http.py 39.6 KB
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#
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.

"""HTTP server module.

"""

import BaseHTTPServer
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import cgi
import logging
import mimetools
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import OpenSSL
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import os
import select
import socket
import sys
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import time
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import signal
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import logging
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import errno

from cStringIO import StringIO
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from ganeti import constants
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from ganeti import serializer
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from ganeti import workerpool
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from ganeti import utils
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HTTP_CLIENT_THREADS = 10

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HTTP_GANETI_VERSION = "Ganeti %s" % constants.RELEASE_VERSION

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WEEKDAYNAME = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
MONTHNAME = [None,
             'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
             'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']

# Default error message
DEFAULT_ERROR_CONTENT_TYPE = "text/html"
DEFAULT_ERROR_MESSAGE = """\
<head>
<title>Error response</title>
</head>
<body>
<h1>Error response</h1>
<p>Error code %(code)d.
<p>Message: %(message)s.
<p>Error code explanation: %(code)s = %(explain)s.
</body>
"""

HTTP_OK = 200
HTTP_NO_CONTENT = 204
HTTP_NOT_MODIFIED = 304

HTTP_0_9 = "HTTP/0.9"
HTTP_1_0 = "HTTP/1.0"
HTTP_1_1 = "HTTP/1.1"

HTTP_GET = "GET"
HTTP_HEAD = "HEAD"
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HTTP_POST = "POST"
HTTP_PUT = "PUT"

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HTTP_ETAG = "ETag"
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HTTP_HOST = "Host"
HTTP_SERVER = "Server"
HTTP_DATE = "Date"
HTTP_USER_AGENT = "User-Agent"
HTTP_CONTENT_TYPE = "Content-Type"
HTTP_CONTENT_LENGTH = "Content-Length"
HTTP_CONNECTION = "Connection"
HTTP_KEEP_ALIVE = "Keep-Alive"
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_SSL_UNEXPECTED_EOF = "Unexpected EOF"

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class SocketClosed(socket.error):
  pass


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class _HttpClientError(Exception):
  """Internal exception for HTTP client errors.

  This should only be used for internal error reporting.

  """
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  pass


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class HTTPException(Exception):
  code = None
  message = None

  def __init__(self, message=None):
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    Exception.__init__(self)
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    if message is not None:
      self.message = message


class HTTPBadRequest(HTTPException):
  code = 400


class HTTPForbidden(HTTPException):
  code = 403


class HTTPNotFound(HTTPException):
  code = 404


class HTTPGone(HTTPException):
  code = 410


class HTTPLengthRequired(HTTPException):
  code = 411


class HTTPInternalError(HTTPException):
  code = 500


class HTTPNotImplemented(HTTPException):
  code = 501


class HTTPServiceUnavailable(HTTPException):
  code = 503


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class HTTPVersionNotSupported(HTTPException):
  code = 505


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class ApacheLogfile:
  """Utility class to write HTTP server log files.

  The written format is the "Common Log Format" as defined by Apache:
  http://httpd.apache.org/docs/2.2/mod/mod_log_config.html#examples

  """
  def __init__(self, fd):
    """Constructor for ApacheLogfile class.

    Args:
    - fd: Open file object

    """
    self._fd = fd

  def LogRequest(self, request, format, *args):
    self._fd.write("%s %s %s [%s] %s\n" % (
      # Remote host address
      request.address_string(),

      # RFC1413 identity (identd)
      "-",

      # Remote user
      "-",

      # Request time
      self._FormatCurrentTime(),

      # Message
      format % args,
      ))
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    self._fd.flush()
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  def _FormatCurrentTime(self):
    """Formats current time in Common Log Format.

    """
    return self._FormatLogTime(time.time())

  def _FormatLogTime(self, seconds):
    """Formats time for Common Log Format.

    All timestamps are logged in the UTC timezone.

    Args:
    - seconds: Time in seconds since the epoch

    """
    (_, month, _, _, _, _, _, _, _) = tm = time.gmtime(seconds)
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    format = "%d/" + MONTHNAME[month] + "/%Y:%H:%M:%S +0000"
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    return time.strftime(format, tm)


class HTTPJsonConverter:
  CONTENT_TYPE = "application/json"

  def Encode(self, data):
    return serializer.DumpJson(data)

  def Decode(self, data):
    return serializer.LoadJson(data)


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class _HttpSocketBase(object):
  """Base class for HTTP server and client.

  """
  def __init__(self):
    self._using_ssl = None
    self._ssl_cert = None
    self._ssl_key = None

  def _CreateSocket(self, ssl_key_path, ssl_cert_path, ssl_verify_peer):
    """Creates a TCP socket and initializes SSL if needed.

