nitely

It's similar to RE2, but it lacks the on the fly DFA, ie: it's just the classic Thompson's NFA with some tweaks. It does not implement find all the same way, though.

Yes, and the client may do multiple requests, and if all take long to be processed you may end up with a lot of open connections at the same time (at least on http1), so there is a point to fast HTTP requests+SSE, instead of slow requests (and no SSE). Granted, if the server is HTTP2 the requests can share the same connection, but then it'd be similar to just using WS for this usage. Also, this allows to queue the work, and processed it either sequentially or concurrently.

By async I meant a process that may take longer than you are willing to do within the request/response cycle, not necessarily async IO.

> What benefit is SSE providing here? Let the client decide when a session starts/ends by generating IDs and let the server maintain that session internally.

The response is generated asynchronously, instead of within the HTTP request/response cycle, and sent over SSE later. But emulating WS with HTTP requests+SSE seems very iffy, indeed.

not if you need bidirectional communication, for example a ping-pong of request/response. That is solved with WS, but hard to do with SSE+requests. The client requests may not even hit the same SSE server depending on your setup. There are workarounds obviously, but it complicates things.

In reality you would build your application server on top of the HTTP/2 server, so you'd not have to deal with multiplexing, the server will hide that from you, so it's the same as an HTTP/1 server (ex: you pass some callback that gets called to handle the request). If you implement HTTP/2 from scratch, multiplexing is not even the most complex part... It's rather the sum of all parts: HPACK, flow-control, stream state, frames, settings, the large amount of validations, and so on.

> A h2 proxy usually wouldn't proxy through the http2 connection, it would instead accept h2, load-balance each request to a backend over a h2 (or h1) connection.

Each connection need to keep state of all processed requests (the HPACK dynamic headers table), so all request for a given connection need to be proxied through the same connection. Not sure I got what you meant, though.

Apart from that, I think the second sentence of my comment makes clear there is no smuggling as long as the connection before/past proxy is http2, and it's not downgraded to http1. That's all that I meant.

In theory request smuggling is not possible with end-to-end HTTP/2. It's only possible if there is a downgrade to HTTP/1 at some point.