# Source code for kafka.consumer.group

    from __future__ import absolute_import, division

    import copy
    import logging
    import socket
    import time

    from kafka.errors import KafkaConfigurationError, UnsupportedVersionError

    from kafka.vendor import six

    from kafka.client_async import KafkaClient, selectors
    from kafka.consumer.fetcher import Fetcher
    from kafka.consumer.subscription_state import SubscriptionState
    from kafka.coordinator.consumer import ConsumerCoordinator
    from kafka.coordinator.assignors.range import RangePartitionAssignor
    from kafka.coordinator.assignors.roundrobin import RoundRobinPartitionAssignor
    from kafka.metrics import MetricConfig, Metrics
    from kafka.protocol.offset import OffsetResetStrategy
    from kafka.structs import TopicPartition
    from kafka.version import __version__

    log = logging.getLogger(__name__)

    class KafkaConsumer(six.Iterator):
        """Consume records from a Kafka cluster.

        The consumer will transparently handle the failure of servers in the Kafka
        cluster, and adapt as topic-partitions are created or migrate between
        brokers. It also interacts with the assigned kafka Group Coordinator node
        to allow multiple consumers to load balance consumption of topics (requires
        kafka >= 0.9.0.0).

        The consumer is not thread safe and should not be shared across threads.

        Arguments:
            *topics (str): optional list of topics to subscribe to. If not set,
                call :meth:`~kafka.KafkaConsumer.subscribe` or
                :meth:`~kafka.KafkaConsumer.assign` before consuming records.

        Keyword Arguments:
            bootstrap_servers: 'host[:port]' string (or list of 'host[:port]'
                strings) that the consumer should contact to bootstrap initial
                cluster metadata. This does not have to be the full node list.
                It just needs to have at least one broker that will respond to a
                Metadata API Request. Default port is 9092. If no servers are
                specified, will default to localhost:9092.
            client_id (str): A name for this client. This string is passed in
                each request to servers and can be used to identify specific
                server-side log entries that correspond to this client. Also
                submitted to GroupCoordinator for logging with respect to
                consumer group administration. Default: 'kafka-python-{version}'
            group_id (str or None): The name of the consumer group to join for dynamic
                partition assignment (if enabled), and to use for fetching and
                committing offsets. If None, auto-partition assignment (via
                group coordinator) and offset commits are disabled.
                Default: None
            key_deserializer (callable): Any callable that takes a
                raw message key and returns a deserialized key.
            value_deserializer (callable): Any callable that takes a
                raw message value and returns a deserialized value.
            fetch_min_bytes (int): Minimum amount of data the server should
                return for a fetch request, otherwise wait up to
                fetch_max_wait_ms for more data to accumulate. Default: 1.
            fetch_max_wait_ms (int): The maximum amount of time in milliseconds
                the server will block before answering the fetch request if
                there isn't sufficient data to immediately satisfy the
                requirement given by fetch_min_bytes. Default: 500.
            fetch_max_bytes (int): The maximum amount of data the server should
                return for a fetch request. This is not an absolute maximum, if the
                first message in the first non-empty partition of the fetch is
                larger than this value, the message will still be returned to
                ensure that the consumer can make progress. NOTE: consumer performs
                fetches to multiple brokers in parallel so memory usage will depend
                on the number of brokers containing partitions for the topic.
                Supported Kafka version >= 0.10.1.0. Default: 52428800 (50 MB).
            max_partition_fetch_bytes (int): The maximum amount of data
                per-partition the server will return. The maximum total memory
                used for a request = #partitions * max_partition_fetch_bytes.
                This size must be at least as large as the maximum message size
                the server allows or else it is possible for the producer to
                send messages larger than the consumer can fetch. If that
                happens, the consumer can get stuck trying to fetch a large
                message on a certain partition. Default: 1048576.
            request_timeout_ms (int): Client request timeout in milliseconds.
                Default: 305000.
            retry_backoff_ms (int): Milliseconds to backoff when retrying on
                errors. Default: 100.
            reconnect_backoff_ms (int): The amount of time in milliseconds to
                wait before attempting to reconnect to a given host.
                Default: 50.
            reconnect_backoff_max_ms (int): The maximum amount of time in
                milliseconds to backoff/wait when reconnecting to a broker that has
                repeatedly failed to connect. If provided, the backoff per host
                will increase exponentially for each consecutive connection
                failure, up to this maximum. Once the maximum is reached,
                reconnection attempts will continue periodically with this fixed
                rate. To avoid connection storms, a randomization factor of 0.2
                will be applied to the backoff resulting in a random range between
                20% below and 20% above the computed value. Default: 1000.
            max_in_flight_requests_per_connection (int): Requests are pipelined
                to kafka brokers up to this number of maximum requests per
                broker connection. Default: 5.
            auto_offset_reset (str): A policy for resetting offsets on
                OffsetOutOfRange errors: 'earliest' will move to the oldest
                available message, 'latest' will move to the most recent. Any
                other value will raise the exception. Default: 'latest'.
            enable_auto_commit (bool): If True , the consumer's offset will be
                periodically committed in the background. Default: True.
            auto_commit_interval_ms (int): Number of milliseconds between automatic
                offset commits, if enable_auto_commit is True. Default: 5000.
            default_offset_commit_callback (callable): Called as
                callback(offsets, response) response will be either an Exception
                or an OffsetCommitResponse struct. This callback can be used to
                trigger custom actions when a commit request completes.
            check_crcs (bool): Automatically check the CRC32 of the records
                consumed. This ensures no on-the-wire or on-disk corruption to
                the messages occurred. This check adds some overhead, so it may
                be disabled in cases seeking extreme performance. Default: True
            metadata_max_age_ms (int): The period of time in milliseconds after
                which we force a refresh of metadata, even if we haven't seen any
                partition leadership changes to proactively discover any new
                brokers or partitions. Default: 300000
            partition_assignment_strategy (list): List of objects to use to
                distribute partition ownership amongst consumer instances when
                group management is used.
                Default: [RangePartitionAssignor, RoundRobinPartitionAssignor]
            max_poll_records (int): The maximum number of records returned in a
                single call to :meth:`~kafka.KafkaConsumer.poll`. Default: 500
            max_poll_interval_ms (int): The maximum delay between invocations of
                :meth:`~kafka.KafkaConsumer.poll` when using consumer group
                management. This places an upper bound on the amount of time that
                the consumer can be idle before fetching more records. If
                :meth:`~kafka.KafkaConsumer.poll` is not called before expiration
                of this timeout, then the consumer is considered failed and the
                group will rebalance in order to reassign the partitions to another
                member. Default 300000
            session_timeout_ms (int): The timeout used to detect failures when
                using Kafka's group management facilities. The consumer sends
                periodic heartbeats to indicate its liveness to the broker. If
                no heartbeats are received by the broker before the expiration of
                this session timeout, then the broker will remove this consumer
                from the group and initiate a rebalance. Note that the value must
                be in the allowable range as configured in the broker configuration
                by group.min.session.timeout.ms and group.max.session.timeout.ms.
                Default: 10000
            heartbeat_interval_ms (int): The expected time in milliseconds
                between heartbeats to the consumer coordinator when using
                Kafka's group management facilities. Heartbeats are used to ensure
                that the consumer's session stays active and to facilitate
                rebalancing when new consumers join or leave the group. The
                value must be set lower than session_timeout_ms, but typically
                should be set no higher than 1/3 of that value. It can be
                adjusted even lower to control the expected time for normal
                rebalances. Default: 3000
            receive_buffer_bytes (int): The size of the TCP receive buffer
                (SO_RCVBUF) to use when reading data. Default: None (relies on
                system defaults). The java client defaults to 32768.
            send_buffer_bytes (int): The size of the TCP send buffer
                (SO_SNDBUF) to use when sending data. Default: None (relies on
                system defaults). The java client defaults to 131072.
            socket_options (list): List of tuple-arguments to socket.setsockopt
                to apply to broker connection sockets. Default:
                [(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)]
            consumer_timeout_ms (int): number of milliseconds to block during
                message iteration before raising StopIteration (i.e., ending the
                iterator). Default block forever [float('inf')].
            security_protocol (str): Protocol used to communicate with brokers.
                Valid values are: PLAINTEXT, SSL, SASL_PLAINTEXT, SASL_SSL.
                Default: PLAINTEXT.
            ssl_context (ssl.SSLContext): Pre-configured SSLContext for wrapping
                socket connections. If provided, all other ssl_* configurations
                will be ignored. Default: None.
            ssl_check_hostname (bool): Flag to configure whether ssl handshake
                should verify that the certificate matches the brokers hostname.
                Default: True.
            ssl_cafile (str): Optional filename of ca file to use in certificate
                verification. Default: None.
            ssl_certfile (str): Optional filename of file in pem format containing
                the client certificate, as well as any ca certificates needed to
                establish the certificate's authenticity. Default: None.
            ssl_keyfile (str): Optional filename containing the client private key.
                Default: None.
            ssl_password (str): Optional password to be used when loading the
                certificate chain. Default: None.
            ssl_crlfile (str): Optional filename containing the CRL to check for
                certificate expiration. By default, no CRL check is done. When
                providing a file, only the leaf certificate will be checked against
                this CRL. The CRL can only be checked with Python 3.4+ or 2.7.9+.
                Default: None.
            ssl_ciphers (str): optionally set the available ciphers for ssl
                connections. It should be a string in the OpenSSL cipher list
                format. If no cipher can be selected (because compile-time options
                or other configuration forbids use of all the specified ciphers),
                an ssl.SSLError will be raised. See ssl.SSLContext.set_ciphers
            api_version (tuple): Specify which Kafka API version to use. If set to
                None, the client will attempt to infer the broker version by probing
                various APIs. Different versions enable different functionality.

