream = None |
| |
| transfer.done.set() |
| |
| def _start_write_transfer(self, transfer: _Transfer) -> None: |
| """Begins a new write transfer, opening the stream if it isn't.""" |
| |
| self._write_transfers[transfer.id] = transfer |
| |
| if not self._write_stream: |
| # TODO(frolv): Make the actual RPC call. |
| self._write_stream = self._service.Write( |
| lambda _, chunk: self._loop.call_soon_threadsafe( |
| self._write_chunk_queue.put_nowait, chunk)) |
| |
| _LOG.debug('Starting new write transfer %d', transfer.id) |
| self._loop.call_soon_threadsafe(self._new_transfer_queue.put_nowait, |
| transfer) |
| |
| def _end_write_transfer(self, transfer: _Transfer, status: Status) -> None: |
| """Completes a write transfer.""" |
| del self._write_transfers[transfer.id] |
| |
| if not status.ok(): |
| _LOG.error('Write transfer %d terminated with status %s', |
| transfer.id, status) |
| transfer.status = status |
| |
| # If no more transfers are using the write stream, close it. |
| if not self._write_transfers and self._write_stream: |
| self._write_stream.cancel() |
| self._write_stream = None |
| |
| transfer.done.set() |
| |
| |
| class Error(Exception): |
| """Exception raised when a transfer fails. |
| |
| Stores the ID of the failed transfer and the error that occurred. |
| """ |
| def __init__(self, transfer_id: int, status: Status): |
| super().__init__(f'Transfer {transfer_id} failed with status {status}') |
| self.transfer_id = transfer_id |
| self.status = status |
