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Poppy I/O

Note: This README, and Poppy I/O in general, is an active work in progress. It's definitely incomplete and the parts that aren't are probably wrong.

Poppy I/O is a concept for a JavaScript API and set of protocols for cloud file pickers and other similar things - in Poppy I/O parlance, poppies.

A poppy is a web page that provides a service to other, client web pages, and is activated by the client web page opening the poppy in a popup dialog window. By this definition Dropbox Choosers and Twitter Web Intents would count as poppies (although they don't use Poppy I/O).

Since poppies handle all the complicated parts of integrating with a service, they can present a very simple API to client applications. The idea of Poppy I/O is that that these APIs are so simple, we can create common APIs for any poppy to implement, allowing client apps to work any number of poppies.

And if a client app can work with any random poppy implementing the right API, why not let the user pick the poppy?

Poppy I/O is Web Intents 2.0 😎

Here's what it looks like.

<button id='pickButton'>Pick Photo</button>
<script type='module'>
  import Poppy from "https://js.poppy.io/0.0.4/use-en.mjs";
  pickButton.onclick = async () => {
    let pick = await Poppy.accept("image/*");
    if (pick) {
      let img = new Image;
      img.src = pick.data.location || URL.createObjectURL(pick.data.contents);

But you don't need a browser that supports ES modules or async/await for Poppy I/O to work; here's the same code in more conventional ES5.

<script src="https://js.poppy.io/0.0.4/target/bundle/poppyio.en.min.js" nomodule></script>
<script nomodule>
  poppyio.Poppy.any().iePrelude = "/"; // hack for Internet Explorer 10
  pickButton.onclick = function () {
    poppyio.Poppy.accept("image/*").then(function (pick) {
      if (pick) {
        var img = new Image;
        img.src = pick.data.location || URL.createObjectURL(pick.data.contents);

Poppy I/O should support any browser that supports channel messaging, which is almost all of them. Internet Explorer requires a Promise polyfill (the bundles come with promiscuous) and a small hack (the iePrelude above).

Try it

Check out https://primitive.5apps.com for an example client app. For a poppy to use, try:

  • f4r.poppy.io to pick an image from the Flickr Commons or upload an image to your Flickr account
  • i3r.poppy.io to anonymously upload an image to imgur.

README Contents

The Elements of Poppy I/O

Poppy I/O is all about two webpages, one of which has something to offer which the other page accepts. One of those pages is the client application - the page the user is already on - and the other is the poppy - a service webpage that launches in a popup dialog window to perform some action on behalf of the client page.

That action might be something like:

  • Picking a file to use in the app. The client accepts a file offered by the poppy.
  • Saving a file they created in the app. The poppy accepts a file offered by the client.
  • Sharing a link. The poppy accepts a link offered by the client.

The client might start out with a specific poppy in mind, in which case it just opens up its URL in the dialog window. But the Poppy I/O ideal is that the user gets to pick the poppy.

How the user picks their poppy is through the launcher. This is a page that opens up inside the dialog window if the client app doesn't open a specific poppy. It provides a user interface to let the user pick one instead.

The launcher would ideally be something provided in the user's browser, and Poppy I/O is designed to work with an optional browser extension to provide that (it only exists as a proof of concept at this point).

But without a browser extension, the client can provide a launcher of its own, or delegate it to a centralized directory launcher. To allow users to select poppies not in any directory, there's a domain resolution procedure to take a user-entered domain name and determine if there's a poppy at the domain, and what its URL is. (The poppyio JavaScript library includes a minimal embedded "starter" launcher).

Note that it can be dangerous to send the user to a poppy by domain name if the user enters it incorrectly - for example if they intend to upload a file to dropbox.com but accidentally type dropbox.cm and send the file there instead - so a safety check should be performed on any entered domain, Poppy I/O includes a feature called Namecheck where services can provide digital certificates signed by some authority verifying a domain as not misleading. That authority is currently me.

