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Comment by londons_explore | Hacker News Reader

A decent number of corporate firewalls still don't support web sockets...

That means if you build something that requires web sockets, prepare to have a deluge of support/refund requests from the most valuable clients who think your site is broken.

I suggest just having a once-per-second polling fallback, perhaps with an info bar saying 'the network you are connected to is degrading your experience'.

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Certainty this can’t be true? I believe you but do you have any actual examples?

All UK government offices doesn't seem to allow it... That's a couple of million potential users right away.

Just use SignalR. It'll automatically choose whatever comes through.

Yes it's true. At Ably we support websockets, SSE and comet fallbacks (simple long-polling and streamed long-polling). It's less and less common but there are firewalls that fail to handle websockets correctly, or simply block them. I can't name specific companies/examples, but call centers are one example - the network and desktop environments are fully locked down.

We also see in these cases that streamed HTTP can also be broken by the firewall - for example a chunked response can be held back by the firewall and only forwarded to the client when the request ends, as a fixed-length response. Obviously that breaks SSE and means you can't just use streamed comet as a fallback when websockets don't work.

Wild, thanks!

This is all addressed in the article

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