masaori335 opened a new pull request, #13475:
URL: https://github.com/apache/trafficserver/pull/13475
## Motivation
A sliced PURGE only removed the blocks before the first gap. The walk
stopped at
the first block that was not in cache, so any object whose cached blocks
were not
a contiguous run from block 0 was partially purged — and the client still
got a
`200`. A gap in the middle left every block behind it cached; an uncached
first
block purged nothing and relayed that block's `404`; and `bytes=-N`
deleted the
head while leaving the tail it had named.
The stop was load-bearing rather than a stray early return: the walk's
only other
terminator needs the object length, which slice learns from a `206`'s
`Content-Range`, and a PURGE response has none.
## Changes
**ATS core** — report the purged object's extent as
`X-Purged-Content-Range` on a
PURGE cache hit, so a caller holding one piece of a larger resource can
learn its
extent. Deliberately not `Content-Range`: on a `200` that is meaningless
under RFC
9110, and `cache_range_requests` reads the pair as a stored `206` being
served as
`200` and rewrites the status.
**Slice plugin** — give PURGE its own state machine, so it no longer
routes through
`handleFirstServerHeader` and cannot leak a block's `404` to the client.
It walks
every block, steps over a `404`, takes the extent as the largest any block
reports
(blocks disagree when the origin object was replaced in place), and
synthesizes the
response only once the walk finishes: `200` if any block was removed,
`404` if none.
Until some block reports an extent the walk is bounded by
`--purge-probe-blocks`
(default 8), overridable per request via `--purge-probe-header`. A suffix
range is
widened to the whole object; an unparseable range is refused with `400`.
## Tests
`slice_purge_gaps` covers the traversal over gaps, both open-ended range
forms, the
miss bound and its override, and the refusal. `slice_stale_generation`
reproduces
the client-visible failures of an origin object replaced in place, which
is how
this was found.
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