Smart Contract （中文版链接）

Languages

In Nebulas, there are two supported smart contract languages:

JavaScript
TypeScript

They are supported by the integration of Chrome V8, a widely used JavaScript engine developed by The Chromium Project for Google Chrome and Chromium web browsers.

Execution Model

The diagram below is the Execution Model of Smart Contract:

All src of Smart Contract and arguments are packaged in Transaction and deployed on Nebulas.
The execution of Smart Contract are divided into two phases:
1. Preprocess: inject tracing instruction, etc.
2. Execute: generate executable src and execute it.

Contracts

Contracts in Nebulas are similar to classes in object-oriented languages. They contain persistent data in state variables and functions that can modify these variables.

Writing Contract

A contract must be a Prototype Object or Class in JavaScript or TypeScript.

A Contract must include an init function, it will be executed only once when deploying. Functions, named starting with _ are private, can't be executed in Transaction. The others are all public and can be executed in Transaction.

Since Contract is executed in Chrome V8, all instance variables are in memory, it's not wise to save all of them to state trie in Nebulas. In Nebulas, we provide LocalContractStorage and GlobalContractStorage objects to help developers define fields needing to be saved to state trie. And those fields should be defined in constructor of Contract, before other functions.

The following is a sample contract:

class Rectangle {
    constructor() {
        // define fields stored to state trie.
        LocalContractStorage.defineProperties(this, {
            height: null,
            width: null,
        });
    }

    // init function.
    init(height, width) {
        this.height = height;
        this.width = width;
    }

    // calc area function.
    calcArea() {
        return this.height * this.width;
    }

    // verify function.
    verify(expected) {
        let area = this.calcArea();
        if (expected != area) {
            throw new Error("Error: expected " + expected + ", actual is " + area + ".");
        }
    }
}

Visibility

In JavaScript, there is no function visibility, all functions defined in prototype object are public.

In Nebulas, we define two kinds of visibility public and private:

public All functions whose name matches regexp ^[a-zA-Z$][A-Za-z0-9_$]*$ are public, except init. Public functions can be called via Transaction.
private All functions whose name starts with _ are private. A private function can only be called by public functions.

Global Objects

console

The console module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers.

The global console can be used without calling require('console').

console.info([...args])

...args <any> The console.info() function is an alias for console.log().

console.log([...args])

...args <any> Print args to Nebulas Logger at level info.

console.debug([...args])

...args <any> Print args to Nebulas Logger at level debug.

console.warn([...args])

...args <any> Print args to Nebulas Logger at level warn.

console.error([...args])

...args <any> Print args to Nebulas Logger at level error.

LocalContractStorage

The LocalContractStorage module provides a state trie based storage capability. It accepts string only key value pairs. And all data are stored to a private state trie associated with current contract address, only the contract can access them.

interface Descriptor {
    // serialize value to string;
    stringify?(value: any): string;

    // deserialize value from string;
    parse?(value: string): any;
}

interface DescriptorMap {
    [fieldName: string]: Descriptor;
}

interface ContractStorage {
    // get and return value by key from Native Storage.
    rawGet(key: string): string;
    // set key and value pair to Native Storage,
    // return 0 for success, otherwise failure.
    rawSet(key: string, value: string): number;

    // define a object property named `fieldname` to `obj` with descriptor.
    // default descriptor is JSON.parse/JSON.stringify descriptor.
    // return this.
    defineProperty(obj: any, fieldName: string, descriptor?: Descriptor): any;

    // define object properties to `obj` from `props`.
    // default descriptor is JSON.parse/JSON.stringify descriptor.
    // return this.
    defineProperties(obj: any, props: DescriptorMap): any;

    // define a StorageMap property named `fieldname` to `obj` with descriptor.
    // default descriptor is JSON.parse/JSON.stringify descriptor.
    // return this.
    defineMapProperty(obj: any, fieldName: string, descriptor?: Descriptor): any;

    // define StorageMap properties to `obj` from `props`.
    // default descriptor is JSON.parse/JSON.stringify descriptor.
    // return this.
    defineMapProperties(obj: any, props: DescriptorMap): any;

    // delete key from Native Storage.
    // return 0 for success, otherwise failure.
    del(key: string): number;

    // get value by key from Native Storage,
    // deserialize value by calling `descriptor.parse` and return.
    get(key: string): any;

    // set key and value pair to Native Storage,
    // the value will be serialized to string by calling `descriptor.stringify`.
    // return 0 for success, otherwise failure.
    set(key: string, value: any): number;
}

interface StorageMap {
    // delete key from Native Storage, return 0 for success, otherwise failure.
    del(key: string): number;

    // get value by key from Native Storage,
    // deserialize value by calling `descriptor.parse` and return.
    get(key: string): any;

    // set key and value pair to Native Storage,
    // the value will be serialized to string by calling `descriptor.stringify`.
    // return 0 for success, otherwise failure.
    set(key: string, value: any): number;
}

BigNumber

The BigNumber module use the bignumber.js(v4.1.0), a JavaScript library for arbitrary-precision decimal and non-decimal arithmetic. The contract can use BigNumber directly to handle the value of the transaction and other values transfer.

var value = new BigNumber(0);
value.plus(1);
...

