iostream.py

#!/usr/bin/env python
#
# Copyright 2009 Facebook
#
# 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.

"""A utility class to write to and read from a non-blocking socket."""

from __future__ import with_statement

import collections
import errno
import logging
import socket
import sys
import re

import ioloop
import stack_context
from utils import b, bytes_type

try:
    import ssl # Python 2.6+
except ImportError:
    ssl = None

class IOStream(object):
    r"""A utility class to write to and read from a non-blocking socket.

    We support a non-blocking ``write()`` and a family of ``read_*()`` methods.
    All of the methods take callbacks (since writing and reading are
    non-blocking and asynchronous).

    The socket parameter may either be connected or unconnected.  For
    server operations the socket is the result of calling socket.accept().
    For client operations the socket is created with socket.socket(),
    and may either be connected before passing it to the IOStream or
    connected with IOStream.connect.

    A very simple (and broken) HTTP client using this class::

        from tornado import ioloop
        from tornado import iostream
        import socket

        def send_request():
            stream.write("GET / HTTP/1.0\r\nHost: friendfeed.com\r\n\r\n")
            stream.read_until("\r\n\r\n", on_headers)

        def on_headers(data):
            headers = {}
            for line in data.split("\r\n"):
               parts = line.split(":")
               if len(parts) == 2:
                   headers[parts[0].strip()] = parts[1].strip()
            stream.read_bytes(int(headers["Content-Length"]), on_body)

        def on_body(data):
            print data
            stream.close()
            ioloop.IOLoop.instance().stop()

        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
        stream = iostream.IOStream(s)
        stream.connect(("friendfeed.com", 80), send_request)
        ioloop.IOLoop.instance().start()

    """
    def __init__(self, socket, io_loop=None, max_buffer_size=104857600,
                 read_chunk_size=4096):
        self.socket = socket
        self.socket.setblocking(False)
        self.io_loop = io_loop or ioloop.IOLoop.instance()
        self.max_buffer_size = max_buffer_size
        self.read_chunk_size = read_chunk_size
        self._read_buffer = collections.deque()
        self._write_buffer = collections.deque()
        self._read_buffer_size = 0
        self._write_buffer_frozen = False
        self._read_delimiter = None
        self._read_regex = None
        self._read_bytes = None
        self._read_until_close = False
        self._read_callback = None
        self._streaming_callback = None
        self._write_callback = None
        self._close_callback = None
        self._connect_callback = None
        self._connecting = False
        self._state = None
        self._pending_callbacks = 0

    def connect(self, address, callback=None):
        """Connects the socket to a remote address without blocking.

        May only be called if the socket passed to the constructor was
        not previously connected.  The address parameter is in the
        same format as for socket.connect, i.e. a (host, port) tuple.
        If callback is specified, it will be called when the
        connection is completed.

        Note that it is safe to call IOStream.write while the
        connection is pending, in which case the data will be written
        as soon as the connection is ready.  Calling IOStream read
        methods before the socket is connected works on some platforms
        but is non-portable.
        """
        self._connecting = True
        try:
            self.socket.connect(address)
        except socket.error, e:
            # In non-blocking mode connect() always raises an exception
            if e.args[0] not in (errno.EINPROGRESS, errno.EWOULDBLOCK):
                raise
        self._connect_callback = stack_context.wrap(callback)
        self._add_io_state(self.io_loop.WRITE)

    def read_until_regex(self, regex, callback):
        """Call callback when we read the given regex pattern."""
        assert not self._read_callback, "Already reading"
        self._read_regex = re.compile(regex)
        self._read_callback = stack_context.wrap(callback)
        while True:
            # See if we've already got the data from a previous read
            if self._read_from_buffer():
                return
            self._check_closed()
            if self._read_to_buffer() == 0:
                break
        self._add_io_state(self.io_loop.READ)

    def read_until(self, delimiter, callback):
        """Call callback when we read the given delimiter."""
        assert not self._read_callback, "Already reading"
        self._read_delimiter = delimiter
        self._read_callback = stack_context.wrap(callback)
        while True:
            # See if we've already got the data from a previous read
            if self._read_from_buffer():
                return
            self._check_closed()
            if self._read_to_buffer() == 0:
                break
        self._add_io_state(self.io_loop.READ)

    def read_bytes(self, num_bytes, callback, streaming_callback=None):
        """Call callback when we read the given number of bytes.

