StoreSource now hashes content itself and holds the per-hash
contentLock across the whole store (file write plus accounting row
inserts); evictSourceBlob holds the same lock across its whole
operation (row deletion transaction through file unlink). A concurrent
store and eviction of identical content bytes can no longer
interleave: either runs to completion before the other starts, so a
fresh row can never be left pointing at a file the other side is
mid-unlink on.
ContentStorage gains StoreHashed for callers that need the hash before
writing; Store is refactored to share the write-if-absent logic with
it, with no change to its existing behavior or signature.
internal/imgcache/eviction_test.go:
TestEvictSourceBlobExcludesConcurrentStoreOfIdenticalContent proves it:
pauses eviction (via evictSourceBlobTestHook) in the exact window
between commit and unlink, asserts a concurrent StoreSource for
identical content blocks rather than completing, then verifies no
dangling reference and that the store's data survives once eviction
releases the hash.
Adds an instrumentation seam (evictSourceBlobTestHook, fired after the
row-deletion transaction commits and before the content file is
unlinked) and a test that pauses eviction there while a concurrent
StoreSource for identical content bytes races it. Currently red: the
store completes immediately instead of being excluded, which is
exactly the window the review flagged between evictSourceBlob's commit
and its unlink.
Migration 002 adds a variant_content table (processed variants were
untracked on disk) and an LRU timestamp on source_content. Total usage
is two SUMs, never a directory scan on the hot path; hits touch LRU
timestamps best-effort. A background goroutine evicts globally
least-recently-used entries (variants and source blobs merged) until
usage is under MaxBytes, woken by a periodic ticker and by non-blocking
write-pressure notifications from stores. Evicting a source blob
deletes all source_metadata rows referencing it plus its
source_content row in one transaction before the file is unlinked, so
multi-referenced blobs are removed only with all their references and
rows never point at deleted files; JSON sidecars are cleaned up too. A
one-time startup reconciliation walk adopts untracked variant files,
drops rows whose files are missing, removes unreachable source blobs,
and sweeps stale temp files. CacheConfig.DisableDiskCache turns the
disk cache off entirely (config maps cache_max_bytes: 0 to it): no
directories, lookups miss, stores no-op, no evictor. Handlers wire the
limit, start eviction on startup, and stop it on shutdown.
Red phase for #51: covers strict cache_max_bytes parsing (invalid
explicit values abort naming key and value), the computed default of
max(75% of free space, 500 MiB) via an injectable free-space probe,
explicit-value-no-floor, zero-disables-cache, size accounting over
source blobs and variants, LRU eviction under the limit, the
multi-referenced blob case, write-pressure and periodic eviction
triggers, and startup reconciliation. Minimal API skeletons keep the
tree compiling and lint-clean; only the new tests fail.
