Easily create a microservice for generating PDFs using headless Chrome.
pdf-bot is installed on a server and will receive URLs to turn into PDFs through its API or CLI. pdf-bot will manage a queue of PDF jobs. Once a PDF job has run it will notify you using a webhook so you can fetch the API. pdf-bot supports storing PDFs on S3 out of the box. Failed PDF generations and Webhook pings will be retryed after a configurable decaying schedule.
pdf-bot uses html-pdf-chrome under the hood and supports all the settings that it supports. Major thanks to @westy92 for making this possible.
Imagine you have an app that creates invoices. You want to save those invoices as PDF. You install pdf-bot on a server as an API. Your app server sends the URL of the invoice to the pdf-bot server. A cronjob on the pdf-bot server keeps checking for new jobs, generates a PDF using headless Chrome and sends the location back to the application server using a webhook.
$ npm install -g pdf-bot
$ pdf-bot installMake sure the node path is in your $PATH
pdf-bot install will prompt for some basic configurations and then create a storage folder where your database and pdf files will be saved.
pdf-bot comes packaged with sensible defaults. At the very minimum you must have a config file in the same folder from which you are executing pdf-bot with a storagePath given. However, in reality what you probably want to do is use the pdf-bot install command to generate a configuration file and then use an alias ALIAS pdf-bot = "pdf-bot -c /home/pdf-bot.config.js"
pdf-bot.config.js
var htmlPdf = require('html-pdf-chrome')
module.exports = {
api: {
token: 'crazy-secret'
},
generator: {
completionTrigger: new htmlPdf.CompletionTrigger.Timer(1000) // 1 sec timeout
},
storagePath: 'storage'
}$ pdf-bot -c ./pdf-bot.config.js push https://esbenp.github.ioSee a full list of the available configuration options.
pdf-bot is meant to be a microservice that runs a server to generate PDFs for you. That usually means you will send requests from your application server to the PDF server to request an url to be generated as a PDF. pdf-bot will manage a queue and retry failed generations. Once a job is successfully generated a path to it will be sent back to your application server.
Let us check out the flow for an app that generates PDF invoices.
1. (App server): An invoice is created ----> Send URL to invoice to pdf-bot server
2. (pdf-bot server): Put the URL in the queue
3. (pdf-bot server): PDF is generated using headless Chrome
4. (pdf-bot server): (if failed try again using 1 min, 3 min, 10 min, 30 min, 60 min delay)
5. (pdf-bot server): Upload PDF to storage (e.g. Amazon S3)
6. (pdf-bot server): Send S3 location of PDF back to the app server
7. (App server): Receive S3 location of PDF -> Check signature sum matches for security
8. (App server): Handle PDF however you see fit (move it, download it, save it etc.)
You can send meta data to the pdf-bot server that will be sent back to the application. This can help you identify what PDF you are receiving.
On your pdf-bot server start by creating a config file pdf-bot.config.js. You can see an example file here
pdf-bot.config.js
module.exports = {
api: {
port: 3000,
token: 'api-token'
},
storage: {
's3': createS3Config({
bucket: '',
accessKeyId: '',
region: '',
secretAccessKey: ''
})
},
webhook: {
secret: '1234',
url: 'http://localhost:3000/webhooks/pdf'
}
}As a minimum you should configure an access token for your API. This will be used to authenticate jobs sent to your pdf-bot server. You also need to add a webhook configuration to have pdf notifications sent back to your application server. You should add a secret that will be used to generate a signature used to check that the request has not been tampered with during transfer.
Start your API using
pdf-bot -c ./pdf-bot.config.js api
This will start an express server that listens for new jobs on port 3000.
pdf-bot uses html-pdf-chrome which in turns uses chrome-launcher to launch chrome. You should check out those two resources on how to properly setup Chrome. However, with chrome-launcher Chrome should be started automatically. Otherwise, html-pdf-chrome has a small guide on how to have it running as a process using pm2.
