Web Monetization Receiver

Server-side library for advanced Web Monetization integrations

• Overview
• Examples
• API
  • Monetizer
  • Monetizer.koa
  • Monetizer.generateSPSPResponse
  • Monetizer.listen
  • Monetizer.getBucket
  • Bucket
  • Bucket.fund
  • Bucket.spend
  • Bucket.awaitBalance
  • Bucket.awaitAndSpend
  • Bucket.monetizeStream
  • Payer
  • Payer.pay

Overview

Lots of sites can benefit from Web Monetization. Most of the time, you can add a little bit of javascript that causes Web Monetization enabled users to donate to you (The scripts are available here).

Some sites might want to do more than this. For example, an image gallery might want to offer some images only to its Web Monetization enabled users. Or a video site might charge per second of video streamed.

This repository contains tools which aim to make these advanced integrations easier.

Examples

Run npm install in this repository's root, then follow the README of the example you want to run.

• Serve Paid Images
• Serve Paid Video

API

Monetizer

const { Monetizer } = require('web-monetization-receiver')
const monetizer = new Monetizer()

Creates a "Monetizer" that wraps an ILP/STREAM server and exposes an easy to use API.

You can use Monetizer to charge for different actions on your server using Web Monetization. It's best suited for web apps where your user is browsing your site and paying continuously with Web Monetization.

Parameters

• opts: Object - (Optional) Options for this Monetizer.

• opts.plugin: IlpPlugin - (Optional) ILP Plugin to listen for payments with. By default, Monetizer creates a plugin to your local moneyd server.

• opts.buckets: Object - (Optional) Options regarding buckets of payment that have been received by different site users.

• opts.buckets.timeout: Number - (Optional) How long to wait before clearing an unused bucket.

• opts.buckets.capacity: Number - (Optional) Maximum amount of payment to accumulate in a single bucket.

Monetizer.koa

app.use(monetizer.koa())

Connects this Monetizer instance to a Koa app.

• Adds an SPSP receiver to the server (responds to requests with Accept: application/spsp4+json)

• Sets a webMonetization cookie on every client that hits the site. This is then used to associate each client with a bucket of payment, so that they can request paid resources from the server.

• Adds ctx.webMonetization to the server, with the payment bucket associate with the current client. This can be used to charge for requests server-side. Look at the Examples section to see some ways to use it, or keep reading the API.

Parameters

• opts: Object - (Optional) Additional options for the receiver

• opts.spsp: boolean - (Optional) (Default true) Whether to respond to SPSP requests. If this is set to false, you must write an SPSP receiver endpoint yourself using the generateSPSPResponse function.

Return

• Async middleware function for use by Koa.

Monetizer.generateSPSPResponse

const jsonResponse = await monetizer.generateSPSPResponse(tag)

Returns an SPSP response that allows a client to pay us. If you're using the monetizer.koa() you don't need to call this function anywhere. If you're not using Koa, then return await monetizer.generateSPSPResponse(tag) for any request that has Accept of application/spsp4+json. The tag should be a cookie that identifies the user.

Parameters

• tag: string - (Optional) Tag corresponding to this user.

Return

• response: Object - SPSP details that let your client pay you over Interledger. If they pay to these details, then their payment will accumulate in a bucket identified by their tag.

• response.destination_account: string - ILP address for the client to pay to.

• response.shared_secret: string - Shared secret used for authentication and encryption of data passed over Interledger.

Monetizer.listen

await monetizer.listen()

Initializes the STREAM server of this Monetizer. If you use generateSPSPResponse then it will call this function automatically.

Parameters

• None

Return

• Promise to null, resolves when server is initialized.

Monetizer.getBucket

const bucket = monetizer.getBucket(tag)

Gets a bucket associated with a given tag. If you're using the Koa middleware then on any route you can access ctx.webMonetization to access the current user's bucket (equivalent of monetizer.getBucket(ctx.cookie.get('webMonetization'))).

If no money has been paid into the bucket, you'll just get an empty bucket.

After a timeout (configurable via opts.buckets.timeout in the Monetizer constructor) any bucket that hasn't been used will be cleaned up.

Parameters

• tag: string - Tag corresponding to this user.

Return

• bucket: Bucket - Bucket of payment for this user

Bucket

A bucket represents the payment received by the server from a specific user. You can use a bucket object to add/spend funds.