    @type ssl_key_path: string
    @param ssl_key_path: Path to file containing SSL key in PEM format
    @type ssl_cert_path: string
    @param ssl_cert_path: Path to file containing SSL certificate in PEM format
    @type ssl_verify_peer: bool
    @param ssl_verify_peer: Whether to require client certificate and compare
                            it with our certificate

    """
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    # Should we enable SSL?
    self._using_ssl = (ssl_cert_path and ssl_key_path)

    if not self._using_ssl:
      return sock

    ctx = OpenSSL.SSL.Context(OpenSSL.SSL.SSLv23_METHOD)
    ctx.set_options(OpenSSL.SSL.OP_NO_SSLv2)

    ssl_key_pem = utils.ReadFile(ssl_key_path)
    ssl_cert_pem = utils.ReadFile(ssl_cert_path)

    cr = OpenSSL.crypto
    self._ssl_cert = cr.load_certificate(cr.FILETYPE_PEM, ssl_cert_pem)
    self._ssl_key = cr.load_privatekey(cr.FILETYPE_PEM, ssl_key_pem)
    del cr

    ctx.use_privatekey(self._ssl_key)
    ctx.use_certificate(self._ssl_cert)
    ctx.check_privatekey()

    if ssl_verify_peer:
      ctx.set_verify(OpenSSL.SSL.VERIFY_PEER |
                     OpenSSL.SSL.VERIFY_FAIL_IF_NO_PEER_CERT,
                     self._SSLVerifyCallback)

    return OpenSSL.SSL.Connection(ctx, sock)

  def _SSLVerifyCallback(self, conn, cert, errnum, errdepth, ok):
    """Verify the certificate provided by the peer

    We only compare fingerprints. The client must use the same certificate as
    we do on our side.

    """
    assert self._ssl_cert and self._ssl_key, "SSL not initialized"

    return (self._ssl_cert.digest("sha1") == cert.digest("sha1") and
            self._ssl_cert.digest("md5") == cert.digest("md5"))


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class _HttpConnectionHandler(object):
  """Implements server side of HTTP

  This class implements the server side of HTTP. It's based on code of Python's
  BaseHTTPServer, from both version 2.4 and 3k. It does not support non-ASCII
  character encodings. Keep-alive connections are not supported.

  """
  # The default request version.  This only affects responses up until
  # the point where the request line is parsed, so it mainly decides what
  # the client gets back when sending a malformed request line.
  # Most web servers default to HTTP 0.9, i.e. don't send a status line.
  default_request_version = HTTP_0_9

  # Error message settings
  error_message_format = DEFAULT_ERROR_MESSAGE
  error_content_type = DEFAULT_ERROR_CONTENT_TYPE

  responses = BaseHTTPServer.BaseHTTPRequestHandler.responses

  def __init__(self, server, conn, client_addr, fileio_class):
    """Initializes this class.

    Part of the initialization is reading the request and eventual POST/PUT
    data sent by the client.

    """
    self._server = server

    # We default rfile to buffered because otherwise it could be
    # really slow for large data (a getc() call per byte); we make
    # wfile unbuffered because (a) often after a write() we want to
    # read and we need to flush the line; (b) big writes to unbuffered
    # files are typically optimized by stdio even when big reads
    # aren't.
    self.rfile = fileio_class(conn, mode="rb", bufsize=-1)
    self.wfile = fileio_class(conn, mode="wb", bufsize=0)

    self.client_addr = client_addr

    self.request_headers = None
    self.request_method = None
    self.request_path = None
    self.request_requestline = None
    self.request_version = self.default_request_version

    self.response_body = None
    self.response_code = HTTP_OK
    self.response_content_type = None
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    self.response_headers = {}
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    self.should_fork = False

    try:
      self._ReadRequest()
      self._ReadPostData()
    except HTTPException, err:
      self._SetErrorStatus(err)

  def Close(self):
    if not self.wfile.closed:
      self.wfile.flush()
    self.wfile.close()
    self.rfile.close()

  def _DateTimeHeader(self):
    """Return the current date and time formatted for a message header.

    """
    (year, month, day, hh, mm, ss, wd, _, _) = time.gmtime()
    return ("%s, %02d %3s %4d %02d:%02d:%02d GMT" %
            (WEEKDAYNAME[wd], day, MONTHNAME[month], year, hh, mm, ss))

  def _SetErrorStatus(self, err):
    """Sets the response code and body from a HTTPException.

    @type err: HTTPException
    @param err: Exception instance

    """
    try:
      (shortmsg, longmsg) = self.responses[err.code]
    except KeyError:
      shortmsg = longmsg = "Unknown"

    if err.message:
      message = err.message
    else:
      message = shortmsg

    values = {
      "code": err.code,
      "message": cgi.escape(message),
      "explain": longmsg,
      }

    self.response_code = err.code
    self.response_content_type = self.error_content_type
    self.response_body = self.error_message_format % values

  def HandleRequest(self):
    """Handle the actual request.

    Calls the actual handler function and converts exceptions into HTTP errors.

