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Alex Mironov
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NAME

Net::Kafka - High-performant Perl client for Apache Kafka

SYNOPSIS

    use Net::Kafka::Producer;
    use Net::Kafka::Consumer;
    use AnyEvent;

    # Produce 1 message into "my_topic"
    my $condvar     = AnyEvent->condvar;
    my $producer    = Net::Kafka::Producer->new(
        'bootstrap.servers' => 'localhost:9092'
    );
    $producer->produce(
        payload => "message",
        topic   => "my_topic"
    )->then(sub {
        my $delivery_report = shift;
        $condvar->send;
        print "Message successfully delivered with offset " . $delivery_report->{offset};
    }, sub {
        my $error = shift;
        $condvar->send;
        die "Unable to produce a message: " . $error->{error} . ", code: " . $error->{code};
    });
    $condvar->recv;

    # Consume message from "my_topic"
    my $consumer    = Net::Kafka::Consumer->new(
        'bootstrap.servers'     => 'localhost:9092',
        'group.id'              => 'my_consumer_group',
        'enable.auto.commit'    => 'true',
    );

    $consumer->subscribe( [ "my_topic" ] );
    while (1) {
        my $msg = $kafka->consumer_poll(1000);
        if ($msg) {
            if ( $msg->err ) {
                say "Error: ", Net::Kafka::Error::to_string($err);
            }
            else {
                say $msg->payload;
            }
        }
    }

DESCRIPTION

This module provides Perl bindings to librdkafka C client library. It is heavily inspired by Kafka::Librd module originally developed by Pavel Shaydo.

Please refer to the following modules documentation in order to understand how to use it:

  • Net::Kafka::Producer - asynchronous producer interface

  • Net::Kafka::Consumer - consumer interface that supports both Simple and Distributed modes

REQUIREMENTS

  • GNU make

  • librdkafka >= 1.0.0

INSTALLATION

First install librdkafka (https://github.com/edenhill/librdkafka#installation).

BUILD FROM CPAN

    cpanm install Net::Kafka

BUILD FROM SOURCE

Sources are available on Github: https://github.com/bookingcom/perl-Net-Kafka.

    perl Makefile.pl
    make
    make test
    make install

Net::Kafka::Producer

The Net::Kafka::Producer module provides interface to librdkafka's producer methods. It utilizes signal pipes, AnyEvent watcher and AnyEvent::XSPromises to make its behaviour asynchronous. Taking that into consideration you need to make sure to properly create condvar and send/recv in order to collect all outstanding promises. It is highly suggested to familirize yourself with both AnyEvent and AnyEvent::XSPromises modules. See "SYNOPSIS" for example.

METHODS

new()
    my $producer = Net::Kafka::Producer->new(
        'bootstrap.servers' => 'localhost:9092'
    );

Create an instance of Net::Kafka::Producer. Accept hash where keys are equal to property names of librdkafka (see https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.md). Note that only error_cb and stats_cb callbacks are supported for Producer. Message delivery reports are served automatically through Promise based produce method (see below).

produce()
    my $promise = $producer->produce(
        payload     => "my_message",
        topic       => "my_topic",
        key         => "my_key",    # optional
        timestamp   => 1234567,   # optional, if not specified current local timestamp will be used
        partition   => 0          # optional, if not specified internal librdkafka partitioner will be used
        headers     => $headers,  # Optional, see Net::Kafka::Headers
    )->then(sub {
        my $delivery_report = shift;
        print "Message is sent with offset " . $delivery_report->{offset};
    })->catch(sub {
        my $error = shift;
        print $error->{error} . "\n";
    });

Sends a message to Kafka. Accepts hash with parameters.

Returns back an instance of Promise that will be resolved/rejected later. In case message is successfully send "resolve" callback will receive a delievry report in the form of the hash that contains offset, partition and timestamp. If message delivery has failed "reject" callback will receive a hash that contains error (a human readable error description) and (optionally) error_code that is equal to librdkafka's error code. All error codes are mapped and exported by Net::Kafka module as constants (e.g. Net::Kafka::RD_KAFKA_RESP_ERR__PREV_IN_PROGRESS) for simplicity.

partitions_for()
    my $partitions = $producer->partitions_for("my_topic", $timeout_ms);

Returns an ARRAYREF that contains partition metadata information about the given topic (leader, replicas, ISR replicas);

close()
    $producer->close();

Explicitly closees Net::Kafka::Producer instance and underlying librdkafka handles.

Net::Kafka::Consumer

The Net::Kafka::Consumer class provides interface to librdkafka's consumer functionality. It supports both "distributed" (subscription based) and "simple" (manual partition assignment) modes of work.

METHODS

new()
    my $consumer = Net::Kafka::Consumer->new(
        'bootstrap.servers'  => 'localhost:9092',
        'group.id'           => "my_consumer_group",
        'enable.auto.commit' => "true",
    );

Create an instance of Net::Kafka::Consumer. Accept hash where keys are equal to property names of librdkafka (see https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.md). Note that not all callbacks are supported at the moment. Supported ones are: error_cb, rebalance_cb, commit_cb and stats_cb.

subscribe()
    $consumer->subscribe([ 'my_topic' ]);

Subscribe to topic set using balanced consumer groups. The main entry-point for "distributed" consumer mode - partitions will be assigned automatically using Kafka's GroupApi semantics. Wildcard/regex topics are supported so matching topics will be added to the subscription list.

unsubscribe()
    $consumer->unsubscribe();

Unsubscribe from the current subscription set.

