Contract Instantiation

Before interacting with smart contracts on the BCH network, the CashScript SDK needs to instantiate a Contract object. This is done by providing the contract's information and constructor arguments. After this instantiation, the CashScript SDK can interact with BCH contracts.

Contract class

The Contract class is used to represent a CashScript contract in a JavaScript object. These objects can be used to retrieve information such as the contract's address and balance. They can be used to interact with the contract by calling the contract's functions.

Constructor

new Contract(
artifact: Artifact,
constructorArgs: Argument[],
provider?: NetworkProvider,
)

A CashScript contract can be instantiated by providing an Artifact object, a list of constructor arguments, and optionally a NetworkProvider.

An Artifact object is the result of compiling a CashScript contract. See the Language Documentation for more information on Artifacts. Compilation can be done using the standalone cashc CLI or programmatically with the cashc NPM package (see CashScript Compiler).

A NetworkProvider is used to manage network operations for the CashScript contract. By default, a mainnet ElectrumNetworkProvider is used, but alternative network providers can be used. See the section on NetworkProvider below.

Example

const { Contract, ElectrumNetworkProvider } = require('cashscript');
const { compileFile } = require('cashc');
// Import an artifact JSON file that was compiled earlier
const P2PKH = require('./p2pkh.json');
// Or compile a contract file
const P2PKH = compileFile(path.join(__dirname, 'p2pkh.cash'));
const provider = new ElectrumNetworkProvider('testnet');
const contract = new Contract(P2PKH, [alicePkh], provider);

address

contract.address: string

A contract's address can be retrieved through the address member field.

Example

console.log(contract.address)

opcount

contract.opcount: number

The number of opcodes in the contract's bytecode can be retrieved through the opcount member field. This is useful to ensure that the contract is not too big, since Bitcoin Cash smart contracts can contain a maximum of 201 opcodes.

Example

assert(contract.opcount <= 201)

bytesize

contract.bytesize: number

The size of the contract's bytecode in bytes can be retrieved through the bytesize member field. This is useful to ensure that the contract is not too big, since Bitcoin Cash smart contracts can be 520 bytes at most.

note

When writing covenant contracts, the de facto limit is actually closer to 360 bytes due to technical factors.

Example

console.log(contract.bytesize)

getRedeemScriptHex()

contract.getRedeemScriptHex: string

Returns the contract's redeem script encoded as a hex string.

Example

console.log(contract.getRedeemScriptHex())

getBalance()

async contract.getBalance(): Promise<number>

Returns the total balance of the contract in satoshis. Both confirmed and unconfirmed balance is included in this figure.

Example

const contractBalance = await contract.getBalance()

GetUtxos()

async contract.getUtxos(): Promise<Utxo[]>

Returns all UTXOs that can be spent by the contract. Both confirmed and unconfirmed UTXOs are included.

Example

const utxos = await contract.getUtxos()

Contract functions

contract.functions.<functionName>(...args: Argument[]): Transaction

The main way to use smart contracts once they have been instantiated is through the functions defined in the CashScript source code. These functions can be found by their name under functions member field of a contract object. To call these functions, the parameters need to match ones defined in the CashScript code.

These contract functions return an incomplete Transaction object, which needs to be completed by providing outputs of the transaction. More information about sending transactions is found on the Sending Transactions page.

Example

import { alice } from './somewhere';
const tx = await contract.functions
.transfer(new SignatureTemplate(alice))
.to('bitcoincash:qrhea03074073ff3zv9whh0nggxc7k03ssh8jv9mkx', 10000)
.send()

SignatureTemplate

new SignatureTemplate(signer: Keypair | Uint8Array | string, hashtype?: HashType)

You may notice the SignatureTemplate object in the example above. When a contract function has a sig parameter, it requires a cryptographic signature over the spending transaction. But to generate this signature, the transaction needs to be built first, which is not yet the case when a contract function is first called.

So in the place of a signature, a SignatureTemplate can be passed, which will automatically generate the correct signature using the signer parameter. This signer can be any representation of a private key, including BITBOX/BCHJS' ECPair, bitcore-lib-cash' PrivateKey, WIF strings, or raw private key buffers. This ensures that any BCH library can be used.

caution

When calling a covenant function, the first SignatureTemplate parameter is used to generate the required sighash preimage. This is generally fine, but you should take extra care when using non-default hashtypes.

Example

const wif = 'L4vmKsStbQaCvaKPnCzdRArZgdAxTqVx8vjMGLW5nHtWdRguiRi1';
const sig = new SignatureTemplate(wif, HashType.SIGHASH_ALL);

NetworkProvider

The CashScript SDK needs to connect to the BCH network to perform certain operations, like retrieving the contract's balance, or sending transactions. All network functionality that the CashScript SDK needs is encapsulated in a network provider. This allows different network providers to be used and makes it easy to swap out dependencies.

