Stupid solutions: Live server push without JS

https://underjord.io/live-server-push-without-js.html

by lawik • 6 years ago

342 79 6 years ago

allanrbo• 6 years ago

He mentioned chunk streaming text in an iframe I think as a joke, but I remember actually implementing a decent chat web app exactly like that years ago in the IE5 days or so.

robertlagrant• 6 years ago

Yeah you basically never close the response, right? Just keep appending! Chat is a good use case for it.

Maybe with CSS these days you could make only the last child of a div visible, and have constant updates with no need for JS.

Anyway. I quite like this idea of no JS. I know he said it would be evil to serve ads using MJPEG, but I'd probably prefer it if my page had less JS on it.

lukeramsden• 6 years ago

Anyway. I quite like this idea of no JS. I know he said it would be evil to serve ads using MJPEG, but I'd probably prefer it if my page had less JS on it.

Honestly I don't see how it's more evil, just because it doesn't use JS surely doesn't mean uBlock and such can't still block it? To be evil all ads full stop would have to be evil. As you say, I would much prefer this to ads that use JavaScript. If you can still show me ads on your news article when I haven't got JS enabled I'm not going to be too bothered, because hopefully everything should load plenty fast. It also means the rest of the site can load while the ads are loading.

ks• 6 years ago

A company I worked for in 2001 used chucked streaming to provide search results. The search results were collected by performing live searches in parallel (server side) with multiple partners and then aggregated into a single stream of chunked content. Basically the HTTP connection was kept open until all searches were complete, which would take a few minutes. The results were pushed incrementally to the browser as soon as they were available

This worked surprisingly well. They started with almost pure HTML with the results split into multiple tables to produce what looked like a single table of results. The only drawback was that the columns needed fixed width so that they would align properly.

After a while they switched to a Javascript based solution with dynamic filters. They used the same backend streaming engine to output chunks of Javascript code inside <script>-tags, which called a global "addResult(...)" method to update the state. If the search was cached, it would first render HTML code server side, which was then "hydrated" by the javascript code if needed.

Later it was replaced with a standard XHR polling mechanism.

It is interesting to look back at what we had to do that is trivial with today's technology.

alex_duf• 6 years ago

Yep, I've done that to send the status of a large upload, that must have been around 2008 or so.

We had a progress bar that would show the upload percentage, then the unzipping, then the virus scan on the server, then it would be marked as done.

finiteloop• 6 years ago

At FriendFeed, when we first introduced real-time comments and likes (pretty sure we were the first social network to do this), we did it with long-polling via an iFrame because web sockets did not exist. It actually worked pretty well!

https://www.ft.com/content/87b8107e-9c6d-3d3f-a60d-3e4f6315d...

nudpiedo3• 6 years ago

I have the feeling that as soon as the web got obsessed with HTTP(s) only transactions between nodes, people reinvented/rediscovered/hack-reimplemented socket's semantics on top of it.

necovek2• 6 years ago

It's hard for the web to become "obsessed with HTTP", because web is HTTP.

Pedantry aside, as soon as web/HTTP became The Internet (protocol of choice), you are right that the rest was bound to happen.

However, exactly the fact that it wasn't too constrained and allowed a lot of messing around (including with HTML, compared to eg gopher which was more semantic) is what made it "win" over all the other protocols except maybe email (and even there, >50% of people read it with web clients).

lgessler• 6 years ago

I think GP's talking not just about server-client connections but also server-server connections? In the latter case HTTP(S) wasn't as popular as it is today until the late aughts.

nudpiedo3• 6 years ago

I was speaking about the web as a net-work (not just web as in HTTP webpages). There are other protocols such as FTP, SMTP, and direct socket connections over TCP and UDP, but many of these use cases were absorved by REST only (HTTP) transactions and now websockets.

arraypad• 6 years ago

The core of this is of course the response header "Content-Type: multipart/x-mixed-replace" which in theory lets the server push updated chunks of any content type (although apparently only images in Chrome since 2013 [1]).

While it's a crude and handy way to update some content after the initial load without JS, it was also widely used with JS before Web Sockets - to push messages to clients with less latency than XHR polling.

[1] https://en.wikipedia.org/wiki/Multipart/x-mixed-replace#Mixe...

pronoiac• 6 years ago

omg! I thought it would slowly create and send along an mjpeg video file. Server push animation is a 90's thing. I wrote something up about it in 2009, and posted a still-working demo, because of a thread here. https://pronoiac.org/misc/2009/10/server-push-animation/

bullen• 6 years ago

The big problem with this spec (which is shared today by all the HTTP uploads in the world) is that you have to check for the delimiter every byte!

"Content-Type: chunked" is much better because it gives you the size of each chunk upfront! But that requires .js and also was buggy in IE until version 7.