        If a ``streaming_callback`` is given, it will be called with chunks
        of data as they become available, and the argument to the final
        ``callback`` will be empty.
        """
        assert not self._read_callback, "Already reading"
        assert isinstance(num_bytes, int)
        self._read_bytes = num_bytes
        self._read_callback = stack_context.wrap(callback)
        self._streaming_callback = stack_context.wrap(streaming_callback)
        while True:
            if self._read_from_buffer():
                return
            self._check_closed()
            if self._read_to_buffer() == 0:
                break
        self._add_io_state(self.io_loop.READ)

    def read_until_close(self, callback, streaming_callback=None):
        """Reads all data from the socket until it is closed.

        If a ``streaming_callback`` is given, it will be called with chunks
        of data as they become available, and the argument to the final
        ``callback`` will be empty.

        Subject to ``max_buffer_size`` limit from `IOStream` constructor if
        a ``streaming_callback`` is not used.
        """
        assert not self._read_callback, "Already reading"
        if self.closed():
            self._run_callback(callback, self._consume(self._read_buffer_size))
            return
        self._read_until_close = True
        self._read_callback = stack_context.wrap(callback)
        self._streaming_callback = stack_context.wrap(streaming_callback)
        self._add_io_state(self.io_loop.READ)

    def write(self, data, callback=None):
        """Write the given data to this stream.

        If callback is given, we call it when all of the buffered write
        data has been successfully written to the stream. If there was
        previously buffered write data and an old write callback, that
        callback is simply overwritten with this new callback.
        """
        assert isinstance(data, bytes_type)
        self._check_closed()
        self._write_buffer.append(data)
        self._write_callback = stack_context.wrap(callback)
        self._handle_write()
        if self._write_buffer:
            self._add_io_state(self.io_loop.WRITE)
        self._maybe_add_error_listener()

    def set_close_callback(self, callback):
        """Call the given callback when the stream is closed."""
        self._close_callback = stack_context.wrap(callback)

    def close(self):
        """Close this stream."""
        if self.socket is not None:
            if self._read_until_close:
                callback = self._read_callback
                self._read_callback = None
                self._read_until_close = False
                self._run_callback(callback,
                                   self._consume(self._read_buffer_size))
            if self._state is not None:
                self.io_loop.remove_handler(self.socket.fileno())
                self._state = None
            self.socket.close()
            self.socket = None
            if self._close_callback and self._pending_callbacks == 0:
                # if there are pending callbacks, don't run the close callback
                # until they're done (see _maybe_add_error_handler)
                cb = self._close_callback
                self._close_callback = None
                self._run_callback(cb)

    def reading(self):
        """Returns true if we are currently reading from the stream."""
        return self._read_callback is not None

    def writing(self):
        """Returns true if we are currently writing to the stream."""
        return bool(self._write_buffer)

    def closed(self):
        """Returns true if the stream has been closed."""
        return self.socket is None

    def _handle_events(self, fd, events):
        if not self.socket:
            logging.warning("Got events for closed stream %d", fd)
            return
        try:
            if events & self.io_loop.READ:
                self._handle_read()
            if not self.socket:
                return
            if events & self.io_loop.WRITE:
                if self._connecting:
                    self._handle_connect()
                self._handle_write()
            if not self.socket:
                return
            if events & self.io_loop.ERROR:
                # We may have queued up a user callback in _handle_read or
                # _handle_write, so don't close the IOStream until those
                # callbacks have had a chance to run.
                self.io_loop.add_callback(self.close)
                return
            state = self.io_loop.ERROR
            if self.reading():
                state |= self.io_loop.READ
            if self.writing():
                state |= self.io_loop.WRITE
            if state != self._state:
                assert self._state is not None, \
                    "shouldn't happen: _handle_events without self._state"
                self._state = state
                self.io_loop.update_handler(self.socket.fileno(), self._state)
        except Exception:
            logging.error("Uncaught exception, closing connection.",
                          exc_info=True)
            self.close()
            raise