                Examples:
                    (0, 9) enables full group coordination features with automatic
                        partition assignment and rebalancing,
                    (0, 8, 2) enables kafka-storage offset commits with manual
                        partition assignment only,
                    (0, 8, 1) enables zookeeper-storage offset commits with manual
                        partition assignment only,
                    (0, 8, 0) enables basic functionality but requires manual
                        partition assignment and offset management.

                Default: None
            api_version_auto_timeout_ms (int): number of milliseconds to throw a
                timeout exception from the constructor when checking the broker
                api version. Only applies if api_version set to None.
            connections_max_idle_ms: Close idle connections after the number of
                milliseconds specified by this config. The broker closes idle
                connections after connections.max.idle.ms, so this avoids hitting
                unexpected socket disconnected errors on the client.
                Default: 540000
            metric_reporters (list): A list of classes to use as metrics reporters.
                Implementing the AbstractMetricsReporter interface allows plugging
                in classes that will be notified of new metric creation. Default: []
            metrics_num_samples (int): The number of samples maintained to compute
                metrics. Default: 2
            metrics_sample_window_ms (int): The maximum age in milliseconds of
                samples used to compute metrics. Default: 30000
            selector (selectors.BaseSelector): Provide a specific selector
                implementation to use for I/O multiplexing.
                Default: selectors.DefaultSelector
            exclude_internal_topics (bool): Whether records from internal topics
                (such as offsets) should be exposed to the consumer. If set to True
                the only way to receive records from an internal topic is
                subscribing to it. Requires 0.10+ Default: True
            sasl_mechanism (str): Authentication mechanism when security_protocol
                is configured for SASL_PLAINTEXT or SASL_SSL. Valid values are:
                PLAIN, GSSAPI, OAUTHBEARER, SCRAM-SHA-256, SCRAM-SHA-512.
            sasl_plain_username (str): username for sasl PLAIN and SCRAM authentication.
                Required if sasl_mechanism is PLAIN or one of the SCRAM mechanisms.
            sasl_plain_password (str): password for sasl PLAIN and SCRAM authentication.
                Required if sasl_mechanism is PLAIN or one of the SCRAM mechanisms.
            sasl_kerberos_service_name (str): Service name to include in GSSAPI
                sasl mechanism handshake. Default: 'kafka'
            sasl_kerberos_domain_name (str): kerberos domain name to use in GSSAPI
                sasl mechanism handshake. Default: one of bootstrap servers
            sasl_oauth_token_provider (AbstractTokenProvider): OAuthBearer token provider
                instance. (See kafka.oauth.abstract). Default: None

