path: root/kafka/conn.py

import collections
import copy
import errno
import logging
import io
from random import shuffle
import socket
import ssl
import struct
from threading import local
import time
import warnings

import six

import kafka.errors as Errors
from kafka.future import Future
from kafka.protocol.api import RequestHeader
from kafka.protocol.commit import GroupCoordinatorResponse
from kafka.protocol.types import Int32
from kafka.version import __version__


if six.PY2:
    ConnectionError = socket.error
    BlockingIOError = Exception

log = logging.getLogger(__name__)

DEFAULT_SOCKET_TIMEOUT_SECONDS = 120
DEFAULT_KAFKA_PORT = 9092

# support older ssl libraries
try:
    assert ssl.SSLWantReadError
    assert ssl.SSLWantWriteError
    assert ssl.SSLZeroReturnError
except:
    log.warning('old ssl module detected.'
                ' ssl error handling may not operate cleanly.'
                ' Consider upgrading to python 3.5 or 2.7')
    ssl.SSLWantReadError = ssl.SSLError
    ssl.SSLWantWriteError = ssl.SSLError
    ssl.SSLZeroReturnError = ssl.SSLError


class ConnectionStates(object):
    DISCONNECTING = '<disconnecting>'
    DISCONNECTED = '<disconnected>'
    CONNECTING = '<connecting>'
    HANDSHAKE = '<handshake>'
    CONNECTED = '<connected>'


InFlightRequest = collections.namedtuple('InFlightRequest',
    ['request', 'response_type', 'correlation_id', 'future', 'timestamp'])


class BrokerConnection(object):
    DEFAULT_CONFIG = {
        'client_id': 'kafka-python-' + __version__,
        'request_timeout_ms': 40000,
        'reconnect_backoff_ms': 50,
        'max_in_flight_requests_per_connection': 5,
        'receive_buffer_bytes': None,
        'send_buffer_bytes': None,
        'security_protocol': 'PLAINTEXT',
        'ssl_context': None,
        'ssl_check_hostname': True,
        'ssl_cafile': None,
        'ssl_certfile': None,
        'ssl_keyfile': None,
        'api_version': (0, 8, 2),  # default to most restrictive
        'state_change_callback': lambda conn: True,
    }

    def __init__(self, host, port, afi, **configs):
        self.host = host
        self.port = port
        self.afi = afi
        self.in_flight_requests = collections.deque()

        self.config = copy.copy(self.DEFAULT_CONFIG)
        for key in self.config:
            if key in configs:
                self.config[key] = configs[key]

        self.state = ConnectionStates.DISCONNECTED
        self._sock = None
        self._ssl_context = None
        if self.config['ssl_context'] is not None:
            self._ssl_context = self.config['ssl_context']
        self._rbuffer = io.BytesIO()
        self._receiving = False
        self._next_payload_bytes = 0
        self.last_attempt = 0
        self.last_failure = 0
        self._processing = False
        self._correlation_id = 0
        self._gai = None
        self._gai_index = 0

    def connect(self):
        """Attempt to connect and return ConnectionState"""
        if self.state is ConnectionStates.DISCONNECTED:
            self.close()
            log.debug('%s: creating new socket', str(self))
            # if self.afi is set to AF_UNSPEC, then we need to do a name
            # resolution and try all available address families
            if self.afi == socket.AF_UNSPEC:
                if self._gai is None:
                    # XXX: all DNS functions in Python are blocking. If we really
                    # want to be non-blocking here, we need to use a 3rd-party
                    # library like python-adns, or move resolution onto its
                    # own thread. This will be subject to the default libc
                    # name resolution timeout (5s on most Linux boxes)
                    self._gai = socket.getaddrinfo(self.host, self.port,
                                                   socket.AF_UNSPEC,
                                                   socket.SOCK_STREAM)
                    self._gai_index = 0
                else:
                    # if self._gai already exists, then we should try the next
                    # name
                    self._gai_index += 1
                while True:
                    if self._gai_index >= len(self._gai):
                        log.error('Unable to connect to any of the names for {0}:{1}'.format(
                            self.host, self.port
                        ))
                        self.close()
                        return
                    afi, _, __, ___, sockaddr = self._gai[self._gai_index]
                    if afi not in (socket.AF_INET, socket.AF_INET6):
                        self._gai_index += 1
                        continue
                    break
                self.host, self.port = sockaddr[:2]
                self._sock = socket.socket(afi, socket.SOCK_STREAM)
            else:
                self._sock = socket.socket(self.afi, socket.SOCK_STREAM)
            if self.config['receive_buffer_bytes'] is not None:
                self._sock.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF,
                                      self.config['receive_buffer_bytes'])
            if self.config['send_buffer_bytes'] is not None:
                self._sock.setsockopt(socket.SOL_SOCKET, socket.SO_SNDBUF,
                                      self.config['send_buffer_bytes'])
            self._sock.setblocking(False)
            if self.config['security_protocol'] in ('SSL', 'SASL_SSL'):
                self._wrap_ssl()
            self.state = ConnectionStates.CONNECTING
            self.last_attempt = time.time()
            self.config['state_change_callback'](self)

