Hcs Consensus

Overview

HCS provides globally ordered, timestamped messages on topics — ideal for tamper-evident logs without deploying contracts. Pair ledger submissions with Mirror Node reads/subscriptions per Consensus Service SDK docs.

When to use this skill

• Building append-only audit feeds with nanosecond-resolution consensus timestamps.
• Splitting payloads larger than single-message limits using deterministic chunk framing.

Prerequisites

• Operator account with HBAR for topic creation + message submits.

Workflow

1. Create topic — TopicCreateTransaction; optionally set submitKey, adminKey, memo.

   Reference: scripts/create-topic.js.

2. Submit message — TopicMessageSubmitTransaction with UTF-8 or binary payloads.

   Reference: scripts/submit-message.js.

3. Chunk large payloads — iterate chunks ≤ ~900 bytes payload budget per submit after overhead — verify limits on network release notes.

   Reference: scripts/chunked-submit.js.

4. Subscribe (mirror GRPC) — TopicMessageQuery.subscribe(client, onErr, onMsg) streams live messages.

   Reference: scripts/subscribe-topic.js.

5. Poll REST — GET /api/v1/topics/{id}/messages with topic.timestamp pagination parameters.

6. Delete topic — TopicDeleteTransaction requires admin key signatures.

Examples

Example 1

“Log ERP audit events with immutable ordering.”

Publish compact JSON lines to HCS; consumers replay via Mirror REST sorted by consensus_timestamp.

Example 2

“Only our payroll signer may publish.”

Set submitKey to payroll public key; rotations via TopicUpdateTransaction.

Example 3

“Payload is a 50 KB JSON file.”

Chunk + store manifest linking chunk sequence — verify ordering during reassembly.

Troubleshooting

References

• Local: references/hcs-use-cases.md, references/chunking.md, references/nano-timestamps.md
• Docs: Create a topic, Submit a message