Canton Explicit Contract Disclosure

Overview

In Daml, visibility is set by stakeholder annotations — normally you'd recreate a contract to change who sees it. Explicit contract disclosure instead delegates read rights to non-stakeholders off-ledger, so a party can use a contract it doesn't own as a transaction input. This is efficient, scalable data sharing (it's on by default; disable with participants.participant.ledger-api.enable-explicit-disclosure = false).

Why it exists — e.g. serve stock prices via a normal Web2 API and feed only the current price back into the ledger at the moment of use (instead of subscribing to thousands of updates), while keeping the same validation/security. It's the mechanism behind the Token Standard's disclosedContracts (canton-token-standard).

Read delegation

A party can acquire read rights during command submission over a contract where it's neither stakeholder nor informee — by attaching the contract to the command. Example: a Buyer exercises Offer_Accept on a Seller's Offer and must reference a Stock and a PriceQuotation it can't see. Without disclosure the submission fails citing missing visibility; with disclosure the Buyer attaches those contracts.

Disclosure bypasses visibility, not authorization: the command must still be well-authorized — actors must be properly authorized for the action.

The DisclosedContract

A stakeholder fetches the contract's CreatedEvent from the Ledger API and shares it off-ledger (HTTPS/SFTP/email). A DisclosedContract is built from three fields of that event:

• template_id — the contract's template id
• contract_id — the contract id
• created_event_blob — opaque blob encoding the contract

The created_event_blob is populated only on demand: request it with includeCreatedEventBlob: true on GetActiveContracts / GetUpdates / GetUpdateTrees (the same flag the Token Standard's InterfaceFilter uses). Only contracts created from Canton 2.8+ can be disclosed.