Blockchain

The Blockchain module provides a object for contracts to obtain transactions and blocks executed by the current contract. Also, the NAS can be transferred from the contract and the address check is provided.

Blockchain API:

// current block 
Blockchain.block;

// current transaction, transaction's value/gasPrice/gasLimit auto change to BigNumber object
Blockchain.transaction;

// transfer NAS from contract to address
Blockchain.transfer(address, value);

// verify address
Blockchain.verifyAddress(address);

// get accout state
Blockchain.getAccountState(address);

// get previous block's hash
Blockchain.getPreBlockHash(offset);

// get previous block's random seed
Blockchain.getPreBlockSeed(offset);

properties:

block: current block for contract execution
- timestamp: block timestamp
- seed: random seed
- height: block height
transaction: current transaction for contract execution
- hash: transaction hash
- from: transaction from address
- to: transaction to address
- value: transaction value, a BigNumber object for contract use
- nonce: transaction nonce
- timestamp: transaction timestamp
- gasPrice: transaction gasPrice, a BigNumber object for contract use
- gasLimit: transaction gasLimit, a BigNumber object for contract use
transfer(address, value): transfer NAS from contract to address
- params:
  - address: nebulas address to receive NAS
  - value: transfer value, a BigNumber/Uint(recommended) object. The unit is wei, only integer value is valid.
- return (boolean value):
  - true: transfer success
  - false: transfer failed
verifyAddress(address): verify address
- params:
  - address: address need to check
- return (number value):
  - 87: user wallet address
  - 88: smart-contract address
  - 0: address is invalid
getAccountState(address): get account's balance and nonce
- params:
  - address: whose address you want to get
- return (JSON object):
  - balance: account's balance
  - nonce: account's nonce
getPreBlockHash(offset): get a previous block's hash
- params:
  - offset: the offset between the block and current block. This param should be an integer larger then 0 and less than current height. eg: If you want to get the hash of the previous block just before current block, the offset should be set as 1.
- return(string value):
  - hash: block hash
getPreBlockSeed(offset): get a previous block's seed
- params:
  - offset: same as the one in Blockchain.getPreBlockHash()
- return(string value):
  - seed: block random seed Example to use:

'use strict';

var SampleContract = function () {
    LocalContractStorage.defineProperties(this, {
        name: null,
        count: null
    });
    LocalContractStorage.defineMapProperty(this, "allocation");
};

SampleContract.prototype = {
    init: function (name, count, allocation) {
        this.name = name;
        this.count = count;
        allocation.forEach(function (item) {
            this.allocation.put(item.name, item.count);
        }, this);
        console.log('init: Blockchain.block.coinbase = ' + Blockchain.block.coinbase);
        console.log('init: Blockchain.block.hash = ' + Blockchain.block.hash);
        console.log('init: Blockchain.block.height = ' + Blockchain.block.height);
        console.log('init: Blockchain.transaction.from = ' + Blockchain.transaction.from);
        console.log('init: Blockchain.transaction.to = ' + Blockchain.transaction.to);
        console.log('init: Blockchain.transaction.value = ' + Blockchain.transaction.value);
        console.log('init: Blockchain.transaction.nonce = ' + Blockchain.transaction.nonce);
        console.log('init: Blockchain.transaction.hash = ' + Blockchain.transaction.hash);
    },
    transfer: function (address, value) {
        var result = Blockchain.transfer(address, value);
        console.log("transfer result:", result);
        Event.Trigger("transfer", {
			Transfer: {
				from: Blockchain.transaction.to,
				to: address,
				value: value
			}
		});
    },
    verifyAddress: function (address) {
    	 var result = Blockchain.verifyAddress(address);
        console.log("verifyAddress result:", result);
    },
	getAccountState: function (address) {
		var state = Blockchain.getAccountState(address);
		console.log("getAccountState result:", state);
	},
	getPreBlockHash: function (offset) {
		var hash = Blockchain.getPreBlockHash(offset);
		console.log("getPreBlockHash result", hash);
	},
	getPreBlockSeed: function (offset) {
		var seed = Blockchain.getPreBlockSeed(offset);
		console.log("getPreBlockSeed result", seed);
	}
};

module.exports = SampleContract;

Event

The Event module records execution events in contract. The recorded events are stored in the event trie on the chain, which can be fetched by GetEventsByHashAPI with the execution transaction hash. All contract event topics have a chain.contract. prefix before the topic they set in contract.