So an example of how things might work would be:

  1. You've signed up to a website and want to upload a profile photo.
  2. You see the site lets you do that using Poppy I/O, and click the "Pick From Poppy" button.
  3. You don't have a Poppy I/O browser extension installed (because one doesn't exist yet), but the launcher provided by the website lets you enter the domain of the poppy you want.
  4. You keep your photos on your own Nextcloud install with a Poppy I/O app (which also doesn't exist yet), so you type in the domain of your VPS.
  5. The launcher throws up a scary warning about the name being unverified.
  6. But you expected that since you never submitted it for Namecheck, so you click "I understand the risks" or whatever and get sent to your Nextcloud poppy.
  7. You pick the photo you want.
  8. The photo gets sent back to the setup page and the poppy closes automatically.


This has changed before and might change again, but for now:

  • Poppy.io is the name of the project and its website domain name.
  • Poppy I/O is the set of protocols and general concept.
  • poppyio is the JavaScript library implementing Poppy I/O.
  • A poppy is a Poppy I/O service web page.

Poppy I/O isn't related to the Poppy robotics project.

Using Poppy I/O


Web Browsers

Any browser that supports channel messaging should work; that means Internet Explorer 10+ and all recent versions of Chrome, Safari, Firefox, and Edge.

Internet Explorer requires a Promise polyfill to be installed. If you use the single-file <script> bundle one is provided but if you use one of the module formats you'll have to supply it. Also, Internet Explorer 10 and older versions of Internet Explorer 11 require a small hack to work, which is disabled by default.

(Also there are currently significant UI display issues in the lauch UI on Internet Explorer, but communication works fine)

A browser extension isn't required for Poppy I/O to work (and indeed at this point exists only as a proof of concept), but the browser extension hooks are designed with Chrome and the WebExtensions API in mind.


Client apps don't need anything on the server in general, but if you allow users to pick poppies by domain and are using the starter launcher then it needs to be able to make cross-origin requests to other servers - if you have a CSP in place that prevents then that it won't work.

For a poppy service, in order to allow for users to locate your poppy by domain name you need to have a /.well-known/host-meta.json file on your server that is configured to allow anonymous cross-origin access. That file is used to look up the location of the poppy for the domain.

As a rule, any data exchanged by URLs over Poppy I/O should allow anonymous cross-origin access unless the receiving peer indicates CORS isn't required.

Getting poppyio

poppyio isn't ready to be published to npm, but you can still add it as a dependency to your package.json. The package contains both ES modules in .mjs files and CommonJS ES5 modules in adjacent .js files. AMD versions of the modules are under the amd directory.

  $ npm install https://js.poppy.io/0.0.4/poppyio-0.0.4.tgz

You can also bower install the same URL if you use Bower.

The simplest way to get started is to use the browser bundle. Everything get exported to the poppyio global namespace:

  <script src="https://js.poppy.io/0.0.4/bundle/poppyio.en.js"></script>

import or require the "use-en" module (in whatever format you're using) to include the English language user interface for the launcher. The browser bundle already has it (which is why there's an en in the name). If you're using a module format you'll have to add a Promise polyfill for Internet Explorer support. The bundle already includes one.

The examples will assume you're using the browser bundle.

Picking a file from a Poppy

Client side

Letting the user pick a poppy

The entry point to poppyio from the client side is the Poppy class.

// import Poppy from "poppio/use-en"
// var Poppy = require("poppyio/use-en").default;
function pick() {
    .then(function (file) {
      if (file) console.log(file.data.location || file.data.contents && "Got Blob");
    .catch(function (error) {

Poppy.accept() lets you ask for an object. You specify what kind of object in the first parameter. It can be a string


Or a list of strings.

Poppy.accept(["image/*", ".png", ".jpeg", ".jpg", ".gif", ".bmp"])

Different types should be listed in order of preference from most desired to least.

It may also be an object. The object lets you specify extra information about what you support, for example if you will accept URLs that don't offer CORS:

Poppy.accept({kind:["image/*", ".png", ".jpeg", ".jpg", ".gif", ".bmp"], noCors: true})

You can use both file extensions and MIME media types to identify what kind of file you want, since not every cloud drive will know exactly what MIME type every file is. Note that the MIME type is only advisory, so be sure to check that the file you get is the kind of file you want.

Poppy.accept() returns a Promise for an object that contains what was accepted. It may resolve to undefined if the poppy never offered anything. That might be because the user cancelled before picking anything, or it also could be because the poppy that was chosen didn't have anything to offer.

