@trayio/falafel

# falafel

A Node.js framework for making it crazy easy to build connectors. Built on top of the threadneedle allowing for a declarative operation based approach.

Falafel uses JavaScript-based schemas as a superset of connectors.json, but unlike connectors.json, the schema also has a direct impact on the running of operations. For example, the use of required makes a field required in connectors.json as well as on the operational level.

Table of contents:

• Getting started
• Project structuring
  • Schema
  • Model
  • Sample response
• Globals
• Private methods
• Trigger connectors
  • Init and init destroy
  • Handling triggers
• Generating connectors.json

## Getting started

Create a connector using the Yeoman generator, inputting the settings when prompted:

yo trayio-nodejs-connector

Next up, start the server in development mode (will auto-generate connectors.json):

NODE_ENV=development node main.js

## Project structuring

Falafel requires you to follow a strict folder structure for organising connectors:

connectors/ 
  connectorname/
  	my-message/
  		model.js
  		schema.js
  		response.sample.json
  	my-second-message/
  		model.js
  		schema.js
  		response.sample.json
    connector.js
    global.js (optional)

### Connector file

The connector.js file contains high level config about the connector, mostly related to how the connector appears in the builder UI.

module.exports = {

 // Title as it will appear in the builder UI
 title: 'MailChimp',
 
 // Description as it will appear in the builder UI
 description: 'Interact with the MailChimp API.',
 
 // Version of the schema
 version: '1.0',
 
 // Tags 
 tags: ['service'],
 
 // Icon 
 icon: {
   type: 'url',
   value: 'http://images.tray.io.s3.amazonaws.com/static/icons/placeholder.png',
 },
 
 // Help link
 help_link: 'http://docs.tray.io/'

};

### Messages

On a high level, the following rules apply for each message.

• The schema.js handles the input schema
• The model.js handles the running of the operation
• The response.sample.json provides a sample output - for the output schema

### Schema

The schema.js file is a higher level JavaScript version of the connectors.json file. It takes a declarative approach, allowing for inline advanced and required variables, auto-generating message and property title attributes, and allowing for JavaScript utility functions:

module.exports = {

  input: {

    access_token: {
      type: 'string',
      advanced: true,
      required: true,
      defaultJsonPath: '$.auth.access_token'  
    },

    id: {
      type: 'string',
      description: 'The MailChimp list ID.',
      required: true
    }

  })

};

This schema will be used to generate the input_schema for each message. Also, the required variable applies a validation before the operation executes at runtime.

### Model

Any options in the model.js file will be automatically be passed to a threadneedle method for the operation. For example:

module.exports = {

  url: 'https://{{dc}}.api.mailchimp.com/2.0/lists/list?apikey={{apiKey}}',
  method: 'get',
  expects: 200

};

Variables passed in the input schema will be passed into a Mustache template system.

### Sample response

Output schemas are important in tray - they allow connectors to reference the
data coming from a previous connector. However, you don't need fine grained control, handling variables like required and advanced.

Falafel means you don't have to explicitly declare an output schema for each message. Just add a response.sample.json file for each and a JSON schema generator will automatically generate an output schema when building the connectors.json.

## Globals

Threadneedle has a "globals" approach which allows for shared logic across multiple messages. If you declare the connectors/myconnector/global.js file, the options in it will be globalized for the connector across all methods:

module.exports = {
  
  before: function (params) {
    params.dc = 'us5';
    // you can also return a promise that should resolve after modifying `params` 
  }

};

Tip: If you'd like to disable global logic for an operation, just set globals: false in the model.js config file.

See the threadneedle docs for more information on globals.

Private methods

Sometimes you'll want to create an internal method that should not be exposed to the UI. Typically the main use for this will be a generic method called in before, providing key data to enable the main method to run.

This is simple - just don't add a schema.js file in the message folder.

Note: the operation will be still be created, but it won't be added to the connectors.json config (so won't appear in the UI).

## Trigger connectors

Trigger connectors follow a normal file structure, but you'll also need to:

• Add a trigger.js file
• Add init_destroy methods for each message

connectors/
  mailchimp_trigger/
    user_subscribe/
      model.js
      schema.js
      response.sample.json
    user_subscribe_destroy/
      model.js
    trigger.js
    connector.js
    global.js (optional)

### Init and init destroy

Init messages are usually to set up things like webhooks. These normally correspond to a singular API call as a result - just like any normal operation.

As such, init and init_destroy messages should be declared in separate folders, just like any other message. Just add _destroy on the end of whatever your init message is called.

Tip: you don't need to declare a schema or provide a sample response for init_destroy messages as they're never exposed to the UI.

Handling triggers

The trigger.js file within the connector folder will be passed straight to connector.trigger(fn) in the Node.js SDK.

Encodings are automatically handled behind the scenes based on the Content-Type header:

• application/json - parsed as JSON
• application/x-www-form-urlencoded - parsed as encoded URL
• text/html - parsed as text

module.exports = function (req, res, metadata, requestMetadata, triggerWorkflow) {
  
  // Respond ok
  res.status(200).json({ success: true });

  // Trigger the workflow
  triggerWorkflow(req.body);

};

For reference:

• req - the express request object
• res - the express response object
• metadata - the data originally sent to the init operation
• requestMetadata - metadata that the cluster service adds
• triggerWorkflow - a function to trigger the workflow

Generating connectors.json

The connectors.json file will get auto generated when starting the server with NODE_ENV set to development.

Depends on the generate-schema module being installed as a devDependency. (It is automatically from the Yeoman generator)