Kafka::Consumer - Perl interface for Kafka consumer client.
This documentation refers to Kafka::Consumer version 1.001012 .
Kafka::Consumer
use 5.010; use strict; use warnings; use Scalar::Util qw( blessed ); use Try::Tiny; use Kafka qw( $DEFAULT_MAX_BYTES $DEFAULT_MAX_NUMBER_OF_OFFSETS $RECEIVE_EARLIEST_OFFSETS ); use Kafka::Connection; use Kafka::Consumer; my ( $connection, $consumer ); try { #-- Connection $connection = Kafka::Connection->new( host => 'localhost' ); #-- Consumer $consumer = Kafka::Consumer->new( Connection => $connection ); # Get a list of valid offsets up max_number before the given time my $offsets = $consumer->offsets( 'mytopic', # topic 0, # partition $RECEIVE_EARLIEST_OFFSETS, # time $DEFAULT_MAX_NUMBER_OF_OFFSETS # max_number ); if ( @$offsets ) { say "Received offset: $_" foreach @$offsets; } else { warn "Error: Offsets are not received\n"; } # Consuming messages my $messages = $consumer->fetch( 'mytopic', # topic 0, # partition 0, # offset $DEFAULT_MAX_BYTES # Maximum size of MESSAGE(s) to receive ); if ( $messages ) { foreach my $message ( @$messages ) { if ( $message->valid ) { say 'payload : ', $message->payload; say 'key : ', $message->key; say 'offset : ', $message->offset; say 'next_offset: ', $message->next_offset; } else { say 'error : ', $message->error; } } } } catch { my $error = $_; if ( blessed( $error ) && $error->isa( 'Kafka::Exception' ) ) { warn 'Error: (', $error->code, ') ', $error->message, "\n"; exit; } else { die $error; } }; # Closes the consumer and cleans up undef $consumer; $connection->close; undef $connection;
Kafka consumer API is implemented by Kafka::Consumer class.
The main features of the Kafka::Consumer class are:
Provides an object-oriented API for consuming messages.
Provides Kafka FETCH and OFFSETS requests.
Supports parsing the Apache Kafka 0.9+ Wire Format protocol.
Works with 64-bit elements of the Kafka Wire Format protocol on 32 bit systems.
The Kafka consumer response returns ARRAY references for offsets and fetch methods.
offsets
fetch
Array returned by offsets contains offset integers.
Array returned by fetch contains objects of Kafka::Message class.
new
Creates a new consumer client object. Returns the created Kafka::Consumer object.
new() takes arguments in key-value pairs. The following arguments are recognized:
new()
Connection => $connection
$connection is the Kafka::Connection object responsible for communication with the Apache Kafka cluster.
$connection
CorrelationId => $correlation_id
Optional, default is undef.
undef
Correlation is a user-supplied integer. It will be passed back in the response by the server, unmodified. The $correlation_id should be an integer number.
Correlation
$correlation_id
CorrelationId will be auto-assigned (random negative number) if it was not provided on creation of Kafka::Producer object.
CorrelationId
An exception is thrown if CorrelationId sent with request does not match CorrelationId received in response.
ClientId => $client_id
This is a user supplied identifier (string) for the client application.
ClientId will be auto-assigned if not passed in when creating Kafka::Producer object.
ClientId
MaxWaitTime => $max_time
The maximum amount of time (ms) to wait when no sufficient data is available at the time the request was issued.
Optional, default is $DEFAULT_MAX_WAIT_TIME.
$DEFAULT_MAX_WAIT_TIME
$DEFAULT_MAX_WAIT_TIME is the default time that can be imported from the Kafka module.
The $max_time must be a positive integer.
$max_time
MinBytes => $min_bytes
The minimum number of bytes of messages that must be available to give a response. If the client sets this to $MIN_BYTES_RESPOND_IMMEDIATELY the server will always respond immediately. If it is set to $MIN_BYTES_RESPOND_HAS_DATA, the server will respond as soon as at least one partition has at least 1 byte of data or the specified timeout occurs. Setting higher values in combination with the bigger timeouts allows reading larger chunks of data.
$MIN_BYTES_RESPOND_IMMEDIATELY
$MIN_BYTES_RESPOND_HAS_DATA
Optional, int32 signed integer, default is $MIN_BYTES_RESPOND_IMMEDIATELY.
$MIN_BYTES_RESPOND_IMMEDIATELY, $MIN_BYTES_RESPOND_HAS_DATA are the defaults that can be imported from the Kafka module.
The $min_bytes must be a non-negative int32 signed integer.
$min_bytes
MaxBytes => $max_bytes
The maximum bytes to include in the message set for this partition.
Optional, int32 signed integer, default = $DEFAULT_MAX_BYTES (1_000_000).
