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Server-sent events

developer.mozilla.org

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Re: Server-sent events

#91

Post by bkyan »

roblabla wrote: post #83
bkyan wrote: post #82

I'm a little confused by how this is used. The trivial example provided on developer.mozilla.org is a PHP script that's fully self-contained. As far as I could tell, a self-contained PHP script doesn't provide much value. I would have expected something to happen on the server, like a database record getting updated, which triggers the PHP to send an SSE message to the browser, but how do you trigger that particular…

You could have some kind of event system running that pushes the event down to php. For instance, redis has a PUBSUB system, and postgresql has NOTIFY.

Ah, the part that was missing from my mental map was having the PHP instance act as a subscriber in a pubsub system. Thanks!

Re: Server-sent events

#92

Post by cassepipe »

DaiPlusPlus wrote: post #63
twic wrote: post #37

Earlier quoted context omitted.

The big problem i've run into with SSE is the connection limit [1]: > Warning: When not used over HTTP/2, SSE suffers from a limitation to the maximum number of open connections, which can be specially painful when opening various tabs as the limit is per browser and set to a very low number (6). The issue has been marked as "Won't fix" in Chrome and Firefox. This limit is per browser + domain, so that means that you…

> The natural way to use SSE is to create an EventSource on each page. If you do this, and your user opens six tabs, they can now no longer make HTTP requests to your site. Not just SSE requests, any HTTP requests at all! You can use EventSource in a singleton worker and use postMessage to forward messages to all open browser tabs for the same origin.

This SO answer seems to say that it wouldn't work : https://stackoverflow.com/questions/61041389/managing-server...

If you have an answer to that answer I'd be very much interested

Re: Server-sent events

#93

Post by nine_k »

twic wrote: post #37
no_wizard wrote: post #2

I know alot of websites and engineers use Websocket for push only data. SSE is tailored made for real time one sided updates! In fact, I think it made a better chat protocol, when we built a chat system at a previous job, similar to Slack. We ended up leveraging SSE to push updates to channels and traditional HTTP requests to send data to the server, resulting in lower latency and less overhead on the server side. We…

The big problem i've run into with SSE is the connection limit [1]: > Warning: When not used over HTTP/2, SSE suffers from a limitation to the maximum number of open connections, which can be specially painful when opening various tabs as the limit is per browser and set to a very low number (6). The issue has been marked as "Won't fix" in Chrome and Firefox. This limit is per browser + domain, so that means that you…

In short, it reads to me as "HTTP/2 or don't bother".

Not an unreasonable requirement for a serious modern web app.

Re: Server-sent events

#94

Post by cassepipe »

tehbeard wrote: post #80
DaiPlusPlus wrote: post #63

Earlier quoted context omitted.

> The natural way to use SSE is to create an EventSource on each page. If you do this, and your user opens six tabs, they can now no longer make HTTP requests to your site. Not just SSE requests, any HTTP requests at all! You can use EventSource in a singleton worker and use postMessage to forward messages to all open browser tabs for the same origin.

SharedWorker (the thing needed for a "singleton worker") only just made it into Safari the end of last year... plus you now have to handle multiplexing and demultiplexing for different tabs on both server and client. By the time that arrived and HTTP/2 had wide enough adoption, everyone's already used to building atop Websocket... Also the EventSource in the browser is heavily gimped. GET only, No custom headers, and…

Not sure if that's what you are asking but there's a `withCredentials` option (which IIRC is the only possible option)

I was looking at : https://stackoverflow.com/questions/61041389/managing-server...

Shared worker would actually allow for SSE in a service worker ! That's nice.

Re: Server-sent events

#95

Post by cassepipe »

nine_k wrote: post #93
twic wrote: post #37

Earlier quoted context omitted.

The big problem i've run into with SSE is the connection limit [1]: > Warning: When not used over HTTP/2, SSE suffers from a limitation to the maximum number of open connections, which can be specially painful when opening various tabs as the limit is per browser and set to a very low number (6). The issue has been marked as "Won't fix" in Chrome and Firefox. This limit is per browser + domain, so that means that you…

In short, it reads to me as "HTTP/2 or don't bother". Not an unreasonable requirement for a serious modern web app.

Yes, but weirdly enough the most popular javascript for handling http, express, does not support HTTP2 ! Fastify does

Re: Server-sent events

#96

Post by cassepipe »

jongjong wrote: post #87
mort96 wrote: post #79

Earlier quoted context omitted.

