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https://github.com/sCrypt-Inc/scryptlib

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# scryptlib

Javascript/TypeScript SDK for integration of Bitcoin SV Smart Contracts written in the sCrypt language.



[![Build Status](https://travis-ci.com/sCrypt-Inc/scryptlib.svg?branch=master)](https://travis-ci.com/sCrypt-Inc/scryptlib)



You can install `scryptlib` in your project as below:



```

$ npm install scryptlib

```



A smart contract is compiled to a locking script template. A contract function call is transformed to an unlocking script. Developers are responsible for setting the locking and unlocking scripts of a transaction properly before sending it to the Bitcoin network. This may include some actions described below:



* Instantiate locking script: replace the constructor formal parameters, represented by placeholders in the locking script template, with actual parameters/arguments to form the complete locking script.



* Assemble unlocking script: convert the arguments of a contract function call to script format and concatenate them to form the unlocking script.



By using `scryptlib`, both scripts can be obtained with ease.



## Contract Artifact File



The compiler output results in a JSON file. It’s a representation used to build locking and unlocking scripts. We call this file a [**contract artifact file**](docs/counter_debug.json).



There are three ways to generate this file (named as `.json`):



1. Use [**sCrypt VS Code extension**](https://marketplace.visualstudio.com/items?itemName=bsv-scrypt.sCrypt) to compile manually;

2. Use the function `compile` programmatically:

```javascript

  import { compile } from 'scryptlib';



  ...



  compile(

    {

      path: contractFilePath  //  the file path of the contract

    },

    {

      artifact: true  // set this flag to be `true` to get the artifact file output

      asm: true // set this flag to be `true` to get the asm file output

      optimize: false //set this flag to be `true` to get optimized asm opcode

      sourceMap: true //set this flag to be `true` to get source map

      hex: true //set this flag to be `true` to get hex format script

      stdout: false//set this flag to be `true` to make that the compiler will output the compilation result through stdout

    }

  );

```



3. `compileAsync` is the asynchronous version of the function `compile`



```javascript

  import { compileAsync } from 'scryptlib';



  ...



  compileAsync(

    {

      path: contractFilePath  //  the file path of the contract

    },

    settings

  ) : Promise;

```



4. Run `npx` command in CLI:

```sh

  # install compiler binary

  npx scryptlib download

  # the latest compiler may be incompatible with the current scryptlib

  npx scryptlib download latest

  # compiling contract

  npx scryptlib compile your_directory/your_scrypt.scrypt

```



## Types



### 1. Basic Types

All basic types of the **sCrypt** language have their corresponding javascript classes in scryptlib. In this way, the type of parameters could be checked and potential bugs can be detected before running.



|  Types (scrypt) | scryptlib (javascript/typescript)|

| :---------: | :--------: |

| `int` | `Int(1)` or `number` or `bigint` |

| `bool` | `Bool(true)` or `boolean` |

| `bytes` | `Bytes('0001')` or `stringToBytes("hello world 😊")`|

| `PubKey` | `PubKey('0001')`|

| `PrivKey` | `PrivKey(1)`|

| `Sig` | `Sig('0001')`|

| `Ripemd160` | `Ripemd160('0001')`|

| `Sha1` | `Sha1('0001')`|

| `Sha256` | `Sha256('0001')`|

| `SigHashType` | `SigHashType('01')`|

| `SigHashPreimage` | `SigHashPreimage('010001')`|

| `OpCodeType` | `OpCodeType('76')`|



### 2. Array Types



scryptlib uses javascript array to represent the array types of the **sCrypt** language.



```typescript



[[1, 3, 1]] // represent `int[1][3]` in **sCrypt** language



[Bytes("00"), Bytes("00"), Bytes("00")] // represent `bytes[3]` in **sCrypt** language



```



### 3. Structure and Type Aliases



The structure in sCrypt needs to be represented by object in **SDK**. When creating a structure, all members must specify values. Use `.` to access structure members.



A type alias needs to be represented by a value corresponding to the original type



Structure and type aliases defined in sCrypt:



```ts

/*Person is structure and Male, Female are type aliases */

struct Person {

    bytes addr;

    bool isMale;

    int age;

}



type Male = Person;

type Female = Person;



contract PersonContract {

    Male man;

    Female woman;

    ...



}

```



Access Structure and type aliases by **SDK** :



```typescript



const PersonContract = buildContractClass(loadArtifact('person.json'));



let man = {

    isMale: true,

    age: 14n,

    addr: Bytes("68656c6c6f20776f726c6421")

  };



man.age = 20n;



let woman = {

    isMale: false,

    age: 18n,

    addr: Bytes("68656c6c6f20776f726c6421")

  };



woman.addr = Bytes("")



const instance = new PersonContract(man, woman);

```



### 4. HashedMap

[HashedMap](./docs/hashedmap_en.md) is a hashtable-like data structure.



### 5. Library



Library is another composite types. When the constructor parameter of the contract contains library, we have to pass an array according to the constructor parameter of the library.



Library defined in sCrypt:



```javascript

library L {

  private int x;



  constructor(int a, int b) {

    this.x = a + b;

  }

  function f() : int {

    return this.x;

  }

}



contract Test {

  public int x;

  L l;



  public function unlock(int x) {

    require(this.l.f() == x + this.x);

  }

}

```



Access Library by **SDK** :



```typescript



const Test = buildContractClass(loadArtifact('test.json'));



let l = [1n, 2n];



let test = new Test(1n, l);

```



Sometimes the constructor parameters of the library may be generic types. At this time, the sdk will deduce the generic type based on the constructor arguments you pass.



