Routing object-lock buckets off the distributed lock needs the retention and
legal-hold check to run atomically with the write, under the per-path lock. Move
just the comparison into the filer, not the S3 semantics: two generic clause
kinds on an extended attribute.
IF_EXTENDED_NOT_EQUAL blocks while extended[ext_key] equals ext_value (a legal
hold). IF_EXTENDED_TIME_ELAPSED blocks while extended[ext_key], read as a unix-
second deadline, is in the future against the filer's clock (retention); a
malformed deadline fails safe. The caller composes these from the object-lock
state and, for a governance bypass, simply omits the retention clause once the
bypass is authorized -- the filer makes no authorization decision and keeps no
S3 knowledge.
Add an optional WriteCondition to CreateEntryRequest. When set, the filer
evaluates it against the current entry while holding the per-path lock, so the
check and the write are atomic on this filer, and returns PRECONDITION_FAILED
when it does not hold. The caller must route the key's writes to the owner filer
for the check to be authoritative.
A condition is a list of clauses that all must hold (logical AND). One clause is
the common case; several express what a single comparison cannot: an ETag set
(If-Match / If-None-Match with multiple values), weak-ETag comparison, and
compound conditions. ETag comparison mirrors the S3 gateway's precedence (stored
Seaweed ETag attribute, then the Md5/chunk fallback) and follows RFC 7232
strong/weak rules, so results match without coupling the filer to S3 handling.
Condition parsing and evaluation live in filer_grpc_server_condition.go.
Chris Lu