Get topic messages

Subscribe to Hedera Consensus Service (HCS) topic messages with TopicMessageQuery over gRPC to stream new and historical messages from a mirror node.

Subscribe to a topic ID’s messages from a mirror node. You will receive all messages for the specified topic or within the defined start and end time.

Query Fees

• The SDK uses the Hedera Consensus Service gRPC APIs provided by the mirror node to perform this function for free.

Methods

Method	Type	Description	Requirement
setTopicId(<topicId>)	TopicId	The topic ID to subscribe to	Required
setStartTime(<startTime>)	Instant	The time to start subscribing to a topic’s messages	Optional
setEndTime(<endTime>)	Instant	The time to stop subscribing to a topic’s messages	Optional
setLimit(<limit>)	long	The number of messages to return	Optional
subscribe(<client, onNext)	SubscriptionHandle	Client, Consumer<TopicMessage>	Required

Java

//Create the query
new TopicMessageQuery()
    .setTopicId(newTopicId)
    .subscribe(client, topicMessage -> {
        System.out.println("at " + topicMessage.consensusTimestamp + " ( seq = " + topicMessage.sequenceNumber + " ) received topic message of " + topicMessage.contents.length + " bytes");
    });

//v2.0.0

//Create the query
new TopicMessageQuery()
        .setTopicId(topicId)
        .setStartTime(0)
        .subscribe(
            client,
            (message) => console.log(Buffer.from(message.contents, "utf8").toString())
        );
//v2.0.0

//Create the query
_, err = hedera.NewTopicMessageQuery().
    SetTopicID(topicID).
    Subscribe(client, func(message hedera.TopicMessage) {
        if string(message.Contents) == content {
        wait = false
    }
})

if err != nil {
    panic(err)
}

//v2.0.0