@meshsdk/hydra

A powerful TypeScript SDK for interacting with Hydra Heads on Cardano.

Overview

Hydra is a layer 2 protocol for Cardano that enables fast, low-cost transactions by creating off-chain "heads" where multiple parties can interact. This package provides a complete SDK for:

• Connecting to and managing Hydra Heads
• Committing and decommitting funds
• Building and submitting transactions within Hydra Heads
• Handling all Hydra protocol operations (init, abort, close, contest, fanout)
• Event-driven architecture for real-time updates

Installation

npm install @meshsdk/hydra

Quick Start

Basic Setup

import { HydraProvider, HydraInstance } from "@meshsdk/hydra";
import { BlockfrostProvider } from "@meshsdk/core";

const hydraProvider = new HydraProvider({
  httpUrl: "http://localhost:4001", // Your Hydra node URL
});

await hydraProvider.connect();

const blockchainProvider = new BlockfrostProvider("YOUR_BLOCKFROST_KEY");

const hydraInstance = new HydraInstance({
  provider: hydraProvider,
  fetcher: blockchainProvider,
  submitter: blockchainProvider,
});

Initialize a Head

await hydraProvider.init();

// Wait for all parties to commit
// Once all parties have committed, the head will open automatically

Commit Funds

const emptyCommitTx = await hydraInstance.commitEmpty();
await wallet.submitTx(emptyCommitTx);

Submit Transactions in Hydra Head

const txHash = await hydraProvider.newTx({
  type: "Tx ConwayEra",
  cborHex: unsignedTransactionCbor,
});

API Reference

HydraProvider

The main class for connecting to and managing Hydra Heads.

Constructor

new HydraProvider({
  httpUrl: string;       
  wsUrl?: string;      
  history?: boolean;     
  address?: string;      
})

Methods

Connection Management

• connect() - Establishes connection to the Hydra Head
• disconnect(timeout?: number) - Disconnects from the Hydra Head (default timeout: 5 minutes)

Head Lifecycle Commands

• init() - Initializes a new Hydra Head (only when status is Idle)
• abort() - Aborts a head before it opens (only during Initializing phase)
• close() - Closes an open head, starting the contest period
• contest() - Contests a closed head if needed
• fanout() - Finalizes the head closure and distributes funds

Transaction Operations

• newTx(transaction: hydraTransaction) - Submits a transaction to the open head
• recover(txHash: string) - Recovers a deposit transaction by its hash

Data Fetching (implements IFetcher)

• fetchUTxOs(address?: string) - Fetches UTxOs from the Hydra Head
• fetchProtocolParameters() - Fetches protocol parameters

Transaction Submission (implements ISubmitter)

• submitTx(tx: string) - Submits a transaction to the Hydra Head

Event Handling

• onStatusChange(event: string, callback: Function) - Listen to Hydra events
• onMessage(callback: Function) - Register a callback for all messages

Events

The provider emits various events:

• Greetings - Initial connection message with head status
• HeadIsInitializing - Head initialization started
• HeadIsOpen - Head is now open and ready
• HeadIsClosed - Head has been closed
• HeadIsAborted - Head was aborted
• TxValid - Transaction was accepted
• TxInvalid - Transaction was rejected
• Snapshot - New snapshot created
• Commit - New commit received
• Decommit - Decommit occurred
• And more...

HydraInstance

A higher-level interface for interacting with Hydra Heads, providing convenient methods for common operations.

Constructor

new HydraInstance({
  provider: HydraProvider;
  fetcher: 'blockchainProvider';       
  submitter: 'blockchainProvider';   
})

Methods

Commit Operations

• commitEmpty() - Creates an empty commit transaction (no funds)
• commitFunds(txHash: string, outputIndex: number) - Commits a specific UTxO to the head
• commitBlueprint(txHash: string, outputIndex: number, transaction: hydraTransaction) - Commits a UTxO as a blueprint transaction

Decommit Operations

• decommit() - Decommits all your funds from the head

Examples

Complete Workflow Example

import { HydraProvider, HydraInstance } from "@meshsdk/hydra";
import { BlockfrostProvider, MeshTxBuilder, MeshWallet } from "@meshsdk/core";

// Setup providers
const hydraProvider = new HydraProvider({
  httpUrl: "http://localhost:4001",
});

const blockchainProvider = new BlockfrostProvider("YOUR_BLOCKFROST_KEY");

const hydraInstance = new HydraInstance({
  provider: hydraProvider,
  fetcher: blockchainProvider,
  submitter: blockchainProvider,
});

await hydraProvider.connect();
await hydraProvider.init();

const commitTx = await hydraInstance.commitFunds(txHash, outputIndex);
await wallet.submitTx(commitTx);

hydraProvider.onMessage("HeadIsOpen", async () => {
  const txBuilder = new MeshTxBuilder({
    fetcher: blockchainProvider,
    submitter: blockchainProvider,
    params: await hydraProvider.fetchProtocolParameters(),
    isHydra: true, 
  });

  // Add your transaction logic
  const unsignedTx = await txBuilder
    .sendLovelace(address, "1000000")
    .complete();

  const txHash = await hydraProvider.newTx({
    type: "Tx ConwayEra",
    cborHex: unsignedTx,
  });

  console.log("Transaction submitted:", txHash);
});

// When done, close the head
await hydraProvider.close();
await hydraProvider.fanout();

Event-Driven Example

const hydraProvider = new HydraProvider({
  httpUrl: "http://localhost:4001",
});

await hydraProvider.connect();

hydraProvider.onMessage((message) => {
  switch (message.tag) {
    case "Greetings":
      console.log("Connected! Head status:", message.headStatus);
      break;
    case "HeadIsOpen":
      console.log("Head is now open!");
      break;
    case "TxValid":
      console.log("Transaction accepted:", message.transactionId);
      break;
    case "TxInvalid":
      console.error("Transaction rejected:", message.validationError);
      break;
    case "Snapshot":
      console.log("New snapshot:", message.snapshot);
      break;
  }
});

Requirements

• Node.js 16+ or modern browser with ES module support
• Access to a Hydra node (local or remote)
• Mesh SDK peer dependencies installed

Documentation

For more detailed documentation, examples, and guides, visit:

• Official Documentation: meshjs.dev/hydra
• Hydra Protocol Docs: hydra.family/head-protocol

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the terms specified in the LICENSE file.

Support

For support and questions:

• Check the documentation
• Open an issue on GitHub
• Visit the Mesh community forums

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