@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
    • after_headers
  • Sample response
• Global models
• Global message schemas
• Private methods
• File handling
  • API download / Falafel upload
  • API upload / Falafel download
• Trigger connectors
  • Init
  • Destroy
  • Request
  • Response
• Dynamic output schemas
• Generating connectors.json
• Utils
• Raw HTTP Request
• Testing the connector

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_model.js (optional)
    global_schema.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.

after_headers

For function models (only), the afterHeaders function can be specified in a after_headers.js file, exporting a function accepting the arguments error, body, and params.

module.exports = function (error, params, body) {
	return {
	//Must return an object
	};
};

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.

Global models

Threadneedle has a "global models" approach which allows for shared logic across multiple messages. If you declare the connectors/myconnector/global_model.js (previously 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.

Global message schemas

Sometimes you'll want to use the same generic data as inputs in every single message. A good example is passing API keys or other authentication data.

You don't have to add these to every single message - you can specify them in a global_schema.js file:

// global_schema.js
module.exports = {

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

};

Tip: if you'd like to disable global schemas a particular message, specify globals: false in the message schema.js file.

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 the schema.js and response.sample.json files 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).

File handling

In tray.io workflows, files are handled by uploading files to bucket in AWS S3, and the using a pointer object to reference the file in workflows. The default bucket is workflow-file-uploads, except in development mode, in which case it is workflow-file-uploads-dev; in both cases the region is us-west-2.

The file pointer object takes the following formatting:

{
    "name": "[File name]",
    "url": "[Signed S3 URL]",
    "mime_type": "[File's mime type]",
    "expires": [Expiration time in seconds]
}

Example:

{
    "name": "galaxy.tif",
    "url": "https://workflow-file-uploads-dev.s3.us-west-2.amazonaws.com/13dd4143-02d4-4526-9a9c-65a20a2e97c5?AWSAccessKeyId=AKIAJHNCMU22PD3C6T6A&Expires=1570571246&Signature=O%2FotP%2B2UExhXA%2FihpNNQOo9E8tI%3D",
    "mime_type": "image/tiff",
    "expires": 1570571246
}

API download / Falafel upload

Generally, when an API provides a download endpoint, one of falafel's upload functions will need to be used. All three of the following upload promise functions will return a file pointer object when they resolve.

Note: all signed URLs return an expiry time of 6 hours.

CONNECTOR_FILE_REGION and CONNECTOR_FILE_BUCKET environment variables can be set to override the default region and bucket.

falafel.files.streamUpload (recommended)

The falafel.files.streamUpload accepts the following object:

{
    readStream: [A node read stream], //required
    name: '[File name]', //required
    length: [File size in bytes], //required
    contentType: '[Mime type of file]', //optional (falafel will attempt to derive it from name if not provided)

    bucket: '[AWS bucket]', //optional target bucket
    region: '[AWS region]' //optional target region
}

falafel.files.streamMPUpload

The falafel.files.streamMPUpload is the same as streamUpload, but does not require a length to be specified. However, this is less performant since the lack of content length information will default the AWS SDK to split the stream into 5MB chunks and upload them individually. Only use this if it is not possible to determine the content size beforehand without downloading the whole file to memory and/or local storage.

falafel.files.upload

The falafel.files.upload accepts the following object:

{
    file: '[File path]', //required
    name: '[File name]', //required
    length: [File size in bytes], //required
    contentType: '[Mime type of file]', //optional (falafel will attempt to derive it from name if not provided)

    bucket: '[AWS bucket]', //optional target bucket
    region: '[AWS region]' //optional target region
}

This function assumes the file is in local storage and will attempt to createReadStream from it; as such this is the least recommended upload option.

API upload / Falafel download

Generally, when an API provides an upload endpoint, one of falafel's download functions will need to be used. Both of the following download promise functions expect a file pointer object to be passed in.

needleOptions

Both falafel.files.streamDownload and falafel.files.download accept a second argument, needleOptions, which is an object that can be used to override the default needle options defined by falafel when downloading the file (except the output property for falafel.files.download - falafel takes precedence for this property).

falafel.files.streamDownload (recommended)

The falafel.files.streamDownload resolving with the following object:

{
	readStream, //A read stream of the file contents from S3
	name, //Name of the file
	mime_type, //Mime type of the file
	expires, //The expiry time in seconds
	size //The content length of the file
}

falafel.files.download

The falafel.files.download resolving with the following object:

{
	file, //The file path in local storage
	name, //Name of the file
	mime_type, //Mime type of the file
	expires, //The expiry time in seconds
	size //The content length of the file
}

Similarly to falafel.file.upload, since this function requires keeping the file in local storage, this is the least recommended download option.

Note: when using falafel.files.download, needle.get is internally used along with the output option; needle however only creates a file if the statusCode is 200. If a file needs to be created in the /tmp directory for non-200 statusCodes, use falafel.files.streamDownload.

