cmd/tailscaled: use alternate DHCP package?

[bradfitz]

tailscaled depends on github.com/insomniacslk/dhcp/dhcpv4 for its little-used tap mode.

But github.com/insomniacslk/dhcp/dhcpv4 depends on github.com/u-root/uio/uio (for *uio.Lexer and uio.NewBigEndianBuffer primarily) which now also depends on github.com/pierrec/lz4/v4 (and thus github.com/pierrec/lz4/v4/internal/lz4block and github.com/pierrec/lz4/v4/internal/lz4errors and github.com/pierrec/lz4/v4/internal/lz4stream and github.com/pierrec/lz4/v4/internal/xxh32).

Maybe we should just fork off the DHCPv4 stuff we need rather than keep growing our dep tree that's out of our control.

cc @hugelgupf in case he has ideas.

[danderson]

If we need a DHCP server, I wrote the bones of one years ago for pixiecore: https://pkg.go.dev/go.universe.tf/netboot/dhcp4 and https://pkg.go.dev/go.universe.tf/netboot/dhcp6. Neither are super maintained, but they have encoders/decoders for the wire protocol which is mostly the irritating part of DHCP with the fiddly option encoding. That'd be easy to clean up and use if we want.

Those packages don't implement any of the DHCP client/server state machines though, so if we're after a package that correctly does the semantics of DISCOVER/OFFER/REQUEST/RESPONSE/RELEASE/etc. and keeps track of allocated IPs and does all the conformant "probe an IP before allocating to find rogue users" and stuff, then it's a bunch more work on top of those serdes libs.

[bradfitz]

IIRC we just need the v4 message {un,}marshallers and no state machine.

[danderson]

Then yeah, my dhcp4 package has no external deps other than stdlib and x/net for some net.Conn tricks, and has marshallers that were good enough to make PXE work. The dhcp6 package was contrib and has a bit more cruft than I'd have personally put in there, but also has no deps outside stdlib and x/net.

[bradfitz]

It's old school and uses net.IP! :)

[danderson]

Patches welcome! :zany_face: Or I can modernize pixiecore tomorrow, it'll be a fun trip down memory lane

[bradfitz]

Do you care about breaking API for your users? https://pkg.go.dev/go.universe.tf/netboot/dhcp4?tab=importedby

[danderson]

Hmm, none of those ever talked to me. Most seem abandoned, except maybe Mirantis/virtlet but it looks like it'd be a very simple conversion. I say let's update away and I can send Mirantis a PR.