    def _run_callback(self, callback, *args):
        def wrapper():
            self._pending_callbacks -= 1
            try:
                callback(*args)
            except Exception:
                logging.error("Uncaught exception, closing connection.",
                              exc_info=True)
                # Close the socket on an uncaught exception from a user callback
                # (It would eventually get closed when the socket object is
                # gc'd, but we don't want to rely on gc happening before we
                # run out of file descriptors)
                self.close()
                # Re-raise the exception so that IOLoop.handle_callback_exception
                # can see it and log the error
                raise
            self._maybe_add_error_listener()
        # We schedule callbacks to be run on the next IOLoop iteration
        # rather than running them directly for several reasons:
        # * Prevents unbounded stack growth when a callback calls an
        #   IOLoop operation that immediately runs another callback
        # * Provides a predictable execution context for e.g.
        #   non-reentrant mutexes
        # * Ensures that the try/except in wrapper() is run outside
        #   of the application's StackContexts
        with stack_context.NullContext():
            # stack_context was already captured in callback, we don't need to
            # capture it again for IOStream's wrapper.  This is especially
            # important if the callback was pre-wrapped before entry to
            # IOStream (as in HTTPConnection._header_callback), as we could
            # capture and leak the wrong context here.
            self._pending_callbacks += 1
            self.io_loop.add_callback(wrapper)

    def _handle_read(self):
        while True:
            try:
                # Read from the socket until we get EWOULDBLOCK or equivalent.
                # SSL sockets do some internal buffering, and if the data is
                # sitting in the SSL object's buffer select() and friends
                # can't see it; the only way to find out if it's there is to
                # try to read it.
                result = self._read_to_buffer()
            except Exception:
                self.close()
                return
            if result == 0:
                break
            else:
                if self._read_from_buffer():
                    return

    def _read_from_socket(self):
        """Attempts to read from the socket.

        Returns the data read or None if there is nothing to read.
        May be overridden in subclasses.
        """
        try:
            chunk = self.socket.recv(self.read_chunk_size)
        except socket.error, e:
            if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
                return None
            else:
                raise
        if not chunk:
            self.close()
            return None
        return chunk

    def _read_to_buffer(self):
        """Reads from the socket and appends the result to the read buffer.

        Returns the number of bytes read.  Returns 0 if there is nothing
        to read (i.e. the read returns EWOULDBLOCK or equivalent).  On
        error closes the socket and raises an exception.
        """
        try:
            chunk = self._read_from_socket()
        except socket.error, e:
            # ssl.SSLError is a subclass of socket.error
            logging.warning("Read error on %d: %s",
                            self.socket.fileno(), e)
            self.close()
            raise
        if chunk is None:
            return 0
        self._read_buffer.append(chunk)
        self._read_buffer_size += len(chunk)
        if self._read_buffer_size >= self.max_buffer_size:
            logging.error("Reached maximum read buffer size")
            self.close()
            raise IOError("Reached maximum read buffer size")
        return len(chunk)

    def _read_from_buffer(self):
        """Attempts to complete the currently-pending read from the buffer.

        Returns True if the read was completed.
        """
        if self._read_bytes is not None:
            if self._streaming_callback is not None and self._read_buffer_size:
                bytes_to_consume = min(self._read_bytes, self._read_buffer_size)
                self._read_bytes -= bytes_to_consume
                self._run_callback(self._streaming_callback,
                                   self._consume(bytes_to_consume))
            if self._read_buffer_size >= self._read_bytes:
                num_bytes = self._read_bytes
                callback = self._read_callback
                self._read_callback = None
                self._streaming_callback = None
                self._read_bytes = None
                self._run_callback(callback, self._consume(num_bytes))
                return True
        elif self._read_delimiter is not None:
            _merge_prefix(self._read_buffer, sys.maxint)
            loc = self._read_buffer[0].find(self._read_delimiter)
            if loc != -1:
                callback = self._read_callback
                delimiter_len = len(self._read_delimiter)
                self._read_callback = None
                self._streaming_callback = None
                self._read_delimiter = None
                self._run_callback(callback,
                                   self._consume(loc + delimiter_len))
                return True
        elif self._read_regex is not None:
            _merge_prefix(self._read_buffer, sys.maxint)
            m = self._read_regex.search(self._read_buffer[0])
            if m:
                callback = self._read_callback
                self._read_callback = None
                self._streaming_callback = None
                self._read_regex = None
                self._run_callback(callback, self._consume(m.end()))
                return True
        elif self._read_until_close:
            if self._streaming_callback is not None and self._read_buffer_size:
                self._run_callback(self._streaming_callback,
                                   self._consume(self._read_buffer_size))
        return False

