Previously the hickory-dns representation of ECH configs found in
SVCB/HTTPS records held and exposed its own non-standard representation
of the encoded ECH configs. Notably, it stripped the TLS-encoded list
length prefix from the remaining data. Similarly, it's presentation
format was the BASE64 encoding of this non-standard form.
Downstream consumers are likely to want the wire-encoding format
unmodified, because ECH is of most use to TLS libraries where they will
have already implemented a generic TLS-encoded list decoder that expects
the length prefix. In practice, popular tools like `dig`
are also encoding the presentation format BASE64 of the data in DNS for
some popular test servers with the prefix included.
This commit updates hickory-dns's representation to not do the
pre-processing it was before. This is trivial for a consumer to do if
they need it, and avoids having to restore it manually in order to use
other pre-existing TLS encoder/decoders with the value from hickory-dns.
Again, since ECH adoption is in very early days it doesn't seem
worthwhile to try and come up with a backwards compatible interface for
those that need the old behaviour. It should be straightforward to
remove the length prefix manually if required.
5e23b5e587