#!/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.

"""Utility classes to write to and read from non-blocking files and sockets.

Contents:

* `BaseIOStream`: Generic interface for reading and writing.
* `IOStream`: Implementation of BaseIOStream using non-blocking sockets.
* `SSLIOStream`: SSL-aware version of IOStream.
* `PipeIOStream`: Pipe-based IOStream implementation.
"""

from __future__ import absolute_import, division, with_statement

import collections
import errno
import os
import socket
import sys
import re

from tornado import ioloop
from tornado.log import gen_log, app_log
from tornado import stack_context
from tornado.util import b, bytes_type

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

try:
    from tornado.platform.posix import _set_nonblocking
except ImportError:
    _set_nonblocking = None

class StreamClosedError(IOError):
    pass

class BaseIOStream(object):
    """A utility class to write to and read from a non-blocking file or 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).

    When a stream is closed due to an error, the IOStream's `error`
    attribute contains the exception object.

    Subclasses must implement `fileno`, `close_fd`, `write_to_fd`,
    `read_from_fd`, and optionally `get_fd_error`.
    """
    def __init__(self, io_loop=None, max_buffer_size=104857600,
                 read_chunk_size=4096):
        self.io_loop = io_loop or ioloop.IOLoop.instance()
        self.max_buffer_size = max_buffer_size
        self.read_chunk_size = read_chunk_size
        self.error = None
        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
        self._closed = False

    def fileno(self):
        """Returns the file descriptor for this stream."""
        raise NotImplementedError()

    def close_fd(self):
        """Closes the file underlying this stream.

        ``close_fd`` is called by `BaseIOStream` and should not be called
        elsewhere; other users should call `close` instead.
        """
        raise NotImplementedError()

    def write_to_fd(self, data):
        """Attempts to write ``data`` to the underlying file.

        Returns the number of bytes written.
        """
        raise NotImplementedError()

    def read_from_fd(self):
        """Attempts to read from the underlying file.

        Returns ``None`` if there was nothing to read (the socket returned
        EWOULDBLOCK or equivalent), otherwise returns the data.  When possible,
        should return no more than ``self.read_chunk_size`` bytes at a time.
        """
        raise NotImplementedError()

    def get_fd_error(self):
        """Returns information about any error on the underlying file.

        This method is called after the IOLoop has signaled an error on the
        file descriptor, and should return an Exception (such as `socket.error`
        with additional information, or None if no such information is
        available.
        """
        return None

    def read_until_regex(self, regex, callback):
        """Call callback when we read the given regex pattern."""
        self._set_read_callback(callback)
        self._read_regex = re.compile(regex)
        self._try_inline_read()

    def read_until(self, delimiter, callback):
        """Call callback when we read the given delimiter."""
        self._set_read_callback(callback)
        self._read_delimiter = delimiter
        self._try_inline_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.
        """
        self._set_read_callback(callback)
        assert isinstance(num_bytes, (int, long))
        self._read_bytes = num_bytes
        self._streaming_callback = stack_context.wrap(streaming_callback)
        self._try_inline_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.
        """
        self._set_read_callback(callback)
        self._streaming_callback = stack_context.wrap(streaming_callback)
        if self.closed():
            if self._streaming_callback is not None:
                self._run_callback(self._streaming_callback,
                                   self._consume(self._read_buffer_size))
            self._run_callback(self._read_callback,
                               self._consume(self._read_buffer_size))
            self._streaming_callback = None
            self._read_callback = None
            return
        self._read_until_close = True
        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()
        # We use bool(_write_buffer) as a proxy for write_buffer_size>0,
        # so never put empty strings in the buffer.
        if data:
            # Break up large contiguous strings before inserting them in the
            # write buffer, so we don't have to recopy the entire thing
            # as we slice off pieces to send to the socket.
            WRITE_BUFFER_CHUNK_SIZE = 128 * 1024
            if len(data) > WRITE_BUFFER_CHUNK_SIZE:
                for i in range(0, len(data), WRITE_BUFFER_CHUNK_SIZE):
                    self._write_buffer.append(data[i:i + WRITE_BUFFER_CHUNK_SIZE])
            else:
                self._write_buffer.append(data)
        self._write_callback = stack_context.wrap(callback)
        if not self._connecting:
            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 not self.closed():
            if any(sys.exc_info()):
                self.error = sys.exc_info()[1]
            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.fileno())
                self._state = None
            self.close_fd()
            self._closed = True
        self._maybe_run_close_callback()

