Why can't I send UDP packets from a browser?

You can't because it is a terrible idea, and yet this post explains a really reasonable way forward. My first thought was hopefully the same as yours, "That is absolute insanity, won't someone think of the DDOS?". Glenn Fiedler is responsible for the most pervasive game networking tutorial , it is the beej net guide for games.

This isn't a general interface for UDP, that is of course insane. Instead it is networking library specifically for real time games. It uses http authentication to generate a security token then offers a frame locked secure datagram API for moving real time data. The proposed API has hard timeouts, latency and bandwidth expectations, really not useful for anything other than games.

Right now there is a c library available on github. It will be interesting to see a prototype javascript interface.

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