stratumn-agent

Stratumn agent for NodeJS

This NodeJS module exposes functions to create Stratumn agents using Javascript.

Copyright 2017 Stratumn SAS. All rights reserved.

Unless otherwise noted, the Stratumn Agent Javascript Library source files are distributed under the Apache License 2.0 found in the LICENSE file.

Creating an HTTP server for an agent

var express = require('express');
var Agent = require('stratumn-agent');
var plugins = Agent.plugins;
 
// Load actions.
// Assumes your actions are in ./lib/actions.
var actions = require('./lib/actions');
 
// Creates an HTTP store client to save segments.
// Assumes an HTTP store server is available on env.STRATUMN_STORE_URL or http://store:5000.
var storeHttpClient = Agent.storeHttpClient(process.env.STRATUMN_STORE_URL || 'http://store:5000');
 
// Creates an HTTP fossilizer client to fossilize segments.
// Assumes an HTTP fossilizer server is available on env.STRATUMN_FOSSILIZER_URL or http://fossilizer:6000.
var fossilizerHttpClient = Agent.fossilizerHttpClient(process.env.STRATUMN_FOSSILIZER_URL || 'http://fossilizer:6000');
 
// Creates an agent
var agent = Agent.create({
    agentUrl: 'http://localhost:3000',               // the agent needs to know its root URL,·
});
 
// Adds a process from a name, its actions, the store client, and the fossilizer client.
// As many processes as one needs can be added. A different storeHttpClient and fossilizerHttpClient may be used.
agent.addProcess("my_first_process", actions, storeHttpClient, fossilizerHttpClient, {
  salt: process.env.STRATUMN_SALT || Math.random(), // change to a unique salt
  plugins: [plugins.localTime]                     // pick any plugins from src/plugins or develop your own - order matters
});
 
// Creates an HTTP server for the agent with CORS enabled.
var agentHttpServer = Agent.httpServer(agent, { cors: {} });
 
// Create the Express server.
const app = express();
app.disable('x-powered-by');
 
// Mount agent on the root path of the server.
app.use('/', agentHttpServer);
 
// Create server by binding app and websocket connection
const server = Agent.websocketServer(app, storeHttpClient);
 
// Start the server
server.listen(3000, () => {
  console.log('Listening on ' + server.address().port);
});
 
// You can also add processes on-the-fly after the server has started listening
agent.addProcess("my_second_process", actions, storeHttpClient, fossilizerHttpClient, {
  salt: process.env.STRATUMN_SALT || Math.random(),
  plugins: [plugins.localTime]
});

Advanced usage

• create creates an agent instance.
• storeHttpClient creates an instance to work with stores via HTTP.
• fossilizerHttpClient creates an instance to work with fossilizers via HTTP.
• httpServer creates an app for the agent
• websocketServerbind websocket connection to app and returns server

Plugins

An agent plugin enriches the content of a segment. It may implement four methods:

• willCreate(link) is called right before a transition function from the agent's actions. It takes the existing link as an argument. It should be updated in-place.

• didCreateLink(link) is called whenever a link has been created by a transition function. It takes the new link as an argument. It should be updated in-place.

• didCreateSegment(segment) is called whenever a new segment has been computed from a new link. It take the new segment as an argument. It should be updated in-place. At this point the linkHash has already been computed so the link part should not be updated. Should it be the case sanity checks on the segment would fail.

• filterSegment(segment) is called when segments are retrieved by the agent from the underlying storage. It should return true if the plugins accepts the segment, false otherwise. Filters are applied sequentially in the reverse order they are defined.

All methods are optional. They can either be synchronous or return a Promise.

Available plugins:

• actionArgs: Saves the action and its arguments in link meta information.
• agentUrl: Saves in segment meta the URL that can be used to retrieve a segment.
• encryptedState: Encrypts the state before the segment is saved. Filters out segment that cannot be decrypted.
• localTime: Saves the local timestamp in the link meta information.
• signedState: Signs the state before the segment is saved. Filters out segments whose signature is invalid.
• stateHash: Computes and adds the hash of the state in meta.