I don't think I understand. Both WebSockets and server-sent events are just a long lived TCP socket, right? Why would SSE be lower overhead? Why wouldn't it be more overhead to go through the whole HTTP request handling machinery for EVRY chat message everyone sends? You already have an underlying 2-way connection in the TCP socket, why not use it? And why would latency be lower with HTTP requests + SSE than with web…

It's not. SSE has higher overhead and there are browser limits as to how many concurrent channels a single client can consume. Also, SSE encourages you to shift complexity to the back end where it would be more appropriate on the front end. For example, the client knows which channels it needs, so why not let the client decide which channels to subscribe to over a single WebSocket connection? With SSE, you end up hav…

In NestJs it is quite easy to manage in the backend, there's a SSE decorator for you SSE service and then you just return an observable on a subject. (See RxJs) Sending message events sends to all observers on the subject and when the `observed` property` becomes false, you just close the connection.

Re: Server-sent events

#97

Post by jraph »

cassepipe wrote: post #92
DaiPlusPlus wrote: post #63

Earlier quoted context omitted.

> The natural way to use SSE is to create an EventSource on each page. If you do this, and your user opens six tabs, they can now no longer make HTTP requests to your site. Not just SSE requests, any HTTP requests at all! You can use EventSource in a singleton worker and use postMessage to forward messages to all open browser tabs for the same origin.

This SO answer seems to say that it wouldn't work : https://stackoverflow.com/questions/61041389/managing-server... If you have an answer to that answer I'd be very much interested

You can use BroadcastChannel [1] to communicate between tabs. It works well and does not require service workers. It's used in Tracim [2], for some reason we could not move to HTTP/2 at the time I was working on this project so we indeed learned about this connection limit soon enough…

Even on HTTP/2, I believe it's best avoid sending 6 times the same message to the user just because they opened 6 tabs. It's less wasteful both for the server and the client.

[1] https://developer.mozilla.org/en-US/docs/Web/API/BroadcastCh...

[2] https://github.com/tracim/tracim/blob/develop/frontend_lib/s...

Re: Server-sent events

#98

Post by yababa_y »

bullen wrote: post #69
asynchronous wrote: post #4

Love to see stuff like this on the HN front page, when I know tons of web devs that have never even heard of SSE. Tangentially, I’m having a massive problem with SSE datastreams erroring out about two minutes in for “ERR: Network chunk encoding” reasons, anyone else seen this before?

You need to send "keep-alive" "noop" to keep the routers happy, I do it ever 5 seconds.

“Operator, please keep this line clear!”

Re: Server-sent events

#99

Post by bullen »

jraph wrote: post #86
bullen wrote: post #70

Earlier quoted context omitted.

You need to multi-thread your server on shared memory to build many-to-many solutions. The simplest way to get that working is Java + NIO with concurrent package, I have done it for you: http://github.com/tinspin/rupy My web server outperforms everything on the planet for multiplayer. Websockets are notoriously hard to parallelize if you want shared memory which you need for many-to-many, mostly because JavaScript an…

> You need to multi-thread your server on shared memory to build many-to-many solutions Not necessarily, it depends on the needs, but in any case I would not expect SSE and WebSockets to be different in this regard. I'm not sure what's specifically hard to parallelize with WebSockets. Shared memory may be hard to handle but that does not seem specific to WebSockets which are just regular two way communication channel…

Websockets use one TCP socket for starters with SE you use separate sockets from ingress and egress which is much simpler to scale from an infrastructural point of view.

I clearly said many-to-many, everything else is trivial to scale because only many-to-many requires strictly shared memory atomic parallelization.

You could write a better server in Java than javascript/c(++) but I haven't found any, and to be honest the extra complication of the binary protocol doesn't even make me curious enough to waste 5 seconds to google it.

SSE over HTTP/1.1 is the final solution. Everything else is a waste of time for eternity.

Re: Server-sent events

#100

Post by rawoke083600 »

I love SSE.

I fear years back I made a Monopoly Deal game with a client-server arch.

Server was in Go with SSE, and client was in JS/Svelte with SVG and a lot of CSS.

It work so so well ! The clientside cmds (like "place this card there") was vanilla ajax send to Go Server, but the "state" was always send via SSE to connected clients.

I was surprised to see how far Joe Average (Yea I use bootstrap for most things) can push CSS for nice looking card game.

PS: Oops I mean "WildDeal" not "Monopoly Deal", no need to get sued

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