pulsar/reader.go

// Licensed to the Apache Software Foundation (ASF) under one
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// to you under the Apache License, Version 2.0 (the
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// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// specific language governing permissions and limitations
// under the License.

package pulsar

import "context"

// ReaderMessage package Reader and Message as a struct to use
type ReaderMessage struct {
	Reader
	Message
}

// ReaderOptions abstraction Reader options to use.
type ReaderOptions struct {
	// Topic specify the topic this consumer will subscribe on.
	// This argument is required when constructing the reader.
	Topic string

	// Name set the reader name.
	Name string

	// Attach a set of application defined properties to the reader
	// This properties will be visible in the topic stats
	Properties map[string]string

	// StartMessageID initial reader positioning is done by specifying a message id. The options are:
	//  * `pulsar.EarliestMessage` : Start reading from the earliest message available in the topic
	//  * `pulsar.LatestMessage` : Start reading from the end topic, only getting messages published after the
	//                           reader was created
	//  * `MessageID` : Start reading from a particular message id, the reader will position itself on that
	//                  specific position. The first message to be read will be the message next to the specified
	//                  messageID
	StartMessageID MessageID

	// If true, the reader will start at the `StartMessageID`, included.
	// Default is `false` and the reader will start from the "next" message
	StartMessageIDInclusive bool

	// MessageChannel sets a `MessageChannel` for the consumer
	// When a message is received, it will be pushed to the channel for consumption
	MessageChannel chan ReaderMessage

	// ReceiverQueueSize sets the size of the consumer receive queue.
	// The consumer receive queue controls how many messages can be accumulated by the Reader before the
	// application calls Reader.readNext(). Using a higher value could potentially increase the consumer
	// throughput at the expense of bigger memory utilization.
	// Default value is {@code 1000} messages and should be good for most use cases.
	ReceiverQueueSize int

	// SubscriptionRolePrefix set the subscription role prefix. The default prefix is "reader".
	SubscriptionRolePrefix string

	// If enabled, the reader will read messages from the compacted topic rather than reading the full message backlog
	// of the topic. This means that, if the topic has been compacted, the reader will only see the latest value for
	// each key in the topic, up until the point in the topic message backlog that has been compacted. Beyond that
	// point, the messages will be sent as normal.
	//
	// ReadCompacted can only be enabled when reading from a persistent topic. Attempting to enable it on non-persistent
	// topics will lead to the reader create call throwing a PulsarClientException.
	ReadCompacted bool
}

// Reader can be used to scan through all the messages currently available in a topic.
type Reader interface {
	// Topic from which this reader is reading from
	Topic() string

	// Next read the next message in the topic, blocking until a message is available
	Next(context.Context) (Message, error)

	// HasNext check if there is any message available to read from the current position
	HasNext() bool

	// Close the reader and stop the broker to push more messages
	Close()
}