    def _handle_connect(self):
        err = self.socket.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
        if err != 0:
            # IOLoop implementations may vary: some of them return
            # an error state before the socket becomes writable, so
            # in that case a connection failure would be handled by the
            # error path in _handle_events instead of here.
            logging.warning("Connect error on fd %d: %s",
                            self.socket.fileno(), errno.errorcode[err])
            self.close()
            return
        if self._connect_callback is not None:
            callback = self._connect_callback
            self._connect_callback = None
            self._run_callback(callback)
        self._connecting = False

    def _handle_write(self):
        while self._write_buffer:
            try:
                if not self._write_buffer_frozen:
                    # On windows, socket.send blows up if given a
                    # write buffer that's too large, instead of just
                    # returning the number of bytes it was able to
                    # process.  Therefore we must not call socket.send
                    # with more than 128KB at a time.
                    _merge_prefix(self._write_buffer, 128 * 1024)
                num_bytes = self.socket.send(self._write_buffer[0])
                if num_bytes == 0:
                    # With OpenSSL, if we couldn't write the entire buffer,
                    # the very same string object must be used on the
                    # next call to send.  Therefore we suppress
                    # merging the write buffer after an incomplete send.
                    # A cleaner solution would be to set
                    # SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER, but this is
                    # not yet accessible from python
                    # (http://bugs.python.org/issue8240)
                    self._write_buffer_frozen = True
                    break
                self._write_buffer_frozen = False
                _merge_prefix(self._write_buffer, num_bytes)
                self._write_buffer.popleft()
            except socket.error, e:
                if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
                    self._write_buffer_frozen = True
                    break
                else:
                    logging.warning("Write error on %d: %s",
                                    self.socket.fileno(), e)
                    self.close()
                    return
        if not self._write_buffer and self._write_callback:
            callback = self._write_callback
            self._write_callback = None
            self._run_callback(callback)

    def _consume(self, loc):
        if loc == 0:
            return b("")
        _merge_prefix(self._read_buffer, loc)
        self._read_buffer_size -= loc
        return self._read_buffer.popleft()

    def _check_closed(self):
        if not self.socket:
            raise IOError("Stream is closed")

    def _maybe_add_error_listener(self):
        if self._state is None and self._pending_callbacks == 0:
            if self.socket is None:
                cb = self._close_callback
                if cb is not None:
                    self._close_callback = None
                    self._run_callback(cb)
            else:
                self._add_io_state(0)

    def _add_io_state(self, state):
        """Adds `state` (IOLoop.{READ,WRITE} flags) to our event handler.

        Implementation notes: Reads and writes have a fast path and a
        slow path.  The fast path reads synchronously from socket
        buffers, while the slow path uses `_add_io_state` to schedule
        an IOLoop callback.  Note that in both cases, the callback is
        run asynchronously with `_run_callback`.

        To detect closed connections, we must have called
        `_add_io_state` at some point, but we want to delay this as
        much as possible so we don't have to set an `IOLoop.ERROR`
        listener that will be overwritten by the next slow-path
        operation.  As long as there are callbacks scheduled for
        fast-path ops, those callbacks may do more reads.
        If a sequence of fast-path ops do not end in a slow-path op,
        (e.g. for an @asynchronous long-poll request), we must add
        the error handler.  This is done in `_run_callback` and `write`
        (since the write callback is optional so we can have a
        fast-path write with no `_run_callback`)
        """
        if self.socket is None:
            # connection has been closed, so there can be no future events
            return
        if self._state is None:
            self._state = ioloop.IOLoop.ERROR | state
            with stack_context.NullContext():
                self.io_loop.add_handler(
                    self.socket.fileno(), self._handle_events, self._state)
        elif not self._state & state:
            self._state = self._state | state
            self.io_loop.update_handler(self.socket.fileno(), self._state)


class SSLIOStream(IOStream):
    """A utility class to write to and read from a non-blocking SSL socket.

    If the socket passed to the constructor is already connected,
    it should be wrapped with::

        ssl.wrap_socket(sock, do_handshake_on_connect=False, **kwargs)

    before constructing the SSLIOStream.  Unconnected sockets will be
    wrapped when IOStream.connect is finished.
    """
    def __init__(self, *args, **kwargs):
        """Creates an SSLIOStream.