assign()
    # manually assign partitions 0 and 1 to be consumed
    my $tp_list = Net::Kafka::TopicPartitionList->new();
    $tp_list->add("my_topic", 0);
    $tp_list->add("my_topic", 1);
    $consumer->assign($tp_list);

Atomic assignment of partitions to consume. The main entry-point for "simple" consumer mode - partitions are assigned manually.

poll()
    my $message = $consumer->poll($timeout_ms);

Poll the consumer for messages or events. Returns instance of Net::Kafka::Message. Will block for at most timeout_ms milliseconds. An application should make sure to call poll at regular intervals.

committed()
    my $tp_list = Net::Kafka::TopicPartitionList->new();
    $tp_list->add("my_topic", 0);
    $consumer->committed($tp_list);
    my $offset = $tp_list->offset("my_topic_, 0);

Retrieve committed offsets for topics+partitions.

offsets_for_times()
    my $tp_list = Net::Kafka::TopicPartitionList->new();
    $tp_list->add("my_topic", 0);
    $tp_list->set_offset("my_topic", 0, 958349923); # timestamp if passed through offset field
    $consumer->offsets_for_times($tp_list);
    my $offset = $tp_list->offset("my_topic");

Look up the offsets for the given partitions by timestamp.

pause()
    my $tp_list = Net::Kafka::TopicPartitionList->new();
    $tp_list->add("my_topic", 0);
    $consumer->pause($tp_list); # pauses consumption of partition 0 of "my_topic"

Pause consumption for the provided list of partitions.

resume()
    my $tp_list = Net::Kafka::TopicPartitionList->new();
    $tp_list->add("my_topic", 0);
    $consumer->resume($tp_list); # resumes consumption of partition 0 of "my_topic"

Resume consumption for the provided list of partitions.

subscription()
    my $topics = $consumer->subscription();

Returns the current topic subscription

partitions_for()
    my $partitions = $producer->partitions_for("my_topic");

Returns an ARRAYREF that contains partition metadata information about the given topic (leader, replicas, ISR replicas);

commit()
    $consumer->commit(); # commit current partition assignment (blocking call)
    $consumer->commit(1); # commit current partition assignment (non-blocking call)
    my $tp_list = Net::Kafka::TopicPartitionList->new();
    $tp_list->add("my_topic", 0);
    $tp_list->set_offset("my_topic", 0, 12345);
    $consumer->commit(0, $tp_list); # commit $tp_list assignment (blocking call);

Commit offsets on broker for the provided list of partitions. If no partitions provided current assignment is committed instead.

commit_message();
    my $message = $consumer->poll(1000);
    $consumer->commit_message(0, $message); # commit message (blocking call);
    $consumer->commit_message(1, $message); # commit message (non-blocking call);

Commit message's offset on broker for the message's partition.

position()
    my $position_list = Net::Kafka::TopicPartitionList->new();
    $position_list->add("my_topic", 0);
    $consumer->position($position_list);
    my $position = $position_list->offset("my_topic", 0);

Retrieve current positions (offsets) for topics+partitions. The \p offset field of each requested partition will be set to the offset of the last consumed message + 1, or RD_KAFKA_OFFSET_INVALID in case there was no previous message.

Note: in this context the last consumed message is the offset consumed by the current librdkafka instance and, in case of rebalancing, not necessarily the last message fetched from the partition.

seek()
    $consumer->seek("my_topic", 0, 12345); # seek partition 0 of "my_topic" to offset "12345"
    $consumer->seek("my_topic", 0, RD_KAFKA_OFFSET_BEGINNING); # seek to the beginning of "my_topic" partition 0
    $consumer->seek("my_topic", 0, RD_KAFKA_OFFSET_END); # seek to the end of "my_topic" partition 0

Seek consumer for topic+partition to offset which is either an absolute or logical offset.

query_watermark_offsets()
    my ($low, $high) = $consumer->query_watermark_offsets("my_topic", 0);

Queries Kafka Broker for lowest and highest watermark offsets in the given topic-partition.

close()
    $consumer->close();

Close all consumer handles. Make sure to call it before destroying your application to make sure that all outstanding requests to be flushed.

Net::Kafka::Message

This class maps to rd_kafka_message_t structure from librdkafka and represents message or event. Objects of this class have the following methods:

err()

return error code from the message

topic()

return topic name

partition()

return partition number

offset()

return offset. Note, that the value is truncated to 32 bit if your perl doesn't support 64 bit integers.

key()

return message key

payload()

return message payload

headers()

return a copy of message headers

detach_headers()

return message headers and removes them from the message

Net::Kafka::Headers

This class contains a list of Kafka headers (it allows duplicates). Objects of this class have the following methods:

new()

create a new instance

add(name, value)

append a new name/value pair to the header list

remove(name)

remove all headers with the given name, if any

get_last(name)

return the last value associated with a given name

to_hash()

return an hash-of-arrays containing all headers

Net::Kafka::Err

This class provides static methods to convert error codes into names and descriptions.

rd_kafka_get_err_descs()
    rd_kafka_get_err_descs()

returns a hash mapping error codes to description strings.

to_string()
    to_string($code)

return the description string for this error code.

to_name()
    to_name($code)

return the name of this error code.

CAVEATS

Message offset is truncated to 32 bit if perl is compiled without support for 64 bit integers.

SEE ALSO

LICENSE AND COPYRIGHT

Copyright (C) 2016, 2017 Pavel Shaydo

Copyright (C) 2018, 2019 Booking.com

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.