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from __future__ import annotations
import codecs
import queue
import threading
from typing import Any, Callable, Iterable, Iterator
from ..exceptions import ConcurrencyError
from ..frames import OP_BINARY, OP_CONT, OP_TEXT, Frame
from ..typing import Data
from .utils import Deadline
__all__ = ["Assembler"]
UTF8Decoder = codecs.getincrementaldecoder("utf-8")
class Assembler:
"""
Assemble messages from frames.
:class:`Assembler` expects only data frames. The stream of frames must
respect the protocol; if it doesn't, the behavior is undefined.
Args:
pause: Called when the buffer of frames goes above the high water mark;
should pause reading from the network.
resume: Called when the buffer of frames goes below the low water mark;
should resume reading from the network.
"""
def __init__(
self,
high: int | None = None,
low: int | None = None,
pause: Callable[[], Any] = lambda: None,
resume: Callable[[], Any] = lambda: None,
) -> None:
# Serialize reads and writes -- except for reads via synchronization
# primitives provided by the threading and queue modules.
self.mutex = threading.Lock()
# Queue of incoming frames.
self.frames: queue.SimpleQueue[Frame | None] = queue.SimpleQueue()
# We cannot put a hard limit on the size of the queue because a single
# call to Protocol.data_received() could produce thousands of frames,
# which must be buffered. Instead, we pause reading when the buffer goes
# above the high limit and we resume when it goes under the low limit.
if high is not None and low is None:
low = high // 4
if high is None and low is not None:
high = low * 4
if high is not None and low is not None:
if low < 0:
raise ValueError("low must be positive or equal to zero")
if high < low:
raise ValueError("high must be greater than or equal to low")
self.high, self.low = high, low
self.pause = pause
self.resume = resume
self.paused = False
# This flag prevents concurrent calls to get() by user code.
self.get_in_progress = False
# This flag marks the end of the connection.
self.closed = False
def get_next_frame(self, timeout: float | None = None) -> Frame:
# Helper to factor out the logic for getting the next frame from the
# queue, while handling timeouts and reaching the end of the stream.
if self.closed:
try:
frame = self.frames.get(block=False)
except queue.Empty:
raise EOFError("stream of frames ended") from None
else:
try:
frame = self.frames.get(block=True, timeout=timeout)
except queue.Empty:
raise TimeoutError(f"timed out in {timeout:.1f}s") from None
if frame is None:
raise EOFError("stream of frames ended")
return frame
def reset_queue(self, frames: Iterable[Frame]) -> None:
# Helper to put frames back into the queue after they were fetched.
# This happens only when the queue is empty. However, by the time
# we acquire self.mutex, put() may have added items in the queue.
# Therefore, we must handle the case where the queue is not empty.
frame: Frame | None
with self.mutex:
queued = []
try:
while True:
queued.append(self.frames.get(block=False))
except queue.Empty:
pass
for frame in frames:
self.frames.put(frame)
# This loop runs only when a race condition occurs.
for frame in queued: # pragma: no cover
self.frames.put(frame)
def get(self, timeout: float | None = None, decode: bool | None = None) -> Data:
"""
Read the next message.
:meth:`get` returns a single :class:`str` or :class:`bytes`.
If the message is fragmented, :meth:`get` waits until the last frame is
received, then it reassembles the message and returns it. To receive
messages frame by frame, use :meth:`get_iter` instead.
Args:
timeout: If a timeout is provided and elapses before a complete
message is received, :meth:`get` raises :exc:`TimeoutError`.
decode: :obj:`False` disables UTF-8 decoding of text frames and
returns :class:`bytes`. :obj:`True` forces UTF-8 decoding of
binary frames and returns :class:`str`.
Raises:
EOFError: If the stream of frames has ended.
UnicodeDecodeError: If a text frame contains invalid UTF-8.
ConcurrencyError: If two coroutines run :meth:`get` or
:meth:`get_iter` concurrently.
TimeoutError: If a timeout is provided and elapses before a
complete message is received.