## Deploy a Contract and Call Its Function



Both **deploying a contract** and **calling a contract function** are achieved by sending a transaction. Generally speaking,



* deploying a contract needs the locking script in the output of this transaction to be set properly;

* calling a contract function needs the unlocking script in the input of this transaction to be set properly.



There are 2 steps.

### 1. Get Locking and Unlocking Script

You can use the artifact file to build a reflected contract class in Javascript/TypeScript like this:

```typescript

const MyContract = buildContractClass(JSON.parse(artifactFileContent));

```

To create an instance of the contract class, for example:

```typescript

const instance = new MyContract(1234n, true, ...parameters);

```

To get the locking script, use:

```typescript

const lockingScript = instance.lockingScript;

// To convert it to ASM/hex format

const lockingScriptASM = lockingScript.toASM();

const lockingScriptHex = lockingScript.toHex();

```

To get the unlocking script, just call the function and turn the result to `bsv.Script` object, for example:

```typescript

const funcCall = instance.someFunc(new Sig('0123456'), new Bytes('aa11ff'), ...parameters);

const unlockingScript = funcCall.toScript();

// To convert it to ASM/hex format

const unlockingScriptASM = unlockingScript.toASM();

const unlockingScriptHex = unlockingScript.toHex();

```



### 2. Wrap Locking and Unlocking Script into a Transaction

[Chained APIs](./docs/chained_api_en.md) make building transactions super easy.



## Local Unit Tests



A useful method `verify(txContext)` is provided for each contract function call. It would execute the function call with the given context locally. The `txContext` argument provides some context information of the current transaction, **needed only if signature is checked inside the contract**.

```typescript

{

  tx?: bsv.Transaction;                 // current transaction represented in bsv.Transaction object

  inputIndex?: number;      // input index, default value: 0

  /**

   * @deprecated no need any more

   */

  inputSatoshis?: number;   // input amount in satoshis

  opReturn?: string;        // contract state in ASM format

  opReturnHex?: string;     // contract state in hex format

}

```

It returns an object:

```typescript

{

  success: boolean;       // script evaluates to true or false

  error: string;          // error message, empty if success

}

```



It usually appears in unit tests, like:



```typescript

const context = { tx, inputIndex, inputSatoshis };



// 1) set context per verify()

const funcCall = instance.someFunc(Sig('0123456'), Bytes('aa11ff'), ...parameters);

const result = funcCall.verify(context);

// 2) alternatively, context can be set at instance level and all following verify() will use it

instance.txContext = context;

const result = funcCall.verify();



expect(result.success, result.error).to.be.true;

assert.isFalse(result.success, result.error);

```



## Contracts with State

sCrypt offers [stateful contracts](https://scryptdoc.readthedocs.io/en/latest/state.html#stateful-contract). Declare any property that is part of the state with a decorator `@state` in a contract, for example:

```typescript

contract Counter {

    @state

    int counter;



    constructor(int counter) {

        this.counter = counter;

    }

}

```



Use the initial state to instantiate the contract and read the state by accessing the properties of the contract instance.



```typescript

const instance = new Counter(0n);



let state = instance.counter;

// update state

instance.counter++;

```



Then use `instance.getNewStateScript()` to get a locking script that includes the new state. It accepts an object as a parameter. Each key of the object is the name of a state property, and each value is the value of the state property. You should provide all state properties in the object.



```typescript

const tx = newTx(inputSatoshis);

let newLockingScript = instance.getNewStateScript({

    counter: 1

});



tx.addOutput(new bsv.Transaction.Output({

  script: newLockingScript,

  satoshis: outputAmount

}))



preimage = getPreimage(tx, instance.lockingScript, inputSatoshis)



```



You can also access the state of the contract by accessing the properties of the instance.



```typescript



instance.counter++;

instance.person.name = Bytes('0001');



```



You can also maintain state manually to, for example, optimize your contract or use customized state de/serialization [rawstate](docs/rawstate.md).



## Instantiate Inline Assembly Variables

Assembly variables can be replaced with literal Script in ASM format using `replace()`. Each variable is prefixed by its unique scope, namely, the contract and the function it is under.

```typescript

const asmVars = {

  'contract1.function1.variable1': 'ff41',

  'contract2.function2.variable2': 'OP_4'

};

instance.replaceAsmVars(asmVars);

```



You could find more examples using `scryptlib` in the [boilerplate](https://github.com/sCrypt-Inc/boilerplate) repository.



## Construct contracts from raw transactions



In addition to using a constructor to create a contract, you can also use a raw transaction to construct it.



```typescript

const axios = require('axios');



const Counter = buildContractClass(loadArtifact("counter_debug.json"));

let response = await axios.get("https://api.whatsonchain.com/v1/bsv/test/tx/7b9bc5c67c91a3caa4b3212d3a631a4b61e5c660f0369615e6e3a969f6bef4de/hex")

// constructor from raw Transaction.

let counter = Counter.fromTransaction(response.data, 0/** output index**/);



// constructor from Utxo lockingScript

let counterClone = Counter.fromHex(counter.lockingScript.toHex());



```



## Support browsers that are not compatible with BigInt



Some contracts use ``Bigint`` to construct or unlock. but some browsers do not support ``Bigint``, such as IE11. In this case, we use strings to build ``Bigint``.



```typescript



// polyfill



import 'react-app-polyfill/ie11';  

import 'core-js/features/number';

import 'core-js/features/string';

import 'core-js/features/array';



let demo = new Demo(Int("11111111111111111111111111111111111"), 1n);



let result = demo.add(Int("11111111111111111111111111111111112")).verify();



console.assert(result.success, result.error)

```