screentinker/Dockerfile
screentinker 13c9c67335
Drop sharp: pure-JS image ops on a worker thread (#263)
* spike: replace sharp with pure-JS image ops (jimp + jsquash WASM)

Removes the last native dependency from the ingest path, so the server no longer
needs a per-platform/per-ABI prebuilt to thumbnail an image. Motivated by getting
the server onto hardware with no toolchain, but the ABI tax is paid on every
install — it is the same failure class lib/preflight-deps.js exists to explain.

lib/image-ops.js is the whole surface: metadata() and writeThumbnail(), which are
the only two things ingest ever asked sharp for.

Format parity holds. jpeg/png/gif/tiff/bmp are native to Jimp; webp and avif go
through @jsquash WASM, whose bundled .wasm must be compiled by hand because the
packages locate it with fetch(file://) and Node has no file:// fetch — the only
symptom otherwise is a bare "fetch failed". heic is unsupported, as it already
was: sharp advertises heif but its prebuilt libvips refuses HEVC.

#170 is preserved by a different mechanism. Jimp applies EXIF orientation at
decode and rewrites the tag to 1, so metadata() reports display dimensions and
imageDisplayDims() runs as a no-op instead of swapping W/H a second time. The
helper stays in the path so the rule keeps living in one place.

Verified: 1643/1643 tests pass, and ingest was exercised in a child process with
node_modules/sharp moved aside — jpeg, EXIF-rotated jpeg, png, webp, avif, gif
all measured and thumbnailed correctly, corrupt input still yields nulls with no
phantom thumbnail_path.

KNOWN BLOCKER, do not ship as-is: Jimp is pure JS on the main thread, where sharp
handed work to a libvips threadpool. A 12MP photo goes 65ms -> 1079ms, and the
event loop stalls for 1003ms of it (sharp: zero stalls). thumbnail-backfill.js
walks a whole library at boot, so this reproduces #240 exactly — blocked loop,
missed heartbeats, panels marked offline, reconnect churn. Needs a worker_thread
offload before this is viable; image-ops.js is the seam for it.

* Run image decoding on a worker thread

Fixes the blocker the previous commit shipped with. Pure-JS decoding costs ~1s of
solid CPU for a 12MP photo, and in-process that is not a slow upload but a stalled
event loop — no heartbeats, no socket traffic. thumbnail-backfill.js walks a whole
library at boot, so it reproduced #240 (blocked loop -> missed heartbeats -> panels
offline -> reconnect churn) from our own maintenance. sharp never did this because
libvips works on a threadpool.

image-ops.js is now a dispatcher over image-ops-worker.js; the work moved unchanged
to image-ops-core.js, so callers and their failure contract are untouched.

Measured on a 12MP photo: 1079ms wall with the loop stalled 1003ms, to 1881ms wall
for two ops with ZERO stalls and 185 timer ticks serviced. Wall time is worse and
that is fine — it is off the main thread now.

Design notes, all load-bearing:
  - ONE JOB AT A TIME. A decoded 12MP bitmap is ~48MB of RGBA; overlapping jobs
    multiply peak memory by queue depth, which is the wrong failure on the small
    targets this change exists to reach. Costs no throughput — the work is CPU-bound
    and one busy worker already saturates its core.
  - unref'd while idle, ref'd only in flight. Otherwise scripts/backfill-rotation-
    dims.js never exits and `node --test` hangs forever. Verified: a CLI-style run
    exits in 104ms, code 0.
  - decode failures reply as messages, so one bad upload cannot tear down the worker
    and take unrelated queued jobs with it.
  - in-process fallback if a thread cannot be had, warned rather than silent.

test/image-ops.test.js pins the loop-liveness property, which no functional test
would catch. Its thresholds were mutation-tested against the inline path: the first
version passed there too (4MP stalls only ~355ms, under a non-flaky threshold), so
the fixture is 12MP and the thresholds sit in the gap between the two behaviours —
worker ~90 ticks/~0ms, inline ~3 ticks/~897ms. It now fails inline, as a guard must.

1647/1647 pass. Ingest re-verified with node_modules/sharp moved aside.

* Measure and thumbnail an image from a single decode

Ingest asked for metadata() then writeThumbnail(), which decoded the file twice.
That pairing was free under sharp, whose .metadata() only parses the header, but
every decode here is a full one — ~1s for a 12MP photo — so the naive translation
doubled the most expensive thing on the ingest path.

image-ops.measureAndThumbnail() returns both from one decode. Full ingest of a
12MP photo: 2 decodes/~1.9s -> 1150ms, still with zero event-loop stalls.