        if self.state is ConnectionStates.CONNECTING:
            # in non-blocking mode, use repeated calls to socket.connect_ex
            # to check connection status
            request_timeout = self.config['request_timeout_ms'] / 1000.0
            ret = None
            try:
                ret = self._sock.connect_ex((self.host, self.port))
                # if we got here through a host lookup, we've found a host,port,af tuple
                # that works save it so we don't do a GAI lookup again
                if self._gai is not None:
                    self.afi = self._sock.family
                    self._gai = None
            except socket.error as err:
                ret = err

            # Connection succeeded
            if not ret or ret == errno.EISCONN:
                log.debug('%s: established TCP connection', str(self))
                if self.config['security_protocol'] in ('SSL', 'SASL_SSL'):
                    log.debug('%s: initiating SSL handshake', str(self))
                    self.state = ConnectionStates.HANDSHAKE
                else:
                    self.state = ConnectionStates.CONNECTED
                self.config['state_change_callback'](self)

            # Connection failed
            # WSAEINVAL == 10022, but errno.WSAEINVAL is not available on non-win systems
            elif ret not in (errno.EINPROGRESS, errno.EALREADY, errno.EWOULDBLOCK, 10022):
                log.error('Connect attempt to %s returned error %s.'
                          ' Disconnecting.', self, ret)
                self.close()

            # Connection timedout
            elif time.time() > request_timeout + self.last_attempt:
                log.error('Connection attempt to %s timed out', self)
                self.close() # error=TimeoutError ?

            # Needs retry
            else:
                pass

        if self.state is ConnectionStates.HANDSHAKE:
            if self._try_handshake():
                log.debug('%s: completed SSL handshake.', str(self))
                self.state = ConnectionStates.CONNECTED
                self.config['state_change_callback'](self)

        return self.state

    def _wrap_ssl(self):
        assert self.config['security_protocol'] in ('SSL', 'SASL_SSL')
        if self._ssl_context is None:
            log.debug('%s: configuring default SSL Context', str(self))
            self._ssl_context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)  # pylint: disable=no-member
            self._ssl_context.options |= ssl.OP_NO_SSLv2  # pylint: disable=no-member
            self._ssl_context.options |= ssl.OP_NO_SSLv3  # pylint: disable=no-member
            self._ssl_context.verify_mode = ssl.CERT_OPTIONAL
            if self.config['ssl_check_hostname']:
                self._ssl_context.check_hostname = True
            if self.config['ssl_cafile']:
                log.info('%s: Loading SSL CA from %s', str(self), self.config['ssl_cafile'])
                self._ssl_context.load_verify_locations(self.config['ssl_cafile'])
                self._ssl_context.verify_mode = ssl.CERT_REQUIRED
            if self.config['ssl_certfile'] and self.config['ssl_keyfile']:
                log.info('%s: Loading SSL Cert from %s', str(self), self.config['ssl_certfile'])
                log.info('%s: Loading SSL Key from %s', str(self), self.config['ssl_keyfile'])
                self._ssl_context.load_cert_chain(
                    certfile=self.config['ssl_certfile'],
                    keyfile=self.config['ssl_keyfile'])
        log.debug('%s: wrapping socket in ssl context', str(self))
        try:
            self._sock = self._ssl_context.wrap_socket(
                self._sock,
                server_hostname=self.host,
                do_handshake_on_connect=False)
        except ssl.SSLError:
            log.exception('%s: Failed to wrap socket in SSLContext!', str(self))
            self.close()
            self.last_failure = time.time()

