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TZGyn f3e6fc8fa6 Poll sync cheaply and make the server deployable

Polling re-downloaded the whole store, photos included, every five
seconds. The app now checks a tiny version endpoint and only fetches the
payload when it actually moved, and the server gained request logging,
graceful shutdown, and self-hosting docs so it can run on a VPS instead
of only on localhost.

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Assisted-by: Crush:kimi-k3

2026-10-08 10:19:55 +08:00

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Prompt sync server

Small Go service that stores one JSON blob per sync group, keyed by an 8-digit code (1234-5678). There is no authentication: the code is the shared secret, so anyone who knows it can read and overwrite that group. It is meant to be self-hosted for personal use, not exposed as a public service.

Requirements

Postgres (any recent version; developed against 18)
A host both Macs can reach — a VPS, a home server, or a Tailscale node

Run it

createdb prompt_sync
cd Server
PROMPT_SYNC_DATABASE_URL="postgres://localhost:5432/prompt_sync?sslmode=disable" \
  go run .            # or: go build -o prompt-sync . && ./prompt-sync

Env var	Default
`PROMPT_SYNC_ADDR`	`:8080`
`PROMPT_SYNC_DATABASE_URL`	`postgres://localhost:5432/prompt_sync?sslmode=disable`

The schema is created on startup. Every request is logged as METHOD PATH STATUS DURATION; SIGTERM/SIGINT shut down gracefully so an in-flight push is not cut off mid-write.

Deploy to a Linux host

# from the repo root, on the Mac
cd Server
GOOS=linux GOARCH=arm64 go build -o prompt-sync .    # amd64 for x86 hosts
scp prompt-sync <host>:/tmp/ && ssh <host> 'sudo mv /tmp/prompt-sync /usr/local/bin/'

# on the host: create the database and role, then
sudo cp Server/prompt-sync.service /etc/systemd/system/
sudo systemctl edit --full prompt-sync   # set PROMPT_SYNC_DATABASE_URL
sudo systemctl enable --now prompt-sync
journalctl -u prompt-sync -f             # verify it is listening

Put it behind TLS if it is reachable from the internet — the code is the only secret, and it travels in the URL path. Both plain HTTP and HTTPS work from the app; an HTTP URL is often fine over a LAN or Tailscale.

Endpoints

Method	Path	Behaviour
`POST`	`/api/codes`	Generates a unique code, inserts an empty group
`GET`	`/api/sync/{code}`	`{"version":N,"updatedAt":…,"data":{…}\|null}`, 404 if unknown
`GET`	`/api/sync/{code}/version`	`{"version":N}` — cheap poll used by the app
`PUT`	`/api/sync/{code}`	Upserts the payload, returns the incremented version
`GET`	`/healthz`	Liveness (200)

Payloads are opaque JSONB; the server never parses note contents. Bodies are capped at 50 MB, which is generous enough for base64 photos.

Backups

The whole state is one table, so pg_dump prompt_sync is a complete backup:

pg_dump prompt_sync | gzip > prompt_sync-$(date +%F).sql.gz

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