"""
with self.mutex:
if self.get_in_progress:
raise ConcurrencyError("get() or get_iter() is already running")
self.get_in_progress = True
# Locking with get_in_progress prevents concurrent execution
# until get() fetches a complete message or times out.
try:
deadline = Deadline(timeout)
# First frame
frame = self.get_next_frame(deadline.timeout())
with self.mutex:
self.maybe_resume()
assert frame.opcode is OP_TEXT or frame.opcode is OP_BINARY
if decode is None:
decode = frame.opcode is OP_TEXT
frames = [frame]
# Following frames, for fragmented messages
while not frame.fin:
try:
frame = self.get_next_frame(deadline.timeout())
except TimeoutError:
# Put frames already received back into the queue
# so that future calls to get() can return them.
self.reset_queue(frames)
raise
with self.mutex:
self.maybe_resume()
assert frame.opcode is OP_CONT
frames.append(frame)
finally:
self.get_in_progress = False
data = b"".join(frame.data for frame in frames)
if decode:
return data.decode()
else:
return data
def get_iter(self, decode: bool | None = None) -> Iterator[Data]:
"""
Stream the next message.
Iterating the return value of :meth:`get_iter` yields a :class:`str` or
:class:`bytes` for each frame in the message.
The iterator must be fully consumed before calling :meth:`get_iter` or
:meth:`get` again. Else, :exc:`ConcurrencyError` is raised.
This method only makes sense for fragmented messages. If messages aren't
fragmented, use :meth:`get` instead.
Args:
decode: :obj:`False` disables UTF-8 decoding of text frames and
returns :class:`bytes`. :obj:`True` forces UTF-8 decoding of
binary frames and returns :class:`str`.
Raises:
EOFError: If the stream of frames has ended.
UnicodeDecodeError: If a text frame contains invalid UTF-8.
ConcurrencyError: If two coroutines run :meth:`get` or
:meth:`get_iter` concurrently.
"""
with self.mutex:
if self.get_in_progress:
raise ConcurrencyError("get() or get_iter() is already running")
self.get_in_progress = True
# Locking with get_in_progress prevents concurrent execution
# until get_iter() fetches a complete message or times out.
# If get_iter() raises an exception e.g. in decoder.decode(),
# get_in_progress remains set and the connection becomes unusable.
# First frame
frame = self.get_next_frame()
with self.mutex:
self.maybe_resume()
assert frame.opcode is OP_TEXT or frame.opcode is OP_BINARY
if decode is None:
decode = frame.opcode is OP_TEXT
if decode:
decoder = UTF8Decoder()
yield decoder.decode(frame.data, frame.fin)
else:
yield frame.data
# Following frames, for fragmented messages
while not frame.fin:
frame = self.get_next_frame()
with self.mutex:
self.maybe_resume()
assert frame.opcode is OP_CONT
if decode:
yield decoder.decode(frame.data, frame.fin)
else:
yield frame.data
self.get_in_progress = False
def put(self, frame: Frame) -> None:
"""
Add ``frame`` to the next message.
Raises:
EOFError: If the stream of frames has ended.
"""
with self.mutex:
if self.closed:
raise EOFError("stream of frames ended")
self.frames.put(frame)
self.maybe_pause()
# put() and get/get_iter() call maybe_pause() and maybe_resume() while
# holding self.mutex. This guarantees that the calls interleave properly.
# Specifically, it prevents a race condition where maybe_resume() would
# run before maybe_pause(), leaving the connection incorrectly paused.
# A race condition is possible when get/get_iter() call self.frames.get()
# without holding self.mutex. However, it's harmless — and even beneficial!
# It can only result in popping an item from the queue before maybe_resume()
# runs and skipping a pause() - resume() cycle that would otherwise occur.
def maybe_pause(self) -> None:
"""Pause the writer if queue is above the high water mark."""
# Skip if flow control is disabled
if self.high is None:
return
assert self.mutex.locked()
# Check for "> high" to support high = 0
if self.frames.qsize() > self.high and not self.paused:
self.paused = True
self.pause()
def maybe_resume(self) -> None:
"""Resume the writer if queue is below the low water mark."""
# Skip if flow control is disabled
if self.low is None:
return
assert self.mutex.locked()
# Check for "<= low" to support low = 0
if self.frames.qsize() <= self.low and self.paused:
self.paused = False
self.resume()
def close(self) -> None:
"""
End the stream of frames.
Callling :meth:`close` concurrently with :meth:`get`, :meth:`get_iter`,
or :meth:`put` is safe. They will raise :exc:`EOFError`.
"""
with self.mutex:
if self.closed:
return
self.closed = True
if self.get_in_progress:
# Unblock get() or get_iter().
self.frames.put(None)
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