        Note:
            Configuration parameters are described in more detail at
            https://kafka.apache.org/documentation/#consumerconfigs
        """
        DEFAULT_CONFIG = {
            'bootstrap_servers': 'localhost',
            'client_id': 'kafka-python-' + __version__,
            'group_id': None,
            'key_deserializer': None,
            'value_deserializer': None,
            'fetch_max_wait_ms': 500,
            'fetch_min_bytes': 1,
            'fetch_max_bytes': 52428800,
            'max_partition_fetch_bytes': 1 * 1024 * 1024,
            'request_timeout_ms': 305000, # chosen to be higher than the default of max_poll_interval_ms
            'retry_backoff_ms': 100,
            'reconnect_backoff_ms': 50,
            'reconnect_backoff_max_ms': 1000,
            'max_in_flight_requests_per_connection': 5,
            'auto_offset_reset': 'latest',
            'enable_auto_commit': True,
            'auto_commit_interval_ms': 5000,
            'default_offset_commit_callback': lambda offsets, response: True,
            'check_crcs': True,
            'metadata_max_age_ms': 5 * 60 * 1000,
            'partition_assignment_strategy': (RangePartitionAssignor, RoundRobinPartitionAssignor),
            'max_poll_records': 500,
            'max_poll_interval_ms': 300000,
            'session_timeout_ms': 10000,
            'heartbeat_interval_ms': 3000,
            'receive_buffer_bytes': None,
            'send_buffer_bytes': None,
            'socket_options': [(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)],
            'sock_chunk_bytes': 4096,  # undocumented experimental option
            'sock_chunk_buffer_count': 1000,  # undocumented experimental option
            'consumer_timeout_ms': float('inf'),
            'security_protocol': 'PLAINTEXT',
            'ssl_context': None,
            'ssl_check_hostname': True,
            'ssl_cafile': None,
            'ssl_certfile': None,
            'ssl_keyfile': None,
            'ssl_crlfile': None,
            'ssl_password': None,
            'ssl_ciphers': None,
            'api_version': None,
            'api_version_auto_timeout_ms': 2000,
            'connections_max_idle_ms': 9 * 60 * 1000,
            'metric_reporters': [],
            'metrics_num_samples': 2,
            'metrics_sample_window_ms': 30000,
            'metric_group_prefix': 'consumer',
            'selector': selectors.DefaultSelector,
            'exclude_internal_topics': True,
            'sasl_mechanism': None,
            'sasl_plain_username': None,
            'sasl_plain_password': None,
            'sasl_kerberos_service_name': 'kafka',
            'sasl_kerberos_domain_name': None,
            'sasl_oauth_token_provider': None,
            'legacy_iterator': False, # enable to revert to < 1.4.7 iterator
        }
        DEFAULT_SESSION_TIMEOUT_MS_0_9 = 30000

        def __init__(self, *topics, **configs):
            # Only check for extra config keys in top-level class
            extra_configs = set(configs).difference(self.DEFAULT_CONFIG)
            if extra_configs:
                raise KafkaConfigurationError("Unrecognized configs: %s" % (extra_configs,))

            self.config = copy.copy(self.DEFAULT_CONFIG)
            self.config.update(configs)

            deprecated = {'smallest': 'earliest', 'largest': 'latest'}
            if self.config['auto_offset_reset'] in deprecated:
                new_config = deprecated[self.config['auto_offset_reset']]
                log.warning('use auto_offset_reset=%s (%s is deprecated)',
                            new_config, self.config['auto_offset_reset'])
                self.config['auto_offset_reset'] = new_config

            connections_max_idle_ms = self.config['connections_max_idle_ms']
            request_timeout_ms = self.config['request_timeout_ms']
            fetch_max_wait_ms = self.config['fetch_max_wait_ms']
            if not (fetch_max_wait_ms < request_timeout_ms < connections_max_idle_ms):
                raise KafkaConfigurationError(
                    "connections_max_idle_ms ({}) must be larger than "
                    "request_timeout_ms ({}) which must be larger than "
                    "fetch_max_wait_ms ({})."
                    .format(connections_max_idle_ms, request_timeout_ms, fetch_max_wait_ms))

            metrics_tags = {'client-id': self.config['client_id']}
            metric_config = MetricConfig(samples=self.config['metrics_num_samples'],
                                         time_window_ms=self.config['metrics_sample_window_ms'],
                                         tags=metrics_tags)
            reporters = [reporter() for reporter in self.config['metric_reporters']]
            self._metrics = Metrics(metric_config, reporters)
            # TODO _metrics likely needs to be passed to KafkaClient, etc.

            # api_version was previously a str. Accept old format for now
            if isinstance(self.config['api_version'], str):
                str_version = self.config['api_version']
                if str_version == 'auto':
                    self.config['api_version'] = None
                else:
                    self.config['api_version'] = tuple(map(int, str_version.split('.')))
                log.warning('use api_version=%s [tuple] -- "%s" as str is deprecated',
                            str(self.config['api_version']), str_version)

            self._client = KafkaClient(metrics=self._metrics, **self.config)

            # Get auto-discovered version from client if necessary
            if self.config['api_version'] is None:
                self.config['api_version'] = self._client.config['api_version']

