dhcp-server: T9267: make client-class substring matching contains-anywhere

The Mikrotik configuration referenced by T9267 uses
matching-type=substring, documented to match the value anywhere within
the option string. This PR's "substring" match instead compared a
fixed-length slice at a fixed byte offset (default 0) for exact
equality - effectively an anchored prefix match, not a substring
search - which does not reliably reproduce the ticket's own use case
of picking a device model string (e.g. "T42S") out of a longer,
variably-formatted hostname.

Rebuild "hostname substring"/"vendor-class-id substring" on Kea's
match()+lcase() instead of substring()==, so a configured value now
matches anywhere in the option content and case-insensitively (options
like vendor-class-id are not guaranteed to arrive in a fixed case).
Drop the "offset" leaf together with it, since it has no remaining
purpose once matching is no longer anchored to a fixed position, and
there is no released behavior to preserve.

Raw hex input and values containing a literal single quote are
rejected for substring matching in verify(), since neither can be
safely embedded into the generated Kea regular expression; exact
"value" matching is unaffected and still accepts both.

Reported by alexk37 in review of PR #5436.

0 files changed, 0 insertions, 0 deletions