    """
    # Don't do anything if there's already been a problem
    if self.response_code != HTTP_OK:
      return

    assert self.request_method, "Status code %s requires a method" % HTTP_OK

    # Check whether client is still there
    self.rfile.read(0)

    try:
      try:
        result = self._server.HandleRequest(self)

        # TODO: Content-type
        encoder = HTTPJsonConverter()
        body = encoder.Encode(result)

        self.response_content_type = encoder.CONTENT_TYPE
        self.response_body = body
      except (HTTPException, KeyboardInterrupt, SystemExit):
        raise
      except Exception, err:
        logging.exception("Caught exception")
        raise HTTPInternalError(message=str(err))
      except:
        logging.exception("Unknown exception")
        raise HTTPInternalError(message="Unknown error")

    except HTTPException, err:
      self._SetErrorStatus(err)

  def SendResponse(self):
    """Sends response to the client.

    """
    # Check whether client is still there
    self.rfile.read(0)

    logging.info("%s:%s %s %s", self.client_addr[0], self.client_addr[1],
                 self.request_requestline, self.response_code)

    if self.response_code in self.responses:
      response_message = self.responses[self.response_code][0]
    else:
      response_message = ""

    if self.request_version != HTTP_0_9:
      self.wfile.write("%s %d %s\r\n" %
                       (self.request_version, self.response_code,
                        response_message))
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      self._SendHeader(HTTP_SERVER, HTTP_GANETI_VERSION)
      self._SendHeader(HTTP_DATE, self._DateTimeHeader())
      self._SendHeader(HTTP_CONTENT_TYPE, self.response_content_type)
      self._SendHeader(HTTP_CONTENT_LENGTH, str(len(self.response_body)))
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      for key, val in self.response_headers.iteritems():
        self._SendHeader(key, val)

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      # We don't support keep-alive at this time
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      self._SendHeader(HTTP_CONNECTION, "close")
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      self.wfile.write("\r\n")

    if (self.request_method != HTTP_HEAD and
        self.response_code >= HTTP_OK and
        self.response_code not in (HTTP_NO_CONTENT, HTTP_NOT_MODIFIED)):
      self.wfile.write(self.response_body)

  def _SendHeader(self, name, value):
    if self.request_version != HTTP_0_9:
      self.wfile.write("%s: %s\r\n" % (name, value))

  def _ReadRequest(self):
    """Reads and parses request line

    """
    raw_requestline = self.rfile.readline()

    requestline = raw_requestline
    if requestline[-2:] == '\r\n':
      requestline = requestline[:-2]
    elif requestline[-1:] == '\n':
      requestline = requestline[:-1]

    if not requestline:
      raise HTTPBadRequest("Empty request line")

    self.request_requestline = requestline

    logging.debug("HTTP request: %s", raw_requestline.rstrip("\r\n"))

    words = requestline.split()

    if len(words) == 3:
      [method, path, version] = words
      if version[:5] != 'HTTP/':
        raise HTTPBadRequest("Bad request version (%r)" % version)

      try:
        base_version_number = version.split('/', 1)[1]
        version_number = base_version_number.split(".")

        # RFC 2145 section 3.1 says there can be only one "." and
        #   - major and minor numbers MUST be treated as
        #      separate integers;
        #   - HTTP/2.4 is a lower version than HTTP/2.13, which in
        #      turn is lower than HTTP/12.3;
        #   - Leading zeros MUST be ignored by recipients.
        if len(version_number) != 2:
          raise HTTPBadRequest("Bad request version (%r)" % version)

        version_number = int(version_number[0]), int(version_number[1])
      except (ValueError, IndexError):
        raise HTTPBadRequest("Bad request version (%r)" % version)

      if version_number >= (2, 0):
        raise HTTPVersionNotSupported("Invalid HTTP Version (%s)" %
                                      base_version_number)

    elif len(words) == 2:
      version = HTTP_0_9
      [method, path] = words
      if method != HTTP_GET:
        raise HTTPBadRequest("Bad HTTP/0.9 request type (%r)" % method)

    else:
      raise HTTPBadRequest("Bad request syntax (%r)" % requestline)

    # Examine the headers and look for a Connection directive
    headers = mimetools.Message(self.rfile, 0)

    self.request_method = method
    self.request_path = path
    self.request_version = version
    self.request_headers = headers

  def _ReadPostData(self):
    """Reads POST/PUT data

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    Quoting RFC1945, section 7.2 (HTTP/1.0): "The presence of an entity body in
    a request is signaled by the inclusion of a Content-Length header field in
    the request message headers. HTTP/1.0 requests containing an entity body
    must include a valid Content-Length header field."