    def _try_handshake(self):
        assert self.config['security_protocol'] in ('SSL', 'SASL_SSL')
        try:
            self._sock.do_handshake()
            return True
        # old ssl in python2.6 will swallow all SSLErrors here...
        except (ssl.SSLWantReadError, ssl.SSLWantWriteError):
            pass
        except ssl.SSLZeroReturnError:
            log.warning('SSL connection closed by server during handshake.')
            self.close()
        # Other SSLErrors will be raised to user

        return False

    def blacked_out(self):
        """
        Return true if we are disconnected from the given node and can't
        re-establish a connection yet
        """
        if self.state is ConnectionStates.DISCONNECTED:
            backoff = self.config['reconnect_backoff_ms'] / 1000.0
            if time.time() < self.last_attempt + backoff:
                return True
        return False

    def connected(self):
        """Return True iff socket is connected."""
        return self.state is ConnectionStates.CONNECTED

    def connecting(self):
        """Returns True if still connecting (this may encompass several
        different states, such as SSL handshake, authorization, etc)."""
        return self.state in (ConnectionStates.CONNECTING,
                              ConnectionStates.HANDSHAKE)

    def disconnected(self):
        """Return True iff socket is closed"""
        return self.state is ConnectionStates.DISCONNECTED

    def close(self, error=None):
        """Close socket and fail all in-flight-requests.

        Arguments:
            error (Exception, optional): pending in-flight-requests
                will be failed with this exception.
                Default: kafka.errors.ConnectionError.
        """
        if self.state is not ConnectionStates.DISCONNECTED:
            self.state = ConnectionStates.DISCONNECTING
            self.config['state_change_callback'](self)
        if self._sock:
            self._sock.close()
            self._sock = None
        self.state = ConnectionStates.DISCONNECTED
        self.last_failure = time.time()
        self._receiving = False
        self._next_payload_bytes = 0
        self._rbuffer.seek(0)
        self._rbuffer.truncate()
        if error is None:
            error = Errors.ConnectionError(str(self))
        while self.in_flight_requests:
            ifr = self.in_flight_requests.popleft()
            ifr.future.failure(error)
        self.config['state_change_callback'](self)

    def send(self, request, expect_response=True):
        """send request, return Future()

        Can block on network if request is larger than send_buffer_bytes
        """
        future = Future()
        if self.connecting():
            return future.failure(Errors.NodeNotReadyError(str(self)))
        elif not self.connected():
            return future.failure(Errors.ConnectionError(str(self)))
        elif not self.can_send_more():
            return future.failure(Errors.TooManyInFlightRequests(str(self)))
        correlation_id = self._next_correlation_id()
        header = RequestHeader(request,
                               correlation_id=correlation_id,
                               client_id=self.config['client_id'])
        message = b''.join([header.encode(), request.encode()])
        size = Int32.encode(len(message))
        try:
            # In the future we might manage an internal write buffer
            # and send bytes asynchronously. For now, just block
            # sending each request payload
            self._sock.setblocking(True)
            for data in (size, message):
                total_sent = 0
                while total_sent < len(data):
                    sent_bytes = self._sock.send(data[total_sent:])
                    total_sent += sent_bytes
                assert total_sent == len(data)
            self._sock.setblocking(False)
        except (AssertionError, ConnectionError) as e:
            log.exception("Error sending %s to %s", request, self)
            error = Errors.ConnectionError("%s: %s" % (str(self), e))
            self.close(error=error)
            return future.failure(error)
        log.debug('%s Request %d: %s', self, correlation_id, request)

        if expect_response:
            ifr = InFlightRequest(request=request,
                                  correlation_id=correlation_id,
                                  response_type=request.RESPONSE_TYPE,
                                  future=future,
                                  timestamp=time.time())
            self.in_flight_requests.append(ifr)
        else:
            future.success(None)

        return future

    def can_send_more(self):
        """Return True unless there are max_in_flight_requests."""
        max_ifrs = self.config['max_in_flight_requests_per_connection']
        return len(self.in_flight_requests) < max_ifrs

    def recv(self):
        """Non-blocking network receive.