The object the poppy offered to you is stored in the data property. You can send any kind of object with Poppy I/O - not just files - and what that data property contains would depend on what kind of object is sent. But for files it will look like this:

    // One of the following is required
    location: // a URL to use to download the file. Will support anonymous CORS.
    contents: // a Blob containing the file data

    // Optional
    filename: // The file name
    hotlink: // "prohibited", "permitted", or "perferred"

    // Optional Dublin Core metadata. http://dublincore.org/documents/dces/
    format: // content type
    title: // title
    description: // description
    // etc...

Using a specific poppy

The Poppy.accept() method is short for Poppy.any().accept(). What Poppy.any() does is return a base poppy opener set up by the "use-en" module. You can customize this object using the with() method. You can use the url property to specify the URL of the poppy.

poppyio.Poppy.with({ url: "https://www.example.com/poppy" }).accept("image/*")

Poppy.with() is in turn short for Poppy.any().with(). The with() method returns a new object that uses the object you called it on as its prototype, as a template basically.

Poppy opener objects can be re-used to open as many poppies as you want.

Service Side

The host-meta.json file

If you want users to be able to launch your poppy by domain name, you have to have a JRD file at /.well-known/host-meta.json on your server that includes a link to the poppy dialog page. Since it may be accessed directly by client-side JavaScript, it has to be accessible via anonymous CORS.

The file looks like this:

  "links": [
      "rel": "https://poppy.io/a/poppy",
      "href": "/poppy.html"

The href should be absolute if possible, but a relative URL will work if your domain only contains ASCII characters. It's the URL of the poppy.

Listening for a request

The entry point to poppyio from the service/poppy side is the PoppyService class. Poppy I/O works asynchronously, so you provide a callback that will be notified when we know there's a client. You can tell if the client is accepting something with the client.accepts() method.

// import PoppyService from "poppyio/poppy-service"
// var Poppy = require("poppyio/poppy-service").default;
poppyio.PoppyService.onClient(function (client, error) {
  // showError and showPickUi are placeholders for your own implementation.
  if (error) {
    showError(error.message || error);
  } else if (client.accepts("File")) {
  } else {
    showError("The client isn't accepting a file");

The client object passed to the callback is also saved in the PoppyService.client static variable.

You should only call PoppyService.onClient() once per page, but can call it as many times as you want on different pages until you actually connect to the client. So the poppy doesn't have to be a single-page application.

Sending the object

Once the user has selected a file to use, the poppy sends it back to the client with the client.offer() method.

function sendPhoto() {
  // showError is a placeholder for your own implementation
  poppyio.PoppyService.client.offer("image/png", {
    location: "https://www.example.com/photo.png",
    title: "A sample photo"
  }).then(function () {
  }).catch(function (error) {
    showError(error.message || error);

The first parameter is the same as that of the Poppy.accept() method - the kind of thing you are sending. The second parameter is the object to send to the client. It can also be a function that returns the object to send, or a Promise that resolves with the object to send, or a function that returns a Promise that resolves with the object to send.

The offer() method returns a Promise that resolves after the transfer is complete. It's the poppy's responsibility to close itself afterwards - it may also stay open after the transfer is complete if it needs to show some information to the user. You can do that with window.close() but should use PoppyService.close().

If there's an error the poppy should show an error message instead of just closing; otherwise the poppy will disappear without any indication that something went wrong.

Saving a file to a poppy


The Protocol

Underlying the JavaScript API is a protocol, or rather a set of protocols, built on top of cross-document messaging, channel messaging, DOM custom events, cross-origin resource sharing, and web host metadata.

There are basically five steps:

  1. Open a popup window
  2. Navigate to the poppy URL
  3. Establish a connection to the poppy
  4. Transfer data over the connection
  5. Close the popup

Launch: Open a popup window

The first thing a client needs to do is open a popup window, since it must be done synchronously in response to a user action. For safety, the popup is launched using an <iframe> element as its parent with a sandbox without the allow-top-navigation permission (where a poppy could navigate the client web page away from the page they were on while the user wasn't paying attention).