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    """
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    # While not according to specification, we only support an entity body for
    # POST and PUT.
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    if (not self.request_method or
        self.request_method.upper() not in (HTTP_POST, HTTP_PUT)):
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      self.request_post_data = None
      return

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    content_length = None
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    try:
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      if HTTP_CONTENT_LENGTH in self.request_headers:
        content_length = int(self.request_headers[HTTP_CONTENT_LENGTH])
    except TypeError:
      pass
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    except ValueError:
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      pass

    # 411 Length Required is specified in RFC2616, section 10.4.12 (HTTP/1.1)
    if content_length is None:
      raise HTTPLengthRequired("Missing Content-Length header or"
                               " invalid format")
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    data = self.rfile.read(content_length)

    # TODO: Content-type, error handling
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    if data:
      self.request_post_data = HTTPJsonConverter().Decode(data)
    else:
      self.request_post_data = None
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    logging.debug("HTTP POST data: %s", self.request_post_data)


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class HttpServer(_HttpSocketBase):
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  """Generic HTTP server class

  Users of this class must subclass it and override the HandleRequest function.

  """
  MAX_CHILDREN = 20

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  def __init__(self, mainloop, local_address, port,
               ssl_key_path=None, ssl_cert_path=None, ssl_verify_peer=False):
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    """Initializes the HTTP server

    @type mainloop: ganeti.daemon.Mainloop
    @param mainloop: Mainloop used to poll for I/O events
    @type local_addess: string
    @param local_address: Local IP address to bind to
    @type port: int
    @param port: TCP port to listen on
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    @type ssl_key_path: string
    @param ssl_key_path: Path to file containing SSL key in PEM format
    @type ssl_cert_path: string
    @param ssl_cert_path: Path to file containing SSL certificate in PEM format
    @type ssl_verify_peer: bool
    @param ssl_verify_peer: Whether to require client certificate and compare
                            it with our certificate
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    """
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    _HttpSocketBase.__init__(self)

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    self.mainloop = mainloop
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    self.local_address = local_address
    self.port = port
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    self.socket = self._CreateSocket(ssl_key_path, ssl_cert_path, ssl_verify_peer)
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    # Allow port to be reused
    self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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    if self._using_ssl:
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      self._fileio_class = _SSLFileObject
    else:
      self._fileio_class = socket._fileobject

    self._children = []

    mainloop.RegisterIO(self, self.socket.fileno(), select.POLLIN)
    mainloop.RegisterSignal(self)

  def Start(self):
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    self.socket.bind((self.local_address, self.port))
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    self.socket.listen(5)

  def Stop(self):
    self.socket.close()

  def OnIO(self, fd, condition):
    if condition & select.POLLIN:
      self._IncomingConnection()

  def OnSignal(self, signum):
    if signum == signal.SIGCHLD:
      self._CollectChildren(True)

  def _CollectChildren(self, quick):
    """Checks whether any child processes are done

    @type quick: bool
    @param quick: Whether to only use non-blocking functions

    """
    if not quick:
      # Don't wait for other processes if it should be a quick check
      while len(self._children) > self.MAX_CHILDREN:
        try:
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          # Waiting without a timeout brings us into a potential DoS situation.
          # As soon as too many children run, we'll not respond to new
          # requests. The real solution would be to add a timeout for children
          # and killing them after some time.
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          pid, status = os.waitpid(0, 0)
        except os.error:
          pid = None
        if pid and pid in self._children:
          self._children.remove(pid)

    for child in self._children:
      try:
        pid, status = os.waitpid(child, os.WNOHANG)
      except os.error:
        pid = None
      if pid and pid in self._children:
        self._children.remove(pid)

  def _IncomingConnection(self):
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    """Called for each incoming connection
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    """
    (connection, client_addr) = self.socket.accept()
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    self._CollectChildren(False)

    pid = os.fork()
    if pid == 0:
      # Child process
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      logging.info("Connection from %s:%s", client_addr[0], client_addr[1])

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      try:
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        try:
          try:
            handler = None
            try:
              # Read, parse and handle request
              handler = _HttpConnectionHandler(self, connection, client_addr,
                                               self._fileio_class)
              handler.HandleRequest()
            finally:
              # Try to send a response
              if handler:
                handler.SendResponse()
                handler.Close()
          except SocketClosed:
            pass
        finally:
          logging.info("Disconnected %s:%s", client_addr[0], client_addr[1])
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      except:
        logging.exception("Error while handling request from %s:%s",
                          client_addr[0], client_addr[1])
        os._exit(1)
      os._exit(0)
    else:
      self._children.append(pid)

  def HandleRequest(self, req):
    raise NotImplementedError()


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class HttpClientRequest(object):
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  def __init__(self, host, port, method, path, headers=None, post_data=None,
               ssl_key_path=None, ssl_cert_path=None, ssl_verify_peer=False):
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    """Describes an HTTP request.

