Hedera Consensus Service gRPC API

The Hedera Consensus Service (HCS) gRPC API is a public mirror node managed by Hedera for the testnet. It offers the ability to subscribe to HCS topics and receive messages for the topic subscribed.

HCS Mirror Node Endpoints:
hcs.testnet.mirrornode.hedera.com:5600 
hcs.mainnet.mirrornode.hedera.com:5600
Community supported mirror node information can be found here:
Hedera Hashgraph
/
Build a Mirror Node Client
Constructor
Description
MirrorClient(<endpoint>)
Initializes the MirrorClient object
Java
JavaScript
Java
final MirrorClient mirrorClient = new MirrorClient(MIRROR_NODE_ADDRESS);
JavaScript
const mirrorClient = new MirrorClient(mirrorNodeAddress);
Concurrent Subscription Limit
A single client can make a maximum of 5 concurrent subscription calls per connection. 
Subscribe to a topic
Constructor
Description
MirrorConsensusTopicQuery()
Initializes the MirrorConsensusTopicQuery object
Method
Type
Description
setTopicId(<topicId>)
ConsensusTopicId
ID of the topic
subscribe(<mirrorClient, onNext, onError>)
MirrorClient, Consumer<MirrorConsensusTopicResponse>, Consumer<Throwable>
Subscribe to a topic
setStartTime(<startTime>)
Instant
The time to start receiving messages from the topic
setEndTime(<endTime>)
Instant
The time to stop receiving messages from the topic
setLimit(<limit>)
long
The limit to the number of messages to receive for that topic
Java
JavaScript
Java
new MirrorConsensusTopicQuery()
    .setTopicId(topicId)
    .subscribe(mirrorClient, resp -> {
        String messageAsString = new String(resp.message, StandardCharsets.UTF_8);
​
        System.out.println(resp.consensusTimestamp + " received topic message: " + messageAsString);
    },
        // On gRPC error, print the stack trace
        Throwable::printStackTrace);
JavaScript
new MirrorConsensusTopicQuery()
    .setTopicId(topicId)
    .subscribe(
        consensusClient,
        (message) => console.log(message.toString()),
        (error) => console.log(`Error: ${error}`)
    );

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Constructor	Description
`MirrorClient(<endpoint>)`	Initializes the MirrorClient object

Constructor	Description
`MirrorConsensusTopicQuery()`	Initializes the MirrorConsensusTopicQuery object

Method	Type	Description
`setTopicId(<topicId>)`	ConsensusTopicId	ID of the topic
`subscribe(<mirrorClient, onNext, onError>)`	MirrorClient, Consumer<MirrorConsensusTopicResponse>, Consumer<Throwable>	Subscribe to a topic
`setStartTime(<startTime>)`	Instant	The time to start receiving messages from the topic
`setEndTime(<endTime>)`	Instant	The time to stop receiving messages from the topic
`setLimit(<limit>)`	long	The limit to the number of messages to receive for that topic