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platform/docs/file-sync.md
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pastilhasandClaude Opus 5 bc52ce6361 docs: phone photo backup contract, and the file-sync decision
photo sync turned out to be mostly built already. officer proxies immich through
officer-photos, and that sidecar's allow-list already permits the `assets`
resource for GET/POST/PUT/DELETE — so immich's own upload and bulk-upload-check
endpoints are already reachable with officer's auth in front and the immich key
never leaving the sidecar. the deliverable is therefore the contract, not a new
ingest service.

three gaps are written down rather than papered over:
  - immich is not currently connected in officer (_health says configured:false),
    so none of it could be verified live. the api key moved out of .env and was
    never re-entered in the ui. owner action.
  - upload bodies are buffered twice, once in createSidecarProxy and once in the
    photos sidecar. nothing fails at phone-photo sizes; a video library would be
    unpleasant. fixing it touches the shared factory, so it is a decision.
  - no resumable upload. immich's own app has the same limitation.

file sync is design-only, as agreed. the recommendation is syncthing supervised
as a sidecar rather than reimplementing nextcloud's sync protocol — a mount is
not a sync, and the local-first replica is the whole feature.

the iOS answer is stated plainly because it changes the design: continuous
background sync is not possible there, which is why nextcloud's own iOS app is
manual too. if iOS matters, webdav becomes first-class rather than optional, and
that is the owner's call to make before any code is written.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
2026-08-04 03:27:01 +00:00

7.0 KiB

File sync

Written 2026-08-04. The "final boss" of the NextCloud replacement — separated from nextcloud-replacement.md because the answer is genuinely different from calendar and contacts, and conflating them is how this becomes a six-month project.

The ask: "the synced files functionality that I can run on each computer and phone", with the same acceptance test as the rest — it has to just work.


The distinction that decides everything

A mount is not a sync.

Mount (WebDAV, SMB, sshfs) Sync (NextCloud client, Syncthing, Dropbox)
Offline Nothing works Everything works
Open a 2 GB file Streams over the network Local disk read
Flaky connection Failed saves, hung apps Queues, retries
Conflicts Last writer wins, silently Detected and surfaced
Cost to build Days The rest of the year

What NextCloud's desktop client actually gives you is a local-first replica: a full copy on every device, a local database of file state, change detection via filesystem watching, transfer scheduling, and explicit conflict handling. That is the thing being asked for, and it is a genuinely hard, well-studied distributed-systems problem.


Decision: run Syncthing, do not write a sync engine

Same reasoning as choosing Radicale over writing CalDAV, only more so.

Option Verdict
Syncthing Chosen. Mature (since 2013), open source, peer-to-peer, real clients on Linux/macOS/Windows/Android, explicit conflict files, block-level transfer, no server account model to build.
WebDAV from the caldav sidecar Radicale is calendars and contacts only, so this would be a second server anyway — and it solves "see my files remotely", not "have my files offline". Complementary, not a substitute. Cheap to add later.
Reimplement NextCloud's sync protocol Chunked upload, ETag bookkeeping, a local state DB, conflict resolution, and a client on three platforms. The single largest item on the whole list, to arrive at something worse than what exists.

Why Syncthing fits this platform specifically

It is peer-to-peer, so there is no server-side account model to build — devices authenticate each other by device ID. That removes the entire class of work that a Dropbox-alike would need. Officer's job shrinks to: run it, own its config, show its state, and point the file browser at the folder.

It also composes with what is already here: the machine already runs Headscale, so devices are already on a private network and Syncthing's discovery/relay layer can be turned down or off entirely.


Shape of the work

officer-syncthing sidecar

Same pattern as officer-caldav (supervise a real server) crossed with officer-memos (hold a credential, proxy an API).

  • Supervise the syncthing binary on a loopback port, like Radicale.
  • Generate its config at boot rather than hand-maintaining it — same reasoning as caldav/radicale.ts: config is derived state, and a hand-edit that disagrees with what the code believes is very hard to debug.
  • Syncthing's own REST API is authenticated with an API key it writes into its config; the sidecar reads that key and holds it. The platform never sees it.
  • Storage under DATA_PATH/sync/, so it is inside the existing backup story.

Platform side

Sixteen lines of createSidecarProxy at /api/sync, exactly like memos and transmission. No sync knowledge in the platform, ever.

UI — replicate Syncthing's own UI first

Per the standing rule: reproduce what the service already ships, then extend. Syncthing's own web UI covers folders, devices, sync status/percentage, and conflicts. Those are the four panels. The extension Officer can add that Syncthing cannot is the interesting part: the synced tree is just a directory, so the existing file browser, code editor and file viewer all work on it for free. That is the integration nothing else offers.

Build order

  1. Sidecar supervising syncthing + config generation + registration.
  2. /api/sync proxy.
  3. Status panel (folders, devices, completion) — read-only.
  4. Add/remove folder and device pairing from the UI.
  5. Surface the synced root in the file browser as a first-class location.

The honest problem: iOS

There is no good Syncthing on iOS, and there will not be one. iOS does not allow a general-purpose background daemon doing continuous filesystem work; the only always-on sync clients that exist there are ones Apple grants entitlements for. This is also why NextCloud's own iOS app is a manual, foreground, tap-to-upload experience rather than a real sync client — the platform, not the software, is the limit.

So "on each computer and phone" splits:

  • Linux/macOS/Windows — solved by Syncthing, properly, today.
  • Android — solved by Syncthing (there are maintained forks; verify which is current before recommending one).
  • iOSnot solvable as continuous sync. The realistic shape is a WebDAV mount for browsing and on-demand download, plus explicit upload from the Officer mobile app. That is a different feature with a different backend, and it is a decision for the owner rather than something to assume.

This is worth deciding before step 1, because "iOS matters" changes the answer: if it does, a WebDAV server becomes a first-class part of the design rather than an optional later addition, and it may be worth serving both from one place.


What this does NOT do

  • It is not a replacement for the file browser. Officer already has one, and it already reaches the whole filesystem. Syncthing adds replication, not access.
  • It is not backup. Sync propagates deletions. A synced folder is not a backup of itself, and anyone who believes otherwise finds out at the worst moment. Versioning (Syncthing has several strategies) should be enabled and surfaced in the UI precisely so this is not confused.
  • It is not sharing. Single-user remains a hard platform invariant.

Status

Design only. Nothing built — this was written before implementation on the night of 2026-08-04 and the implementation ran out of night. The two things to settle before writing code are the iOS question above and whether the synced root should live under DATA_PATH or somewhere the owner picks.