How are HTTP/2 connections managed?

[JustinBeckwith]

Greetings! Lovely library - I'm a big fan :) I was reading the docs, and saw that HTTP/2 is supported via a simple flag - rad! I'm curious:

• How are you managing the underlying ClientHttp2Session objects?
• If I make two HTTP requests in a row, is it going to re-use the same underlying connection?
• If you are re-using connections, how do you know when to close the session?

The biggest advantage I see to using an HTTP/2 client over HTTP/1.1 is taking advantage of the multiplexing over an existing TCP/IP connection. I'd love to understand how this works.

Full disclosure - I'm trying to figure this out in gaxios as well.

[szmarczak]

Sorry for late reply, I haven't been able to do much coding in the past month. I'm more than happy to answer your questions.

How are you managing the underlying ClientHttp2Session objects?

I could talk about this for ages: http2-wrapper/source/agent.js
If you got any specific questions, please ask right away.

If I make two HTTP requests in a row, is it going to re-use the same underlying connection?

Yes. There is a queue.

If you are re-using connections, how do you know when to close the session?

Good question. If a session's origin set is a subset of another session's origin set, it's closed. Another example is when maxFreeSessions option is set to 0. A session can be created when there were no free sessions, and when it connected, another session can steal the listeners from the queue. In that case, the session is closed. If a session has cleared all its requests and all the seats for free sessions are taken, it's closed too. Also there is a timeout applied.

The biggest advantage I see to using an HTTP/2 client over HTTP/1.1 is taking advantage of the multiplexing over an existing TCP/IP connection. I'd love to understand how this works.

Got is using http2-wrapper which provides an API which is almost the same as the HTTP/1 Node.js API. There's also an API for automatic ALPN negotiation, so it knows when to use HTTP/1 or HTTP/2.

Full disclosure - I'm trying to figure this out in gaxios as well.

Amazing! Please note that it doesn't support h2c (unsecure HTTP2).

Note: node-fetch considered the use of http2-wrapper. If you share their view, you may want to use fetch-h2. Beware that they don't support multiple origins (cuz few websites do). Also they don't support multiple sessions either, so if you connect to a site that says "hey you cannot do more than 100 pending requests per session" (maxConcurrentStreams SETTINGS property) and exceed that limit, you will end up waiting till the first request(s) are finished.

OTOH, http2-wrapper session management is heavily tested. The only things that are missing for now are TypeScript support and detailed proxy example.