String() in SVCBAlpn conversion doesn't escape properly

[shane-kerr]

I think the idea is that String() routines should provide something that is presentation format, suitable for DNS zone files.

The SVCBAlpn type contains an array of strings. If set via the unpack() function (or by direct initialization) it can contain non-printable characters, but the corresponding String() function does not attempt to escape them. Such DNS messages are bogus, of course, but such is DNS. The code in the SVCBLocal type properly escapes any values.

If this is a bug that makes sense to fix, I can submit a PR.

Note that the code in PR #1359 seems to have a similar issue.

[shane-kerr]

Here's a simple program demonstrating the issue:
https://go.dev/play/p/QjQB7IRdRB0

[miekg]

yes, Stringyfied value should be suitable for inclusion in zone files, so PR welcome.

thanks!

[shane-kerr]

Fixes merged!