            # Coordinator configurations are different for older brokers
            # max_poll_interval_ms is not supported directly -- it must the be
            # the same as session_timeout_ms. If the user provides one of them,
            # use it for both. Otherwise use the old default of 30secs
            if self.config['api_version'] < (0, 10, 1):
                if 'session_timeout_ms' not in configs:
                    if 'max_poll_interval_ms' in configs:
                        self.config['session_timeout_ms'] = configs['max_poll_interval_ms']
                    else:
                        self.config['session_timeout_ms'] = self.DEFAULT_SESSION_TIMEOUT_MS_0_9
                if 'max_poll_interval_ms' not in configs:
                    self.config['max_poll_interval_ms'] = self.config['session_timeout_ms']

            if self.config['group_id'] is not None:
                if self.config['request_timeout_ms'] <= self.config['session_timeout_ms']:
                    raise KafkaConfigurationError(
                        "Request timeout (%s) must be larger than session timeout (%s)" %
                        (self.config['request_timeout_ms'], self.config['session_timeout_ms']))

            self._subscription = SubscriptionState(self.config['auto_offset_reset'])
            self._fetcher = Fetcher(
                self._client, self._subscription, self._metrics, **self.config)
            self._coordinator = ConsumerCoordinator(
                self._client, self._subscription, self._metrics,
                assignors=self.config['partition_assignment_strategy'],
                **self.config)
            self._closed = False
            self._iterator = None
            self._consumer_timeout = float('inf')

            if topics:
                self._subscription.subscribe(topics=topics)
                self._client.set_topics(topics)

        def bootstrap_connected(self):
            """Return True if the bootstrap is connected."""
            return self._client.bootstrap_connected()

        def assign(self, partitions):
            """Manually assign a list of TopicPartitions to this consumer.

            Arguments:
                partitions (list of TopicPartition): Assignment for this instance.

            Raises:
                IllegalStateError: If consumer has already called
                :meth:`~kafka.KafkaConsumer.subscribe`.

            Warning:
                It is not possible to use both manual partition assignment with
                :meth:`~kafka.KafkaConsumer.assign` and group assignment with
                :meth:`~kafka.KafkaConsumer.subscribe`.

            Note:
                This interface does not support incremental assignment and will
                replace the previous assignment (if there was one).

            Note:
                Manual topic assignment through this method does not use the
                consumer's group management functionality. As such, there will be
                no rebalance operation triggered when group membership or cluster
                and topic metadata change.
            """
            self._subscription.assign_from_user(partitions)
            self._client.set_topics([tp.topic for tp in partitions])

        def assignment(self):
            """Get the TopicPartitions currently assigned to this consumer.

            If partitions were directly assigned using
            :meth:`~kafka.KafkaConsumer.assign`, then this will simply return the
            same partitions that were previously assigned.  If topics were
            subscribed using :meth:`~kafka.KafkaConsumer.subscribe`, then this will
            give the set of topic partitions currently assigned to the consumer
            (which may be None if the assignment hasn't happened yet, or if the
            partitions are in the process of being reassigned).

            Returns:
                set: {TopicPartition, ...}
            """
            return self._subscription.assigned_partitions()

        def close(self, autocommit=True):
            """Close the consumer, waiting indefinitely for any needed cleanup.

            Keyword Arguments:
                autocommit (bool): If auto-commit is configured for this consumer,
                    this optional flag causes the consumer to attempt to commit any
                    pending consumed offsets prior to close. Default: True
            """
            if self._closed:
                return
            log.debug("Closing the KafkaConsumer.")
            self._closed = True
            self._coordinator.close(autocommit=autocommit)
            self._metrics.close()
            self._client.close()
            try:
                self.config['key_deserializer'].close()
            except AttributeError:
                pass
            try:
                self.config['value_deserializer'].close()
            except AttributeError:
                pass
            log.debug("The KafkaConsumer has closed.")

        def commit_async(self, offsets=None, callback=None):
            """Commit offsets to kafka asynchronously, optionally firing callback.

            This commits offsets only to Kafka. The offsets committed using this API
            will be used on the first fetch after every rebalance and also on
            startup. As such, if you need to store offsets in anything other than
            Kafka, this API should not be used. To avoid re-processing the last
            message read if a consumer is restarted, the committed offset should be
            the next message your application should consume, i.e.: last_offset + 1.

            This is an asynchronous call and will not block. Any errors encountered
            are either passed to the callback (if provided) or discarded.

            Arguments:
                offsets (dict, optional): {TopicPartition: OffsetAndMetadata} dict
                    to commit with the configured group_id. Defaults to currently
                    consumed offsets for all subscribed partitions.
                callback (callable, optional): Called as callback(offsets, response)
                    with response as either an Exception or an OffsetCommitResponse
                    struct. This callback can be used to trigger custom actions when
                    a commit request completes.

            Returns:
                kafka.future.Future
            """
            assert self.config['api_version'] >= (0, 8, 1), 'Requires >= Kafka 0.8.1'
            assert self.config['group_id'] is not None, 'Requires group_id'
            if offsets is None:
                offsets = self._subscription.all_consumed_offsets()
            log.debug("Committing offsets: %s", offsets)
            future = self._coordinator.commit_offsets_async(
                offsets, callback=callback)
            return future

        def commit(self, offsets=None):
            """Commit offsets to kafka, blocking until success or error.

            This commits offsets only to Kafka. The offsets committed using this API
            will be used on the first fetch after every rebalance and also on
            startup. As such, if you need to store offsets in anything other than
            Kafka, this API should not be used. To avoid re-processing the last
            message read if a consumer is restarted, the committed offset should be
            the next message your application should consume, i.e.: last_offset + 1.

            Blocks until either the commit succeeds or an unrecoverable error is
            encountered (in which case it is thrown to the caller).

            Currently only supports kafka-topic offset storage (not zookeeper).

            Arguments:
                offsets (dict, optional): {TopicPartition: OffsetAndMetadata} dict
                    to commit with the configured group_id. Defaults to currently
                    consumed offsets for all subscribed partitions.
            """
            assert self.config['api_version'] >= (0, 8, 1), 'Requires >= Kafka 0.8.1'
            assert self.config['group_id'] is not None, 'Requires group_id'
            if offsets is None:
                offsets = self._subscription.all_consumed_offsets()
            self._coordinator.commit_offsets_sync(offsets)

        def committed(self, partition, metadata=False):
            """Get the last committed offset for the given partition.

