Fix high cpu usage with IPv6 recursor address. Closes #6120

[42wim]

No description provided.

[hashicorp-cla]

All committers have signed the CLA.

[banks]

Thanks for the PR!

[mkeeler]

Thanks for the PR. While it would definitely fix the linked issue I believe there is a small hole that would allow input to be used that was not valid (such as when foo::53 is provided as the recursor address).

I made some suggestions for how to fix it. (basically just ensure that we have a plain IPv6 address when we get that particular error).

[mkeeler]

I took a quick look at the implementation of SplitHostPort and there are several other real error cases where the too many colons in address can be returned. In those cases we would not want to use the FormatAddressPort logic with the default port but rather return the error.

I think something like the following should be sufficient to only assume a non-bracketed IPv6 address when we get that error.

if ae, ok := err.(*net.AddrError); ok {
  if ae.Err == "missing port in address" {
    recursor = ipaddr.FormatAddressPort(recursor, 53)
    goto START
  } else if ae.Err == "too many colons in address" {
    if ip := net.ParseIp(recursor); ip != nil && ip.To4() == nil {
      recursor = ipaddr.FormatAddressPort(recursor, 53)
      goto START
    }
  }
}

I haven't tested that myself but basically it just ensures that in the case of the too many colons error that the address is a valid IPv6 address and we didn't get that error for any other reason.

In addition, it would be great to also add a test for foo::53 as that should return with the too many colons in address error but we should not attempt to turn it into an actual recursor.

[swills]

What is the status of this? I'm hitting this error too.

[hanshasselberg]

@42wim This looks like something we would like to fix. Any updates on this one?

[42wim]

@i0rek seems like I forgot about this issue, I'll try to fix this soon.

[hanshasselberg]

Thank you!

[42wim]

changes pushed

[hanshasselberg]

Thank you! Looks great now!

[mkeeler]

LGTM