        Return response if available
        """
        assert not self._processing, 'Recursion not supported'
        if not self.connected():
            log.warning('%s cannot recv: socket not connected', self)
            # If requests are pending, we should close the socket and
            # fail all the pending request futures
            if self.in_flight_requests:
                self.close()
            return None

        elif not self.in_flight_requests:
            log.warning('%s: No in-flight-requests to recv', self)
            return None

        elif self._requests_timed_out():
            log.warning('%s timed out after %s ms. Closing connection.',
                        self, self.config['request_timeout_ms'])
            self.close(error=Errors.RequestTimedOutError(
                'Request timed out after %s ms' %
                self.config['request_timeout_ms']))
            return None

        # Not receiving is the state of reading the payload header
        if not self._receiving:
            try:
                bytes_to_read = 4 - self._rbuffer.tell()
                data = self._sock.recv(bytes_to_read)
                # We expect socket.recv to raise an exception if there is not
                # enough data to read the full bytes_to_read
                # but if the socket is disconnected, we will get empty data
                # without an exception raised
                if not data:
                    log.error('%s: socket disconnected', self)
                    self.close(error=Errors.ConnectionError('socket disconnected'))
                    return None
                self._rbuffer.write(data)
            except ssl.SSLWantReadError:
                return None
            except ConnectionError as e:
                if six.PY2 and e.errno == errno.EWOULDBLOCK:
                    return None
                log.exception('%s: Error receiving 4-byte payload header -'
                              ' closing socket', self)
                self.close(error=Errors.ConnectionError(e))
                return None
            except BlockingIOError:
                if six.PY3:
                    return None
                raise

            if self._rbuffer.tell() == 4:
                self._rbuffer.seek(0)
                self._next_payload_bytes = Int32.decode(self._rbuffer)
                # reset buffer and switch state to receiving payload bytes
                self._rbuffer.seek(0)
                self._rbuffer.truncate()
                self._receiving = True
            elif self._rbuffer.tell() > 4:
                raise Errors.KafkaError('this should not happen - are you threading?')

        if self._receiving:
            staged_bytes = self._rbuffer.tell()
            try:
                bytes_to_read = self._next_payload_bytes - staged_bytes
                data = self._sock.recv(bytes_to_read)
                # We expect socket.recv to raise an exception if there is not
                # enough data to read the full bytes_to_read
                # but if the socket is disconnected, we will get empty data
                # without an exception raised
                if not data:
                    log.error('%s: socket disconnected', self)
                    self.close(error=Errors.ConnectionError('socket disconnected'))
                    return None
                self._rbuffer.write(data)
            except ssl.SSLWantReadError:
                return None
            except ConnectionError as e:
                # Extremely small chance that we have exactly 4 bytes for a
                # header, but nothing to read in the body yet
                if six.PY2 and e.errno == errno.EWOULDBLOCK:
                    return None
                log.exception('%s: Error in recv', self)
                self.close(error=Errors.ConnectionError(e))
                return None
            except BlockingIOError:
                if six.PY3:
                    return None
                raise

            staged_bytes = self._rbuffer.tell()
            if staged_bytes > self._next_payload_bytes:
                self.close(error=Errors.KafkaError('Receive buffer has more bytes than expected?'))

            if staged_bytes != self._next_payload_bytes:
                return None

            self._receiving = False
            self._next_payload_bytes = 0
            self._rbuffer.seek(0)
            response = self._process_response(self._rbuffer)
            self._rbuffer.seek(0)
            self._rbuffer.truncate()
            return response

    def _process_response(self, read_buffer):
        assert not self._processing, 'Recursion not supported'
        self._processing = True
        ifr = self.in_flight_requests.popleft()

