github.com/rohankumardubey/aresdb@v0.0.2-0.20190517170215-e54e3ca06b9c/subscriber/common/consumer/consumer.go (about)

     1  //  Copyright (c) 2017-2018 Uber Technologies, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package consumer
    16  
    17  import "io"
    18  
    19  // Message is a single message pulled off a Kafka topic.
    20  type Message interface {
    21  	// Key is a mutable reference to the message's key.
    22  	Key() []byte
    23  	// Value is a mutable reference to the message's value.
    24  	Value() []byte
    25  	// Topic is the topic from which the message was read.
    26  	Topic() string
    27  	// Partition is the ID of the partition from which the message was read.
    28  	Partition() int32
    29  	// Offset is the message's offset.
    30  	Offset() int64
    31  	// Ack the message
    32  	Ack()
    33  	// Nack the message
    34  	Nack()
    35  	// Cluster is the message's originated cluster.
    36  	Cluster() string
    37  }
    38  
    39  // A Consumer allows users to read and process messages from a Kafka topic.
    40  // Consumer processes within the same group use ZooKeeper to negotiate partition
    41  // ownership, so each process sees a stream of messages from one or more
    42  // partitions. Within a partition, messages are linearizable.
    43  type Consumer interface {
    44  	io.Closer
    45  
    46  	// Name returns the name of this consumer group.
    47  	Name() string
    48  	// Topics returns the names of the topics being consumed.
    49  	Topics() []string
    50  	// Errors returns a channel of errors for the topic. To prevent deadlocks,
    51  	// users must read from the error channel.
    52  	//
    53  	// All errors returned from this channel can be safely cast to the
    54  	// consumer.Error interface, which allows structured access to the topic
    55  	// name and partition number.
    56  	Errors() <-chan error
    57  	// Closed returns a channel that unblocks when the consumer successfully shuts
    58  	// down.
    59  	Closed() <-chan struct{}
    60  	// Messages returns a channel of messages for the topic.
    61  	//
    62  	// If the consumer is not configured with nonzero buffer size, the Errors()
    63  	// channel must be read in conjunction with Messages() to prevent deadlocks.
    64  	Messages() <-chan Message
    65  	// CommitUpTo marks this message and all previous messages in the same partition
    66  	// as processed. The last processed offset for each partition is periodically
    67  	// flushed to ZooKeeper; on startup, consumers begin processing after the last
    68  	// stored offset.
    69  	CommitUpTo(Message) error
    70  }