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What is embark

Embark is a framework that allows you to easily develop and deploy DApps.

With Embark you can:

Automatically deploy contracts and make them available in your JS code. Embark watches for changes, and if you update a contract, Embark will automatically redeploy the contracts (if needed) and the dapp.
Use any build pipeline or tool you wish, including grunt and meteor.
Do Test Driven Development with Contracts using Javascript.
Easily deploy to & use decentralized systems such as IPFS.
Keep track of deployed contracts, deploy only when truly needed.
Quickly create advanced DApps using multiple contracts.

See the Wiki for more details.

Installation

Requirements: geth (1.0.0), solc (0.1.0) or serpent (develop), node (0.12.2) and npm

For specs: pyethereum, ethertdd.py

$ npm install -g embark-framework grunt-cli

See Complete Installation Instructions.

Usage - Demo

You can easily create a sample working DApp with the following:

$ embark demo
$ cd embark_demo

To run the ethereum node for development purposes simply run:

$ embark blockchain

By default embark blockchain will mine a minimum amount of ether and will only mine when new transactions come in. This is quite usefull to keep a low CPU. The option can be configured at config/blockchain.yml

Then, in another command line:

$ embark run

This will automatically deploy the contracts, update their JS bindings and deploy your DApp to a local server at http://localhost:8000

Note that if you update your code it will automatically be re-deployed, contracts included. There is no need to restart embark, refreshing the page on the browser will do.

Creating a new DApp

$ embark new AppName
$ cd AppName

DApp Structure

  app/
    |___ contracts/ #solidity or serpent contracts
    |___ html/
    |___ css/
    |___ js/
  config/
    |___ blockchain.yml #environments configuration
    |___ contracts.yml  #contracts configuration
    |___ server.yml     #server configuration
  spec/
    |___ contracts/ #contracts tests

Solidity/Serpent files in the contracts directory will automatically be deployed with embark run. Changes in any files will automatically be reflected in app, changes to contracts will result in a redeployment and update of their JS Bindings

Using Contracts

Embark will automatically take care of deployment for you and set all needed JS bindings. For example, the contract below:

# app/contracts/simple_storage.sol
contract SimpleStorage {
  uint public storedData;

  function SimpleStorage(uint initialValue) {
    storedData = initialValue;
  }

  function set(uint x) {
    storedData = x;
  }
  function get() constant returns (uint retVal) {
    return storedData;
  }
}

Will automatically be available in Javascript as:

# app/js/index.js
SimpleStorage.set(100);
SimpleStorage.get();
SimpleStorage.storedData();

You can specify for each contract and environment its gas costs and arguments:

# config/contracts.yml
  development:
    SimpleStorage:
      gas_limit: 500000
      gas_price: 10000000000000
      args:
        - 100
  ...

If you are using multiple contracts, you can pass a reference to another contract as $ContractName, Embark will automatically replace this with the correct address for the contract.

# config/contracts.yml
  development:
    SimpleStorage:
      args:
        - 100
        - $MyStorage
    MyStorage:
       args:
         - "initial string"
    MyMainContract:
      args:
        - $SimpleStorage
  ...

You can now deploy many instances of the same contract. e.g

# config/contracts.yml
  development:
    Currency:
      deploy: false
      args:
        - 100
    Usd:
      instanceOf: Currency
      args:
        - "initial string"
    MyCoin:
      instanceOf: Currency
      args:
        - $SimpleStorage
  ...

Contracts addresses can be defined, If an address is defined the contract wouldn't be deployed but its defined address will be used instead.

  development:
    UserStorage:
      address: 0x123456
    UserManagement:
       args:
         - $UserStorage
  ...

You can also define contract interfaces (Stubs) and actions to do on deployment

  development:
    DataSource:
      args:
    MyDataSource:
      args:
      instanceOf: DataSource
    Manager:
      stubs:
        - DataSource
      args:
        - $MyDataSource
      onDeploy:
        - Manager.updateStorage($MyDataSource)
        - MyDataSource.set(5)
  ...

Tests

You can run specs with embark spec, it will run any files ending *_spec.js under spec/.

Embark includes a testing lib to fastly run & test your contracts in a EVM.

# spec/contracts/simple_storage_spec.js
Embark = require('embark-framework');
Embark.init();
Embark.blockchainConfig.loadConfigFile('config/blockchain.yml');
Embark.contractsConfig.loadConfigFile('config/contracts.yml');

var files = ['app/contracts/simpleStorage.sol'];
Embark.contractsConfig.init(files, 'development');

var EmbarkSpec = Embark.tests(files);

describe("SimpleStorage", function() {
  beforeAll(function() {
    // equivalent to initializing SimpleStorage with param 150
    SimpleStorage = EmbarkSpec.request("SimpleStorage", [150]);
  });

  it("should set constructor value", function() {
    expect(SimpleStorage.storedData()).toEqual('150');
  });

  it("set storage value", function() {
    SimpleStorage.set(100);
    expect(SimpleStorage.get()).toEqual('100');
  });

})

Embark uses Jasmine by default, but you can use any testing framework you want.

Working with different chains

You can specify which environment to deploy to:

$ embark blockchain staging

$ embark run staging

The environment is a specific blockchain configuration that can be managed at config/blockchain.yml

# config/blockchain.yml
  ...
  staging:
    rpc_host: localhost
    rpc_port: 8101
    rpc_whitelist: "*"
    datadir: default
    network_id: 0
    console: true
    account:
      init: false
      address: 0x123

See Configuration.

Deploying only contracts

Although embark run will automatically deploy contracts, you can choose to only deploy the contracts to a specific environment

$ embark deploy privatenet

embark deploy will deploy all contracts at app/contracts and return the resulting addresses

LiveReload Plugin

Embark works quite well with the LiveReload Plugin

Debugging embark

Because embark is internally using grunt tasks, debugging is not straightforward. Example

you want to debug embark deploy
normally you would write something like node-debug -p 7000 embark -- deploy
This gives you nothing with embark. If you look at deploy command in ./bin/embark you will notice that it internally runs grunt task grunt deploy_contracts:[env]
with this knowledge we can prepare proper command to start debugging
node-debug -p 7000 grunt -- deploy_contracts:development

here is list of all debuggable grunt tasks

EACCESS Error

If you get EACCES (access denied) errors, don't use sudo, try this:

$ mkdir ~/npm-global
$ npm config set prefix ~/npm-global
$ echo 'export PATH="$PATH:$HOME/npm-global/bin"' >>~/.bashrc
$ source ~/.bashrc
$ npm install -g embark-framework grunt-cli

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