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# Multi-Chain Client


MCC or Multi-Chain Client is a Typescript library that:
* allows querying nodes from any blockchain in a unified manner.
* Retrieved data is encapsulated in objects that hold all the original information and allow adding static, named properties.
* Implements a set of common methods used in FDC to calculate accounting information, such as balances, source and destination addresses, etc.

The main focus of the library is the block and transaction data structures and their associated methods for FDC attestation. The library is designed to be used in the Flare ecosystem but can also be used independently for blockchain data querying and processing.

## Underlying nodes

We recommend to deploy nodes from our docker [repo](https://github.com/flare-foundation/connected-chains-docker)

## Development notes

[Want to contribute?](./CONTRIBUTING.md)

## Security

If you have found a possible vulnerability please see [SECURITY.md](./SECURITY.md)

## Installation

The package is published to the NPM registry as [`@flarenetwork/mcc`](https://www.npmjs.com/package/@flarenetwork/mcc).

### Verification of published package

Each release is published with [NPM provenance](https://docs.npmjs.com/viewing-package-provenance),
which links the published package to the exact source commit and CI pipeline that built it.

To verify the integrity of the published package, you can use the following command:

```bash
npm audit signatures
```

This command checks the registry signatures and provenance attestations.
If a package has missing or invalid signatures or attestations, it returns an error.
This could indicate that a package has been tampered with.

# How to use

The most basic use of the MCC client is to query blocks and transactions from different blockchains. The code below demonstrates how to query a transaction from the Bitcoin and Algorand networks, showcasing the unification of query methods as well as the unification of responses.

In the MCC, connections to each blockchain are made through a different [MCC object](./mccClient/mccClient.md).

> **NOTE:**
> Networks are accessed through RPC endpoints that usually require some type of credentials.
> To start a connection credentials must be provided through the `MCCCreate` object, which is different depending on the connected chain.
>
> [Find more details here](./connectConfig.md).

Let's take a look at the minimal example to query a block and a transaction from the Bitcoin network by their height and transaction id (`txid`) respectively:

```javascript
// Configuration object
const connectConfig = {
   url: "https://myAwesomeBtcNode.com/",
   username: "user",
   password: "pass",
};

// MCC object used to connect to Bitcoin node
const MccClient = new MCC.BTC(connectConfig);

// Query block by its height
const block = await MccClient.getBlock(750_000);

// Log some details about the queried block
// Block height
console.log(block.number); // => 750000
// Block hash
console.log(block.blockHash); // => '<hash>'

// Query transaction
const transaction = await MccClient.getTransaction("<txid>");

// Log some details about the queried transaction
// Transaction timestamp
console.log(transaction.unixTimestamp); // => unixTimestamp
// Source addresses
console.log(transaction.sourceAddresses); // => [<address1>, <address2>, ...]
```

Now, to get block and transaction objects from a totally different blockchain such as Ripple, you only need to change the initialization of the MCC client, everything else remains the same.

```javascript
// Configuration object
const connectConfig = {
   url: "https://myAwesomeXrpNode.com/",
};

// MCC object used to connect to Ripple node
const MccClient = new MCC.XRP(connectConfig);

// Query block by its height
const block = await MccClient.getBlock(750_000);

// Log some details about the queried block
// Block height
console.log(block.number); // => 750000
// Block hash
console.log(block.blockHash); // => '<hash>'

// Query transaction
const transaction = await MccClient.getTransaction("<txid>");

// Log some details about the queried transaction
// Transaction timestamp
console.log(transaction.unixTimestamp); // => unixTimestamp
// Source addresses
console.log(transaction.sourceAddresses); // => [<address1>]
```
