Transactions — HCS‑27

Note

• These flows are typically orchestrated by the higher-level SDK client.
• Direct transaction construction is useful for custom pipelines, batching, or advanced key management.

Sources

• Go: GitHub

Topic Memo Convention

Checkpoint topics use the memo format hcs-27:<indexed>:<ttl>:<type>.

TypeScript

// Not yet available.

Go

import "github.com/hashgraph-online/standards-sdk-go/pkg/hcs27"

// Build a topic memo with 1-day TTL
memo := hcs27.BuildTopicMemo(86400)
// => "hcs-27:0:86400:0"

// Parse an existing memo
parsed, ok := hcs27.ParseTopicMemo("hcs-27:0:86400:0")
if ok {
	fmt.Printf("TTL: %d seconds\n", parsed.TTLSeconds)
}

Create Checkpoint Topic

TypeScript

// Not yet available.

Go

import hedera "github.com/hashgraph/hedera-sdk-go/v2"

memo := hcs27.BuildTopicMemo(86400)
tx := hedera.NewTopicCreateTransaction().
	SetTopicMemo(memo).
	SetAdminKey(operatorKey.PublicKey()).
	SetSubmitKey(operatorKey.PublicKey())

response, err := tx.Execute(hederaClient)
if err != nil {
	log.Fatal(err)
}

receipt, err := response.GetReceipt(hederaClient)
topicID := receipt.TopicID.String()

Publish Checkpoint Message

TypeScript

// Not yet available.

Go

import "encoding/json"

metadata := hcs27.CheckpointMetadata{
	Type:   "ans-checkpoint-v1",
	Stream: hcs27.StreamID{Registry: "my-app", LogID: "events"},
	Log: &hcs27.LogProfile{
		Algorithm: "sha-256",
		Leaf:      "rfc6962-leaf",
		Merkle:    "rfc6962-node",
	},
	Root: hcs27.RootCommitment{
		TreeSize:    50,
		RootHashB64: "base64url-encoded-root-hash",
	},
	BatchRange: hcs27.BatchRange{Start: 1, End: 50},
}

metadataBytes, _ := json.Marshal(metadata)

message := hcs27.CheckpointMessage{
	Protocol:  "hcs-27",
	Operation: "register",
	Metadata:  metadataBytes,
	Memo:      "initial checkpoint",
}

payload, _ := json.Marshal(message)
txMemo := hcs27.BuildTransactionMemo() // => "hcs-27:op:0:0"

topic, _ := hedera.TopicIDFromString(topicID)
response, err := hedera.NewTopicMessageSubmitTransaction().
	SetTopicID(topic).
	SetMessage(payload).
	SetTransactionMemo(txMemo).
	Execute(hederaClient)

Merkle Root Construction

TypeScript

// Not yet available.

Go

entries := []any{
	map[string]any{"id": 1, "action": "create", "value": "foo"},
	map[string]any{"id": 2, "action": "update", "value": "bar"},
	map[string]any{"id": 3, "action": "delete", "value": "baz"},
}

rootHash, err := hcs27.MerkleRootFromEntries(entries)
if err != nil {
	log.Fatal(err)
}

rootB64 := base64.RawURLEncoding.EncodeToString(rootHash)
fmt.Printf("Root: %s (tree size: %d)\n", rootB64, len(entries))

Inclusion Proof Verification

TypeScript

// Not yet available.

Go

leafHash, _ := hcs27.LeafHashHexFromEntry(entries[1])

valid, err := hcs27.VerifyInclusionProof(
	1,                   // leafIndex
	3,                   // treeSize
	leafHash,            // leaf hash (hex)
	auditPath,           // []string of base64 sibling hashes
	expectedRootB64,     // expected root (base64)
)
if err != nil {
	log.Fatal(err)
}
fmt.Printf("Inclusion proof valid: %v\n", valid)

Consistency Proof Verification

TypeScript

// Not yet available.

Go

consistent, err := hcs27.VerifyConsistencyProof(
	50,              // old tree size
	150,             // new tree size
	oldRootB64,      // old root (base64)
	newRootB64,      // new root (base64)
	consistencyPath, // []string of base64 proof nodes
)
if err != nil {
	log.Fatal(err)
}
fmt.Printf("Trees are consistent: %v\n", consistent)