"Invalid source address" when accepting proxy protocol with IPv4-mapped v6 address

[jtackaberry]

Another proxy upstream of caddy-l4 (haproxy currently) is sending the following proxy protocol header:

PROXY TCP6 ::ffff:192.168.0.1 ::ffff:192.168.0.1 53740 10001

But caddy-l4 rejects this with:

2023/01/03 04:37:55.017 ERROR   layer4  handling connection     {"remote": "192.168.0.1:33838", "error": "parsing the PROXY header: invalid source address"}

When the src address is a non-IPv4-mapped IPv6 address it works, it's only with the mapped address that it rejects it.

[jtackaberry]

Ah, I see caddy uses another project (github.com/mastercactapus/proxyprotocol) to parse the proxy protocol, and the bug appears to be there.

Specifically, this line will return false with a v4-mapped address.

I'll open an issue with that project.

[mholt]

Thanks for the report! And for opening an issue upstream. It will likely get fixed faster that way :)