            This offset will be used as the position for the consumer
            in the event of a failure.

            This call may block to do a remote call if the partition in question
            isn't assigned to this consumer or if the consumer hasn't yet
            initialized its cache of committed offsets.

            Arguments:
                partition (TopicPartition): The partition to check.
                metadata (bool, optional): If True, return OffsetAndMetadata struct
                    instead of offset int. Default: False.

            Returns:
                The last committed offset (int or OffsetAndMetadata), or None if there was no prior commit.
            """
            assert self.config['api_version'] >= (0, 8, 1), 'Requires >= Kafka 0.8.1'
            assert self.config['group_id'] is not None, 'Requires group_id'
            if not isinstance(partition, TopicPartition):
                raise TypeError('partition must be a TopicPartition namedtuple')
            if self._subscription.is_assigned(partition):
                committed = self._subscription.assignment[partition].committed
                if committed is None:
                    self._coordinator.refresh_committed_offsets_if_needed()
                    committed = self._subscription.assignment[partition].committed
            else:
                commit_map = self._coordinator.fetch_committed_offsets([partition])
                if partition in commit_map:
                    committed = commit_map[partition]
                else:
                    committed = None

            if committed is not None:
                if metadata:
                    return committed
                else:
                    return committed.offset

        def _fetch_all_topic_metadata(self):
            """A blocking call that fetches topic metadata for all topics in the
            cluster that the user is authorized to view.
            """
            cluster = self._client.cluster
            if self._client._metadata_refresh_in_progress and self._client._topics:
                future = cluster.request_update()
                self._client.poll(future=future)
            stash = cluster.need_all_topic_metadata
            cluster.need_all_topic_metadata = True
            future = cluster.request_update()
            self._client.poll(future=future)
            cluster.need_all_topic_metadata = stash

        def topics(self):
            """Get all topics the user is authorized to view.
            This will always issue a remote call to the cluster to fetch the latest
            information.

            Returns:
                set: topics
            """
            self._fetch_all_topic_metadata()
            return self._client.cluster.topics()

        def partitions_for_topic(self, topic):
            """This method first checks the local metadata cache for information
            about the topic. If the topic is not found (either because the topic
            does not exist, the user is not authorized to view the topic, or the
            metadata cache is not populated), then it will issue a metadata update
            call to the cluster.

            Arguments:
                topic (str): Topic to check.

            Returns:
                set: Partition ids
            """
            cluster = self._client.cluster
            partitions = cluster.partitions_for_topic(topic)
            if partitions is None:
                self._fetch_all_topic_metadata()
                partitions = cluster.partitions_for_topic(topic)
            return partitions

        def poll(self, timeout_ms=0, max_records=None, update_offsets=True):
            """Fetch data from assigned topics / partitions.

            Records are fetched and returned in batches by topic-partition.
            On each poll, consumer will try to use the last consumed offset as the
            starting offset and fetch sequentially. The last consumed offset can be
            manually set through :meth:`~kafka.KafkaConsumer.seek` or automatically
            set as the last committed offset for the subscribed list of partitions.

            Incompatible with iterator interface -- use one or the other, not both.

            Arguments:
                timeout_ms (int, optional): Milliseconds spent waiting in poll if
                    data is not available in the buffer. If 0, returns immediately
                    with any records that are available currently in the buffer,
                    else returns empty. Must not be negative. Default: 0
                max_records (int, optional): The maximum number of records returned
                    in a single call to :meth:`~kafka.KafkaConsumer.poll`.
                    Default: Inherit value from max_poll_records.

            Returns:
                dict: Topic to list of records since the last fetch for the
                    subscribed list of topics and partitions.
            """
            # Note: update_offsets is an internal-use only argument. It is used to
            # support the python iterator interface, and which wraps consumer.poll()
            # and requires that the partition offsets tracked by the fetcher are not
            # updated until the iterator returns each record to the user. As such,
            # the argument is not documented and should not be relied on by library
            # users to not break in the future.
            assert timeout_ms >= 0, 'Timeout must not be negative'
            if max_records is None:
                max_records = self.config['max_poll_records']
            assert isinstance(max_records, int), 'max_records must be an integer'
            assert max_records > 0, 'max_records must be positive'
            assert not self._closed, 'KafkaConsumer is closed'

            # Poll for new data until the timeout expires
            start = time.time()
            remaining = timeout_ms
            while True:
                records = self._poll_once(remaining, max_records, update_offsets=update_offsets)
                if records:
                    return records

                elapsed_ms = (time.time() - start) * 1000
                remaining = timeout_ms - elapsed_ms

                if remaining <= 0:
                    return {}

        def _poll_once(self, timeout_ms, max_records, update_offsets=True):
            """Do one round of polling. In addition to checking for new data, this does
            any needed heart-beating, auto-commits, and offset updates.

            Arguments:
                timeout_ms (int): The maximum time in milliseconds to block.

            Returns:
                dict: Map of topic to list of records (may be empty).
            """
            self._coordinator.poll()

            # Fetch positions if we have partitions we're subscribed to that we
            # don't know the offset for
            if not self._subscription.has_all_fetch_positions():
                self._update_fetch_positions(self._subscription.missing_fetch_positions())

            # If data is available already, e.g. from a previous network client
            # poll() call to commit, then just return it immediately
            records, partial = self._fetcher.fetched_records(max_records, update_offsets=update_offsets)
            if records:
                # Before returning the fetched records, we can send off the
                # next round of fetches and avoid block waiting for their
                # responses to enable pipelining while the user is handling the
                # fetched records.
                if not partial:
                    futures = self._fetcher.send_fetches()
                    if len(futures):
                        self._client.poll(timeout_ms=0)
                return records