Event.Trigger(topic, obj);

topic: user-defined topic
obj: JSON object

You can see the example in SampleContract before.

Math.random

Math.random() returns a floating-point, pseudo-random number in the range from 0 inclusive up to but not including 1. The typical usage is:

"use strict";

var BankVaultContract = function () {};

BankVaultContract.prototype = {

	init: function () {},

	game: function(subscript){
	
		var arr =[1,2,3,4,5,6,7,8,9,10,11,12,13];

		for(var i = 0;i < arr.length; i++){
			var rand = parseInt(Math.random()*arr.length);
			var t = arr[rand];
			arr[rand] =arr[i];
			arr[i] = t;
		}

		return arr[parseInt(subscript)];
	},
};
module.exports = BankVaultContract;

Math.random.seed(myseed) if needed, you can use this method to reset random seed. The argument myseed must be a non empty string.

"use strict";

var BankVaultContract = function () {};

BankVaultContract.prototype = {

	init: function () {},
	
	game:function(subscript, myseed){
	
		var arr =[1,2,3,4,5,6,7,8,9,10,11,12,13];
		
		console.log(Math.random());
	
		for(var i = 0;i < arr.length; i++){
		
			if (i == 8) {
				// reset random seed with `myseed`
				Math.random.seed(myseed);
			}

			var rand = parseInt(Math.random()*arr.length);
			var t = arr[rand];
			arr[rand] =arr[i];
			arr[i] = t;
		}
		return arr[parseInt(subscript)];
	},
};

module.exports = BankVaultContract;

Date

All standardized APIs are available. Note that the timezone is fixed to "UTC+0" and locale to "en-US".

"use strict";

var BankVaultContract = function () {};

BankVaultContract.prototype = {
	init: function () {},
	
	test: function(){
		var d = new Date();
		return d.toString();
	}
};

module.exports = BankVaultContract;

Tips:

new Date()/Date.now() returns the timestamp of current block in milliseconds.

accept

this method is aimed to make it possible to send a binary transfer to a contract account. As the to is a smart contact address, which has declared a function accept() and it excutes correctly, the transfer will succeed. If the Tx is a non-binary Tx,it will be treated as a normal function.

"use strict";
var DepositeContent = function (text) {
	if(text){
        	var o = JSON.parse(text);
        	this.balance = new BigNumber(o.balance);//余额信息
        	this.address = o.address;
	}else{
        	this.balance = new BigNumber(0);
        	this.address = "";
        }
};

DepositeContent.prototype = {
	toString: function () {
  		return JSON.stringify(this);
	}
};

var BankVaultContract = function () {
	LocalContractStorage.defineMapProperty(this, "bankVault", {
 		parse: function (text) {
  			return new DepositeContent(text);
 		},
 		stringify: function (o) {
  			return o.toString();
 		}
	});
};

BankVaultContract.prototype = {
	init: function () {},

	save: function () {
  		var from = Blockchain.transaction.from;
  		var value = Blockchain.transaction.value;
  		value = new BigNumber(value);
  		var orig_deposit = this.bankVault.get(from);
  		if (orig_deposit) {
    			value = value.plus(orig_deposit.balance);
  		}
		
  		var deposit = new DepositeContent();
  		deposit.balance = new BigNumber(value);
  		deposit.address = from;
  		this.bankVault.put(from, deposit);
	},

	accept:function(){
		this.save();
		Event.Trigger("transfer", {
			Transfer: {
				from: Blockchain.transaction.from,
				to: Blockchain.transaction.to,
				value: Blockchain.transaction.value,
			}
   		});
	}

};
module.exports = BankVaultContract;

Uint

The Uint encapsulates 4 unsigned integer types based on bignumber.js, i.e., Uint64, Uint128, Uint256, Uint512.

Static properties:

MaxValue: an instance for the maximum value of specific uint type

Instance APIs:

div(o): /
- params:
  - o: divisor, must be the same type with this
- return: arithmetic result of the same type with this
pow(o): ^
- params:
  - o: exponent, must be the same type with this
- return: arithmetic result of the same type with this
minus(o): -
- params:
  - o: subtractor, must be the same type with this
- return: arithmetic result of the same type with this
mod(o): %
- params:
  - o: modulo, must be the same type with this
- return: arithmetic result of the same type with this
mul(o): *
- params:
  - o: multiplier, must be the same type with this
- return: arithmetic result of the same type with this
plus(o): +
- params:
  - o: addend, must be the same type with this
- return: arithmetic result of the same type with this
cmp(o)
- params:
  - o: must be the same type with this
- return:
  - 1: this > o
  - 0: this = o
  - -1: this < o
isZero()
- return:
  - true: this is 0
  - false: this is not 0
toString(base): convert this to string value
- params:
  - base: 2 ~ 64, default 10