The subtlety is the failure contract. In the two-call version width and height
were assigned BEFORE the thumbnail was attempted, so a failed thumbnail still left
usable dimensions on the row — the player needs them to letterbox. Merging naively
would have turned any thumbnail failure into total metadata loss. So a WRITE
failure is reported ({thumbnailWritten:false, thumbnailError}) with the dimensions
intact, and the caller sets thumbnail_path only when the write succeeded, keeping
the phantom-path discipline. A DECODE failure still throws — there is nothing to
report about an unreadable image.

backfill-rotation-dims.js deliberately keeps the separate calls: it probes every
image row but regenerates a thumbnail only for the few whose dimensions changed,
so pairing them there would decode files it has no reason to thumbnail.

Tests count decodes rather than timing them — an exact property, and a wall-clock
comparison would be flaky under load. The count filters for reads of the file under
test: Node's ESM loader also goes through fs.promises.readFile, so a raw call count
picks up jimp's and the WASM codecs' lazy loading and reads 30 instead of 1.

1649/1649 pass. Ingest re-verified across all 7 formats with sharp moved aside.

* Dockerfile: sharp is no longer a production dependency

--omit=dev now leaves it out entirely; better-sqlite3 is the only native module
the builder stage still needs a toolchain for.
2026-08-13 11:40:13 -05:00

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Docker

# ScreenTinker server image: serves the dashboard, the web player, and the
# device API. All mutable state (db, uploads, jwt secret) lives under /data so it
# survives container restarts - mount a volume there. A built ScreenTinker.apk
# can be mounted at /data/ScreenTinker.apk to enable OTA APK downloads.
#
# No TLS in the image: it listens on plain HTTP :3001. Front it with a
# TLS-terminating reverse proxy / Cloudflare in production.
# --- builder: install production deps (better-sqlite3 is the only native one left; image
# decoding is pure JS + WASM since sharp was dropped, and sharp is now a devDependency that
# --omit=dev leaves out entirely) ---
FROM node:20-slim AS builder
WORKDIR /app/server
# build toolchain in case a native prebuild is missing for the target arch
RUN apt-get update \
&& apt-get install -y --no-install-recommends python3 build-essential \
&& rm -rf /var/lib/apt/lists/*
COPY server/package.json server/package-lock.json ./
RUN npm ci --omit=dev
# --- runtime ---
FROM node:20-slim
# ffmpeg (ships ffprobe) powers video thumbnails + duration extraction at upload.
# Without it videos still upload and play, but arrive with no thumbnail or duration.
RUN apt-get update \
&& apt-get install -y --no-install-recommends ffmpeg \
&& rm -rf /var/lib/apt/lists/*
ENV NODE_ENV=production
# Relocate all state onto the volume (config.js reads DATA_DIR; unset would use
# the in-repo paths, which we do not want in a container).
ENV DATA_DIR=/data
WORKDIR /app/server
# App source (node_modules/test/db/uploads/certs are excluded via .dockerignore),
# then the built deps, the frontend the server serves, and the VERSION file it
# reads as ../VERSION.
COPY server/ /app/server/
COPY --from=builder /app/server/node_modules /app/server/node_modules
COPY frontend/ /app/frontend/
# shared/Transitions is a RUNTIME dependency: server/lib/transition-config.js + transition-bundle.js
# require the shader manifest/params/sources from ../../shared at load time (the server won't boot
# without it). Small, and keeps the .glsl files the single source across server + player + Tizen.
COPY shared/ /app/shared/
COPY VERSION /app/VERSION
# the /openapi.yaml route serves ../docs/openapi.yaml (the spec Redoc on /docs fetches);
# without this it 404s in the image even though it serves fine from a dev checkout.
COPY docs/openapi.yaml /app/docs/openapi.yaml
# database.js requires scripts/migrate-multitenancy at boot
COPY scripts/ /app/scripts/
# The BrightSign bridge and sync modules are served to the player from ../brightsign so the copy
# the player loads can never drift from the one on the player's own storage. That RUNTIME path
# does not exist unless the directory is in the image: without this the routes 404 in a container
# while working perfectly from a dev checkout — and a missing player asset fails silently, because
# the SPA fallback answers 200 with HTML where JavaScript was expected.
COPY brightsign/ /app/brightsign/
VOLUME ["/data"]
EXPOSE 3001
CMD ["node", "server.js"]