The bucket constructor shouldn't be called directly, instead you should get it from monetizer.getBucket (or from ctx.webMonetization if you're using Koa).

Bucket.fund

bucket.fund('1000')

This function adds the given number of units to the bucket. There usually is no reason to call this directly, because the Monetizer's SPSP server will automatically fund the necessary buckets whenever payments are received.

Parameters

• amount: string - Amount of units (denominated in the units of your plugin/local moneyd) to add to this bucket.

Return

None

Bucket.spend

if (bucket.spend('300')) {
  return paidContent
} else {
  throw new Error('insufficient funds')
}

Subtracts funds from the bucket. Returns true if there were enough funds, and false otherwise.

Parameters

• amount: string - Amount of units (denominated in the units of your plugin/local moneyd) to subtract from this bucket.

Return

• success: boolean - Whether the bucket had enough funds and was subtracted from.

Bucket.awaitBalance

await bucket.awaitBalance('1000')
console.log('user can spend 1000 units')

Waits until the user has accumulated a certain number of units in their bucket. This is useful for a web server where the client attempts to load all resources immediately but will take some time to pay for all of them (See Examples).

This represents an absolute amount. If you awaitBalance('1000') it waits for the user to have 1000 units total, not 1000 units more than they did when the function was called.

Parameters

• amount: string - Amount of units (denominated in the units of your plugin/local moneyd) to wait for.

Return

• Promise to void which resolves when the amount is reached.

Bucket.awaitAndSpend

await bucket.awaitAndSpend('1000')
return paidContent

Combines awaitBalance and spend into an atomic operation. First the balance is awaited, and then it is spent. If the spend fails, the await is repeated.

Parameters

• amount: string - Amount of units (denominated in the units of your plugin/local moneyd) to wait for and then spend.

Return

• Promise to void which resolves when the amount is reached and spent.

Bucket.monetizeStream

const stream = fs.createReadStream('video.webm')
return bucket.monetizeStream(stream)

const stream = fs.createReadStream('video.webm')
return bucket.monetizeStream(stream, {
  freeBytes: 10000,
  costPerByte: (1 / 5000)
})

Turns a boring regular stream into a cool paid stream. Whenever a chunk of data is ready on the stream being read from, chunk.length * costPerByte units are subtracted from the bucket. If the bucket hasn't got sufficient funds, the read stream is paused. Once the bucket gets sufficient funds, the stream is resumed.

You can use freeBytes to send a certain amount of data upfront without requiring payment (useful for buffering video quickly). costPerByte lets you fine-tune how much payment bandwidth is required to keep up with the stream.

To see an example of usage, refer to the video example.

Parameters

• stream: ReadableStream - Node.js Readable Stream which is being monetized.

• opts: Object - (Optional) Options to fine-tune the payment for this stream.

• opts.freeBytes: Number - (Optional) How many free bytes to send up front. Default 0.

• opts.costPerByte: Number - (Optional) How much to charge per byte sent over this stream. Default 1 / 5000 (on a typical Coil plan, this represents a rate of 500Kb/s)

Return

• stream: ReadableStream - Transformed stream which will charge for money as it goes. This stream also implements a special money event which fires whenever payment is charged for data going through the stream.

Payer

const payer = new Payer({
  streamOpts: {
    minExchangeRatePrecision: 2
  }
})

Creates a Payer object. A Payer can be used to efficiently pay out to many different SPSP receivers. It keeps connections to each of the receivers cached until they time out in order to minimize the amount of connection re-establishment.

Parameters

• opts: Object - (Optional) additional options for this payer
• opts.streamOpts: Object - (Optional) additional override object for IlpStream.createConnection calls. You can read about the format here.

Return

• payer: Payer - Payer object

Payer.pay

await payer.pay('$twitter.xrptipbot.com/interledger', '100')

Sends some money to a payment pointer. If a STREAM connection to this payment pointer already exists then the money is sent over that connection. If no STREAM connection to this payment pointer exists, then one is created.

If the STREAM connection does not exist and cannot be established then this function will reject.

Parameters

• pointer: string - Payment pointer to send funds to.

• amount: string - Amount of units (denominated in the units of your plugin/local moneyd) to send.

Returns

• Promise to void. Rejects if SPSP details cannot be loaded or the STREAM connection fails.