        # verify send/recv correlation ids match
        recv_correlation_id = Int32.decode(read_buffer)

        # 0.8.2 quirk
        if (self.config['api_version'] == (0, 8, 2) and
            ifr.response_type is GroupCoordinatorResponse[0] and
            ifr.correlation_id != 0 and
            recv_correlation_id == 0):
            log.warning('Kafka 0.8.2 quirk -- GroupCoordinatorResponse'
                        ' coorelation id does not match request. This'
                        ' should go away once at least one topic has been'
                        ' initialized on the broker')

        elif ifr.correlation_id != recv_correlation_id:
            error = Errors.CorrelationIdError(
                '%s: Correlation ids do not match: sent %d, recv %d'
                % (str(self), ifr.correlation_id, recv_correlation_id))
            ifr.future.failure(error)
            self.close()
            self._processing = False
            return None

        # decode response
        response = ifr.response_type.decode(read_buffer)
        log.debug('%s Response %d: %s', self, ifr.correlation_id, response)
        ifr.future.success(response)
        self._processing = False
        return response

    def _requests_timed_out(self):
        if self.in_flight_requests:
            oldest_at = self.in_flight_requests[0].timestamp
            timeout = self.config['request_timeout_ms'] / 1000.0
            if time.time() >= oldest_at + timeout:
                return True
        return False

    def _next_correlation_id(self):
        self._correlation_id = (self._correlation_id + 1) % 2**31
        return self._correlation_id

    def check_version(self, timeout=2, strict=False):
        """Attempt to guess the broker version. This is a blocking call."""

        # Monkeypatch the connection request timeout
        # Generally this timeout should not get triggered
        # but in case it does, we want it to be reasonably short
        stashed_request_timeout_ms = self.config['request_timeout_ms']
        self.config['request_timeout_ms'] = timeout * 1000

        # kafka kills the connection when it doesnt recognize an API request
        # so we can send a test request and then follow immediately with a
        # vanilla MetadataRequest. If the server did not recognize the first
        # request, both will be failed with a ConnectionError that wraps
        # socket.error (32, 54, or 104)
        from .protocol.admin import ApiVersionRequest, ListGroupsRequest
        from .protocol.commit import OffsetFetchRequest, GroupCoordinatorRequest
        from .protocol.metadata import MetadataRequest

        # Socket errors are logged as exceptions and can alarm users. Mute them
        from logging import Filter

        class ConnFilter(Filter):
            def filter(self, record):
                if record.funcName in ('recv', 'send'):
                    return False
                return True
        log_filter = ConnFilter()
        log.addFilter(log_filter)

        test_cases = [
            ('0.10', ApiVersionRequest[0]()),
            ('0.9', ListGroupsRequest[0]()),
            ('0.8.2', GroupCoordinatorRequest[0]('kafka-python-default-group')),
            ('0.8.1', OffsetFetchRequest[0]('kafka-python-default-group', [])),
            ('0.8.0', MetadataRequest[0]([])),
        ]

        def connect():
            self.connect()
            if self.connected():
                return
            timeout_at = time.time() + timeout
            while time.time() < timeout_at and self.connecting():
                if self.connect() is ConnectionStates.CONNECTED:
                    return
                time.sleep(0.05)
            raise Errors.NodeNotReadyError()

        for version, request in test_cases:
            connect()
            f = self.send(request)
            # HACK: sleeping to wait for socket to send bytes
            time.sleep(0.1)
            # when broker receives an unrecognized request API
            # it abruptly closes our socket.
            # so we attempt to send a second request immediately
            # that we believe it will definitely recognize (metadata)
            # the attempt to write to a disconnected socket should
            # immediately fail and allow us to infer that the prior
            # request was unrecognized
            self.send(MetadataRequest[0]([]))

            if self._sock:
                self._sock.setblocking(True)
            while not f.is_done:
                self.recv()
            if self._sock:
                self._sock.setblocking(False)

            if f.succeeded():
                log.info('Broker version identifed as %s', version)
                log.info("Set configuration api_version='%s' to skip auto"
                         " check_version requests on startup", version)
                break