            # Send any new fetches (won't resend pending fetches)
            futures = self._fetcher.send_fetches()
            if len(futures):
                self._client.poll(timeout_ms=0)

            timeout_ms = min(timeout_ms, self._coordinator.time_to_next_poll() * 1000)
            self._client.poll(timeout_ms=timeout_ms)
            # after the long poll, we should check whether the group needs to rebalance
            # prior to returning data so that the group can stabilize faster
            if self._coordinator.need_rejoin():
                return {}

            records, _ = self._fetcher.fetched_records(max_records, update_offsets=update_offsets)
            return records

        def position(self, partition):
            """Get the offset of the next record that will be fetched

            Arguments:
                partition (TopicPartition): Partition to check

            Returns:
                int: Offset
            """
            if not isinstance(partition, TopicPartition):
                raise TypeError('partition must be a TopicPartition namedtuple')
            assert self._subscription.is_assigned(partition), 'Partition is not assigned'
            offset = self._subscription.assignment[partition].position
            if offset is None:
                self._update_fetch_positions([partition])
                offset = self._subscription.assignment[partition].position
            return offset

        def highwater(self, partition):
            """Last known highwater offset for a partition.

            A highwater offset is the offset that will be assigned to the next
            message that is produced. It may be useful for calculating lag, by
            comparing with the reported position. Note that both position and
            highwater refer to the *next* offset -- i.e., highwater offset is
            one greater than the newest available message.

            Highwater offsets are returned in FetchResponse messages, so will
            not be available if no FetchRequests have been sent for this partition
            yet.

            Arguments:
                partition (TopicPartition): Partition to check

            Returns:
                int or None: Offset if available
            """
            if not isinstance(partition, TopicPartition):
                raise TypeError('partition must be a TopicPartition namedtuple')
            assert self._subscription.is_assigned(partition), 'Partition is not assigned'
            return self._subscription.assignment[partition].highwater

        def pause(self, *partitions):
            """Suspend fetching from the requested partitions.

            Future calls to :meth:`~kafka.KafkaConsumer.poll` will not return any
            records from these partitions until they have been resumed using
            :meth:`~kafka.KafkaConsumer.resume`.

            Note: This method does not affect partition subscription. In particular,
            it does not cause a group rebalance when automatic assignment is used.

            Arguments:
                *partitions (TopicPartition): Partitions to pause.
            """
            if not all([isinstance(p, TopicPartition) for p in partitions]):
                raise TypeError('partitions must be TopicPartition namedtuples')
            for partition in partitions:
                log.debug("Pausing partition %s", partition)
                self._subscription.pause(partition)

            # Because the iterator checks is_fetchable() on each iteration
            # we expect pauses to get handled automatically and therefore
            # we do not need to reset the full iterator (forcing a full refetch)

        def paused(self):
            """Get the partitions that were previously paused using
            :meth:`~kafka.KafkaConsumer.pause`.

            Returns:
                set: {partition (TopicPartition), ...}
            """
            return self._subscription.paused_partitions()

        def resume(self, *partitions):
            """Resume fetching from the specified (paused) partitions.

            Arguments:
                *partitions (TopicPartition): Partitions to resume.
            """
            if not all([isinstance(p, TopicPartition) for p in partitions]):
                raise TypeError('partitions must be TopicPartition namedtuples')
            for partition in partitions:
                log.debug("Resuming partition %s", partition)
                self._subscription.resume(partition)

        def seek(self, partition, offset):
            """Manually specify the fetch offset for a TopicPartition.

            Overrides the fetch offsets that the consumer will use on the next
            :meth:`~kafka.KafkaConsumer.poll`. If this API is invoked for the same
            partition more than once, the latest offset will be used on the next
            :meth:`~kafka.KafkaConsumer.poll`.

            Note: You may lose data if this API is arbitrarily used in the middle of
            consumption to reset the fetch offsets.

            Arguments:
                partition (TopicPartition): Partition for seek operation
                offset (int): Message offset in partition

            Raises:
                AssertionError: If offset is not an int >= 0; or if partition is not
                    currently assigned.
            """
            if not isinstance(partition, TopicPartition):
                raise TypeError('partition must be a TopicPartition namedtuple')
            assert isinstance(offset, int) and offset >= 0, 'Offset must be >= 0'
            assert partition in self._subscription.assigned_partitions(), 'Unassigned partition'
            log.debug("Seeking to offset %s for partition %s", offset, partition)
            self._subscription.assignment[partition].seek(offset)
            if not self.config['legacy_iterator']:
                self._iterator = None

        def seek_to_beginning(self, *partitions):
            """Seek to the oldest available offset for partitions.

            Arguments:
                *partitions: Optionally provide specific TopicPartitions, otherwise
                    default to all assigned partitions.

            Raises:
                AssertionError: If any partition is not currently assigned, or if
                    no partitions are assigned.
            """
            if not all([isinstance(p, TopicPartition) for p in partitions]):
                raise TypeError('partitions must be TopicPartition namedtuples')
            if not partitions:
                partitions = self._subscription.assigned_partitions()
                assert partitions, 'No partitions are currently assigned'
            else:
                for p in partitions:
                    assert p in self._subscription.assigned_partitions(), 'Unassigned partition'

            for tp in partitions:
                log.debug("Seeking to beginning of partition %s", tp)
                self._subscription.need_offset_reset(tp, OffsetResetStrategy.EARLIEST)
            if not self.config['legacy_iterator']:
                self._iterator = None

        def seek_to_end(self, *partitions):
            """Seek to the most recent available offset for partitions.

            Arguments:
                *partitions: Optionally provide specific TopicPartitions, otherwise
                    default to all assigned partitions.

            Raises:
                AssertionError: If any partition is not currently assigned, or if
                    no partitions are assigned.
            """
            if not all([isinstance(p, TopicPartition) for p in partitions]):
                raise TypeError('partitions must be TopicPartition namedtuples')
            if not partitions:
                partitions = self._subscription.assigned_partitions()
                assert partitions, 'No partitions are currently assigned'
            else:
                for p in partitions:
                    assert p in self._subscription.assigned_partitions(), 'Unassigned partition'

            for tp in partitions:
                log.debug("Seeking to end of partition %s", tp)
                self._subscription.need_offset_reset(tp, OffsetResetStrategy.LATEST)
            if not self.config['legacy_iterator']:
                self._iterator = None

        def subscribe(self, topics=(), pattern=None, listener=None):
            """Subscribe to a list of topics, or a topic regex pattern.

