Ogmios Client Starter Kit

This repo provides a NodeJS package with several examples of how to leverage Ogmios typescript client to:

✓ Execute ledger state and network queries;
✓ Synchronize blocks from the chain;
✓ Monitor a local mempool;
✓ Submit or evaluate transactions

Dev Environment

Option #1: Manual Setup

For running this starter kit you'll need access to an Ogmios instance connected to a fully synced instance of a Cardano Node. You can read the setup instructions on the documentation for each corresponding component

Option #2: Demeter.run

If you don't want to install the required components yourself, you can use Demeter.run platform to create a cloud environment with access to common Cardano infrastrcuture. The following command will open this repo in a private, web-based VSCode IDE with access to a shared Cardano Node and Ogmios.

Getting started

Note The following instructions assumes that you're using a Cardano Workspace.

Once you've finished with the Cardano Workspace creation process, you should be able to access this codebase from a VSCode IDE instance. Open this README file using the Markdown Preview command to continue this guide from inside the workspace.

Since this is a Node.js package, the next step is to install the dependencies. This can be done by opening the embedded terminal within the VSCode IDE.

Note There's no need to install NodeJS or NPM, these tools are already available as part of your workspace.

From within the terminal, run the following yarn command to install the dependencies:

yarn

When yarn finishes, you should be able to execute the examples.

Run the Local-State-Query example

This example shows how to connect to Ogmios using the Local-State-Query mini-protocol, which allows us to execute queries about the state of the node using request / response semantics.

The code for this example lives in src/local-state-query.ts. To start the example, you can run the script called local-state-query defined in the package.json file. Open the embedded VSCode terminal and execute the following command:

yarn local-state-query

Run the Local-Chain-Sync example

This example shows how to connect to Ogmios using the Local-Chain-Sync mini-protocol, which allows us to synchronize the state of the chain by "pulling" block data.

The code for this example lives in src/local-chain-sync.ts. To start the example, you can run the script called local-chain-sync defined in the package.json file. Open the embedded VSCode terminal and execute the following command:

yarn local-chain-sync

Run the Local-Mempool-Monitor example

This example shows a basic scenario of fetching transactions from your node mempool. If your node is running as a simple relay, then the transactions list is likely empty. However, you can try visualizing transactions in the mempool by submitting some while the example scenario is running.

Note that this example never exits and will await for changes in the mempool to happen.

The code for this example lives in src/local-mempool-monitor.ts. To start the example, you can run the script called local-mempool-monitor defined in the package.json file. Open the embedded VSCode terminal and execute the following command:

yarn local-mempool-monitor

---

Warning The local-chain-sync example does not terminate, it'll start synchronizing blocks from the network tip until your stop it (CTRL-C). You'll also notice that it always starts with a Roll backward instruction, from where it'll continue syncing.

FAQ

How do I connect to the Ogmios instance?

Ogmios works as a lightweight bridge between the Cardano Node and HTTP web-socket clients. There are many client libraries available but we'll be using only the Typescript client for this starter-kit.

To initialize the client library, the host and port where the **Ogmios instance is listening needs to be specified.

Note When running inside a Cardano Workspace, these values are already available as environmental variables: OGMIOS_HOST and OGMIOS_PORT.

The following snippet shows an exmample of how to setup an "interaction context" that will hold the connection between your client and the Ogmios instance.

import { createInteractionContext } from '@cardano-ogmios/client'

const context = createInteractionContext(
    err => console.error(err),
    () => console.log("Connection closed."),
    { connection: { host: process.env.OGMIOS_HOST, port: parseInt(process.env.OGMIOS_PORT!) } }
);

Where can I get more info about Ogmios?

Ogmios is developed by Cardano Solutions. The codebase lives in the CardanoSolutions/Ogmios Github repository. Technical documentation and API reference can be found at ogmios.dev.

DIY Ideas

Here are some ideas on how to continue the development of this starter kit as a way to understand the rest of Ogmios features. These tasks can be acomplished by reading the Ogmios typescript client documentation and some extrapolation from the existing examples:

• Query a particular UTxO by output reference.

• Submit a transaction using the Transaction Submission mini-protocol.

• Check the state of the mempool using the Mempool Monitoring mini-protocol.