BrightSign HTML: Where is the Persistent Storage?

BrightSign Media Players work with a number of content management systems.  With a content management system, you can upload a BrightSign presentation as an asset and it will be distributed to the the units out in the field automatically.

Recently, I was investigating what the options are for other persistent storage.  The assets to be managed were not a full presentation, but were a few files that were going to be consumed by a presentation. As expected, the solution needed to be tolerant to a connection being dropped at any moment.  If an updated asset were to be partially downloaded, the expected behavior would be that the BrightSign continues with the last set of good assets that it had until a complete new set could be completely downloaded.

The first thing that I looked into was whether the BrightSign units supported service workers.  If they did, this would be a good area to place an implementation that would check for new content and initiate a download.  I also wanted to know what storage options were supported.  I considered indexedDB, localStorage, and caches.  The most direct way of checking for support was to make an HTML project that would check if the relevant objects were available on the window object.  I placed a few fields on an HTML page and wrote a few lines of JavaScript code to place the results in the HTML page.

Here’s the code and the results.

function main() {
    $('#supportsServiceWorker').text((navigator.serviceWorker)?'supported':'not supported');
    $('#supportsIndexDB').text((window.indexedDB)?'supported':'not supported');
    $('#supportsLocalStorage').text((window.localStorage)?'supported':'not supported');
    $('#supportsCache').text((window.caches)?'supported':'not supported');
    supportsCache
}
$(document).ready(main);
Feature Support
serviceWorker supported
indexedDB supported
localStorage supported
cache supported

Things looked good, at first.  Then, I checked the network request.  While inspection of the objects suggests that the service worker functionality is supported, the call to register a service worker script did not result in the script downloading and executing.  There was no attempt made to access it at all.  This means that service worker functionality is not available.  Bummer.

Usually, I’ve used the cache object from a service worker script.  The use of it there was invisible to the other code that was running in the application.  But with the unavailability of the service worker the code for the presentation will show more awareness of the object.  Not quite what I would like, but I know know that is one of the restrictions in which I must operate.

The Caches object is usually used by a service worker.  But the object can be used by the window, while it is defined as a part of the service worker spec, there’s no requirement that it be only used by it.

The next thing worth trying was to manually cache something and see if it could be retrieved.

if(!window.caches)
return;
window.caches.open(‘cache1’)
.then(function (returnedCache) {
cache = returnedCache;
});

This doesn’t actually do anything with the cache yet.  I just wanted to make sure I could retrieve a cache object.  I ran this locally and it ran just fine.  I tried again, running it on the BrightSign player, and got an unexpected result, window.caches is non-null, and I can call window.caches.open and get a callback.  The problem is that the callback always receives a null object.  It appears that the cache object isn’t actually supported.  It is possible that I made a mistake.  To check on this, I posted a message in the BrightSign forum and moved on to trying the next storage option, localStorage.

The localStorage option didn’t give me the results that I expected on the BrightSign. For the test I made a function that would keep what I hoped to be a persistent count of how many times it ran.

function localStorageTest() { 
    if(!window.localStorage) {
        console.log('local storage is not supported' );
        return;
    }
    var result = localStorage.getItem('bootCount0') || 0;
    console.log('old local storage value is ', result);
    result = Number.parseInt( result) + 1;
    localStorage.setItem('bootCount0', result);
    result = localStorage.getItem('bootCount0', null)
    console.log('new local storage value is ', result);
}

When I first ran this, things ran as expected.  My updated counts were saving to localStorage.  So I tried rebooting.  Instead of saving, the count reset to zero.  On the BrightSign, localStorage had a behavior exactly like sessionStorage.

Based on these results, it appears that persistent storage isn’t available using the HTML APIS.  That doesn’t mean that it is impossible to save content to persistent storage.  The solution to this problem involves NodeJS.  I’ll share more information about how Node works on BrightSign in my next post.  It’s different than how one would usually use it.

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Brightsign: An Interesting HTML Client

Of the many HTML capable clients that I’ve worked with, among them is an interesting family of devices called BrightSign Media Players (made by Roku). One of the things that they do exceptionally well is playing videos.  They support a variety of codecs for that job and it’s easy to have them go from one video to another in response to a network signal, a switch being pressed, or a touch on the screen. I’m using the XT1143 and XT1144 models for my test.

For simple video-only projects, the free tool BrightAuthor works well.  But the scenarios that this is best fit for seem to be scenarios with relatively low amounts of navigation complexity.  For projects with higher amounts of navigational complexity or projects that require more complex logic in general, an HTML based project may be a better choice.

After working on a number of HTML projects for BrightSign, I’ve discovered some of the boundaries of what can and can’t be done to have a different shape than on some other platforms.  I have seen that there are some things that while taxing to other devices, work well on the BrightSign players; and other things that don’t work so well on BrightSign that will work fine on other players.

The BrightSign HTML rendering engine in devices with recent firmware is based on Chromium.

BrightSign Firmware Version Rendering Engine
4.7-5.1 Webkit
6.0-6.1 Chromium 37
6.2-7.1 Chromium 45
8.0 (not released yet) Chromium 65

You can encounter some quirky rendering behaviour if you are on a device with an older firmware version.  At the time that I’m writing this the 8.0 firmware isn’t actually available (coming soon). I’ve found that while the device can render SVG, if I try to animate SVG objects, then performance can suffer greatly.  It is also only possible to have no more than two media items playing at a time (audio or video).  If an attempt is made to play more than two items, then the third item will be queued and will not begin to play until the previous two complete playing.

Rather than spend a lot of time developing and testing something in Chrome before deploying it to a BrightSign, it is better if you start off testing your code on the BrightSign as soon as possible.  The normal deployment process for code that is to run from the BrightSign is to copy a set of files to an HTML card, insert it into the BrightSign, reboot it, and wait a minute or two for the device to start up and render your content.

Compared to something being tested locally ,where you can just hit a refresh button to see how it renders, this process is way too long.  A better alternative, if your development machine and BrightSign are on the same network and sub-net is to make a BrightSign presentation that contains an HTML widget that points back to your development machine.  You’ll need to have a web server up and running on your machine and use the URL for the page of interest in the BrightSign presentation.  You will also want to make sure that you have enabled HTML debugging.  This is necessary for quick refreshes of the page.

When the BrightSign boots up, if everything is properly configured you should see your webpage show up.  You’ve got access to all of the BrightSign specific objects even though the page is being  served from another page.  You can inspect the elements of the page or debug the JavaScript by opening a Chrome browser on your development machine and browsing to the IP address of the BrightSign, port 2999.  Note that only one browser tab instance can be debugging the code running on the BrightSign.

The interface that you see here is identical to what you would see in the Chrome Developer Console when debugging locally.  If you make a change to the HTML, refreshing the page is simply a matter of pressing [CTRL]+[R] from the development window.  This will invoke a refresh on the BrightSign too.

I’ll be working on a BrightSign project over the course of the next few weeks and will be documenting some of the other good-to-know things and things that do or don’t work well on the devices.

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