DAML Cast

Auto generates a fully typed OpenAPI spec from any .dar file.

What is this?

The Canton JSON Ledger API has every contract using the same blank endpoints:

POST /v1/create
Body: {}   - no field names, no types, nothing

DAML Cast reads your compiled .dar file and turns it into this:

POST /Agreement/MultiPartyAgreement/create
Body: {
  proposer:        string (daml-party)
  signatories:     array of party
  requiredParties: array of party
  terms:           string
}

Paste that into Swagger UI or feed it into openapi-generator to get a typed SDK in TypeScript, Python, Java automatically.

How to use it

1. Prerequisites

• Node.js v18+
• Daml SDK: curl -sSL https://get.digitalasset.com/install/install.sh | sh
• A .dar file

2. Inspect your .dar

dpm damlc inspect-dar --json your-contract.dar > inspect.json
unzip -p your-contract.dar "*/YourModule.daml"

The second command prints the Daml source templates, fields, choices.

3. Install dependencies

cd DAML_cast
npm install

4. Run Cast

node cast.js

Output: openapi.yaml

5. View it

cat openapi.yaml | pbcopy

Paste into https://editor.swagger.io ...and you'll see all your endpoints rendered with types.

Type mappings

Daml	JSON Schema	Notes
Text	string
Party	string	Full ID e.g. Alice::122084...
ContractId<T>	string	The long hex IDs from the ledger

and more...

What was built against

This prototype was built against a Sample .dar file present in the root dir test-agreement-1.3.0.dar, Feel free to alter the components based on your .dar needs and choices.

• Template: MultiPartyAgreement
• Fields: proposer, signatories, requiredParties, terms
• Choices:
  • AddParty (non-consuming)
  • Close (consuming)
• Package ID: 01da4dba66c232540ae7d1214cc22e32dc89c9f36c114c7f1dec959ce81b66ac

Generated 4 endpoints, 4 schemas, zero errors in Swagger.