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I tried implementing SSE in a web project of mine recently, and was very surprised when my website totally stopped working when I had more than 6 tabs open. It

I tried implementing SSE in a web project of mine recently, and was very surprised when my website totally stopped working when I had more than 6 tabs open. It turns out, Firefox counts SSE connections against the 6 host max connections limit, and gives absolutely no useful feedback that it's blocking the subsequent requests due to this limit (I don't remember the precise error code and message anymore, but it left me very clueless for a while). It was only when I stared at the lack of corresponding server side logs that it clicked. I don't know if this same problem happens with websockets or not.

uncomplexity_ 2y ago
wait let's check this https://news.ycombinator.com/item?id=42511562 https://news.ycombinator.com/item?id=42511562 at https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events https://developer.mozilla.org/en-US/docs/Web/API/Server-sent... it says "Warning: When not used over HTTP/2, SSE suffers from a limitation to the maximum number of open connections, which can be especially painful when opening multiple tabs, as the limit is per browser and is 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, which means that you can open 6 SSE connections across all of the tabs to www.example1.com and another 6 SSE connections to www.example2.com (per Stack Overflow). When using HTTP/2, the maximum number of simultaneous HTTP streams is negotiated between the server and the client (defaults to 100)." so the fix is just use http/2 on server-side?
- remram 2y ago
  Or a SharedWorker that creates a single SSE connection for all your tabs. SharedWorker is not very complicated but it's another component to add. It would be cool if this was built into SSE instead.
  - uncomplexity_ 2y ago
    okay wtf this is amazing, seems usable with websockets too. usage of Shared Web Workers https://dev.to/ayushgp/scaling-websocket-connections-using-shared-workers-14mj https://dev.to/ayushgp/scaling-websocket-connections-using-s... caniuse Shared Web Workers 45% https://caniuse.com/sharedworkers https://caniuse.com/sharedworkers caniuse BroadcastChannel 96% https://caniuse.com/broadcastchannel https://caniuse.com/broadcastchannel
    - nchmy 2y ago
      Yeah, the issue with SharedWorkers is that Android Chromium doesn't support it yet. https://issues.chromium.org/issues/40290702 https://issues.chromium.org/issues/40290702 But rather than Broadcast Channel, you can also use the Web Locks API (https://developer.mozilla.org/en-US/docs/Web/API/Web_Locks_API https://developer.mozilla.org/en-US/docs/Web/API/Web_Locks_A...) rather than Broadcast Channel This library (https://github.com/pubkey/broadcast-channel/blob/master/src/leader-election.js#L307 https://github.com/pubkey/broadcast-channel/blob/master/src/...) from the fantastic RxDB javascript DB library uses WebLocks with a fallback to Broadcast Channel. But, WebLocks are supported on 96% of browsers, so probably safe to just use it exclusively now.
  - hamandcheese 2y ago
    Ultimately this is what I did. But if you need or want per-tab connection state it will get complicated in a hurry.
- ksec 2y ago
  Even if they don't change the default 6 open connection. They could have at least made it per tab rather than per site. [1] [2] And I dont understand why this hasn't been done in the past 10 years. What am I missing? [1] https://bugzilla.mozilla.org/show_bug.cgi?id=906896 https://bugzilla.mozilla.org/show_bug.cgi?id=906896 [2] https://issues.chromium.org/issues/40329530 https://issues.chromium.org/issues/40329530
mikojan 2y ago
That's only if not used over HTTP/2 and it says so in the docs too[0] [0]: https://developer.mozilla.org/en-US/docs/Web/API/EventSource https://developer.mozilla.org/en-US/docs/Web/API/EventSource
- hamandcheese 2y ago
  AFAIK browsers require https with http2. This is a locally running server/app which will probably never have https. Maybe there is an exception for localhost, I'm not sure.

uncomplexity_ 2y ago

wait let's check this https://news.ycombinator.com/item?id=42511562 https://news.ycombinator.com/item?id=42511562 at https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events https://developer.mozilla.org/en-US/docs/Web/API/Server-sent... it says "Warning: When not used over HTTP/2, SSE suffers from a limitation to the maximum number of open connections, which can be especially painful when opening multiple tabs, as the limit is per browser and is 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, which means that you can open 6 SSE connections across all of the tabs to www.example1.com and another 6 SSE connections to www.example2.com (per Stack Overflow). When using HTTP/2, the maximum number of simultaneous HTTP streams is negotiated between the server and the client (defaults to 100)." so the fix is just use http/2 on server-side?

remram 2y ago
Or a SharedWorker that creates a single SSE connection for all your tabs. SharedWorker is not very complicated but it's another component to add. It would be cool if this was built into SSE instead.
- uncomplexity_ 2y ago
  okay wtf this is amazing, seems usable with websockets too. usage of Shared Web Workers https://dev.to/ayushgp/scaling-websocket-connections-using-shared-workers-14mj https://dev.to/ayushgp/scaling-websocket-connections-using-s... caniuse Shared Web Workers 45% https://caniuse.com/sharedworkers https://caniuse.com/sharedworkers caniuse BroadcastChannel 96% https://caniuse.com/broadcastchannel https://caniuse.com/broadcastchannel
  - nchmy 2y ago
    Yeah, the issue with SharedWorkers is that Android Chromium doesn't support it yet. https://issues.chromium.org/issues/40290702 https://issues.chromium.org/issues/40290702 But rather than Broadcast Channel, you can also use the Web Locks API (https://developer.mozilla.org/en-US/docs/Web/API/Web_Locks_API https://developer.mozilla.org/en-US/docs/Web/API/Web_Locks_A...) rather than Broadcast Channel This library (https://github.com/pubkey/broadcast-channel/blob/master/src/leader-election.js#L307 https://github.com/pubkey/broadcast-channel/blob/master/src/...) from the fantastic RxDB javascript DB library uses WebLocks with a fallback to Broadcast Channel. But, WebLocks are supported on 96% of browsers, so probably safe to just use it exclusively now.
- hamandcheese 2y ago
  Ultimately this is what I did. But if you need or want per-tab connection state it will get complicated in a hurry.
ksec 2y ago
Even if they don't change the default 6 open connection. They could have at least made it per tab rather than per site. [1] [2] And I dont understand why this hasn't been done in the past 10 years. What am I missing? [1] https://bugzilla.mozilla.org/show_bug.cgi?id=906896 https://bugzilla.mozilla.org/show_bug.cgi?id=906896 [2] https://issues.chromium.org/issues/40329530 https://issues.chromium.org/issues/40329530

mikojan 2y ago

That's only if not used over HTTP/2 and it says so in the docs too[0] [0]: https://developer.mozilla.org/en-US/docs/Web/API/EventSource https://developer.mozilla.org/en-US/docs/Web/API/EventSource

hamandcheese 2y ago
AFAIK browsers require https with http2. This is a locally running server/app which will probably never have https. Maybe there is an exception for localhost, I'm not sure.