        If a dictionary is provided as keyword argument ssl_options,
        it will be used as additional keyword arguments to ssl.wrap_socket.
        """
        self._ssl_options = kwargs.pop('ssl_options', {})
        super(SSLIOStream, self).__init__(*args, **kwargs)
        self._ssl_accepting = True
        self._handshake_reading = False
        self._handshake_writing = False

    def reading(self):
        return self._handshake_reading or super(SSLIOStream, self).reading()

    def writing(self):
        return self._handshake_writing or super(SSLIOStream, self).writing()

    def _do_ssl_handshake(self):
        # Based on code from test_ssl.py in the python stdlib
        try:
            self._handshake_reading = False
            self._handshake_writing = False
            self.socket.do_handshake()
        except ssl.SSLError, err:
            if err.args[0] == ssl.SSL_ERROR_WANT_READ:
                self._handshake_reading = True
                return
            elif err.args[0] == ssl.SSL_ERROR_WANT_WRITE:
                self._handshake_writing = True
                return
            elif err.args[0] in (ssl.SSL_ERROR_EOF,
                                 ssl.SSL_ERROR_ZERO_RETURN):
                return self.close()
            elif err.args[0] == ssl.SSL_ERROR_SSL:
                logging.warning("SSL Error on %d: %s", self.socket.fileno(), err)
                return self.close()
            raise
        except socket.error, err:
            if err.args[0] == errno.ECONNABORTED:
                return self.close()
        else:
            self._ssl_accepting = False
            super(SSLIOStream, self)._handle_connect()

    def _handle_read(self):
        if self._ssl_accepting:
            self._do_ssl_handshake()
            return
        super(SSLIOStream, self)._handle_read()

    def _handle_write(self):
        if self._ssl_accepting:
            self._do_ssl_handshake()
            return
        super(SSLIOStream, self)._handle_write()

    def _handle_connect(self):
        self.socket = ssl.wrap_socket(self.socket,
                                      do_handshake_on_connect=False,
                                      **self._ssl_options)
        # Don't call the superclass's _handle_connect (which is responsible
        # for telling the application that the connection is complete)
        # until we've completed the SSL handshake (so certificates are
        # available, etc).


    def _read_from_socket(self):
        try:
            # SSLSocket objects have both a read() and recv() method,
            # while regular sockets only have recv().
            # The recv() method blocks (at least in python 2.6) if it is
            # called when there is nothing to read, so we have to use
            # read() instead.
            chunk = self.socket.read(self.read_chunk_size)
        except ssl.SSLError, e:
            # SSLError is a subclass of socket.error, so this except
            # block must come first.
            if e.args[0] == ssl.SSL_ERROR_WANT_READ:
                return None
            else:
                raise
        except socket.error, e:
            if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
                return None
            else:
                raise
        if not chunk:
            self.close()
            return None
        return chunk

def _merge_prefix(deque, size):
    """Replace the first entries in a deque of strings with a single
    string of up to size bytes.

    >>> d = collections.deque(['abc', 'de', 'fghi', 'j'])
    >>> _merge_prefix(d, 5); print d
    deque(['abcde', 'fghi', 'j'])

    Strings will be split as necessary to reach the desired size.
    >>> _merge_prefix(d, 7); print d
    deque(['abcdefg', 'hi', 'j'])

    >>> _merge_prefix(d, 3); print d
    deque(['abc', 'defg', 'hi', 'j'])

    >>> _merge_prefix(d, 100); print d
    deque(['abcdefghij'])
    """
    if len(deque) == 1 and len(deque[0]) <= size:
        return
    prefix = []
    remaining = size
    while deque and remaining > 0:
        chunk = deque.popleft()
        if len(chunk) > remaining:
            deque.appendleft(chunk[remaining:])
            chunk = chunk[:remaining]
        prefix.append(chunk)
        remaining -= len(chunk)
    # This data structure normally just contains byte strings, but
    # the unittest gets messy if it doesn't use the default str() type,
    # so do the merge based on the type of data that's actually present.
    if prefix:
        deque.appendleft(type(prefix[0])().join(prefix))
    if not deque:
        deque.appendleft(b(""))

def doctests():
    import doctest
    return doctest.DocTestSuite()