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asyncio
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streams.py
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"""Stream-related things.""" __all__ = ['StreamReader', 'StreamWriter', 'StreamReaderProtocol', 'open_connection', 'start_server', 'IncompleteReadError', 'LimitOverrunError', ] import socket if hasattr(socket, 'AF_UNIX'): __all__.extend(['open_unix_connection', 'start_unix_server']) from . import coroutines from . import compat from . import events from . import protocols from .coroutines import coroutine from .log import logger _DEFAULT_LIMIT = 2 ** 16 class IncompleteReadError(EOFError): """ Incomplete read error. Attributes: - partial: read bytes string before the end of stream was reached - expected: total number of expected bytes (or None if unknown) """ def __init__(self, partial, expected): super().__init__("%d bytes read on a total of %r expected bytes" % (len(partial), expected)) self.partial = partial self.expected = expected class LimitOverrunError(Exception): """Reached the buffer limit while looking for a separator. Attributes: - consumed: total number of to be consumed bytes. """ def __init__(self, message, consumed): super().__init__(message) self.consumed = consumed @coroutine def open_connection(host=None, port=None, *, loop=None, limit=_DEFAULT_LIMIT, **kwds): """A wrapper for create_connection() returning a (reader, writer) pair. The reader returned is a StreamReader instance; the writer is a StreamWriter instance. The arguments are all the usual arguments to create_connection() except protocol_factory; most common are positional host and port, with various optional keyword arguments following. Additional optional keyword arguments are loop (to set the event loop instance to use) and limit (to set the buffer limit passed to the StreamReader). (If you want to customize the StreamReader and/or StreamReaderProtocol classes, just copy the code -- there's really nothing special here except some convenience.) """ if loop is None: loop = events.get_event_loop() reader = StreamReader(limit=limit, loop=loop) protocol = StreamReaderProtocol(reader, loop=loop) transport, _ = yield from loop.create_connection( lambda: protocol, host, port, **kwds) writer = StreamWriter(transport, protocol, reader, loop) return reader, writer @coroutine def start_server(client_connected_cb, host=None, port=None, *, loop=None, limit=_DEFAULT_LIMIT, **kwds): """Start a socket server, call back for each client connected. The first parameter, `client_connected_cb`, takes two parameters: client_reader, client_writer. client_reader is a StreamReader object, while client_writer is a StreamWriter object. This parameter can either be a plain callback function or a coroutine; if it is a coroutine, it will be automatically converted into a Task. The rest of the arguments are all the usual arguments to loop.create_server() except protocol_factory; most common are positional host and port, with various optional keyword arguments following. The return value is the same as loop.create_server(). Additional optional keyword arguments are loop (to set the event loop instance to use) and limit (to set the buffer limit passed to the StreamReader). The return value is the same as loop.create_server(), i.e. a Server object which can be used to stop the service. """ if loop is None: loop = events.get_event_loop() def factory(): reader = StreamReader(limit=limit, loop=loop) protocol = StreamReaderProtocol(reader, client_connected_cb, loop=loop) return protocol return (yield from loop.create_server(factory, host, port, **kwds)) if hasattr(socket, 'AF_UNIX'): # UNIX Domain Sockets are supported on this platform @coroutine def open_unix_connection(path=None, *, loop=None, limit=_DEFAULT_LIMIT, **kwds): """Similar to `open_connection` but works with UNIX Domain Sockets.""" if loop is None: loop = events.get_event_loop() reader = StreamReader(limit=limit, loop=loop) protocol = StreamReaderProtocol(reader, loop=loop) transport, _ = yield from loop.create_unix_connection( lambda: protocol, path, **kwds) writer = StreamWriter(transport, protocol, reader, loop) return reader, writer @coroutine def start_unix_server(client_connected_cb, path=None, *, loop=None, limit=_DEFAULT_LIMIT, **kwds): """Similar to `start_server` but works with UNIX Domain Sockets.""" if loop is None: loop = events.get_event_loop() def factory(): reader = StreamReader(limit=limit, loop=loop) protocol = StreamReaderProtocol(reader, client_connected_cb, loop=loop) return protocol return (yield from loop.create_unix_server(factory, path, **kwds)) class FlowControlMixin(protocols.Protocol): """Reusable flow control logic for StreamWriter.drain(). This implements the protocol methods pause_writing(), resume_reading() and connection_lost(). If the subclass overrides these it must