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0.1.3 • Public • Published


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This repository contains the Universal Ledger Agent, a TypeScript/Javascript library that acts as the main component of a plugin system that implements a message-based approach. The library can be used in browsers and Node.js backends.

Data Models

The following common data models are exposed so that independent plugins can exchange meaningful data.


Component interaction

Self Sovereign Identity

The ULA is primarily meant for managing Self Sovereign Identity data. A data model is provided for this purpose. All plugins must be able to translate their own data structures back to this data model.

Component interaction


In an existing project (with package.json), install universal-ledger-agent

npm install universal-ledger-agent --save


Full implementation guide (recommended)

In order to implement all available ULA plugins for the Holder in your Typescript application, please consult the full implementation guide.

Initializing ULA with one plugin (example)

To illustrate the usage of the ULA we will install one Holder plugin: ula-process-eth-barcode.

npm install ula-process-barcode --save

The process-barcode plugin accepts messages of which the type matches the type ethereum-qr. The ULA and plugin can then be used as follows:

import { ProcessEthBarcode } from 'ula-process-barcode'
import { 
} from 'universal-ledger-agent'
// The process-barcode plugin will need a http-service to send outgoing
// messages via http. This http-service is provided by the ULA
const httpService = new BrowserHttpService()
const processEthBarCode = new ProcessEthBarcode(httpService)
// Create an array of plugins  
const plugins = [ processEthBarCode ]
// Initialize the ULA with the plugins
const eventHandler = new EventHandler(plugins)
// A QR-Code contains e.g. the following message
const message = {
  type: "ethereum-qr",
  url: "https://the.issuer.com/ssif/sesion/e6c2c3e6-33b2-471f-875d-14f18917958c"
// the QR-code is captured by a camera device and then offered to
// the ULA. The 'callback' mechanism is used to retrieve information
// back from the plugin (or plugins) that handled the message
eventHandler.processMsg(message, callback)
// The callback function is called with an UlaResponse parameter, but
// this callback is only used when the ula-vp-controller plugin is installed!
const callback = function(response: UlaResponse) {
    console.log('statuscode:', response.statusCode)
    console.log('body:', response.body)

Running tests

Besides unit testing with Mocha, the effectivity of all tests are also measured with the Stryker mutation testing framework.

npm run test
npm run stryker

We aim to achieve a coverage of 100%. Stryker and/or mocha test scores below 80% will fail the build.


The ULA architecture has been designed in collaboration with Workday, Inc.


Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

License and disclaimer

apache-2.0 with a notice.

We discourage the use of this work in production environments as it is in active development and not mature enough.

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npm i universal-ledger-agent

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  • dlamers
  • jnieuwenhuijzen
  • rabomarnix