    @type host: string
    @param host: Hostname
    @type port: int
    @param port: Port
    @type method: string
    @param method: Method name
    @type path: string
    @param path: Request path
    @type headers: dict or None
    @param headers: Additional headers to send
    @type post_data: string or None
    @param post_data: Additional data to send

    """
    if post_data is not None:
      assert method.upper() in (HTTP_POST, HTTP_PUT), \
        "Only POST and GET requests support sending data"

    assert path.startswith("/"), "Path must start with slash (/)"

    self.host = host
    self.port = port
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    self.ssl_key_path = ssl_key_path
    self.ssl_cert_path = ssl_cert_path
    self.ssl_verify_peer = ssl_verify_peer
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    self.method = method
    self.path = path
    self.headers = headers
    self.post_data = post_data

    self.success = None
    self.error = None

    self.resp_status_line = None
    self.resp_version = None
    self.resp_status = None
    self.resp_reason = None
    self.resp_headers = None
    self.resp_body = None


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class HttpClientRequestExecutor(_HttpSocketBase):
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  # Default headers
  DEFAULT_HEADERS = {
    HTTP_USER_AGENT: HTTP_GANETI_VERSION,
    # TODO: For keep-alive, don't send "Connection: close"
    HTTP_CONNECTION: "close",
    }

  # Length limits
  STATUS_LINE_LENGTH_MAX = 512
  HEADER_LENGTH_MAX = 4 * 1024

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  # Timeouts in seconds for socket layer
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  # TODO: Make read timeout configurable per OpCode
  CONNECT_TIMEOUT = 5.0
  WRITE_TIMEOUT = 10
  READ_TIMEOUT = None
  CLOSE_TIMEOUT = 1

  # Parser state machine
  PS_STATUS_LINE = "status-line"
  PS_HEADERS = "headers"
  PS_BODY = "body"
  PS_COMPLETE = "complete"

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  # Socket operations
  (OP_SEND,
   OP_RECV,
   OP_CLOSE_CHECK,
   OP_SHUTDOWN) = range(4)

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  def __init__(self, req):
    """Initializes the HttpClientRequestExecutor class.

    @type req: HttpClientRequest
    @param req: Request object

    """
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    _HttpSocketBase.__init__(self)

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    self.request = req

    self.parser_status = self.PS_STATUS_LINE
    self.header_buffer = StringIO()
    self.body_buffer = StringIO()
    self.content_length = None
    self.server_will_close = None

    self.poller = select.poll()

    try:
      # TODO: Implement connection caching/keep-alive
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      self.sock = self._CreateSocket(req.ssl_key_path,
                                     req.ssl_cert_path,
                                     req.ssl_verify_peer)
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      # Disable Python's timeout
      self.sock.settimeout(None)

      # Operate in non-blocking mode
      self.sock.setblocking(0)

      force_close = True
      self._Connect()
      try:
        self._SendRequest()
        self._ReadResponse()

        # Only wait for server to close if we didn't have any exception.
        force_close = False
      finally:
        self._CloseConnection(force_close)

      self.sock.close()
      self.sock = None

      req.resp_body = self.body_buffer.getvalue()

      req.success = True
      req.error = None

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    except _HttpClientError, err:
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      req.success = False
      req.error = str(err)

  def _BuildRequest(self):
    """Build HTTP request.

    @rtype: string
    @return: Complete request

    """
    # Headers
    send_headers = self.DEFAULT_HEADERS.copy()

    if self.request.headers:
      send_headers.update(req.headers)

    send_headers[HTTP_HOST] = "%s:%s" % (self.request.host, self.request.port)

    if self.request.post_data:
      send_headers[HTTP_CONTENT_LENGTH] = len(self.request.post_data)

    buf = StringIO()

    # Add request line. We only support HTTP/1.0 (no chunked transfers and no
    # keep-alive).
    # TODO: For keep-alive, change to HTTP/1.1
    buf.write("%s %s %s\r\n" % (self.request.method.upper(),
                                self.request.path, HTTP_1_0))

    # Add headers
    for name, value in send_headers.iteritems():
      buf.write("%s: %s\r\n" % (name, value))

    buf.write("\r\n")

    if self.request.post_data:
      buf.write(self.request.post_data)

    return buf.getvalue()

  def _ParseStatusLine(self):
    """Parses the status line sent by the server.

    """
    line = self.request.resp_status_line

    if not line:
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      raise _HttpClientError("Empty status line")
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    try:
      [version, status, reason] = line.split(None, 2)
    except ValueError:
      try:
        [version, status] = line.split(None, 1)
        reason = ""
      except ValueError:
        version = HTTP_9_0

    if version:
      version = version.upper()

    if version not in (HTTP_1_0, HTTP_1_1):
      # We do not support HTTP/0.9, despite the specification requiring it
      # (RFC2616, section 19.6)
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      raise _HttpClientError("Only HTTP/1.0 and HTTP/1.1 are supported (%r)" %
                             line)
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    # The status code is a three-digit number
    try:
      status = int(status)
      if status < 100 or status > 999:
        status = -1
    except ValueError:
      status = -1

    if status == -1:
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      raise _HttpClientError("Invalid status code (%r)" % line)
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    self.request.resp_version = version
    self.request.resp_status = status
    self.request.resp_reason = reason

  def _WillServerCloseConnection(self):
    """Evaluate whether server will close the connection.