call the super methods. StreamWriter.drain() must wait for _drain_helper() coroutine. """ def __init__(self, loop=None): if loop is None: self._loop = events.get_event_loop() else: self._loop = loop self._paused = False self._drain_waiter = None self._connection_lost = False def pause_writing(self): assert not self._paused self._paused = True if self._loop.get_debug(): logger.debug("%r pauses writing", self) def resume_writing(self): assert self._paused self._paused = False if self._loop.get_debug(): logger.debug("%r resumes writing", self) waiter = self._drain_waiter if waiter is not None: self._drain_waiter = None if not waiter.done(): waiter.set_result(None) def connection_lost(self, exc): self._connection_lost = True # Wake up the writer if currently paused. if not self._paused: return waiter = self._drain_waiter if waiter is None: return self._drain_waiter = None if waiter.done(): return if exc is None: waiter.set_result(None) else: waiter.set_exception(exc) @coroutine def _drain_helper(self): if self._connection_lost: raise ConnectionResetError('Connection lost') if not self._paused: return waiter = self._drain_waiter assert waiter is None or waiter.cancelled() waiter = self._loop.create_future() self._drain_waiter = waiter yield from waiter class StreamReaderProtocol(FlowControlMixin, protocols.Protocol): """Helper class to adapt between Protocol and StreamReader. (This is a helper class instead of making StreamReader itself a Protocol subclass, because the StreamReader has other potential uses, and to prevent the user of the StreamReader to accidentally call inappropriate methods of the protocol.) """ def __init__(self, stream_reader, client_connected_cb=None, loop=None): super().__init__(loop=loop) self._stream_reader = stream_reader self._stream_writer = None self._client_connected_cb = client_connected_cb self._over_ssl = False def connection_made(self, transport): self._stream_reader.set_transport(transport) self._over_ssl = transport.get_extra_info('sslcontext') is not None if self._client_connected_cb is not None: self._stream_writer = StreamWriter(transport, self, self._stream_reader, self._loop) res = self._client_connected_cb(self._stream_reader, self._stream_writer) if coroutines.iscoroutine(res): self._loop.create_task(res) def connection_lost(self, exc): if self._stream_reader is not None: if exc is None: self._stream_reader.feed_eof() else: self._stream_reader.set_exception(exc) super().connection_lost(exc) self._stream_reader = None self._stream_writer = None def data_received(self, data): self._stream_reader.feed_data(data) def eof_received(self): self._stream_reader.feed_eof() if self._over_ssl: # Prevent a warning in SSLProtocol.eof_received: # "returning true from eof_received() # has no effect when using ssl" return False return True class StreamWriter: """Wraps a Transport. This exposes write(), writelines(), [can_]write_eof(), get_extra_info() and close(). It adds drain() which returns an optional Future on which you can wait for flow control. It also adds a transport property which references the Transport directly. """ def __init__(self, transport, protocol, reader, loop): self._transport = transport self._protocol = protocol # drain() expects that the reader has an exception() method assert reader is None or isinstance(reader, StreamReader) self._reader = reader self._loop = loop def __repr__(self): info = [self.__class__.__name__, 'transport=%r' % self._transport] if self._reader is not None: info.append('reader=%r' % self._reader) return '<%s>' % ' '.join(info) @property def transport(self): return self._transport def write(self, data): self._transport.write(data) def writelines(self, data): self._transport.writelines(data) def write_eof(self): return self._transport.write_eof() def can_write_eof(self): return self._transport.can_write_eof() def close(self): return self._transport.close() def get_extra_info(self, name, default=None): return self._transport.get_extra_info(name, default) @coroutine def drain(self): """Flush the write buffer. The intended use is to write w.write(data) yield from w.drain() """ if self._reader is not None: exc = self._reader.exception() if exc is not None: raise exc if self._transport is not None: if self._transport.is_closing(): # Yield to the event loop so connection_lost() may be # called. Without this, _drain_helper() would return # immediately, and code that calls # write(...); yield from drain() # in a loop would never call connection_lost(), so it # would not see an error when the socket is closed. yield yield from self._protocol._drain_helper() class StreamReader: def __init__(self, limit=_DEFAULT_LIMIT, loop=None): # The line length limit is a security feature; # it also doubles as half the buffer limit. if limit <= 0: raise ValueError('Limit cannot be <= 0') self._limit = limit if loop is None: self._loop = events.get_event_loop() else: self._loop = loop self._buffer = bytearray() self._eof = False # Whether we're done. self._waiter = None # A future used by _wait_for_data() self._exception = None self._transport = None self._paused = False def __repr__(self): info = ['StreamReader'] if self._buffer: info.append('%d bytes' % len(self._buffer)) if self._eof: info.append('eof') if self._limit != _DEFAULT_LIMIT: info.append('l=%d' % self._limit) if self._waiter: info.append('w=%r' % self._waiter) if self._exception: info.append('e=%r' % self._exception) if self._transport: info.append('t=%r' % self._transport) if self._paused: info.append('paused') return '<%s>' % ' '.join(info) def exception(self): return self._exception def set_exception(self, exc): self._exception = exc waiter = self._waiter if waiter is not None: self._waiter = None if not waiter.cancelled(): waiter.set_exception(exc) def _wakeup_waiter(self): """Wakeup read*() functions waiting for data or EOF.""" waiter = self._waiter if waiter is not None: self._waiter = None if not waiter.cancelled(): waiter.set_result(None) def set_transport(self, transport): assert self._transport is None, 'Transport already set' self._transport = transport def _maybe_resume_transport(self): if self._paused and len(self._buffer) <= self._limit: self._paused = False self._transport.resume_reading() def feed_eof(self): self._eof = True self._wakeup_waiter() def at_eof(self): """Return True if the buffer is empty and 'feed_eof' was called.""" return self._eof and not self._buffer def feed_data(self, data): assert not self._eof, 'feed_data after feed_eof' if not data: return self._buffer.extend(data) self._wakeup_waiter() if (self._transport is not None and not self._paused and len(self._buffer) > 2 * self._limit): try: self._transport.pause_reading() except NotImplementedError: # The transport can't be paused. # We'll just have to buffer all data. # Forget the transport so we don't keep trying. self._transport = None else: self._paused = True @coroutine def _wait_for_data(self, func_name): """Wait until feed_data() or feed_eof() is called. If stream was paused, automatically resume it. """ # StreamReader uses a future to link the protocol feed_data() method # to a read coroutine. Running two read coroutines at the same time # would have an unexpected behaviour. It would not possible to know # which coroutine would get the next data. if self._waiter is not None: raise RuntimeError('%s() called while another coroutine is ' 'already waiting for incoming data' % func_name) assert not self._eof, '_wait_for_data after EOF' # Waiting for data while paused will make deadlock, so prevent it. if self._paused: self._paused = False self._transport.resume_reading() self._waiter = self._loop.create_future() try: yield from self._waiter finally: self._waiter = None @coroutine def readline(self): """Read chunk of data from the stream until newline (b'\n') is found. On success, return chunk that ends with newline. If only partial line can be read due to EOF, return incomplete line without terminating newline. When EOF was reached while no bytes read, empty bytes object is returned. If limit is reached, ValueError will be raised. In that case, if newline was found, complete line including newline will be removed from internal buffer. Else, internal buffer will be cleared. Limit is compared against part of the line without newline. If stream was paused, this function will automatically resume it if needed. """ sep = b'\n' seplen = len(sep) try: line = yield from self.readuntil(sep) except IncompleteReadError as e: return e.partial except LimitOverrunError as e: if self._buffer.startswith(sep, e.consumed): del self._buffer[:e.consumed + seplen] else: self._buffer.clear() self._maybe_resume_transport() raise ValueError(e.args[0]) return line @coroutine def readuntil(self, separator=b'\n'): """Read data from the stream until ``separator`` is found. On success, the data and separator will be removed from the internal buffer (consumed). Returned data will include the separator at the end. Configured stream limit is used to check result. Limit sets the maximal length of data that can be returned, not counting the separator. If an EOF occurs and the complete separator is still not found, an IncompleteReadError exception will be raised, and the internal buffer will be reset. The IncompleteReadError.partial attribute may contain the separator partially. If the data cannot be read because of over limit, a LimitOverrunError exception will be raised, and the data will be left in the internal buffer, so it can be read again. """ seplen = len(separator) if seplen == 0: raise ValueError('Separator should be at least one-byte string') if self._exception is not None: raise self._exception # Consume whole buffer except last bytes, which length is # one less than seplen. Let's