Dual stack (IPv4/IPv6) support

[oktavlachs]

Hello everyone and thanks for your work on this great project 😺

I find it especially helpful in combination with FastAPI, which is my use case.

What I cannot use is the dual stack mode (combined IPv4/IPv6) on the socket used by Uvicorn, which would come in handy in environments in which both IP versions are supported. In this case, I would assume to use the IPv6 host address provided by the user and then add the dual stack mode on top.

From my point of view this would be a pretty straight forward implementation by extending the config method bind_socket HERE when starting a server. You would need to add an OS check and then configure the socket like this:

if socket.has_dualstack_ipv6():
    sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)

Is this something you would support in the product?
If so, would a PR be welcome?

Cheers and have a nice evening,
Oktavlachs

[euri10]

nothing against it, question is how is it testable ?

[17336]

@euri10 Thanks for your support. Actually, I found that dual stack mode can be achieved already by setting the host parameter in the uvicorn Config object to None (needs minor code changes). So like this:

ipv4_config = Config(app=_fastapi_server, host=None, port=8080)

return Server(ipv4_config)

Uvicorn will then hand over None as a value to the loop.create_server() function, which leads to it listening on all interfaces including both IPv4 and IPv6 in dual stack mode. This is confusing, since we both would have expected the function to have a parameter for this, as the socket.create_server() function.

From the official Python documentation:

If host is an empty string or None, all interfaces are assumed and a list of multiple sockets will be returned (most likely one for IPv4 and another one for IPv6).

However, this works fine if you use uvicorn directly in your code, but the CLI currently cannot be used for this, since it always has a host parameter input. So my suggestion is to introduce a new --dualstack parameter, which then overrides whatever was provided as a host and listens on all interfaces.

it works when app.run(debug=False). But if set debug=True, when host is empty it only listen ipv4 and host is None will raise an error.

[Kludex]

The latest version of Uvicorn doesn't even have the debug parameter. 🤔

[rogue73]

Hi, how is the status about support of dual stack?

[pkit]

I see that it doesn't work, too bad. Async "support" in python is at its "best" again. Lol

[pythonwood]

2024-02i test uvicorn 0.20 in ubuntu and macos , uvicorn --host '::' --port 8000 support both ipv6/ipv4
ss check output TCP *:8000 (LISTEN)
curl test by curl 127.0.0.1:8000 '[::1]:8000'
every things ok.

[bmx666]

Hi, any updates?

[QwertyJack]

+1

[bulletmark]

I've been going down this rabbit hole but it seems to me that dual stack IPv4/IPv6 support is disabled in Python asyncio as per these lines of code so I don't think anything can be done about this in uvicorn.

[kamyabnazari]

Hello everyone, so is there an alternative that I can us to deploy and make the dual stack possible with my fast api backend or do I have to switch to another backend framework completely, because right now in my case node js fetch prefers ipv6 and I am not mapping anything on my fast api backend to ipv6 and as such it fails because of "::1" error. So if this is not possible right is there an alternative you guys know about?

Thank you.

[rogue73]

@kamyabnazari Hi, in FastAPI projects where I need dualstack support, I currently choosed to use hypercorn.

[pkit]

@rogue73 I think you need to add that to use hypercorn you MUST bind twice.
I.e. hypercorn --bind '[::1]:8888' --bind '127.0.0.1:8888' ... otherwise it does not bind dualstack too.

[pythonwood]

test in linux hypercorn 0.13.2
but --bind [::]:8888 just equal to --bind '0.0.0.0:8888'， no ipv6

update: may be a linux os problem but not a macos problem.

thans for test

[Kludex]

#1529 (reply in thread)

[pythonwood]

Testing uvicorn 0.20 in ubuntu and macos , uvicorn --host '::' --port 8000 support both ipv6/ipv4
ss check output TCP *:8000 (LISTEN)
curl test by curl 127.0.0.1:8000 '[::1]:8000'
every thing is ok.

[mcanevet]

@pythonwood somehow it does not work for me. I tested with 0.27.1 and it works on IPv6 but not IPv4 with --host '::'

[Strangerxxx]

I've just tried to fix this in the fork
Take a look on PR: #2266

[hanxi]

Both IPv4 and IPv6 are supported, although this is not documented. The following code snippet demonstrates this functionality:

uvicorn.run(app, host=["::", "0.0.0.0"], port=8080)

From https://github.com/hanxi/xiaomusic/blob/e2e74f9459530a2bcdc8cfaf9a294e7e9e677c8b/xiaomusic/cli.py#L80

[amn]

Is it? Looking at

uvicorn/uvicorn/main.py

Line 363 in 5bf788f

host: str,

, the typing hint for host is str, which to me suggests list values cannot be passed with host to the procedure. Looking also at the bind_socket procedure I don't see anything that would suggest there's any looping over values specified with host. This is all from master, mind you.

Which branch of Uvicorn are you using?

[hanxi]

@amn
Uvicorn version is 0.30.1 , The log is :

Uvicorn running on http://['::', '0.0.0.0']:3333 (Press CTRL+C to quit)

netstat output

sudo netstat -tunlp|grep 3333
tcp        0      0 0.0.0.0:3333            0.0.0.0:*               LISTEN      522371/python
tcp6       0      0 :::3333                 :::*                    LISTEN      522371/python

[amn]

Right, thank you -- found now that the sockets are bound by https://docs.python.org/3.12/library/asyncio-eventloop.html#asyncio.loop.create_server and not by the aforementioned bind_socket procedure. The former supports list for host:

If host is a sequence of strings, the TCP server is bound to all network interfaces specified by the sequence.

[mcanevet]

It would still be great to be able to set this through command line because one do not always have access to the code...

[ToroNZ]

This works on Uvicorn 0.30.6

CMD ["uvicorn", "main:app", "--host", "", "--port", "80"]

INFO:     Uvicorn running on http://:80 (Press CTRL+C to quit)              # <-- Binds to all interfaces
INFO:     fd34:acc1:abfd::1:48534 - "GET /openapi.json HTTP/1.1" 200 OK     # <-- Reachable on [::1]
INFO:     172.17.0.1:40830 - "GET /openapi.json HTTP/1.1" 200 OK            # <-- Reachable on 127.0.0.1