Example:

'use strict';

var Uint64 = Uint.Uint64;
// var Uint128 = Uint.Uint128;
// var Uint256 = Uint.Uint256;
// var Uint512 = Uint.Uint512;

var Contract = function() {};

Contract.prototype = {
    init: function() {},

    testUint64: function() {
        var a  = new Uint64(7);
        var b = new Uint64("2");

        return {
            'a+b': a.plus(b).toString(10),  // 9
            'a-b': a.minus(b).toString(10), // 5
            'a*b': a.mul(b).toString(10),   // 14
            'a/b': a.div(b).toString(10),   // 3
            'a%b': a.mod(b).toString(10),   // 1
            'a^b': a.pow(b).toString(10),   // 49
            'a>b': a.cmp(b) == 1,           // true
            'a==0': a.isZero(),             // false
            'a': a.toString(),              // 7
            'MaxUint64': Uint64.MaxValue.toString(16), // ffffffffffffffff
        };
    }
};

module.exports = Contract;

require

The require function is used to explicitly load third-party libraries those Nebulas NVM doesn't load at startup.

Available libraries are:

crypto.js

The typical usage is:

    var crypto = require('crypto.js');
    ...

crypto

The crypto provides several frequently-used cryptographic hash functions. This module need to be explicitly required.

APIs:

sha256(str)
- param:
  - str: any string, case-sensitive
- return:
  - hexadecimal hash string, 64 chars
sha3256(str)
- param:
  - str: any string, case-sensitive
- return:
  - hexadecimal hash string, 64 chars
ripemd160(str)
- param:
  - str: any string, case-sensitive
- return:
  - hexadecimal hash string, 40 chars
md5(str)
- param:
  - str: any string, case-sensitive
- return:
  - hexadecimal hash string, 32 chars
base64(str)
- param:
  - str: any string, case-sensitive
- return:
  - base64 string
recoverAddress(alg, hash, sign): recover signer address from public key
- param:
  - alg: signature algorithm, only one value 1, indicating secp256k1
  - hash: input message, hex string, 64 chars
  - sign: signature, computed with signer's private key on hash
- return:
  - Nebulas address string, or null if failed.

Example:

'use strict';

// explicitly require
var crypto = require('crypto.js');

var Contract = function() {};

Contract.prototype = {
    init: function() {},

    sha256: function(str) {
        // str='Nebulas is a next generation public blockchain, aiming for a continuously improving ecosystem.'

        // return "a32d6d686968192663b9c9e21e6a3ba1ba9b2e288470c2f98b790256530933e0"
        return crypto.sha256(str);
    },

    sha3256: function(str) {
        // str='Nebulas is a next generation public blockchain, aiming for a continuously improving ecosystem.'

        // return "564733f9f3e139b925cfb1e7e50ba8581e9107b13e4213f2e4708d9c284be75b"
        return crypto.sha3256(str);
    },

    ripemd160: function(str) {
        // str='Nebulas is a next generation public blockchain, aiming for a continuously improving ecosystem.'

        // return "4236aa9974eb7b9ddb0f7a7ed06d4bf3d9c0e386"
        return crypto.ripemd160(str);
    },

    md5: function(str) {
        // str='Nebulas is a next generation public blockchain, aiming for a continuously improving ecosystem.'

        // return "9954125a33a380c3117269cff93f76a7"
        return crypto.md5(str);
    },

    base64: function(str) {
        // str='Nebulas is a next generation public blockchain, aiming for a continuously improving ecosystem.'

        // return "TmVidWxhcyBpcyBhIG5leHQgZ2VuZXJhdGlvbiBwdWJsaWMgYmxvY2tjaGFpbiwgYWltaW5nIGZvciBhIGNvbnRpbnVvdXNseSBpbXByb3ZpbmcgZWNvc3lzdGVtLg=="
        return crypto.base64(str);
    },

    recoverAddress: function(alg, hash, sign) {
        // alg = 1
        // hash = '564733f9f3e139b925cfb1e7e50ba8581e9107b13e4213f2e4708d9c284be75b'
        // sign = 'd80e282d165f8c05d8581133df7af3c7c41d51ec7cd8470c18b84a31b9af6a9d1da876ab28a88b0226707744679d4e180691aca6bdef5827622396751a0670c101'

        // return 'n1F8QbdnhqpPXDPFT2c9a581tpia8iuF7o2'
        return crypto.recoverAddress(alg, hash, sign);
    }
};

module.exports = Contract;

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Smart Contract （中文版链接）

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Smart Contract （中文版链接）

Languages

Execution Model

Contracts

Writing Contract

Visibility

Global Objects

console

console.info([...args])

console.log([...args])

console.debug([...args])

console.warn([...args])

console.error([...args])

LocalContractStorage

BigNumber

Blockchain

Event

Math.random

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accept

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