check corner cases with # separator='SEPARATOR': # * we have received almost complete separator (without last # byte). i.e buffer='some textSEPARATO'. In this case we # can safely consume len(separator) - 1 bytes. # * last byte of buffer is first byte of separator, i.e. # buffer='abcdefghijklmnopqrS'. We may safely consume # everything except that last byte, but this require to # analyze bytes of buffer that match partial separator. # This is slow and/or require FSM. For this case our # implementation is not optimal, since require rescanning # of data that is known to not belong to separator. In # real world, separator will not be so long to notice # performance problems. Even when reading MIME-encoded # messages :) # `offset` is the number of bytes from the beginning of the buffer # where there is no occurrence of `separator`. offset = 0 # Loop until we find `separator` in the buffer, exceed the buffer size, # or an EOF has happened. while True: buflen = len(self._buffer) # Check if we now have enough data in the buffer for `separator` to # fit. if buflen - offset >= seplen: isep = self._buffer.find(separator, offset) if isep != -1: # `separator` is in the buffer. `isep` will be used later # to retrieve the data. break # see upper comment for explanation. offset = buflen + 1 - seplen if offset > self._limit: raise LimitOverrunError( 'Separator is not found, and chunk exceed the limit', offset) # Complete message (with full separator) may be present in buffer # even when EOF flag is set. This may happen when the last chunk # adds data which makes separator be found. That's why we check for # EOF *ater* inspecting the buffer. if self._eof: chunk = bytes(self._buffer) self._buffer.clear() raise IncompleteReadError(chunk, None) # _wait_for_data() will resume reading if stream was paused. yield from self._wait_for_data('readuntil') if isep > self._limit: raise LimitOverrunError( 'Separator is found, but chunk is longer than limit', isep) chunk = self._buffer[:isep + seplen] del self._buffer[:isep + seplen] self._maybe_resume_transport() return bytes(chunk) @coroutine def read(self, n=-1): """Read up to `n` bytes from the stream. If n is not provided, or set to -1, read until EOF and return all read bytes. If the EOF was received and the internal buffer is empty, return an empty bytes object. If n is zero, return empty bytes object immediatelly. If n is positive, this function try to read `n` bytes, and may return less or equal bytes than requested, but at least one byte. If EOF was received before any byte is read, this function returns empty byte object. Returned value is not limited with limit, configured at stream creation. If stream was paused, this function will automatically resume it if needed. """ if self._exception is not None: raise self._exception if n == 0: return b'' if n < 0: # This used to just loop creating a new waiter hoping to # collect everything in self._buffer, but that would # deadlock if the subprocess sends more than self.limit # bytes. So just call self.read(self._limit) until EOF. blocks = [] while True: block = yield from self.read(self._limit) if not block: break blocks.append(block) return b''.join(blocks) if not self._buffer and not self._eof: yield from self._wait_for_data('read') # This will work right even if buffer is less than n bytes data = bytes(self._buffer[:n]) del self._buffer[:n] self._maybe_resume_transport() return data @coroutine def readexactly(self, n): """Read exactly `n` bytes. Raise an IncompleteReadError if EOF is reached before `n` bytes can be read. The IncompleteReadError.partial attribute of the exception will contain the partial read bytes. if n is zero, return empty bytes object. Returned value is not limited with limit, configured at stream creation. If stream was paused, this function will automatically resume it if needed. """ if n < 0: raise ValueError('readexactly size can not be less than zero') if self._exception is not None: raise self._exception if n == 0: return b'' # There used to be "optimized" code here. It created its own # Future and waited until self._buffer had at least the n # bytes, then called read(n). Unfortunately, this could pause # the transport if the argument was larger than the pause # limit (which is twice self._limit). So now we just read() # into a local buffer. blocks = [] while n > 0: block = yield from self.read(n) if not block: partial = b''.join(blocks) raise IncompleteReadError(partial, len(partial) + n) blocks.append(block) n -= len(block) assert n == 0 return b''.join(blocks) if compat.PY35: @coroutine def __aiter__(self): return self @coroutine def __anext__(self): val = yield from self.readline() if val == b'': raise StopAsyncIteration return val if compat.PY352: # In Python 3.5.2 and greater, __aiter__ should return # the asynchronous iterator directly. def __aiter__(self): return self