            Partitions will be dynamically assigned via a group coordinator.
            Topic subscriptions are not incremental: this list will replace the
            current assignment (if there is one).

            This method is incompatible with :meth:`~kafka.KafkaConsumer.assign`.

            Arguments:
                topics (list): List of topics for subscription.
                pattern (str): Pattern to match available topics. You must provide
                    either topics or pattern, but not both.
                listener (ConsumerRebalanceListener): Optionally include listener
                    callback, which will be called before and after each rebalance
                    operation.

                    As part of group management, the consumer will keep track of the
                    list of consumers that belong to a particular group and will
                    trigger a rebalance operation if one of the following events
                    trigger:

                    * Number of partitions change for any of the subscribed topics
                    * Topic is created or deleted
                    * An existing member of the consumer group dies
                    * A new member is added to the consumer group

                    When any of these events are triggered, the provided listener
                    will be invoked first to indicate that the consumer's assignment
                    has been revoked, and then again when the new assignment has
                    been received. Note that this listener will immediately override
                    any listener set in a previous call to subscribe. It is
                    guaranteed, however, that the partitions revoked/assigned
                    through this interface are from topics subscribed in this call.

            Raises:
                IllegalStateError: If called after previously calling
                    :meth:`~kafka.KafkaConsumer.assign`.
                AssertionError: If neither topics or pattern is provided.
                TypeError: If listener is not a ConsumerRebalanceListener.
            """
            # SubscriptionState handles error checking
            self._subscription.subscribe(topics=topics,
                                         pattern=pattern,
                                         listener=listener)

            # Regex will need all topic metadata
            if pattern is not None:
                self._client.cluster.need_all_topic_metadata = True
                self._client.set_topics([])
                self._client.cluster.request_update()
                log.debug("Subscribed to topic pattern: %s", pattern)
            else:
                self._client.cluster.need_all_topic_metadata = False
                self._client.set_topics(self._subscription.group_subscription())
                log.debug("Subscribed to topic(s): %s", topics)

        def subscription(self):
            """Get the current topic subscription.

            Returns:
                set: {topic, ...}
            """
            if self._subscription.subscription is None:
                return None
            return self._subscription.subscription.copy()

        def unsubscribe(self):
            """Unsubscribe from all topics and clear all assigned partitions."""
            self._subscription.unsubscribe()
            self._coordinator.close()
            self._client.cluster.need_all_topic_metadata = False
            self._client.set_topics([])
            log.debug("Unsubscribed all topics or patterns and assigned partitions")
            if not self.config['legacy_iterator']:
                self._iterator = None

        def metrics(self, raw=False):
            """Get metrics on consumer performance.

            This is ported from the Java Consumer, for details see:
            https://kafka.apache.org/documentation/#consumer_monitoring

            Warning:
                This is an unstable interface. It may change in future
                releases without warning.
            """
            if raw:
                return self._metrics.metrics.copy()

            metrics = {}
            for k, v in six.iteritems(self._metrics.metrics.copy()):
                if k.group not in metrics:
                    metrics[k.group] = {}
                if k.name not in metrics[k.group]:
                    metrics[k.group][k.name] = {}
                metrics[k.group][k.name] = v.value()
            return metrics

        def offsets_for_times(self, timestamps):
            """Look up the offsets for the given partitions by timestamp. The
            returned offset for each partition is the earliest offset whose
            timestamp is greater than or equal to the given timestamp in the
            corresponding partition.

            This is a blocking call. The consumer does not have to be assigned the
            partitions.

            If the message format version in a partition is before 0.10.0, i.e.
            the messages do not have timestamps, ``None`` will be returned for that
            partition. ``None`` will also be returned for the partition if there
            are no messages in it.

            Note:
                This method may block indefinitely if the partition does not exist.

            Arguments:
                timestamps (dict): ``{TopicPartition: int}`` mapping from partition
                    to the timestamp to look up. Unit should be milliseconds since
                    beginning of the epoch (midnight Jan 1, 1970 (UTC))

            Returns:
                ``{TopicPartition: OffsetAndTimestamp}``: mapping from partition
                to the timestamp and offset of the first message with timestamp
                greater than or equal to the target timestamp.

            Raises:
                ValueError: If the target timestamp is negative
                UnsupportedVersionError: If the broker does not support looking
                    up the offsets by timestamp.
                KafkaTimeoutError: If fetch failed in request_timeout_ms
            """
            if self.config['api_version'] <= (0, 10, 0):
                raise UnsupportedVersionError(
                    "offsets_for_times API not supported for cluster version {}"
                    .format(self.config['api_version']))
            for tp, ts in six.iteritems(timestamps):
                timestamps[tp] = int(ts)
                if ts < 0:
                    raise ValueError(
                        "The target time for partition {} is {}. The target time "
                        "cannot be negative.".format(tp, ts))
            return self._fetcher.get_offsets_by_times(
                timestamps, self.config['request_timeout_ms'])

        def beginning_offsets(self, partitions):
            """Get the first offset for the given partitions.

            This method does not change the current consumer position of the
            partitions.

            Note:
                This method may block indefinitely if the partition does not exist.

            Arguments:
                partitions (list): List of TopicPartition instances to fetch
                    offsets for.

            Returns:
                ``{TopicPartition: int}``: The earliest available offsets for the
                given partitions.

            Raises:
                UnsupportedVersionError: If the broker does not support looking
                    up the offsets by timestamp.
                KafkaTimeoutError: If fetch failed in request_timeout_ms.
            """
            offsets = self._fetcher.beginning_offsets(
                partitions, self.config['request_timeout_ms'])
            return offsets

        def end_offsets(self, partitions):
            """Get the last offset for the given partitions. The last offset of a
            partition is the offset of the upcoming message, i.e. the offset of the
            last available message + 1.

