[smarx007]

> long-timeout HTTP connection that wouldn't be responded to

This open connection IS the overhead. Some approaches have more overhead, some less. Long-polling these days is not needed and can be replaced by SSE [1] (if you are OK with unidirectional communication), websockets (bidirectional), or callback URIs in the request. The latter is a per-request webhook, essentially, and would have the lowest overhead at the cost of ceremony (the client now needs to have a running web server).

By the way, long polling was popularized by Comet [2] around 2006.

[1]: https://en.wikipedia.org/wiki/Server-sent_events

[2]: https://en.wikipedia.org/wiki/Comet_(programming)

[TeMPOraL]

Wait, how is having the client run its own http(s) server and accept regular HTTP(S) requests the lowest overhead option? Sounds like the highest overhead one, with all the protocol statelessness.