            # Only enable strict checking to verify that we understand failure
            # modes. For most users, the fact that the request failed should be
            # enough to rule out a particular broker version.
            if strict:
                # If the socket flush hack did not work (which should force the
                # connection to close and fail all pending requests), then we
                # get a basic Request Timeout. This is not ideal, but we'll deal
                if isinstance(f.exception, Errors.RequestTimedOutError):
                    pass
                elif six.PY2:
                    assert isinstance(f.exception.args[0], socket.error)
                    assert f.exception.args[0].errno in (32, 54, 104)
                else:
                    assert isinstance(f.exception.args[0], ConnectionError)
            log.info("Broker is not v%s -- it did not recognize %s",
                     version, request.__class__.__name__)
        else:
            raise Errors.UnrecognizedBrokerVersion()

        log.removeFilter(log_filter)
        self.config['request_timeout_ms'] = stashed_request_timeout_ms
        return version

    def __repr__(self):
        return "<BrokerConnection host=%s port=%d>" % (self.host, self.port)


def _address_family(address):
    """
        Attempt to determine the family of an address (or hostname)

        :return: either socket.AF_INET or socket.AF_INET6 or socket.AF_UNSPEC if the address family
                 could not be determined
    """
    if address.startswith('[') and address.endswith(']'):
        return socket.AF_INET6
    for af in (socket.AF_INET, socket.AF_INET6):
        try:
            socket.inet_pton(af, address)
            return af
        except (ValueError, AttributeError, socket.error):
            continue
    return socket.AF_UNSPEC


def get_ip_port_afi(host_and_port_str):
    """
        Parse the IP and port from a string in the format of:

            * host_or_ip          <- Can be either IPv4 address literal or hostname/fqdn
            * host_or_ipv4:port   <- Can be either IPv4 address literal or hostname/fqdn
            * [host_or_ip]        <- IPv6 address literal
            * [host_or_ip]:port.  <- IPv6 address literal

        .. note:: IPv6 address literals with ports *must* be enclosed in brackets

        .. note:: If the port is not specified, default will be returned.

        :return: tuple (host, port, afi), afi will be socket.AF_INET or socket.AF_INET6 or socket.AF_UNSPEC
    """
    host_and_port_str = host_and_port_str.strip()
    if host_and_port_str.startswith('['):
        af = socket.AF_INET6
        host, rest = host_and_port_str[1:].split(']')
        if rest:
            port = int(rest[1:])
        else:
            port = DEFAULT_KAFKA_PORT
        return host, port, af
    else:
        if ':' not in host_and_port_str:
            af = _address_family(host_and_port_str)
            return host_and_port_str, DEFAULT_KAFKA_PORT, af
        else:
            # now we have something with a colon in it and no square brackets. It could be
            # either an IPv6 address literal (e.g., "::1") or an IP:port pair or a host:port pair
            try:
                # if it decodes as an IPv6 address, use that
                socket.inet_pton(socket.AF_INET6, host_and_port_str)
                return host_and_port_str, DEFAULT_KAFKA_PORT, socket.AF_INET6
            except AttributeError:
                log.warning('socket.inet_pton not available on this platform.'
                            ' consider pip install win_inet_pton')
                pass
            except (ValueError, socket.error):
                # it's a host:port pair
                pass
            host, port = host_and_port_str.rsplit(':', 1)
            port = int(port)

            af = _address_family(host)
            return host, port, af


def collect_hosts(hosts, randomize=True):
    """
    Collects a comma-separated set of hosts (host:port) and optionally
    randomize the returned list.
    """

    if isinstance(hosts, six.string_types):
        hosts = hosts.strip().split(',')

    result = []
    afi = socket.AF_INET
    for host_port in hosts:

        host, port, afi = get_ip_port_afi(host_port)

        if port < 0:
            port = DEFAULT_KAFKA_PORT

        result.append((host, port, afi))

    if randomize:
        shuffle(result)

    return result


class KafkaConnection(local):
    """A socket connection to a single Kafka broker

    Arguments:
        host: the host name or IP address of a kafka broker
        port: the port number the kafka broker is listening on
        timeout: default 120. The socket timeout for sending and receiving data
            in seconds. None means no timeout, so a request can block forever.
    """
    def __init__(self, host, port, timeout=DEFAULT_SOCKET_TIMEOUT_SECONDS):
        warnings.warn('KafkaConnection has been deprecated and will be'
                      ' removed in a future release', DeprecationWarning)
        super(KafkaConnection, self).__init__()
        self.host = host
        self.port = port
        self.timeout = timeout
        self._sock = None

        self.reinit()

    def __getnewargs__(self):
        return (self.host, self.port, self.timeout)

    def __repr__(self):
        return "<KafkaConnection host=%s port=%d>" % (self.host, self.port)