    def _maybe_run_close_callback(self):
        if (self.closed() and 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._closed

    def _handle_events(self, fd, events):
        if self.closed():
            gen_log.warning("Got events for closed stream %d", fd)
            return
        try:
            if events & self.io_loop.READ:
                self._handle_read()
            if self.closed():
                return
            if events & self.io_loop.WRITE:
                if self._connecting:
                    self._handle_connect()
                self._handle_write()
            if self.closed():
                return
            if events & self.io_loop.ERROR:
                self.error = self.get_fd_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.io_loop.ERROR:
                state |= self.io_loop.READ
            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.fileno(), self._state)
        except Exception:
            gen_log.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:
                app_log.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):
        try:
            try:
                # Pretend to have a pending callback so that an EOF in
                # _read_to_buffer doesn't trigger an immediate close
                # callback.  At the end of this method we'll either
                # estabilsh a real pending callback via
                # _read_from_buffer or run the close callback.
                #
                # We need two try statements here so that
                # pending_callbacks is decremented before the `except`
                # clause below (which calls `close` and does need to
                # trigger the callback)
                self._pending_callbacks += 1
                while not self.closed():
                    # 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.
                    if self._read_to_buffer() == 0:
                        break
            finally:
                self._pending_callbacks -= 1
        except Exception:
            gen_log.warning("error on read", exc_info=True)
            self.close()
            return
        if self._read_from_buffer():
            return
        else:
            self._maybe_run_close_callback()

    def _set_read_callback(self, callback):
        assert not self._read_callback, "Already reading"
        self._read_callback = stack_context.wrap(callback)

    def _try_inline_read(self):
        """Attempt to complete the current read operation from buffered data.

        If the read can be completed without blocking, schedules the
        read callback on the next IOLoop iteration; otherwise starts
        listening for reads on the socket.
        """
        # See if we've already got the data from a previous read
        if self._read_from_buffer():
            return
        self._check_closed()
        try:
            # See comments in _handle_read about incrementing _pending_callbacks
            self._pending_callbacks += 1
            while not self.closed():
                if self._read_to_buffer() == 0:
                    break
        finally:
            self._pending_callbacks -= 1
        if self._read_from_buffer():
            return
        self._maybe_add_error_listener()

    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_fd()
        except (socket.error, IOError, OSError), e:
            # ssl.SSLError is a subclass of socket.error
            if e.args[0] == errno.ECONNRESET:
                # Treat ECONNRESET as a connection close rather than
                # an error to minimize log spam  (the exception will
                # be available on self.error for apps that care).
                self.close()
                return
            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:
            gen_log.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._streaming_callback is not None and self._read_buffer_size:
            bytes_to_consume = self._read_buffer_size
            if self._read_bytes is not None:
                bytes_to_consume = min(self._read_bytes, bytes_to_consume)
                self._read_bytes -= bytes_to_consume
            self._run_callback(self._streaming_callback,
                               self._consume(bytes_to_consume))
        if self._read_bytes is not None and 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:
            # Multi-byte delimiters (e.g. '\r\n') may straddle two
            # chunks in the read buffer, so we can't easily find them
            # without collapsing the buffer.  However, since protocols
            # using delimited reads (as opposed to reads of a known
            # length) tend to be "line" oriented, the delimiter is likely
            # to be in the first few chunks.  Merge the buffer gradually
            # since large merges are relatively expensive and get undone in
            # consume().
            if self._read_buffer:
                while True:
                    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
                    if len(self._read_buffer) == 1:
                        break
                    _double_prefix(self._read_buffer)
        elif self._read_regex is not None:
            if self._read_buffer:
                while True:
                    m = self._read_regex.search(self._read_buffer[0])
                    if m is not None:
                        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
                    if len(self._read_buffer) == 1:
                        break
                    _double_prefix(self._read_buffer)
        return 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.write_to_fd(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:
                    gen_log.warning("Write error on %d: %s",
                                    self.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 self.closed():
            raise StreamClosedError("Stream is closed")

    def _maybe_add_error_listener(self):
        if self._state is None and self._pending_callbacks == 0:
            if self.closed():
                self._maybe_run_close_callback()
            else:
                self._add_io_state(ioloop.IOLoop.READ)

    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.closed():
            # 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.fileno(), self._handle_events, self._state)
        elif not self._state & state:
            self._state = self._state | state
            self.io_loop.update_handler(self.fileno(), self._state)


class IOStream(BaseIOStream):
    r"""Socket-based IOStream implementation.

