|
|
|
|
|
|
by Matthias247
469 days ago
|
|
|
Duplex streams are not really a HTTP/2-only feature. You can do the same bidirectional streaming with HTTP/1.1 too. The flow is always: 1. The client sends a header set. 2. It can then start to stream data in the form of an unlimited-length byte-stream to the server. 3. The server starts to send a header set back to the client. 4. The server can then start to stream data in the form of an unlimited-length byte-stream to the client. There is not even a fixed order between 2) and 3). The server can start sending headers or body data before the client sent any body byte. What is correct is that a lot of servers and clients (including javascript in browsers) don't support this and make stricter assumptions regarding how HTTP requests are used - e.g. that the request bytes are fully sent before the response happens. I think ReadableStream/WritableStream APIs on browsers were supposed to change that, but I haven't followed the progress in the last few years. NGINX falls into the same category. It's HTTP/2 support (and gRPC support) had been built with a very limited use-case in mind. That's also why various CDNs and service meshes use different kinds of HTTP proxies - so that various streaming workloads don't break in case way the protocol is used is not strictly request->response. |
|
|
Anyways, yes, this is technically true, but the streaming semantics are not really that well-defined for HTTP/1.1, probably because it was simply never envisioned. The HTTP/1.1 request and response were viewed as unary entities and the fact that their contents were streamed was mostly an implementation detail. Most HTTP/1.1 software, not just browsers, ultimately treat the requests and responses of HTTP as different and distinct phases. For most uses of HTTP, this makes sense. e.g. for a form post, the entire request entity is going to need to be read before the status can possibly be known.
Even if we do allow bidirectional full-duplex streaming over HTTP/1.1, it will block an entire TCP connection for a given hostname, since HTTP/1.1 is not multiplexed. This is true even if the connection isn't particularly busy. Obviously, this is still an issue even with long-polling, but that's all the more reason why HTTP/2 is simply nicer.
NGINX may always be stuck in an old school HTTP/1 mindset, but modern software like Envoy shows a lot of promise for how architecting around HTTP/2 can work and bring advantages while remaining fully backwards compatible with HTTP/1 software.