    ###################
    #   Private API   #
    ###################

    def _raise_connection_error(self):
        # Cleanup socket if we have one
        if self._sock:
            self.close()

        # And then raise
        raise Errors.ConnectionError("Kafka @ {0}:{1} went away".format(self.host, self.port))

    def _read_bytes(self, num_bytes):
        bytes_left = num_bytes
        responses = []

        log.debug("About to read %d bytes from Kafka", num_bytes)

        # Make sure we have a connection
        if not self._sock:
            self.reinit()

        while bytes_left:

            try:
                # pylint: disable-msg=no-member
                data = self._sock.recv(min(bytes_left, 4096))

                # Receiving empty string from recv signals
                # that the socket is in error.  we will never get
                # more data from this socket
                if data == b'':
                    raise socket.error("Not enough data to read message -- did server kill socket?")

            except socket.error:
                log.exception('Unable to receive data from Kafka')
                self._raise_connection_error()

            bytes_left -= len(data)
            log.debug("Read %d/%d bytes from Kafka", num_bytes - bytes_left, num_bytes)
            responses.append(data)

        return b''.join(responses)

    ##################
    #   Public API   #
    ##################

    # TODO multiplex socket communication to allow for multi-threaded clients

    def get_connected_socket(self):
        if not self._sock:
            self.reinit()
        return self._sock

    def send(self, request_id, payload):
        """
        Send a request to Kafka

        Arguments::
            request_id (int): can be any int (used only for debug logging...)
            payload: an encoded kafka packet (see KafkaProtocol)
        """

        log.debug("About to send %d bytes to Kafka, request %d" % (len(payload), request_id))

        # Make sure we have a connection
        if not self._sock:
            self.reinit()

        try:
            # pylint: disable-msg=no-member
            self._sock.sendall(payload)
        except socket.error:
            log.exception('Unable to send payload to Kafka')
            self._raise_connection_error()

    def recv(self, request_id):
        """
        Get a response packet from Kafka

        Arguments:
            request_id: can be any int (only used for debug logging...)

        Returns:
            str: Encoded kafka packet response from server
        """
        log.debug("Reading response %d from Kafka" % request_id)

        # Make sure we have a connection
        if not self._sock:
            self.reinit()

        # Read the size off of the header
        resp = self._read_bytes(4)
        (size,) = struct.unpack('>i', resp)

        # Read the remainder of the response
        resp = self._read_bytes(size)
        return resp

    def copy(self):
        """
        Create an inactive copy of the connection object, suitable for
        passing to a background thread.

        The returned copy is not connected; you must call reinit() before
        using.
        """
        c = copy.deepcopy(self)
        # Python 3 doesn't copy custom attributes of the threadlocal subclass
        c.host = copy.copy(self.host)
        c.port = copy.copy(self.port)
        c.timeout = copy.copy(self.timeout)
        c._sock = None
        return c

    def close(self):
        """
        Shutdown and close the connection socket
        """
        log.debug("Closing socket connection for %s:%d" % (self.host, self.port))
        if self._sock:
            # Call shutdown to be a good TCP client
            # But expect an error if the socket has already been
            # closed by the server
            try:
                # pylint: disable-msg=no-member
                self._sock.shutdown(socket.SHUT_RDWR)
            except socket.error:
                pass

            # Closing the socket should always succeed
            self._sock.close()
            self._sock = None
        else:
            log.debug("No socket found to close!")

    def reinit(self):
        """
        Re-initialize the socket connection
        close current socket (if open)
        and start a fresh connection
        raise ConnectionError on error
        """
        log.debug("Reinitializing socket connection for %s:%d" % (self.host, self.port))

        if self._sock:
            self.close()

        try:
            self._sock = socket.create_connection((self.host, self.port), self.timeout)
        except socket.error:
            log.exception('Unable to connect to kafka broker at %s:%d' % (self.host, self.port))
            self._raise_connection_error()