How to force enable HTTP/2.0

[ArkadyRudenko]

I have an HTTP/2.0 server and I want to ping/test it using an httpx client.
I use this docs: https://www.python-httpx.org/http2/

And the client send this request

GET /hello HTTP/1.1\r\nHost: localhost:8080\r\nAccept: */*\r\nAccept-Encoding: gzip, deflate\r\nConnection: keep-alive\r\nUser-Agent: python-httpx/0.27.0\r\n\r\n

The server needs a HTTP2-Settings header to send a upgrade response ("RFC: A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly one "HTTP2-Settings" header field")

See RFC: https://datatracker.ietf.org/doc/html/rfc7540#section-3.2 and https://datatracker.ietf.org/doc/html/rfc7540#section-3.2.1

If the server responds with 101 Switching Protocols the client is not ready for this.
Question: How can my server upgrade httpx client to HTTP/2.0?

My client:

import httpx
import asyncio


async def main():
    async with httpx.AsyncClient(http2=True) as client:
        r = await client.get("http://localhost:8080/hello")
        print(r.http_version)


asyncio.run(main())

[tomchristie]

http1=False, http2=True will use force HTTP/2 (prior knowledge), rather than using negotiation.

It looks like this is missing from our docs at the moment... https://www.python-httpx.org/http2/

(Pull requests welcome)

[ArkadyRudenko]

Thaanks! It's working now

pr: #3262

[rafalkrupinski]

Does it mean passing http2=True (with http1 being True by default) doesn't do anything?

[tomchristie]

@rafalkrupinski - No... I've added a clarifying comment against the pull request.

• The default is HTTP/1.1.
• Enabling http2=True switches to either HTTP/1.1 or HTTP/2. Matching standard web-browser behaviours.
• Using http1=False, http2=True forces HTTP/2 to be used. ("prior knowledge")

On reflection I think that we ought to be noting in the documentation that HTTP/2 is typically only supported for https:, not for http:.

[rafalkrupinski]

So OP was expecting httpx would initiate the upgrade with HTTP headers, while it actually negotiates it over alpn. thanks!