    @rtype: bool
    @return: Whether server will close the connection

    """
    hdr_connection = self.request.resp_headers.get(HTTP_CONNECTION, None)
    if hdr_connection:
      hdr_connection = hdr_connection.lower()

    # An HTTP/1.1 server is assumed to stay open unless explicitly closed.
    if self.request.resp_version == HTTP_1_1:
      return (hdr_connection and "close" in hdr_connection)

    # Some HTTP/1.0 implementations have support for persistent connections,
    # using rules different than HTTP/1.1.

    # For older HTTP, Keep-Alive indicates persistent connection.
    if self.request.resp_headers.get(HTTP_KEEP_ALIVE):
      return False

    # At least Akamai returns a "Connection: Keep-Alive" header, which was
    # supposed to be sent by the client.
    if hdr_connection and "keep-alive" in hdr_connection:
      return False

    return True

  def _ParseHeaders(self):
    """Parses the headers sent by the server.

    This function also adjusts internal variables based on the header values.

    """
    req = self.request

    # Parse headers
    self.header_buffer.seek(0, 0)
    req.resp_headers = mimetools.Message(self.header_buffer, 0)

    self.server_will_close = self._WillServerCloseConnection()

    # Do we have a Content-Length header?
    hdr_content_length = req.resp_headers.get(HTTP_CONTENT_LENGTH, None)
    if hdr_content_length:
      try:
        self.content_length = int(hdr_content_length)
      except ValueError:
        pass
      if self.content_length is not None and self.content_length < 0:
        self.content_length = None

    # does the body have a fixed length? (of zero)
    if (req.resp_status in (HTTP_NO_CONTENT, HTTP_NOT_MODIFIED) or
        100 <= req.resp_status < 200 or req.method == HTTP_HEAD):
      self.content_length = 0

    # if the connection remains open and a content-length was not provided,
    # then assume that the connection WILL close.
    if self.content_length is None:
      self.server_will_close = True

  def _CheckStatusLineLength(self, length):
    if length > self.STATUS_LINE_LENGTH_MAX:
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      raise _HttpClientError("Status line longer than %d chars" %
                             self.STATUS_LINE_LENGTH_MAX)
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  def _CheckHeaderLength(self, length):
    if length > self.HEADER_LENGTH_MAX:
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      raise _HttpClientError("Headers longer than %d chars" %
                             self.HEADER_LENGTH_MAX)
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  def _ParseBuffer(self, buf, eof):
    """Main function for HTTP response state machine.

    @type buf: string
    @param buf: Receive buffer
    @type eof: bool
    @param eof: Whether we've reached EOF on the socket
    @rtype: string
    @return: Updated receive buffer

    """
    if self.parser_status == self.PS_STATUS_LINE:
      # Expect status line
      idx = buf.find("\r\n")
      if idx >= 0:
        self.request.resp_status_line = buf[:idx]

        self._CheckStatusLineLength(len(self.request.resp_status_line))

        # Remove status line, including CRLF
        buf = buf[idx + 2:]

        self._ParseStatusLine()

        self.parser_status = self.PS_HEADERS
      else:
        # Check whether incoming data is getting too large, otherwise we just
        # fill our read buffer.
        self._CheckStatusLineLength(len(buf))

    if self.parser_status == self.PS_HEADERS:
      # Wait for header end
      idx = buf.find("\r\n\r\n")
      if idx >= 0:
        self.header_buffer.write(buf[:idx + 2])

        self._CheckHeaderLength(self.header_buffer.tell())

        # Remove headers, including CRLF
        buf = buf[idx + 4:]

        self._ParseHeaders()

        self.parser_status = self.PS_BODY
      else:
        # Check whether incoming data is getting too large, otherwise we just
        # fill our read buffer.
        self._CheckHeaderLength(len(buf))

    if self.parser_status == self.PS_BODY:
      self.body_buffer.write(buf)
      buf = ""

      # Check whether we've read everything
      if (eof or
          (self.content_length is not None and
           self.body_buffer.tell() >= self.content_length)):
        self.parser_status = self.PS_COMPLETE

    return buf

  def _WaitForCondition(self, event, timeout):
    """Waits for a condition to occur on the socket.

    @type event: int
    @param event: ORed condition (see select module)
    @type timeout: float or None
    @param timeout: Timeout in seconds
    @rtype: int or None
    @return: None for timeout, otherwise occured conditions

    """
    check = (event | select.POLLPRI |
             select.POLLNVAL | select.POLLHUP | select.POLLERR)

    if timeout is not None:
      # Poller object expects milliseconds
      timeout *= 1000

    self.poller.register(self.sock, event)
    try:
      while True:
        # TODO: If the main thread receives a signal and we have no timeout, we
        # could wait forever. This should check a global "quit" flag or
        # something every so often.
        io_events = self.poller.poll(timeout)
        if io_events:
          for (evfd, evcond) in io_events:
            if evcond & check:
              return evcond
        else:
          # Timeout
          return None
    finally:
      self.poller.unregister(self.sock)

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  def _SocketOperation(self, op, arg1, error_msg, timeout_msg):
    """Wrapper around socket functions.

