evan.network Developer Documentation

Hello Agent

Let’s write a Smart Agent to interact with the blockchain via a normal web service without installing all the blockchain services and libraries on every computer.

If you want to cheat, just pull it from https://github.com/evannetwork/smart-agent-hello . You will still have to do some setup though.


[Edge Server)(/dev/smart-agents#edge-server)

In the evan.network, the established way to write web services is to use the Edge Server, which is just an ActionHero with some added infrastructure, in particular REDIS, blockchain-core and IPFS. It also uses the version “^18.0”, so asynchronous programming with callbacks is discouraged now.

Installation is straight forward.

$ git clone git@github.com:evannetwork/edge-server-seed.git
$ cd edge-server-seed
$ npm i

This also installs the blockchain-core libraries and all other dependencies in node_modules/ automatically, which can take a while.

If everything is done, test Edge Server and start it with

$ npm start

You should be able now to see the Edge Server greeting page on https://localhost:8080.

Getting the API

Contracts are just bytecode blobs with no real meta-information attached to them. So without a defined protocol, things can get really messy really fast when people don’t know what methods are in a contract and what parameters they need.

In evan.network, the encouraged way to take care of this is DBCP. But this is not always available and a little too complex for a quick tutorial. So we just deployed our Hello World contract via ‘truffle’, and to use those contracts in an evan.network application, we need to import the API of the contract separately.

Which means we first have to export it:

$ cd hello-world/contracts
$ solc --abi hello.sol

Depending on what version of the Solidity compiler you have, you get either a file or stdout output.

Either way, you will find an array with the interface definition in the output.

Copy it somewhere for storing.

Setting up the Project

It is possible to create a project directory and develop a Smart Agent, which is an ActionHero-Plugin, directly in the node_modules/ of the Edge Server. However, the better option is to have a separate directory that can be source controlled separately and just link it into the Edge Server with a symbolic link.

$ mkdir ../smart-agent-hello
$ ln -s ../smart-agent-hello node_modules/smart-agent-hello
$ cd ../smart-agent-hello

Usually, you can have ActionHero create the plugin directory structure. But this doesn’t really work anymore in recent versions. Perhaps it might work again in future, but for now we do it manually, which isn’t too hard either.

$ mkdir config initializers  # this is the minimum of subdirectories needed
$ mkdir actions              # we also need this
$ edit package.json

This can be very small for simple agents. Since we access the blockchain-core libraries via Edge Server, most of the things we need are already available.

    "author": "Me Myself",
    "name": "smart-agent-hello",
    "description": "Changes the string from the hello-world contract",
    "version": "0.0.1",
    "engines": {
        "node": ">=8.0.0"
$ edit config/smart-agent-hello.js

This can be rather simple too.

exports['default'] = {
  smartAgentHello: (api) => {
    return {
      disabled: false,  // a simple way to disable specific smart-agent plugins
      // if you want more control over this without having to edit the config file try this
      // disabled: process.env.SMART_AGENT_HELLO_DISABLED ?  JSON.parse(process.env.SMART_AGENT_DISABLED_DISABLED) : true,
      name: 'HelloAgent',
      account: "the account/identity you have created and created the hello-world contract with",
      contract: 'the contract hash returned in the deploy operation earlier',
      helloAPI: '[{"constant": ..... "constructor"}]'

You need the account ID, because you want to be able to change the contract data, and by default only the owner/ creator can implement changes on contracts.

Here is also the place where we store the generated API object from earlier, in the helloAPI property.

A thing to remember: ActionHero, and thus Edge Server, doesn’t read the plugin configs from the plugin directories, it needs the config to be in its own config directory. The simplest way to do this is this:

$ ln config/smart-agent-hello.js ../edge-server/config/smart-agent-hello.js

You can copy it of course, too. The config that is used is the one in the Edge Server config directory, though.

You still have to tell Edge Server that there is a plugin.

$ edit ../edge-server/config/plugins.js

exports['default'] = {
  plugins: (api) => {
    return {
      'smart-contracts': { path: __dirname + '/../node_modules/smart-contracts' },
      'edge-server-admin-module': { path: __dirname + '/../node_modules/edge-server-admin-module' },
      // ...
      'smart-agent-hello': { path: __dirname + '/../node_modules/smart-agent-hello },

The Initializer

Every plugin needs an initializer. This is usually where most of the code of your Smart Agent resides, especially if there are no actions.

ActionHero is a little sensitive about semicolons to end lines for some reasons, so it is recommended not to use them in Smart Agents.

$ edit initializers/hello.js
'use strict'

const { Initializer, api } = require('actionhero')

module.exports = class SmartAgentHello extends Initializer {
  constructor() {
    this.name = 'HelloAgent'
    this.loadPriority = 7000
    this.startPriority = 7000
    this.stopPriority = 7000

  // put anything you need outside of this file, in here
  // this happens if you need to share functionality
  // between initializer and action (or commands) for example
  // common external dependencies are resolved 
  // through the api object as well

  async initialize() {
    if (api.config.smartAgentHello.disabled) return

    api.bcc.contractLoader.contracts['HelloWorld'] = {
      "interface": api.config.smartAgentHello.helloAPI

    const account = api.config.smartAgentHello.account
    const hello = api.bcc.contractLoader.loadContract('HelloWorld', api.config.smartAgentHello.contract)
    api.smartAgentHello = {
      setMessage: async function (msg){
        // you not only "export" through the api object
        // you also import through it, the configuration for example
        // but also the blockchain core library
        // here a writing contract method call
        return await api.bcc.executor.executeContractTransaction(
          hello, 'setPrompt', { from: account }, msg);

      // here a non-writing call, no need for accountIDs here, because everyone can read everything
      hello: async function (salut) {
        var r = api.bcc.signer.web3.utils.toAscii(
          await api.bcc.executor.executeContractCall(hello, 'hello',  salut ))
        return r
  async stop() {}


An Action

Writing actions is easy too. See how the action uses the smartAgentHello object that was created in the initializer to import objects it needs.

$ edit actions/hello.js
'use strict'
const { Action, api } = require('actionhero')

class SmartAgentHelloHello extends Action {
  constructor() {
    this.name = 'smart-agents/hello/hello'
    this.description = 'Returns a greeting.'
    this.inputs = {
      salut: {
        required: true,
    this.outputExample = { greeting: "greeting" }

  async run({ params, response }) {
    try {
      response.greeting = await api.smartAgentHello.hello(params.salut)
      response.status = 'success'
    } catch (ex) {
      response.status = 'error'
      response.error = ex

module.exports = {


The easiest way to test an actual request is with curl

$ curl -X POST -d "salut=Ciao!" "http://localhost:8080/api/smart-agents/hello/hello?apiVersion=1"

  "greeting": "Grüetzi, Ciao!",
  "status": "success",
  "serverInformation": {
    "serverName": "edge-server",
    "apiVersion": "0.9.0",
    "requestDuration": 33,
    "currentTime": 1526396750067
  "requesterInformation": {
    "id": "ce8131e53aa7e38cd6feb54a83d8afb995876738-28650a51-f53f-4484-a015-ca89fa592166",
    "fingerprint": "ce8131e53aa7e38cd6feb54a83d8afb995876738",
    "remoteIP": "",
    "receivedParams": {
      "apiVersion": "1",
      "salut": "Ciao!",
      "action": "smart-agents/hello/hello"