# dockerpty: io.py # # Copyright 2014 Chris Corbyn # # 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 # # http://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. import os import fcntl import errno import struct import select as builtin_select def set_blocking(fd, blocking=True): """ Set the given file-descriptor blocking or non-blocking. Returns the original blocking status. """ old_flag = fcntl.fcntl(fd, fcntl.F_GETFL) if blocking: new_flag = old_flag &~ os.O_NONBLOCK else: new_flag = old_flag | os.O_NONBLOCK fcntl.fcntl(fd, fcntl.F_SETFL, new_flag) return not bool(old_flag & os.O_NONBLOCK) def select(read_streams, timeout=0): """ Select the streams from `read_streams` that are ready for reading. Uses `select.select()` internally but returns a flat list of streams. """ write_streams = [] exception_streams = [] try: return builtin_select.select( read_streams, write_streams, exception_streams, timeout, )[0] except builtin_select.error as e: # POSIX signals interrupt select() if e[0] == errno.EINTR: return [] else: raise e class Stream(object): """ Generic Stream class. This is a file-like abstraction on top of os.read() and os.write(), which add consistency to the reading of sockets and files alike. """ """ Recoverable IO/OS Errors. """ ERRNO_RECOVERABLE = [ errno.EINTR, errno.EDEADLK, errno.EWOULDBLOCK, ] def __init__(self, fd): """ Initialize the Stream for the file descriptor `fd`. The `fd` object must have a `fileno()` method. """ self.fd = fd def fileno(self): """ Return the fileno() of the file descriptor. """ return self.fd.fileno() def set_blocking(self, value): if hasattr(self.fd, 'setblocking'): self.fd.setblocking(value) return True else: return set_blocking(self.fd, value) def read(self, n=4096): """ Return `n` bytes of data from the Stream, or None at end of stream. """ try: if hasattr(self.fd, 'recv'): return self.fd.recv(n) return os.read(self.fd.fileno(), n) except EnvironmentError as e: if e.errno not in Stream.ERRNO_RECOVERABLE: raise e def write(self, data): """ Write `data` to the Stream. """ if not data: return None while True: try: if hasattr(self.fd, 'send'): self.fd.send(data) return len(data) os.write(self.fd.fileno(), data) return len(data) except EnvironmentError as e: if e.errno not in Stream.ERRNO_RECOVERABLE: raise e def __repr__(self): return "{cls}({fd})".format(cls=type(self).__name__, fd=self.fd) class Demuxer(object): """ Wraps a multiplexed Stream to read in data demultiplexed. Docker multiplexes streams together when there is no PTY attached, by sending an 8-byte header, followed by a chunk of data. The first 4 bytes of the header denote the stream from which the data came (i.e. 0x01 = stdout, 0x02 = stderr). Only the first byte of these initial 4 bytes is used. The next 4 bytes indicate the length of the following chunk of data as an integer in big endian format. This much data must be consumed before the next 8-byte header is read. """ def __init__(self, stream): """ Initialize a new Demuxer reading from `stream`. """ self.stream = stream self.remain = 0 def fileno(self): """ Returns the fileno() of the underlying Stream. This is useful for select() to work. """ return self.stream.fileno() def set_blocking(self, value): return self.stream.set_blocking(value) def read(self, n=4096): """ Read up to `n` bytes of data from the Stream, after demuxing. Less than `n` bytes of data may be returned depending on the available payload, but the number of bytes returned will never exceed `n`. Because demuxing involves scanning 8-byte headers, the actual amount of data read from the underlying stream may be greater than `n`. """ size = self._next_packet_size(n) if size <= 0: return else: return self.stream.read(size) def write(self, data): """ Delegates the the underlying Stream. """ return self.stream.write(data) def _next_packet_size(self, n=0): size = 0 if self.remain > 0: size = min(n, self.remain) self.remain -= size else: data = self.stream.read(8) if data is None: return 0 if len(data) == 8: __, actual = struct.unpack('>BxxxL', data) size = min(n, actual) self.remain = actual - size return size def __repr__(self): return "{cls}({stream})".format(cls=type(self).__name__, stream=self.stream) class Pump(object): """ Stream pump class. A Pump wraps two Streams, reading from one and and writing its data into the other, much like a pipe but manually managed. This abstraction is used to facilitate piping data between the file descriptors associated with the tty and those associated with a container's allocated pty. Pumps are selectable based on the 'read' end of the pipe. """ def __init__(self, from_stream, to_stream): """ Initialize a Pump with a Stream to read from and another to write to. """ self.from_stream = from_stream self.to_stream = to_stream def fileno(self): """ Returns the `fileno()` of the reader end of the Pump. This is useful to allow Pumps to function with `select()`. """ return self.from_stream.fileno() def set_blocking(self, value): return self.from_stream.set_blocking(value) def flush(self, n=4096): """ Flush `n` bytes of data from the reader Stream to the writer Stream. Returns the number of bytes that were actually flushed. A return value of zero is not an error. If EOF has been reached, `None` is returned. """ try: return self.to_stream.write(self.from_stream.read(n)) except OSError as e: if e.errno != errno.EPIPE: raise e def __repr__(self): return "{cls}(from={from_stream}, to={to_stream})".format( cls=type(self).__name__, from_stream=self.from_stream, to_stream=self.to_stream)