$DEFAULT_MAX_BYTES
The $max_bytes must be more than $MESSAGE_SIZE_OVERHEAD (size of protocol overhead - data added by Kafka wire protocol to each message).
$max_bytes
$MESSAGE_SIZE_OVERHEAD
$DEFAULT_MAX_BYTES, $MESSAGE_SIZE_OVERHEAD are the defaults that can be imported from the Kafka module.
MaxNumberOfOffsets => $max_number
Limit the number of offsets returned by Kafka.
That is a non-negative integer.
Optional, int32 signed integer, default = $DEFAULT_MAX_NUMBER_OF_OFFSETS (100).
$DEFAULT_MAX_NUMBER_OF_OFFSETS
$DEFAULT_MAX_NUMBER_OF_OFFSETS is the default that can be imported from the Kafka module.
The following methods are defined for the Kafka::Consumer class:
fetch( $topic, $partition, $start_offset, $max_size )
Get a list of messages to consume one by one up to $max_size bytes.
$max_size
Returns the reference to array of the Kafka::Message objects.
fetch() takes the following arguments:
fetch()
$topic
The $topic must be a normal non-false string of non-zero length.
$partition
The $partition must be a non-negative integer.
$start_offset
Offset in topic and partition to start from (64-bit integer).
The argument must be a non-negative integer. The argument may be a Math::BigInt integer on 32-bit system.
$max_size is the maximum size of the messages set to return. The argument must be a positive int32 signed integer.
The maximum size of a request limited by MAX_SOCKET_REQUEST_BYTES that can be imported from Kafka module.
MAX_SOCKET_REQUEST_BYTES
offsets( $topic, $partition, $time, $max_number )
Get a list of valid offsets up to $max_number before the given time.
$max_number
Returns reference to array of the offset integers (Math::BigInt integers on 32 bit system).
offsets() takes the following arguments:
offsets()
$time
Get offsets before the given time (in milliseconds since UNIX Epoch).
The argument must be a positive number.
The argument may be a Math::BigInt integer on 32 bit system.
The special values $RECEIVE_LATEST_OFFSET (-1), $RECEIVE_EARLIEST_OFFSETS (-2) are allowed.
$RECEIVE_LATEST_OFFSET
$RECEIVE_EARLIEST_OFFSETS
$RECEIVE_LATEST_OFFSET, $RECEIVE_EARLIEST_OFFSETS are the defaults that can be imported from the Kafka module.
$max_number is the maximum number of offsets to retrieve.
Optional. The argument must be a positive int32 signed integer.
When error is detected, an exception, represented by object of Kafka::Exception::Consumer class, is thrown (see Kafka::Exceptions).
Kafka::Exception::Consumer
code and a more descriptive message provide information about thrown exception. Consult documentation of the Kafka::Exceptions for the list of all available methods.
Authors suggest using of Try::Tiny's try and catch to handle exceptions while working with Kafka package.
try
catch
Invalid argument
Invalid argument passed to a new constructor or other method.
Can't send
Request cannot be sent.
Can't recv
Response cannot be received.
Can't bind
TCP connection can't be established on the given host and port.
Can't get metadata
Failed to obtain metadata from Kafka servers.
Leader not found
Missing information about server-leader in metadata.
Mismatch CorrelationId
CorrelationId of response doesn't match one in request.
There are no known brokers
Resulting metadata has no information about cluster brokers.
Received metadata has incorrect internal structure.
The basic operation of the Kafka package modules:
Kafka - constants and messages used by the Kafka package modules.
Kafka::Connection - interface to connect to a Kafka cluster.
Kafka::Producer - interface for producing client.
Kafka::Consumer - interface for consuming client.
Kafka::Message - interface to access Kafka message properties.
Kafka::Int64 - functions to work with 64 bit elements of the protocol on 32 bit systems.
Kafka::Protocol - functions to process messages in the Apache Kafka's Protocol.
Kafka::IO - low-level interface for communication with Kafka server.
Kafka::Exceptions - module designated to handle Kafka exceptions.
Kafka::Internals - internal constants and functions used by several package modules.
A wealth of detail about the Apache Kafka and the Kafka Protocol:
Main page at http://kafka.apache.org/
Kafka Protocol at https://cwiki.apache.org/confluence/display/KAFKA/A+Guide+To+The+Kafka+Protocol
Kafka package is hosted on GitHub: https://github.com/TrackingSoft/Kafka
Sergey Gladkov, <sgladkov@trackingsoft.com>
Alexander Solovey
Jeremy Jordan
Sergiy Zuban
Vlad Marchenko
Copyright (C) 2012-2016 by TrackingSoft LLC.
This package is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic at http://dev.perl.org/licenses/artistic.html.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
To install Kafka, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Kafka
CPAN shell
perl -MCPAN -e shell install Kafka
For more information on module installation, please visit the detailed CPAN module installation guide.