--- name: "Net::Kafka" section: "3pm" platform: "linux" package: "libnet-kafka-perl" version: "1.06-3" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/Net::Kafka" --- # Net::Kafka(3pm) High-performant Perl client for Apache Kafka ## 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 (\). ### BUILD FROM CPAN ``` cpanm install Net::Kafka ``` ### BUILD FROM SOURCE Sources are available on Github: \. ``` 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 \). 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 \). 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.