Before opening up the popup, the client gives any browser extension that may be present the opportunity to intercept the launch. It does this by dispatching a CustomEvent of the type https://poppy.io/a/open on the HTML iframe sandbox. The extension listens for this event and invokes preventDefault() setting the defaultPrevented property of the event to true, which the client uses to determine whether to proceed opening the window.

If an extension intercepts launch it also sets the data-piox-origin attribute on the iframe indicating the origin of the browser extension for cross-document messaging.

If a browser extension did not intercept the launch, the client opens a popup window which will host the poppy. If a specific poppy URL is available the popup is navigated directly to it, otherwise a Launch Page is opened in the popup allowing the user to select a poppy. The user interface may allow the user to enter the domain name of a poppy, in which case a Name Resolution is performed to determine the poppy URL.

If a browser extension did intercept the launch, the client will inform the extension of the requested domain or poppy URL in response to a listen message, as part of the Connect phase.

Name Resolution: Navigate to the poppy URL

Name resolution turns a user-entered domain name, e.g. pickapic.tk into a poppy service URL, e.g. https://pickapic.tk/poppy. It requires CORS, but if the Content Security Policy the client web page is under prohibits connections to arbitrary external servers may be performed server-side.

Given a user-entered domain example.com:

  1. The client web page makes a cross-origin HTTP request to https://example.com/.well-known/host-meta.json
    1. If the file doesn't exist, or CORS headers are not on the host-meta.json file and it is not available to the client, then the resolution fails.
  2. The client web page looks for a link in the host-meta.json file with the relation of https://poppy.io/a/poppy.
    1. If one is found, and there is an href for the link, that is the URL of the poppy.
      • The href should be an absolute URL.
    2. If one is not found, or there is no href, then the resolution fails.

Matching: Establishing a Connection

Matching is the process of establishing a connection.

A connection is initiated through cross-document messaging. The client maintains an Authorized Origin Set. That is initially the origin of the poppy URL; any authorized origin may change it if additional origins are required. The client also always trusts messages from Trusted Origins: the origin of the client and the data-piox-origin attribute in the proxy iframe set by the browser extension if it intercepted the launch.

Service: Signal it is listening

Note the "Service" may not be the final service that the client establishes a connection with - it may be the browser extension, or the launch page, or any other intermediate page that helps the user find a final service to use to perform a desired activity. A client must be able to accept any number of listen messages before a connection is established.

Once a poppy service page is loaded in the poppy, it sends a cross-document listen message to its window.opener indicating it is ready and listening. The message has a target origin of * and looks like this:

    "https://poppy.io/a/to-client": {
        "listen": true

The service also dispatches a CustomEvent of type https://poppy.io/a/listening to it's window.self to allow a browser extension to detect it's listening if there is no window.opener.

The client will only accept messages from trusted origins and origins in the authorized set. Initially that is the origin of the poppy service URL. If other origins need to be trusted, a message may be sent to the window.opener to indicate the new origin set. The message looks like this and has a target origin of *:

    "https://poppy.io/a/to-client": {
        "origins": ["example.com", "example.org"]

The origins list is the new Authorized Origins Set. It does not add to the existing one, it replaces it.

Client: Indicate its request

The client rejects any message if it's not from an origin in the Authorized Origin Set and is not from a Trusted Origin.

In response to a listen message, the clients sends a request message indicating what it is requesting. This will include a Match Set indicating what the client is requesting, a Control Port to use to establish a connection, and, if the message is from a trusted origin a Launch to indicate what URL or domain was requested to be launched.

A client indicates its intent through a Match Set, which is a list of Match Options. Each match option indicates a Protocol, a Side of that protocol, and a Hint.

  • A Protocol is a string identifying the name of a protocol. For the Simple Offer/Accept Protocol this is just the kind of object, e.g. a File.
  • A Side is either accept or offer. Poppy I/O is designed to work with direct client-to-client connections where there is no "server" or "client" side. So instead of separate protocols for e.g. sending and receiving there is just one protocol, the Side indicates whether it is, from a peer's perspective, an send or recieve operation.
  • A Hint is an object that indicates extra information about the capabilities or desires of a peer to help determine if a match is suitable.