    This class supports the read and write methods from `BaseIOStream`
    plus a `connect` method.

    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, *args, **kwargs):
        self.socket = socket
        self.socket.setblocking(False)
        super(IOStream, self).__init__(*args, **kwargs)

    def fileno(self):
        return self.socket.fileno()

    def close_fd(self):
        self.socket.close()
        self.socket = None

    def get_fd_error(self):
        errno = self.socket.getsockopt(socket.SOL_SOCKET,
                                       socket.SO_ERROR)
        return socket.error(errno, os.strerror(errno))

    def read_from_fd(self):
        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 write_to_fd(self, data):
        return self.socket.send(data)

    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 we expect connect() to raise an
            # exception with EINPROGRESS or EWOULDBLOCK.
            #
            # On freebsd, other errors such as ECONNREFUSED may be
            # returned immediately when attempting to connect to
            # localhost, so handle them the same way as an error
            # reported later in _handle_connect.
            if e.args[0] not in (errno.EINPROGRESS, errno.EWOULDBLOCK):
                gen_log.warning("Connect error on fd %d: %s",
                                self.socket.fileno(), e)
                self.close()
                return
        self._connect_callback = stack_context.wrap(callback)
        self._add_io_state(self.io_loop.WRITE)

    def _handle_connect(self):
        err = self.socket.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
        if err != 0:
            self.error = socket.error(err, os.strerror(err))
            # 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.
            gen_log.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


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
        self._ssl_connect_callback = None

    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:
                try:
                    peer = self.socket.getpeername()
                except:
                    peer = '(not connected)'
                gen_log.warning("SSL Error on %d %s: %s",
                                self.socket.fileno(), peer, err)
                return self.close()
            raise
        except socket.error, err:
            if err.args[0] in (errno.ECONNABORTED, errno.ECONNRESET):
                return self.close()
        else:
            self._ssl_accepting = False
            if self._ssl_connect_callback is not None:
                callback = self._ssl_connect_callback
                self._ssl_connect_callback = None
                self._run_callback(callback)

    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 connect(self, address, callback=None):
        # Save the user's callback and run it after the ssl handshake
        # has completed.
        self._ssl_connect_callback = callback
        super(SSLIOStream, self).connect(address, callback=None)

    def _handle_connect(self):
        # When the connection is complete, wrap the socket for SSL
        # traffic.  Note that we do this by overriding _handle_connect
        # instead of by passing a callback to super().connect because
        # user callbacks are enqueued asynchronously on the IOLoop,
        # but since _handle_events calls _handle_connect immediately
        # followed by _handle_write we need this to be synchronous.
        self.socket = ssl.wrap_socket(self.socket,
                                      do_handshake_on_connect=False,
                                      **self._ssl_options)
        super(SSLIOStream, self)._handle_connect()

    def read_from_fd(self):
        if self._ssl_accepting:
            # If the handshake hasn't finished yet, there can't be anything
            # to read (attempting to read may or may not raise an exception
            # depending on the SSL version)
            return None
        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

class PipeIOStream(BaseIOStream):
    """Pipe-based IOStream implementation.

    The constructor takes an integer file descriptor (such as one returned
    by `os.pipe`) rather than an open file object.
    """
    def __init__(self, fd, *args, **kwargs):
        self.fd = fd
        _set_nonblocking(fd)
        super(PipeIOStream, self).__init__(*args, **kwargs)

    def fileno(self):
        return self.fd

    def close_fd(self):
        os.close(self.fd)

    def write_to_fd(self, data):
        return os.write(self.fd, data)

    def read_from_fd(self):
        try:
            chunk = os.read(self.fd, self.read_chunk_size)
        except (IOError, OSError), e:
            if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
                return None
            elif e.args[0] == errno.EBADF:
                # If the writing half of a pipe is closed, select will
                # report it as readable but reads will fail with EBADF.
                self.close()
                return None
            else:
                raise
        if not chunk:
            self.close()
            return None
        return chunk


def _double_prefix(deque):
    """Grow by doubling, but don't split the second chunk just because the
    first one is small.
    """
    new_len = max(len(deque[0]) * 2,
                  (len(deque[0]) + len(deque[1])))
    _merge_prefix(deque, new_len)


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()