ElectrumNetworkProvider

new ElectrumNetworkProvider(network?: Network, electrum?: ElectrumCluster)

The ElectrumNetworkProvider uses electrum-cash to connect to the BCH network. This is the recommended provider for most use cases and is used as the default when no other provider is provided. Both network and electrum parameters are optional, and they default to mainnet and a 2-of-3 ElectrumCluster with a number of reliable electrum servers.

Example

const provider = new ElectrumProvider('testnet');

FullStackNetworkProvider

new FullStackNetworkProvider(network: Network, bchjs: BCHJS)

The FullStackNetworkProvider uses FullStack.cash' infrastructure to connect to the BCH network. FullStack.cash' offers dedicated infrastructure and support plans for larger projects. Both network and bchjs parameters are mandatory, where bchjs is an instance of FullStack.cash' BCHJS.

Example

const BCHJS = require('@psf/bch-js');
const restURL = 'https://api.fullstack.cash/v3/';
const apiToken = 'eyJhbGciO...'; // Your JWT token here.
const bchjs = new BCHJS({ restURL, apiToken });
const provider = new FullStackNetworkProvider('mainnet', bchjs);

BitboxNetworkProvider

new BitboxNetworkProvider(network: Network, bitbox: BITBOX)

The BitboxNetworkProvider uses Bitcoin.com's BITBOX to connect to the BCH network. Because BITBOX is no longer officially maintained it is not recommended to use this network provider, and it is only available for compatibility with older projects. Both network and bitbox parameters are mandatory, where bitbox is a BITBOX instance.

Example

const BITBOX = require('bitbox-sdk');
const bitbox = new BITBOX({ restURL: 'https://rest.bitcoin.com/v2/' });
const provider = new FullStackNetworkProvider('mainnet', bitbox);

BitcoinRpcNetworkProvider

new BitcoinRpcNetworkProvider(network: Network, url: string, options?: any)

The BitcoinRpcNetworkProvider uses a direct connection to a BCH node. Note that a regular node does not have indexing, so any address of interest (e.g. the contract address) need to be registered by the node before sending any funds to those addresses. Because of this it is recommended to use a different network provider unless you have a specific reason to use the RPC provider.

Example

const provider = new BitcoinRpcNetworkProvider('mainnet', 'http://localhost:8332');

Custom NetworkProviders

A big strength of the NetworkProvider setup is that it allows you to implement custom providers. So if new BCH libraries are created in the future, it is simple to use them with CashScript. This also potentially enables the CashScript SDK to be used with other (partially) compatible networks, such as BTC or BSV.

NetworkProvider interface

interface NetworkProvider {
/**
* Variable indicating the network that this provider connects to.
*/
network: Network;
/**
* Retrieve all UTXOs (confirmed and unconfirmed) for a given address.
* @param address The CashAddress for which we wish to retrieve UTXOs.
* @returns List of UTXOs spendable by the provided address.
*/
getUtxos(address: string): Promise<Utxo[]>;
/**
* @returns The current block height.
*/
getBlockHeight(): Promise<number>;
/**
* Retrieve the Hex transaction details for a given transaction ID.
* @param txid Hex transaction ID.
* @throws {Error} If the transaction does not exist
* @returns The full hex transaction for the provided transaction ID.
*/
getRawTransaction(txid: string): Promise<string>;
/**
* Broadcast a raw hex transaction to the network.
* @param txHex The raw transaction hex to be broadcast.
* @throws {Error} If the transaction was not accepted by the network.
* @returns The transaction ID corresponding to the broadcast transaction.
*/
sendRawTransaction(txHex: string): Promise<string>;
}
type Network = 'mainnet' | 'testnet' | 'regtest';
interface Utxo {
txid: string;
vout: number;
satoshis: number;
}

CashScript Compiler

Generally CashScript contracts are compiled to an Artifact JSON file using the CLI compiler. As an alternative to this, CashScript contracts can be compiled from within JavaScript apps using the cashc package. This package needs to be installed separately and exports two compilation functions.

npm install cashc

compileFile()

compileFile(sourceFile: string): Artifact

Compiles a CashScript contract from a source file. This is the recommended compile method if you're using Node.js and you have a source file available.

Example

const P2PKH = compileFile(path.join(__dirname, 'p2pkh.cash'));

compileString()

compileString(sourceCode: string): Artifact

Compiles a CashScript contract from a source code string. This is the recommended compile method if you're building a webapp, because compileFile() only works from a Node.js context. This is also the recommended method if no source file is locally available (e.g. the source code is retrieved with a REST API).

const baseUrl = 'https://raw.githubusercontent.com/Bitcoin-com/cashscript'
const result = await fetch(`${baseUrl}/master/examples/p2pkh.cash`);
const source = await result.text();
const P2PKH = compileString(source);