paypercall

Charge for HTTP APIs on a pay-per-call basis with Bitcoin and Lightning.

Want to require a payment when users take some programmatic action, such as sending an SMS or running imaging processing? That's what paypercall is for.

Available as an express middleware (where a node.js app makes charges directly) or as a reverse proxy (where a reverse proxy requires payment before providing access to an app).

Install

$ npm install paypercall

Server Setup

As a middleware

paypercall can be used as an express middleware to charge payments directly in your node.js apps. Below is an example app that charges 0.1 USD to send SMS messages:

app.js

const pay = require('paypercall')({ chargeUrl: ..., chargeToken: ... })
    , twi = require('twilio')(twilioSid, twilioToken)
    , app = require('express')()

app.use(require('body-parser').urlencoded())

app.post('/sms', pay(0.1, 'USD'), (req, res, next) =>
  twi.messages.create({ from: 'paypercall', to: req.body.to, body: req.body.message })
    .then(msg => res.send({ success: true, sid: msg.sid }))
    .catch(next))

app.listen(4000, _ => console.log('HTTP server running on localhost:4000'))

See ifpaytt for a more full-fledged application using paypercall as a middleware.

As a reverse proxy

Alternatively, you can develop your HTTP server with no payments awareness and use paypercall as a reverse proxy to handle payments. Below is an example using a python app:

app.py

from flask import Flask, request
from twilio.rest import Client as Twilio

app = Flask(__name__)
twi = Twilio(twilioSid, twilioToken)

@app.route("/sms", methods=['POST'])
def sms():
  msg = twi.messages.create(from='paypercall', to=request.form['to'], body=request.form['message'])
  return { 'success': True, 'sid': msg.sid }

@app.run(Port=4001)

Run the python app and the paypercall proxy:

$ FLASK_APP=app.py flask run
* Running on http://localhost:4001/

$ paypercall --charge-token mySecretToken --upstream-url http://localhost:4001 \
             --port 4000 --rates-yaml '{ POST /sms: 0.1 USD }'
HTTP reverse proxy running on http://localhost:4000, proxying to http://localhost:4001

You will now have the python app running on port 4001 (providing API calls free of charge) and the paypercall reverse proxy running on port 4000 (charging on a per-call basis).

Paying for API calls

Users can access paypercall-enabled API endpoints in three steps:

Send an empty request (no body) to the paypercall-enabled endpoint to get the BOLT11 payment request and the X-Token header:

$ curl -i -X POST http://localhost:4000/sms

HTTP/1.1 402 Payment Required
Content-Type: application/vnd.lightning.bolt11
X-Token: lmbdmJeoSQ0ZCB5egtnph.af1eupleFBVuhN2vrbRuDLTlsnnUPYRzDWdL5HtWykY

lnbcrt8925560p1pdfh7n2pp54g5avyupe70l988h30u0hy8agpj2z7qsveu7ejhys97j98rgez0...

Make the payment:

$ lightning-cli pay lnbcrt8925560p1pdfh7n2pp54g5avyupe70l988h30u0hy8agpj2z7qsveu7ejhys97j98rgez0...

Send the request again, this time with the request body and with the X-Token header echoed back:

$ curl -i -X POST http://localhost:4000/sms \
  -H 'X-Token: lmbdmJeoSQ0ZCB5egtnph.af1eupleFBVuhN2vrbRuDLTlsnnUPYRzDWdL5HtWykY' \
  -t to=+972-789456123 \
  -d message='I got lightning working and all I got was this sms!'

HTTP/1.1 200 OK
Content-Type: application/json

{"success":true,"sid":"SMf34fe622a8fe7565fc15be3ce8bc437e"}

Documentation

Middleware

const pay = require('paypercall')(options)

Returns a new payment middleware factory. options can contain the following fields:

chargeUrl: Lightning Charge server URL (optional, defaults to http://localhost:9112)
chargeToken: Lightning Charge access token (required)
dbPath: Path to sqlite database (optional, defaults to ./paypercall.db)
currency: Default currency if none is specified (optional, defaults to BTC)
secret: Secret key used for HMAC tokens (optional, generated based on chargeToken by default)
invoiceExp: How long should invoices be payable for (optional, defaults to 1 hour)
accessExp: How long should paid access tokens remain valid for (optional, defaults to 1 hour)

const payware = pay(amount[, currency])

Returns an express middleware that requires a payment of amount units of currency (or the default currency if none provided) before letting requests pass through.

Can be used as following:

const pay = require('paypercall')({ chargeToken: 'myToken', currency: 'EUR' })
    , app = require('express')

// charge requests to a specific route
app.post('/sms', pay(0.15), (req, res) => { /* send SMS */ })

// charge all requests to /paid-apis/*
app.use('/paid-apis', pay(0.25))

// dynamic pricing (should only be based on the method and path)
app.post('/ocr/:type', (req, res, next) => {
  pay(getPriceForType(req.params.type))(req, res, (err) => {
    if (err) return next(err)
    // payment succesfull, run OCR
    // (the paid invoice is accessible at `req.invoice`)
  })
})

Reverse proxy

$ paypercall --help

  Charge for HTTP APIs on a pay-per-call basis with Bitcoin and Lightning

  Usage
    $ paypercall [options]

  Options
    -c, --charge-url <url>      lightning charge server url [default: http://localhost:9112]
    -t, --charge-token <token>  lightning charge access token [required]

    -u, --upstream-url <url>    the upstream server to reverse proxy [required]
    -r, --rates-path <path>     path to YAML file mapping from endpoints to rates [default: ./rates.yaml]
    -y, --rates-yaml <yaml>     YAML string to use instead of reading from {rates-path}
    -x, --currency <name>       default rate currency if none is specified [default: BTC]
    -d, --db-path <path>        path to store sqlite database [default: ./payperclick.db]

    --invoice-expiry <sec>      how long should invoices be payable for [default: 1 hour]
    --access-expiry <sec>       how long should paid access tokens remain valid for [default: 1 hour]
    --token-secret <secret>     secret key used for HMAC tokens [default: generated based on {charge-token}]

    -p, --port <port>           http server port [default: 4000]
    -i, --host <host>           http server listen address [default: 127.0.0.1]
    -e, --node-env <env>        nodejs environment mode [default: production]
    -h, --help                  output usage information
    -v, --version               output version number

  Example
    $ payperclick -t myAccessToken -u http://upstream-server.com/ \
                  -y '{ POST /sms: 0.0001 BTC, PUT /page/:id: 0.0002 BTC }'

License

MIT

ElementsProject/paypercall

ElementsProject

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