    This function abstracts error handling for socket operations, especially
    for the complicated interaction with OpenSSL.

    """
    if op == self.OP_SEND:
      event_poll = select.POLLOUT
      event_check = select.POLLOUT
      timeout = self.WRITE_TIMEOUT

    elif op in (self.OP_RECV, self.OP_CLOSE_CHECK):
      event_poll = select.POLLIN
      event_check = select.POLLIN | select.POLLPRI
      if op == self.OP_CLOSE_CHECK:
        timeout = self.CLOSE_TIMEOUT
      else:
        timeout = self.READ_TIMEOUT

    elif op == self.OP_SHUTDOWN:
      event_poll = None
      event_check = None

      # The timeout is only used when OpenSSL requests polling for a condition.
      # It is not advisable to have no timeout for shutdown.
      timeout = self.WRITE_TIMEOUT

    else:
      raise AssertionError("Invalid socket operation")

    # No override by default
    event_override = 0

    while True:
      # Poll only for certain operations and when asked for by an override
      if (event_override or
          op in (self.OP_SEND, self.OP_RECV, self.OP_CLOSE_CHECK)):
        if event_override:
          wait_for_event = event_override
        else:
          wait_for_event = event_poll

        event = self._WaitForCondition(wait_for_event, timeout)
        if event is None:
          raise _HttpClientTimeout(timeout_msg)

        if (op == self.OP_RECV and
            event & (select.POLLNVAL | select.POLLHUP | select.POLLERR)):
          return ""

        if not event & wait_for_event:
          continue

      # Reset override
      event_override = 0

      try:
        try:
          if op == self.OP_SEND:
            return self.sock.send(arg1)

          elif op in (self.OP_RECV, self.OP_CLOSE_CHECK):
            return self.sock.recv(arg1)

          elif op == self.OP_SHUTDOWN:
            if self._using_ssl:
              # PyOpenSSL's shutdown() doesn't take arguments
              return self.sock.shutdown()
            else:
              return self.sock.shutdown(arg1)

        except OpenSSL.SSL.WantWriteError:
          # OpenSSL wants to write, poll for POLLOUT
          event_override = select.POLLOUT
          continue

        except OpenSSL.SSL.WantReadError:
          # OpenSSL wants to read, poll for POLLIN
          event_override = select.POLLIN | select.POLLPRI
          continue

        except OpenSSL.SSL.WantX509LookupError:
          continue

        except OpenSSL.SSL.SysCallError, err:
          if op == self.OP_SEND:
            # arg1 is the data when writing
            if err.args and err.args[0] == -1 and arg1 == "":
              # errors when writing empty strings are expected
              # and can be ignored
              return 0

          elif op == self.OP_RECV:
            if err.args == (-1, _SSL_UNEXPECTED_EOF):
              return ""

          raise socket.error(err.args)

        except OpenSSL.SSL.Error, err:
          raise socket.error(err.args)

      except socket.error, err:
        if err.args and err.args[0] == errno.EAGAIN:
          # Ignore EAGAIN
          continue

        raise _HttpClientError("%s: %s" % (error_msg, str(err)))

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  def _Connect(self):
    """Non-blocking connect to host with timeout.

    """
    connected = False
    while True:
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      try:
        connect_error = self.sock.connect_ex((self.request.host,
                                              self.request.port))
      except socket.gaierror, err:
        raise _HttpClientError("Connection failed: %s" % str(err))

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      if connect_error == errno.EINTR:
        # Mask signals
        pass

      elif connect_error == 0:
        # Connection established
        connected = True
        break

      elif connect_error == errno.EINPROGRESS:
        # Connection started
        break

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      raise _HttpClientError("Connection failed (%s: %s)" %
                             (connect_error, os.strerror(connect_error)))
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    if not connected:
      # Wait for connection
      event = self._WaitForCondition(select.POLLOUT, self.CONNECT_TIMEOUT)
      if event is None:
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      # Get error code
      connect_error = self.sock.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
      if connect_error != 0:
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        raise _HttpClientError("Connection failed (%s: %s)" %
                               (connect_error, os.strerror(connect_error)))
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    # Enable TCP keep-alive
    self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)

    # If needed, Linux specific options are available to change the TCP
    # keep-alive settings, see "man 7 tcp" for TCP_KEEPCNT, TCP_KEEPIDLE and
    # TCP_KEEPINTVL.

  def _SendRequest(self):
    """Sends request to server.

    """
    buf = self._BuildRequest()

    while buf:
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      # Send only 4 KB at a time
      data = buf[:4096]
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      sent = self._SocketOperation(self.OP_SEND, data,
                                   "Error while sending request",
                                   "Timeout while sending request")
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      # Remove sent bytes
      buf = buf[sent:]

    assert not buf, "Request wasn't sent completely"

  def _ReadResponse(self):
    """Read response from server.

    Calls the parser function after reading a chunk of data.