You can install chrome on Ubuntu using
sudo apt-get update && apt-get install chromium-browser
If you are testing things on OSX or similar, chrome-launcher should be able to find and automatically startup Chrome for you.
In the examples folder there is a small example on how the application API could look. Basically, you just have to define an endpoint that will receive the webhook and check that the signature matches.
api.post('/hook', function (req, res) {
var signature = req.get('X-PDF-Signature', 'sha1=')
var bodyCrypted = require('crypto')
.createHmac('sha1', '12345')
.update(JSON.stringify(req.body))
.digest('hex')
if (bodyCrypted !== signature) {
res.status(401).send()
return
}
console.log('PDF webhook received', JSON.stringify(req.body))
res.status(204).send()
})Follow the guide under production/ to see how to setup pdf-bot using pm2 and nginx
We setup our crontab to continously look for jobs that have not yet been completed.
* * * * * node $(npm bin -g)/pdf-bot -c ./pdf-bot.config.js shift >> /var/log/pdfbot.log 2>&1
* * * * * node $(npm bin -g)/pdf-bot -c ./pdf-bot.config.js ping:retry-failed >> /var/log/pdfbot.log 2>&1Let us assume I want to generate a PDF for https://esbenp.github.io. I can add the job using the pdf-bot CLI.
$ pdf-bot -c ./pdf-bot.config.js push https://esbenp.github.io --meta '{"id":1}'Next, if my crontab is not setup to run it automatically I can run it using the shift command
$ pdf-bot -c ./pdf-bot.config.js shiftThis will look for the oldest uncompleted job and run it.
This is a common issue with PDF generation. Luckily, html-pdf-chrome has a really awesome API for dealing with Javascript. You can specify a timeout in milliseconds, wait for elements or custom events. To add a wait simply configure the generator key in your configuration. Below are a few examples.
Wait for 5 seconds
var htmlPdf = require('html-pdf-chrome')
module.exports = {
api: {
token: 'api-token'
},
// html-pdf-chrome options
generator: {
completionTrigger: new htmlPdf.CompletionTrigger.Timer(5000), // waits for 5 sec
},
webhook: {
secret: '1234',
url: 'http://localhost:3000/webhooks/pdf'
}
}Wait for event
var htmlPdf = require('html-pdf-chrome')
module.exports = {
api: {
token: 'api-token'
},
// html-pdf-chrome options
generator: {
completionTrigger: new htmlPdf.CompletionTrigger.Event(
'myEvent', // name of the event to listen for
'#myElement', // optional DOM element CSS selector to listen on, defaults to body
5000 // optional timeout (milliseconds)
)
},
webhook: {
secret: '1234',
url: 'http://localhost:3000/webhooks/pdf'
}
}In your Javascript trigger the event when rendering is complete
document.getElementById('myElement').dispatchEvent(new CustomEvent('myEvent'));Wait for variable
var htmlPdf = require('html-pdf-chrome')
module.exports = {
api: {
token: 'api-token'
},
// html-pdf-chrome options
generator: {
completionTrigger: new htmlPdf.CompletionTrigger.Variable(
'myVarName', // optional, name of the variable to wait for. Defaults to 'htmlPdfDone'
5000 // optional, timeout (milliseconds)
)
},
webhook: {
secret: '1234',
url: 'http://localhost:3000/webhooks/pdf'
}
}In your Javascript set the variable when the rendering is complete
window.myVarName = true;You can find more completion triggers in html-pdf-chrome's documentation
Below are given the endpoints that are exposed by pdf-server's REST API
| key | type | required | description |
|---|---|---|---|
| url | string | yes | The URL to generate a PDF from |
| meta | object | Optional meta data object to send back to the webhook url |
curl -X POST -H 'Authorization: Bearer api-token' -H 'Content-Type: application/json' http://pdf-bot.com/ -d '
{
"url":"https://esbenp.github.io",
"meta":{
"type":"invoice",
"id":1
}
}'Currently pdf-bot comes bundled with build-in support for storing PDFs on Amazon S3.