I made a multiplayer online system that relies on chunked: https://github.com/tinspin/fuse

jswrenn• 6 years ago

although apparently only images in Chrome since 2013

I wonder if this includes SVG images...

EDIT: It does!

bawolff2• 6 years ago

Why not just stream a normal video stream?

egil• 6 years ago

mjpeg is a normal, albeit very simple video stream. While you could certainly squeeze the counter in less bytes by using a more advanced codec with interframe coding, it would be overkill for this poc.

bawolff2• 6 years ago

The point im trying to make is more that video streaming is a standard technique with off the shelf solution. The author presents MJPEG as some long lost solution to do this without js, but you can just as easily throw in a <video> tag without JS and call it a day. Except video tags arent as exciting.

lawik6• 6 years ago

Apparently HLS (HTTP Live Streaming) requires JS on every platform aside from Apple's. I was looking at that for streaming video + captions but since it requires JS to run it didn't really achieve what I wanted it to.

Maybe you could build an in-memory video stream for each user and just serve it slowly but then they would likely need to press play or you rely on autoplay and I've no idea how well that would play with buffering behaviour.

This solution maps quite closely to the idea that MJPEG is intended for "live" video. And also I find it adorable that it is just an img tag.

shakna3• 6 years ago

Almost every browser accepts, and sends, byte-range headers for video, which is pretty easy to map for an endless stream - you don't have to return the actual length of the video, and if you don't, browsers will treat it as an endless stream.

Whilst you do have to actually trigger the play somehow, the range will come in controllable chunks, so you can respond in kind without trashing the stream.

pjc50• 6 years ago

HLS is one of those standards that I find absolutely maddening and clearly only exists because a number of things are completely broken. It also makes it much harder to capture or intercept the stream for your own purposes.

Browser/firewall refusing to accept anything other than HTTP? HTTP range requests broken? Connection keepalive broken? I know, we'll segment the video into blocks and send a list of the blocks to download as individual files!

ec109685• 6 years ago

If you did that, wouldn’t you need to keep generating frames regardless of whether they updated or not versus this solution that only sends a new jpg down when concurrents change?

browserface2• 6 years ago

I use MJPEG to livestream headless chrome[1]. You can set it up to use the HTTP endpoint but I just do it over WebSocket.

[1] https://github.com/dosyago/OuterShell

koliber• 6 years ago

There are a few other ways:

- dynamically generated animated GIFs - Content-Type: multipart/x-mixed-replace : the way to animate images on the web since 1993 - before animated GIFs

reaperducer• 6 years ago

since 1993 - before animated GIFs*

Animated GIFs have been around since 1987.

reimertz• 6 years ago

This is so cool and very similar to a hack I did some time ago: Noscript-compatible twitch-plays-Zelda

http://nes-o-png.herokuapp.com

So crazy what you can do with server-side-rendering if you really want to. :)

mercora2• 6 years ago

It is quite cool but for me it wont work without javascript on firefox

Shared404• 6 years ago

Works for me without JS.

notRobot9• 6 years ago

So now we know that a #1 post on HN has about ~450 concurrent visitors

Edit° (~1 hour later): So I've been checking every few minutes, and it's consistently been at ~450, this is a cool metric to have.

°This link was posted to HN ~4 hours ago. I first checked ~1.5 hours after it'd been posted, and it was #1 on the front page. It's still #1 as of this edit. The counter has consistently been between 445 and 455 the whole time.

richrichardsson• 6 years ago

When the Europeans are coming up for midday at least. I wonder how that number will change depending on who's up.

browserface2• 6 years ago

And... It crashed. Image is currently down.

notRobot9• 6 years ago

Update: now it's on #2, and it's hovering around 430

notRobot9• 6 years ago

Update: #3 and ~130. Whoa, dramatic fall.

Edit: #4, post is six hours old, counter up to ~190.

Edit: #5, ~6 hours, 173 points, ~220 current site readers.

Edit: Back to #4, ~6 hours, 186 points, ~300 site readers.

smichel172• 6 years ago

You have to adjust this for people who read the comments but haven't clicked the link :P

notRobot9• 6 years ago

How so?

bdcravens2• 6 years ago

They mean visitors to the link

golergka• 6 years ago

2 hours after your comment, at ~190 concurrent visitors. 4th in the HN top atm.

lawik6• 6 years ago

I think it started falling over around 450. I've been getting 500 on my Nginx for workers, so I bumped that but the resulting Nginx restart killed the count and it is currently at 217 as it has recovered but I probably lost tons of idle tabs.

The application has retained a 3 day uptime. But I don't think the 450 number is entirely true with Nginx causing an artifical cap on it. Would probably be higher if I didn't hit that limit. Drats, upped the limit, hope it recovers.