Trigger connectors

Trigger connectors follow a similar file structure to regular connectors, but the message folder also needs to contain:

• destroy.js - a file to remove the webhook created, if any (message_destroy)
• request.js - a file to handle incoming HTTP triggers (message_request)
• response.js - a file to format and handle the reply from a workflow to the connector (message_response). Only required if your connector is acknowledge (see below for explaination).

connectors/
  mailchimp_trigger/
    user_subscribe/
      model.js
      schema.js
      response.sample.json
      destroy.js
      request.js
      response.js (optional)
    connector.js
    global_model.js (optional)
    global_schema.js (optional)

Delivery mode

Delivery mode controls how the tray platform processes responses to incoming webhooks.

In the schema, on top-level (so next to title, etcs), you can set the delivery field, e.g.:

delivery: 'acknowledge',

It's optional. If not set, the value will default to fire_and_forget.

In most cases, the behaviour will be as follows:

• fire_and_forget - the backend will immediately respond to the webhook with status: 200, even before going through the connector code;
• acknowledge - the backend will invoke the connector first, so the connector can control the response to the webhook;
• request_response - the backend will only allow the workflow itself to respond (using special Trigger-Reply step)

You must use the acknowledge mode if you want to control the reply to the caller, via the response.js file or the reply function

Init (message)

This "trigger initialisation" happens when the workflow is enabled or changed, and is designed to create webhooks in third party systems.

The message coming in triggers the model.js file - which is configured like any other message.

Destroy (message_destroy)

This message should undo whatever the "initialisation" message did above. Usually this means deleting a webhook in a third party system.

This message triggers the destroy.js file method, which is configured like any other message.

Request (message_request)

This is a HTTP trigger message, forwarded by the tray platform to the connector. It comes in to the request.js. file.

This can be declared like so:

module.exports = {

	// Filter function to determine whether the request should result
	// in a workflow being triggered. If you want to pass all http requests
	// to the connector then just return true here.
	// NOTE: this is a sync-only method and does not accept promises.
	filter: function(params, http) {
		return (http.method === 'POST');
	},

	// Async formatting and ad-hoc additional API function. Return a promise
	// for async behaviour.
	before: function(params, http) {
		return {
			data: http.body
		};
	},

	// If you'd like to respond to the HTTP message from the third party because
	// they're expecting a response (Salesforce notification), then also add a reply
	// method here, passing a `http` object.
	reply: function(params, http, output) {
		return {
			status: 200,
			headers: {
				'Content-Type': 'application/xml'
			},
			body: '<myxml>test</myxml>'
		}
	},

	// Use this function to set `trigger_deduplication_id` in the headers if
	// there is a need to know the unique ID of the webhook being processed
	getUniqueTriggerID: function (params, http, output) {
		return http['uniqueWebhookID'];
	}

};

If you'd like more fine grained control, declare it as a function returning a promise:

module.exports = function (params, http) {
  return when.promise(function (resolve, reject) {

    if (http.method === 'post') {
      resolve(http.body);
    } else {
      reject('#no_trigger');
    }

  });
};

Adding a HTTP reply with #no_trigger error code

If a HTTP response needs to be specified along with the #no_trigger rejection code, the following format should be used:

{
	code: '#no_trigger',
	message: 'Rendering form page, no trigger required.',
	http: {
		status_code,
		headers,
		body
	},
}

Response (message_response)

This file handles the formatting of the response to the connector for an acknowledge trigger. The output from this message will be sent in the response back to the third party service.

The formatting is a simple & functional one:

module.exports = function (params, http, reply) {
  return when.resolve(reply);
}

Trigger decoding

By default Falafel automatically parses messages for the following Content-Types:

• application/json
• application/x-www-form-urlencoded

There is also a rawBody object attached to the http object for the request and response messages, which contains the raw HTTP body, rather than the parsed version.

Dynamic output schemas

If an operation is to support dynamic output schemas, an output.js file simply needs to be included in the operation's folder. The file should always export a promise function to be run, like so:

module.exports = function (params) {
	return when.promise(function (resolve, reject) {
		//Return an object or JSON schema
	});
};

Falafel accepts two possibilities for the returned data; either an object or a JSON schema. A JSON schema is identified by having a "$schema" key/property on the top level; thus, if detected, the data will be passed on directly. Otherwise, Falafel will transform the object to JSON schema and then pass it.

Note: Depending on whether a output.js is included or not, Falafel will automatically set the dynamic_output key in connectors.json for each operation; thus dynamic_output attribute does not need to be added in schema.js. Additionally, the dynamic output sub-operation can be referenced as message_dynamic_output.

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 of the parent module. (It is automatically from the Yeoman generator)

Testing the connector

As a server/exposed function

Running the connector with NODE_ENV set to development as an environment variable will spin up a testing HTTP server, to which request to connector operations can be made via a tool like Postman.

HTTP requests are sent to http://localhost:8989/send/123-def with a body format like:

{
  "id": "123-def",
  "header": {
    "message": "[OPERATION NAME]"
  },
  "body": {
    "...[INPUT PARAMETERS]"
  }
}

The id 123-def is used when testing.

Writing tests

Generally, sub-operations like request.js and output.js are not exposed in the falafel['connector name'] object. However, if access is needed for when writing test scripts, setting NODE_ENV to test as an environment variable will add the sub-operations to the falafel['connector name'] object.