    """
    buf = ""
    eof = False
    while self.parser_status != self.PS_COMPLETE:
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      data = self._SocketOperation(self.OP_RECV, 4096,
                                   "Error while reading response",
                                   "Timeout while reading response")
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      if data:
        buf += data
      else:
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        eof = True

      # Do some parsing and error checking while more data arrives
      buf = self._ParseBuffer(buf, eof)

      # Must be done only after the buffer has been evaluated
      if (eof and
          self.parser_status in (self.PS_STATUS_LINE,
                                 self.PS_HEADERS)):
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        raise _HttpClientError("Connection closed prematurely")
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    # Parse rest
    buf = self._ParseBuffer(buf, True)

    assert self.parser_status == self.PS_COMPLETE
    assert not buf, "Parser didn't read full response"

  def _CloseConnection(self, force):
    """Closes the connection.

    """
    if self.server_will_close and not force:
      # Wait for server to close
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      try:
        # Check whether it's actually closed
        if not self._SocketOperation(self.OP_CLOSE_CHECK, 1,
                                     "Error", "Timeout"):
          return
      except (socket.error, _HttpClientError):
        # Ignore errors at this stage
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        pass

    # Close the connection from our side
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    self._SocketOperation(self.OP_SHUTDOWN, socket.SHUT_RDWR,
                          "Error while shutting down connection",
                          "Timeout while shutting down connection")
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class HttpClientWorker(workerpool.BaseWorker):
  """HTTP client worker class.

  """
  def RunTask(self, req):
    HttpClientRequestExecutor(req)


class HttpClientWorkerPool(workerpool.WorkerPool):
  def __init__(self, manager):
    workerpool.WorkerPool.__init__(self, HTTP_CLIENT_THREADS,
                                   HttpClientWorker)
    self.manager = manager


class HttpClientManager(object):
  def __init__(self):
    self._wpool = HttpClientWorkerPool(self)

  def __del__(self):
    self.Shutdown()

  def ExecRequests(self, requests):
    # Add requests to queue
    for req in requests:
      self._wpool.AddTask(req)

    # And wait for them to finish
    self._wpool.Quiesce()

    return requests

  def Shutdown(self):
    self._wpool.TerminateWorkers()


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class _SSLFileObject(object):
  """Wrapper around socket._fileobject

  This wrapper is required to handle OpenSSL exceptions.

  """
  def _RequireOpenSocket(fn):
    def wrapper(self, *args, **kwargs):
      if self.closed:
        raise SocketClosed("Socket is closed")
      return fn(self, *args, **kwargs)
    return wrapper

  def __init__(self, sock, mode='rb', bufsize=-1):
    self._base = socket._fileobject(sock, mode=mode, bufsize=bufsize)

  def _ConnectionLost(self):
    self._base = None

  def _getclosed(self):
    return self._base is None or self._base.closed
  closed = property(_getclosed, doc="True if the file is closed")

  @_RequireOpenSocket
  def close(self):
    return self._base.close()

  @_RequireOpenSocket
  def flush(self):
    return self._base.flush()

  @_RequireOpenSocket
  def fileno(self):
    return self._base.fileno()

  @_RequireOpenSocket
  def read(self, size=-1):
    return self._ReadWrapper(self._base.read, size=size)

  @_RequireOpenSocket
  def readline(self, size=-1):
    return self._ReadWrapper(self._base.readline, size=size)

  def _ReadWrapper(self, fn, *args, **kwargs):
    while True:
      try:
        return fn(*args, **kwargs)

      except OpenSSL.SSL.ZeroReturnError, err:
        self._ConnectionLost()
        return ""

      except OpenSSL.SSL.WantReadError:
        continue

      #except OpenSSL.SSL.WantWriteError:
      # TODO

      except OpenSSL.SSL.SysCallError, (retval, desc):
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        if ((retval == -1 and desc == _SSL_UNEXPECTED_EOF)
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            or retval > 0):
          self._ConnectionLost()
          return ""

        logging.exception("Error in OpenSSL")
        self._ConnectionLost()
        raise socket.error(err.args)

      except OpenSSL.SSL.Error, err:
        self._ConnectionLost()
        raise socket.error(err.args)

  @_RequireOpenSocket
  def write(self, data):
    return self._WriteWrapper(self._base.write, data)

  def _WriteWrapper(self, fn, *args, **kwargs):
    while True:
      try:
        return fn(*args, **kwargs)
      except OpenSSL.SSL.ZeroReturnError, err:
        self._ConnectionLost()
        return 0

      except OpenSSL.SSL.WantWriteError:
        continue

      #except OpenSSL.SSL.WantReadError:
      # TODO

      except OpenSSL.SSL.SysCallError, err:
        if err.args[0] == -1 and data == "":
          # errors when writing empty strings are expected
          # and can be ignored
          return 0

        self._ConnectionLost()
        raise socket.error(err.args)

      except OpenSSL.SSL.Error, err:
        self._ConnectionLost()
        raise socket.error(err.args)