Raphmedia• 6 years ago

This is pretty good considering most people will only stay on the links for a few seconds.

trevor-e• 6 years ago

I had a top post a few years ago and I think in total I had around ~60k visitors over a couple days. Have a bunch of screenshots lying around somewhere for a blog post that I never ended up writing.

donatj4• 6 years ago

I made a little nojs shared drawing board a few years back that worked with MJPEG as the background of an image button ‘<input type="image" ...>’.

Clicking the image button submits the form with x and y click coordinates, and the server returns an HTTP 204 telling it to stay where it is, followed by pushing out the updated jpeg to all connected clients.

It’s pretty fun, and I wanted to have it online all the time but it has a problem I haven’t sorted out where sometimes when a client disconnects the server won’t realize and trying to push them a jpeg locks the whole rendering system.

https://github.com/donatj/imgboard

lawik6• 6 years ago

204 you say. Please don't make this rabbit hole deeper for me :)

donatj4• 6 years ago

204 is a wonderful rabbit hole! You can use it to send messages to the server without refreshing the page without JS. It was a pretty common trick in the early 2000s

forgotmypw17• 6 years ago

Thank you very much for sharing this.

I'm attempting to support every client in every configuration on my web-based forum, and this would be a nice little toy.

IgorPartola• 6 years ago

That problem should definitely be solvable. I used MJEPG to create my own streaming server that wasn’t mjpegstreamer and even with HTTPS and reverse proxying there are ways to detect when to stop sending the data, though it isn’t fun to find all the edge cases.

I need to revisit and update that project sometime but it was a very neat event loop C implementation that reads frames from a cheap consumer webcam and without doing any reencoding feeds it to connected sockets as an MJPEG stream (it does have support for re-encoding if the camera can’t produce JPEGs). Was a really fun exercise in minimalism and efficiency as my goal was to stream multiple cameras from a single Raspberry Pi back when they were super slow.

donatj4• 6 years ago

I have no doubt, I just haven't found the time. The codes kind of a nasty mess / proof of concept.

Sephr• 6 years ago

I envisioned this same concept a decade ago[1] but never implemented it. It's nice to see this actually work in practice!

[1] https://stackoverflow.com/questions/2576715/pushing-data-onc...

0-O-0• 6 years ago

this can be used for evilish things. You can absolutely keep track of how long someone keeps receiving your frames and use that for your analytics

There is nothing evil in analytics by itself - it's invaluable for improving usability.

stanislavb• 6 years ago

In the light of this post, I'd like to share that I made an almost "no js" live monitoring service a few days ago. Again with the help of Elixir (and Phoenix LiveView). It tracks everything that's posted on Hacker News and Reddit in "real-time", and distributes it to everyone listening to it. And it tracks the number of online users, too. Of course.

You can check it out here https://alertcamp.com/live/Apple,Google,Microsoft,Amazon,Fac...

bdcravens2• 6 years ago

I think by "no js" it's not whether you write JS, but whether the page uses it. LiveView relies on WebSockets and Javascript.

lawik6• 6 years ago

When I posted this in another context someone linked this beauty: https://github.com/kkuchta/css-only-chat

fishtoaster• 6 years ago

Hey, that's mine! But yeah, it includes an alternate approach to the same problem: use http chunked encoding and continually append html to the web page (which never quite finishes loading).

Funnily enough, it also uses another evil trick with css background images, which TFA mentions as well: https://underjord.io/is-this-evil.html

leephillips2• 6 years ago

This is great to know about. But on qutebrowser (QT webengine) it doesn't update. When I tried it on Google Chrome, it worked as expected. So maybe not as universal as the author believes.

The-Compiler• 6 years ago

Works for me. Perhaps you're using an older Qt version?

leephillips2• 6 years ago

Hmm. I’ll have to check that, thank you.

Ensorceled• 6 years ago

Quite a few people are having trouble groking the "stupid solutions" part.

baud147258• 6 years ago

a fun hack that simply happens to work across browsers

Didn't work on IE.

But still something really interesting

icedchai• 6 years ago

Why not an iframe with a meta refresh tag? That seems more standard than rendering text using a video stream. Sure, it's not "live" but an update every second or so would be good enough for this use case.

pmontra• 6 years ago

That's what we were using before XHR in IE5 (it had another name but same stuff.)

renewiltord• 6 years ago

I think I've seen this done with an infinite animated GIF as well.

feniv• 6 years ago

Seems like an interesting variant of SSE (Server sent events) without the JS code for retries. Both of these approaches are simpler than websockets, with the limitation that they're one-way (server push).

Stupid solutions: Live server push without JS

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