fe9c4f49 keyed the ETag on the SOURCE file's content hash. That is wrong
whenever the response comes from a satellite table, and for attachments
it is wrong in two ways.
Uploading a preview does not change the file's content, so a
source-keyed ETag does not change either — and with `immutable` set,
clients never revalidate and keep the previous render for up to a year.
The exact staleness fe9c4f49 set out to fix, re-entering through the
attachment path.
Worse: a copy inherits the source hash, so an original and a copy have
identical ETags. Give either one a different uploaded preview and they
serve different bytes under one validator, which a shared cache may hand
to either request. That is a collision, not just staleness.
thumbnail_content_id resolves the identity through the same tier
precedence the read path uses: an attached blob's own hash, else a
derived blob's own hash, else the source-keyed form. An ETag naming a
different tier than the one answering is worse than a coarse one, so the
two orders must not drift.
Derived-hash keying is strictly better than source-keying and never
worse. The sidecar and the derived row are written from the same bytes;
where they can diverge — a sidecar re-rendered while the derived row
stays pinned by ON CONFLICT DO NOTHING — source-keying is wrong too,
because the renderer is not part of that key. This is the step 10 change
arriving early, forced by the attachment case; the plan note stands for
the read-order flip itself.
Known gap: a legacy ext-{file_id}.jpg with no file_attached_blobs row
yet falls through to the source-keyed form. No worse than today, and it
resolves when the import backfills.
attached_thumbnail_copy.hurl now asserts ETags, which is why this went
unnoticed: it compared bytes only, and thumbnail_etag_content_keyed
covers content replacement rather than preview upload. A fresh GET
returned the right bytes throughout — the same "healthy locally, broken
for anyone caching" shape as the two bugs before it.
Completes step 9. The PUT wrote `ext-{file_id}.jpg` and nothing else —
keyed by file id, on local disk. No copy path duplicates it and no other
instance can see it, so a copied file lost the preview its owner
uploaded. Silently: the server falls back to rendering one from the
source, or to 204 for a PDF, which has no render path at all. A
user-supplied preview is not derivable from the content, so once lost it
is gone.
The PUT now also records a storage.file_attached_blobs row, which
copy_file_satellites already duplicates, so both copy paths carry it.
Best-effort: the sidecar has already succeeded by then and the user can
see their thumbnail, so failing the request would report an error for an
operation that visibly worked.
Read path consults attachments ahead of every content-derived tier: an
uploaded preview is an explicit choice about THIS file and must beat
anything rendered from its content. Cached under the per-file key — a
content key would leak those bytes to every other file sharing the
content, which is the poisoning the file-keyed table exists to prevent.
store_attached_blob is ON CONFLICT DO UPDATE, unlike its derived twin:
re-uploading a preview is a deliberate replacement, where a re-derived
thumbnail is the same bytes again. The superseded blob's reference is
released, or it would be pinned forever with nothing pointing at it.
Deletion goes through a trigger, not a hook. file_id is ON DELETE
CASCADE, and on_file_deleted fires AFTER delete_file — by then the
cascade has run and there is nothing left to enumerate. This matters
most for folder deletion, where PG cascades folders to files to
attachments and Rust never sees the rows at all. storage.decrement_blob_ref
keys off OLD.blob_hash and is otherwise table-agnostic, so it is reused
verbatim rather than transcribed into a second trigger that can drift.
DELETE only: a replacement updates in place and is handled in Rust, so
adding UPDATE would double-decrement.
Extracted read_blob_to_bytes, shared by the attached and derived tiers —
the only difference between them is which table produced the hash.
tests/api/attached_thumbnail_copy.hurl guards it. The file is red and
the uploaded thumbnail is green, so a render could never produce the
uploaded bytes; the pre-upload render is captured first and required to
change, which stops three identical renders from satisfying the
byte-equality. Then both copy paths must serve the upload, and after the
original is purged and GC runs, both copies must still serve it — each
holds its own reference, because the rows are duplicated rather than
shared.
Edouard Vanbelle