Support listen on vsock

[jeffrey4l]

metrics can be retrive without nic between host and qemu guest through vsock.

more info check

• https://man7.org/linux/man-pages/man7/vsock.7.html
• https://wiki.qemu.org/Features/VirtioVsock

[SuperQ]

Interesting idea. This also needs to be added to the Go documentation and probably the flag help string in web/kingpinflag/flag.go.

[SuperQ]

Please add documentation to the ListenAndServe func docs (before like 285). A link to https://wiki.qemu.org/Features/VirtioVsock would be useful there.

[SuperQ]

Thanks, looks good.

[bwplotka]

👍🏽

[SuperQ]

Would you please rebase to fix the conflict?

[jesusvazquez]

LGTM

I'd like some testing for ListenAndServe here

exporter-toolkit/web/tls_config_test.go

Lines 479 to 492 in 48431d7

	go func() {
	defer func() {
	if recover() != nil {
	recordConnectionError(errors.New("Panic starting server"))
	}
	}()
	flags := FlagConfig{
	WebListenAddresses: &([]string{port}),
	WebSystemdSocket: OfBool(false),
	WebConfigFile: &test.YAMLConfigPath,
	}
	err := ListenAndServe(server, &flags, testlogger)
	recordConnectionError(err)
	}()

To make sure it listens both on tcp and vsock if specified.

But I won't block on this if other people don't think this is necessary 👍

[Leonid99]

Shouldn't this be return err? It silently swallows an error condition.

[Leonid99]

Would you please rebase to fix the conflict?

For your consideration, I rebased this branch as #220 to allow it to be merged (with original authorship of @jeffrey4l). The only conflict is go.mod.

[septatrix]

This behavior can already be archived using the existing systemd socket use case as those are not only able to listen on TCP/IP (AF_INET/AF_INET6) and Unix Domain Sockets (AF_UNIX), but also on Vsock (AF_VSOCK) - among some others.

[SuperQ]

@septatrix

Interesting, so you're saying that this isn't needed? Do we just need to update the documentation?

[septatrix]

@septatrix

Interesting, so you're saying that this isn't needed? Do we just need to update the documentation?

Yes, at least for systems using systemd (or a compatible implementation of the listener interface). See man:systemd.socket:

If the address string is a string in the format "vsock:x:y", it is read as CID x on a port y address in the AF_VSOCK family. The CID is a unique 32-bit integer identifier in AF_VSOCK analogous to an IP address. Specifying the CID is optional, and may be set to the empty string. "vsock" may be replaced with "vsock-stream", "vsock-dgram" or "vsock-seqpacket" to force usage of the corresponding socket type.

[Leonid99]

that this isn't needed

@SuperQ
I would advocate to merge this change anyway. Using systemd for sockets translation isn't different from other methods of socket translation, such as socat, i.e. it's always possible, for example, expose a socket that listens on a TCP port to local domain sockets, etc., but most network services support listening on both natively, without socat or systemd.

Also, another reminder that a rebased version of this PR exists as #220. (I am not trying to claim credit, I'm just interested in having this merged).

[SuperQ]

Closing in favor of #220