Feel free to contribute a PR if you want to see other storage plugins in pdf-bot!
To install S3 storage add a key to the storage configuration. Notice, you can add as many different locations you want by giving them different keys.
var createS3Config = require('pdf-bot/src/storage/s3')
module.exports = {
api: {
token: 'api-token'
},
storage: {
'my_s3': createS3Config({
bucket: '[YOUR BUCKET NAME]',
accessKeyId: '[YOUR ACCESS KEY ID]',
region: '[YOUR REGION]',
secretAccessKey: '[YOUR SECRET ACCESS KEY]'
})
},
webhook: {
secret: '1234',
url: 'http://localhost:3000/webhooks/pdf'
}
}var decaySchedule = [
1000 * 60, // 1 minute
1000 * 60 * 3, // 3 minutes
1000 * 60 * 10, // 10 minutes
1000 * 60 * 30, // 30 minutes
1000 * 60 * 60 // 1 hour
];
module.exports = {
// The settings of the API
api: {
// The port your express.js instance listens to requests from. (default: 3000)
port: 3000,
// The token used to validate requests to your API. Not required, but 100% recommended.
token: 'api-token'
},
// html-pdf-chrome
generator: {
// Triggers that specify when the PDF should be generated
completionTrigger: new htmlPdf.CompletionTrigger.Timer(1000), // waits for 1 sec
// The port to listen for Chrome (default: 9222)
port: 9222
},
queue: {
// How frequent should pdf-bot retry failed generations?
// (default: 1 min, 3 min, 10 min, 30 min, 60 min)
generationRetryStrategy: function(job, retries) {
return decaySchedule[retries - 1] ? decaySchedule[retries - 1] : 0
},
// How many times should pdf-bot try to generate a PDF?
// (default: 5)
generationMaxTries: 5,
// How frequent should pdf-bot retry failed webhook pings?
// (default: 1 min, 3 min, 10 min, 30 min, 60 min)
webhookRetryStrategy: function(job, retries) {
return decaySchedule[retries - 1] ? decaySchedule[retries - 1] : 0
},
// How many times should pdf-bot try to ping a webhook?
// (default: 5)
webhookMaxTries: 5,
// In what path should the database be stored?
path: 'storage/db/db.json',
// pdf-bot uses lowdb. You can pass options to it here.
lowDbOptions: {
}
},
storage: {
's3': createS3Config({
bucket: '',
accessKeyId: '',
region: '',
secretAccessKey: ''
})
},
webhook: {
// The prefix to add to all pdf-bot headers on the webhook response.
// I.e. X-PDF-Transaction and X-PDF-Signature. (default: X-PDF-)
headerNamespace: 'X-PDF-',
// Extra request options to add to the Webhook ping.
requestOptions: {
},
// The secret used to generate the hmac-sha1 signature hash.
// !Not required, but should definitely be included!
secret: '1234',
// The endpoint to send PDF messages to.
url: 'http://localhost:3000/webhooks/pdf'
}
}pdf-bot comes with a full CLI included! Use -c to pass a configuration to pdf-bot. You can also use --help to get a list of all commands. An example is given below.
$ pdf-bot.js --config ./examples/pdf-bot.config.js --help
Usage: pdf-bot [options] [command]
Options:
-V, --version output the version number
-c, --config <path> Path to configuration file
-h, --help output usage information
Commands:
api Start the API
install
generate [jobID] Generate PDF for job
jobs [options] List all completed jobs
ping [jobID] Attempt to ping webhook for job
ping:retry-failed
pings [jobId] List pings for a job
purge [options] Will remove all completed jobs
push [options] [url] Push new job to the queue
shift Run the next job in the queuepdf-bot uses debug for debug messages. You can turn on debugging by setting the environment variable DEBUG=pdf:* like so
DEBUG=pdf:* pdf-bot jobs$ npm run testPlease report issues to the issue tracker
The MIT License (MIT). Please see License File for more information.