            This method does not change the current consumer position of the
            partitions.

            Note:
                This method may block indefinitely if the partition does not exist.

            Arguments:
                partitions (list): List of TopicPartition instances to fetch
                    offsets for.

            Returns:
                ``{TopicPartition: int}``: The end offsets for the given partitions.

            Raises:
                UnsupportedVersionError: If the broker does not support looking
                    up the offsets by timestamp.
                KafkaTimeoutError: If fetch failed in request_timeout_ms
            """
            offsets = self._fetcher.end_offsets(
                partitions, self.config['request_timeout_ms'])
            return offsets

        def _use_consumer_group(self):
            """Return True iff this consumer can/should join a broker-coordinated group."""
            if self.config['api_version'] < (0, 9):
                return False
            elif self.config['group_id'] is None:
                return False
            elif not self._subscription.partitions_auto_assigned():
                return False
            return True

        def _update_fetch_positions(self, partitions):
            """Set the fetch position to the committed position (if there is one)
            or reset it using the offset reset policy the user has configured.

            Arguments:
                partitions (List[TopicPartition]): The partitions that need
                    updating fetch positions.

            Raises:
                NoOffsetForPartitionError: If no offset is stored for a given
                    partition and no offset reset policy is defined.
            """
            # Lookup any positions for partitions which are awaiting reset (which may be the
            # case if the user called :meth:`seek_to_beginning` or :meth:`seek_to_end`. We do
            # this check first to avoid an unnecessary lookup of committed offsets (which
            # typically occurs when the user is manually assigning partitions and managing
            # their own offsets).
            self._fetcher.reset_offsets_if_needed(partitions)

            if not self._subscription.has_all_fetch_positions():
                # if we still don't have offsets for all partitions, then we should either seek
                # to the last committed position or reset using the auto reset policy
                if (self.config['api_version'] >= (0, 8, 1) and
                    self.config['group_id'] is not None):
                    # first refresh commits for all assigned partitions
                    self._coordinator.refresh_committed_offsets_if_needed()

                # Then, do any offset lookups in case some positions are not known
                self._fetcher.update_fetch_positions(partitions)

        def _message_generator_v2(self):
            timeout_ms = 1000 * (self._consumer_timeout - time.time())
            record_map = self.poll(timeout_ms=timeout_ms, update_offsets=False)
            for tp, records in six.iteritems(record_map):
                # Generators are stateful, and it is possible that the tp / records
                # here may become stale during iteration -- i.e., we seek to a
                # different offset, pause consumption, or lose assignment.
                for record in records:
                    # is_fetchable(tp) should handle assignment changes and offset
                    # resets; for all other changes (e.g., seeks) we'll rely on the
                    # outer function destroying the existing iterator/generator
                    # via self._iterator = None
                    if not self._subscription.is_fetchable(tp):
                        log.debug("Not returning fetched records for partition %s"
                                  " since it is no longer fetchable", tp)
                        break
                    self._subscription.assignment[tp].position = record.offset + 1
                    yield record

        def _message_generator(self):
            assert self.assignment() or self.subscription() is not None, 'No topic subscription or manual partition assignment'
            while time.time() < self._consumer_timeout:

                self._coordinator.poll()

                # Fetch offsets for any subscribed partitions that we arent tracking yet
                if not self._subscription.has_all_fetch_positions():
                    partitions = self._subscription.missing_fetch_positions()
                    self._update_fetch_positions(partitions)

                poll_ms = min((1000 * (self._consumer_timeout - time.time())), self.config['retry_backoff_ms'])
                self._client.poll(timeout_ms=poll_ms)

                # after the long poll, we should check whether the group needs to rebalance
                # prior to returning data so that the group can stabilize faster
                if self._coordinator.need_rejoin():
                    continue

                # We need to make sure we at least keep up with scheduled tasks,
                # like heartbeats, auto-commits, and metadata refreshes
                timeout_at = self._next_timeout()

                # Short-circuit the fetch iterator if we are already timed out
                # to avoid any unintentional interaction with fetcher setup
                if time.time() > timeout_at:
                    continue

                for msg in self._fetcher:
                    yield msg
                    if time.time() > timeout_at:
                        log.debug("internal iterator timeout - breaking for poll")
                        break
                    self._client.poll(timeout_ms=0)

                # An else block on a for loop only executes if there was no break
                # so this should only be called on a StopIteration from the fetcher
                # We assume that it is safe to init_fetches when fetcher is done
                # i.e., there are no more records stored internally
                else:
                    self._fetcher.send_fetches()

        def _next_timeout(self):
            timeout = min(self._consumer_timeout,
                          self._client.cluster.ttl() / 1000.0 + time.time(),
                          self._coordinator.time_to_next_poll() + time.time())
            return timeout

        def __iter__(self):  # pylint: disable=non-iterator-returned
            return self

        def __next__(self):
            if self._closed:
                raise StopIteration('KafkaConsumer closed')
            # Now that the heartbeat thread runs in the background
            # there should be no reason to maintain a separate iterator
            # but we'll keep it available for a few releases just in case
            if self.config['legacy_iterator']:
                return self.next_v1()
            else:
                return self.next_v2()

        def next_v2(self):
            self._set_consumer_timeout()
            while time.time() < self._consumer_timeout:
                if not self._iterator:
                    self._iterator = self._message_generator_v2()
                try:
                    return next(self._iterator)
                except StopIteration:
                    self._iterator = None
            raise StopIteration()

        def next_v1(self):
            if not self._iterator:
                self._iterator = self._message_generator()

            self._set_consumer_timeout()
            try:
                return next(self._iterator)
            except StopIteration:
                self._iterator = None
                raise

        def _set_consumer_timeout(self):
            # consumer_timeout_ms can be used to stop iteration early
            if self.config['consumer_timeout_ms'] >= 0:
                self._consumer_timeout = time.time() + (
                    self.config['consumer_timeout_ms'] / 1000.0)