A match option for a client indicating it wants to accept a File looks like this:

    "accept": "File",
    "hint": {
        "types": ["image/*", ".png", ".jpeg", ".jpg", ".gif", ".bmp"]

A match option for a client indicating it wants to offer a File looks like this:

    "accept": "File",
    "hint": {
        "types": ["image/png", ".png"]

A Match Set is an array of these match option objects. A match set may contain both offer and accept match options. A protocol may only appear once as an offer or accept option but may be both an offer and an accept - This is to allow for protocols where there is no logical offer or accept side.

The Launch for trusted origins includes a service indicating the poppy service URL, a clientName with the user-facing name of the client, and an activityName with a user-facing description of what activity is being performed (e.g. picking a photo).

Additionally, a lang is sent indicating the language being used.

A full request message in response to a listen looks like this:

    "https://poppy.io/a/to-host": {
        "request": [
                "accept": "File",
                "hint": {
                    "types": ["image/*", ".png", ".jpeg", ".jpg", ".gif", ".bmp"]
        "launch": {
            "activityName": "Pick a Photo"
        "lang": "en"

Finally, a MessageChannel is created and one MessagePort is sent along with the message back to the Service. This MessagePort is the Connect Port which is used to establish a connection.

The request is sent in a cross-document message to the source of the triggering listen message. This may not be the popup window, or if there is a browser extension involved, there may not be a popup at all. The target origin of the message is the origin of the triggering listen message.

Client pages may receive any number of listen messages and must reply to each of them with a request.

Service: Connect

The service examines the Match Set and determines if it is able to service the request. It is able to service the request if it supports one of the protocols in the matchlist from the other side - if it is able to accept a protocol the client is offering, or offer a protocol the client is accepting. Further it may examine the hint object in the Match Option.

Once a service can commit to handling a request, it sends a connect message back to the client. This message is sent using the Control Port that the client provided with the request message. The message also includes another MessagePort, a Data Port which is used for the actual data transfer between the client and the service.

Aside from the Data Port, the message includes:

  • The Data Protocol which is the protocol to use over the Data Port, and which side the service will assume, indicated by setting the accept or offer property on the message to the Data Protocol name.
  • A response Match Set which will include a Match Option for the Data Protocol, which is where the hint for the data protocol will go. The Match Set may include other match options for other protocols the client requested.

A connect message looks like this:

    "connect": true,
    "offer": "File",
    "matchset": [
            "offer": "File",
            "hint": {
                "types": ["image/png"]

Once the client recieves the connect message, both client and service have a direct MessageChannel over which to send data, and a matching accept/offer pair and a session is established.

Client/Service: The Session

The simple offer/exchange protocol ("SOAP") is the standard means of transferring data using Poppy I/O using the data port. However, any protocol may be used if both sides agree to it.

The protocol has four steps:

  1. The offer side sends a message to the accept side over the data channel containing the object, along with any message ports.
  2. The accept side sends a response message to the offer side over the data channel, which may contain no data.
  3. The offer side sends a release message to the accept side over the data channel, indicating it has received the reply and the channel can be closed. The contents of the message are ignored.
  4. The accept sends a message consisting of the string release on the control channel.

The reason for step 3 is to prevent a service poppy from closing too soon. The client may detect the popup closing before the response is received, in which case it may ignore the message because it thinks the client is closed.

Step 4 is to signal the session may be closed. However, in a client/poppy exchange, the poppy always closes the session unless there is an error causing the session to be cancelled, and the service knows based on the data channel exchange that closing the session is safe. This is because the poppy is what the user is interacting with and may have information it needs to display to the user. Step 4 is for direct client-to-client sessions. In that case, the "service" role is assumed by an intermedary (e.g. a browser extension) and needs to be informed it's time to close the session.

Non-SOAP exchanges

If offer and accept may be for a protocol that does not use SOAP. In that case, one side must send a release message on the control channel to indicate it is safe to close the session to any intermediary if the session is a client-to-client peer-to-peer exchange.

Service: Close the Session

After the primary exchange is complete, the poppy may close automatically, or it may stay open if it has extra information to display to the user. The client should not close the session, or the dialog, unless there is an error. In the event that the client does close the dialog, it should display a message to the user explaining why.

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