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. (for 1.x, plugins coming soon for 2.x series)
• 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.
• Manage different chains (e.g testnet, private net, livenet)
• Quickly create advanced DApps using multiple contracts that can interact with decentralized infrastructure for storage and comunication.

Installation

Requirements: geth (1.4.4 or higher), node (5.0.0) and npm Optional: serpent (develop) if using contracts with Serpent, testrpc or ethersim if using the simulator or the test functionality. Further: depending on the dapp stack you choose: IPFS

$ npm -g install embark

# If you plan to use the simulator instead of a real ethereum node.
$ npm -g install testrpc

See Complete Installation Instructions.

Usage - Demo

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

$ embark demo
$ cd embark_demo

To run a ethereum rpc simulator simply run:

$ embark simulator

Or Alternatively, you can run a REAL ethereum node for development purposes:

$ 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.json

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.json #environments configuration
    |___ contracts.json  #contracts configuration
  test/
    |___ #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.json
{
  "development": {
    "gas": "auto",
    "contracts": {
      "SimpleStorage": {
        "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.json
{
  ...
  "development": {
    "contracts": {
      "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.json
{
  "development": {
    "contracts": {
      "Currency": {
        "deploy": false,
        "args": [
          100
        ]
      },
      "Usd": {
        "instanceOf": "Currency",
        "args": [
          200
        ]
      },
      "MyCoin": {
        "instanceOf": "Currency",
        "args": [
          200
        ]
      }
    }
  }
}
  ...

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

# config/contracts.json
{
  ...
  "development": {
    "contracts": {
      "UserStorage": {
        "address": "0x123456"
      },
      "UserManagement": {
        "args": [
          "$UserStorage"
        ]
      }
    }
  }
  ...
}

EmbarkJS

EmbarkJS is a javascript library meant to abstract and facilitate the development of DApps.

promises

methods in EmbarkJS contracts will be converted to promises.

  var myContract = new EmbarkJS.Contract({abi: abiObject, address: "0x123"});
  myContract.get().then(function(value) { console.log("value is " + value.toNumber) });

deployment

Client side deployment will be automatically available in Embark for existing contracts:

  var myContract = new EmbarkJS.Contract({abi: abiObject, code: code});
  myContract.deploy().then(function(address) {});

or it can be manually definied as

  var myContract = new EmbarkJS.Contract({abi: abiObject, code: code});
  myContract.deploy().then(function(address) {});

EmbarkJS - Storage

initialization

The current available storage is IPFS. it can be initialized as

  EmbarkJS.Storage.setProvider('ipfs',{server: 'localhost', port: '5001'})

Saving Text

  EmbarkJS.Storage.saveText("hello world").then(function(hash) {});

Retrieving Data/Text

  EmbarkJS.Storage.get(hash).then(function(content) {});

Uploading a file

  <input type="file">

  var input = $("input[type=file"]);
  EmbarkJS.Storage.uploadFile(input).then(function(hash) {});

Generate URL to file

  EmbarkJS.Storage.getUrl(hash);

EmbarkJS - Communication

initialization

The current available communication is Whisper.

listening to messages

  EmbarkJS.Messages.listenTo({topic: ["achannel", "anotherchannel"]}).then(function(message) { console.log("received: " + message); })

sending messages

you can send plain text

  EmbarkJS.Messages.sendMessage({topic: "achannel", data: 'hello world'})

or an object

  EmbarkJS.Messages.sendMessage({topic: "achannel", data: {msg: 'hello world'}})

Tests

You can run specs with embark test, it will run any test files under test/.

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

# test/simple_storage_spec.js

var assert = require('assert');
var Embark = require('embark-framework');
var EmbarkSpec = Embark.initTests();
var web3 = EmbarkSpec.web3;

describe("SimpleStorage", function() {
  before(function(done) {
    var contractsConfig = {
      "SimpleStorage": {
        args: [100]
      }
    };
    EmbarkSpec.deployAll(contractsConfig, done);
  });

  it("should set constructor value", function(done) {
    SimpleStorage.storedData(function(err, result) {
      assert.equal(result.toNumber(), 100);
      done();
    });
  });

  it("set storage value", function(done) {
    SimpleStorage.set(150, function() {
      SimpleStorage.get(function(err, result) {
        assert.equal(result.toNumber(), 150);
        done();
      });
    });
  });

});

Embark uses Mocha 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 production

$ embark run production

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

# config/blockchain.json
  ...
   "livenet": {
    "networkType": "livenet",
    "rpcHost": "localhost",
    "rpcPort": 8545,
    "rpcCorsDomain": "http://localhost:8000",
    "account": {
      "password": "config/production/password"
    }
  },
  ...

Structuring Application

Embark is quite flexible and you can configure you're own directory structure using embark.json

# embark.json
{
  "contracts": ["app/contracts/**"],
  "app": {
    "css/app.css": ["app/css/**"],
    "js/app.js": ["embark.js", "app/js/**"],
    "index.html": "app/index.html"
  },
  "buildDir": "dist/",
  "config": "config/"
}

Deploying to IPFS

To deploy a dapp to IPFS, all you need to do is run a local IPFS node and then run embark ipfs. If you want to deploy to the livenet then after configuring you account on config/blockchain.json on the production environment then you can deploy to that chain by specifying the environment embark ipfs production.

LiveReload Plugin

Embark works quite well with the LiveReload Plugin