Node SDK (HCS18Client)

HCS18Client is your orchestrator for discovery and formation. It signs with your operator credentials, reads from mirror‑node, and exposes ergonomic helpers for each HCS‑18 operation.

Use it when:

• Your service coordinates multiple petals (e.g., proposing, tracking responses, creating the Flora)
• You need to poll and build local discovery state reliably
• You want to trigger HCS‑16 creation once you have a quorum

Initialize

import { HCS18Client, NetworkType } from '@hashgraphonline/standards-sdk';

const client = new HCS18Client({
  network: 'testnet' as NetworkType,
  operatorId: process.env.HEDERA_ACCOUNT_ID!,
  operatorKey: process.env.HEDERA_PRIVATE_KEY!,
});

Create Discovery Topic (when you’re bootstrapping)

const { topicId } = await client.createDiscoveryTopic({ ttlSeconds: 300 });

Announce (show up on the airwaves)

await client.announce({
  discoveryTopicId: topicId,
  data: {
    account: process.env.HEDERA_ACCOUNT_ID!,
    petal: { name: 'Petal-A', priority: 700 },
    capabilities: { protocols: ['hcs-16', 'hcs-18'] },
    valid_for: 10000,
  },
  memo: 'ready', // transaction memo (optional)
});

Propose / Respond (build consent)

const { sequenceNumber: proposalSeq } = await client.propose({
  discoveryTopicId: topicId,
  data: {
    proposer: '0.0.123',
    members: [
      { account: '0.0.123', priority: 700 },
      { account: '0.0.456', priority: 600, announce_seq: 101 },
    ],
    config: { name: 'Demo Flora', threshold: 2, purpose: 'testing' },
  },
});

await client.respond({
  discoveryTopicId: topicId,
  data: { responder: '0.0.456', proposal_seq: proposalSeq, decision: 'accept' },
});

Completion (hand‑off to HCS‑16)

import { FloraAccountManager } from '@hashgraphonline/standards-sdk';

// After enough acceptances, create the Flora and emit `complete`
const floraMgr = new FloraAccountManager(hederaClient, 'testnet');
const flora = await floraMgr.createFlora({
  displayName: 'Demo Flora',
  members: [
    { accountId: '0.0.123', publicKey: pubA, privateKey: privA },
    { accountId: '0.0.456', publicKey: pubB },
  ],
  threshold: 2,
  initialBalance: 10,
});

await client.complete({
  discoveryTopicId: topicId,
  data: {
    proposer: '0.0.123',
    proposal_seq: proposalSeq,
    flora_account: flora.floraAccountId.toString(),
    topics: {
      communication: flora.topics.communication.toString(),
      transaction: flora.topics.transaction.toString(),
      state: flora.topics.state.toString(),
    },
  },
});

Reading Discovery State (keep it tidy)

const messages = await client.getDiscoveryMessages(topicId, { sequenceNumber: 'gt:0', order: 'asc' });
// Filter by op and track announcements/proposals locally

Helper: Acceptance (a sensible default)

// proposal: { data: { members: [...] }, responses: Map<string, RespondData> }
const ready = client.isProposalReady(proposal);

Operational Tips

• Persist last seen sequence number per discovery topic.
• Tolerate mirror‑node lag: retry reads with small backoff windows.
• Log proposals and responses with timestamps for audits.
• Avoid hammering mirror‑node: batch reads and limit pages.