DarkRoom/docs/dev/distribution.md

# DarkRoom — Distribution

**Satisfies:** NFR-COMPAT-2 (v1 channels) · FR-PLAT-LIN-3 (sandboxed distribution)
**Companion to:** [requirements.md](requirements.md) §3.8, §4.8 · [storage.md](storage.md)

NFR-COMPAT-2 asks for the v1 channels to be *stated*, and says why in its own
second sentence: the channel decision and the storage design are coupled. A
channel is not a build target. It is a set of constraints that reach back into
the code — what the application is allowed to see, what it may ask for, and
what it must be able to do without asking. This document records which channels
v1 targets and what each one costs, and it is where to look before adding a
permission to a package rather than after.

---

## 1. The channels

| Platform | Channel | State | What it constrains |
|---|---|---|---|
| Linux | Arch source package — [`packaging/PKGBUILD`](../../packaging/PKGBUILD) | Built, in tree | Nothing. Full filesystem access, system Vulkan, system secret daemon |
| Linux | Flatpak — [`packaging/flatpak/`](../../packaging/flatpak/) | Manifest in tree; folders chosen through the FileChooser portal since 0.17.0, **never built or run here** (§4) | Portals only. No `--filesystem=`, no host mount table, no typed paths |
| Linux | AppImage | v1 channel, **recipe not yet written** (§5) | Oldest supported glibc, and no sandbox at all |
| Android | F-Droid | v1 channel, not yet submitted | GPLv3-clean build, reproducible, no proprietary blobs |
| Android | Play Store | **Not v1** (§6) | Would make ARCH §6.9 binding as policy rather than as engineering |
| Windows | NSIS per-user installer, cross-built — [windows.md](windows.md) | Built by CI, **untested on Windows**. Not v1 | Known folders in place of XDG; no sandbox; unsigned until there is a certificate |

Four of these six exist as recipes and two do not. That is stated rather than
smoothed over, because the value of writing the channels down is knowing which
constraints are already being met and which are promises.

### What every channel has to get right

Independent of packaging format, and each of these has bitten a package
somewhere:

- **One identifier, four places.** `paris.tourolle.darkroom` is the AppStream
  component id, the `.desktop` basename, the Flatpak application id, and the
  string `dr_ui::run` sets as the Wayland `app_id` and X11 `WM_CLASS`. A rename
  that misses one of them costs the icon in the shell or the association in the
  software centre, and neither failure announces itself.
- **The metainfo, not just the desktop entry.**
  [`packaging/paris.tourolle.darkroom.metainfo.xml`](../../packaging/paris.tourolle.darkroom.metainfo.xml)
  is the single description of the application, installed by every channel that
  has somewhere to put it. Its `metadata_license` is CC0-1.0 and its
  `project_license` is GPL-3.0-or-later; those differ on purpose — see the
  comment in the file.
- **Vulkan is a requirement, not a preference.** The develop pipeline is
  compute shaders through wgpu, and NFR-R8 was decided on 2026-09-19 against a
  CPU pipeline: without a device the library, the grid and the judgements work
  on embedded previews, and develop and export say they are unavailable. A
  package that installs onto a machine with no working ICD produces an
  application that starts and cannot develop.
- **A Secret Service implementation, or an honest degraded mode.** FR-NC-2 is
  explicit that the absence of a secrets daemon is a stated degraded mode and
  never a silent fall back to plaintext. Packages express this as an optional
  dependency (the PKGBUILD) or a talk hole (the Flatpak manifest), never as a
  hard dependency — a headless or minimal-WM install is a supported way to run.
- **The face models are Git LFS objects.** A checkout without `git lfs pull`
  has ~130-byte pointers where 11 MB models should be. Both the PKGBUILD and
  the Flatpak manifest check the file size and refuse, because the alternative
  is a package whose face indexing fails inside the graph loader on a user's
  machine rather than on the packager's.
- **So are the manual's pictures.** Since 0.15.0 the Arch package, the Windows
  installer and the APK carry `docs/manual/index.html` and its `media/`, where
  `dr_ui::manual` looks for them (`/usr/share/darkroom/manual`, `manual\` beside
  `darkroom.exe`, the APK's `assets/manual`), and each refuses a pointer where a
  picture should be — shipped, a pointer is a manual of broken images that
  nothing reports. The Flatpak manifest does not install it yet.

---

## 2. Why Flatpak is the channel that matters most

Not because it is expected to be the most used. Because it is the only one that
tests anything.

The Arch package and an AppImage both hand the application the same
unrestricted process the developer runs it in, so neither can discover that a
design assumed unrestricted access. Flatpak takes that assumption away, and
FR-PLAT-LIN-3 exists to make the discovery happen deliberately rather than in a
bug report. §4 is what it discovered, and what has been done about it.

The same argument runs the other way on Android, where SAF has been the only
option since before the first line was written (ARCH §6.9) and `SourceRef`
exists because of it. Linux got the abstraction — `LocalStorage::grant` is the
one place a `Path` enters — and never got the constraint that would have proved
it worked.

---

## 3. What already works inside the sandbox, unchanged

Worth listing, because it is the part FR-PLAT-LIN-1 quietly paid for in
advance:

- **XDG directories.** Flatpak redirects `XDG_CONFIG_HOME`, `XDG_DATA_HOME` and
  `XDG_CACHE_HOME` into `~/.var/app/paris.tourolle.darkroom/`. Settings
  (`settings_store.rs`), accounts (`dr_sync::account`), the catalog and the
  thumbnail store all read those variables, so every one of them lands in the
  application's own directory with no code change and no permission.
- **The face models.** `system_face_models_dirs()` reads `$XDG_DATA_DIRS`
  rather than hard-coding `/usr/share`, which is exactly why `/app/share`
  inside a Flatpak is found by the same lookup that finds the Arch package's
  copy.
- **Opening a photograph from a file manager.** The `.desktop` entry declares
  the RAW MIME types and `Exec=darkroom-desktop %F`; under Flatpak the file is
  exported through the document portal and arrives in `argv` as a path under
  `/run/user/$UID/doc/`, which is mounted in every sandbox. `main.rs` takes
  paths from `argv` and `collect()` handles a file or a directory. This is
  genuine portal-mediated access and it needs nothing new.
- **The Nextcloud sign-in browser.** `open_in_browser` spawns `xdg-open`; the
  freedesktop runtime's `xdg-open` forwards to the OpenURI portal, and portal
  calls need no `--talk-name` because Flatpak always permits them. FR-NC-1's
  "system browser, never an embedded webview" therefore holds inside the
  sandbox for the same reason it holds outside it.
- **Credentials.** The keyring crate speaks the Secret Service D-Bus interface,
  reached through the session-bus proxy with one talk hole. The app password
  stays visible to `secret-tool` and Seahorse, which is what keeps it
  individually revocable by the user.

---

## 4. Choosing a library: built, not yet proved in the sandbox

**FR-PLAT-LIN-3 was not satisfied up to 0.16.0, and is still not shown to
be.** What changed in 0.17.0 is the code; what has not changed is that no
Flatpak has been built here, so nothing below has been observed inside one.

Up to 0.16.0 a folder library was chosen by typing an absolute path, and
nothing in the tree called the FileChooser portal. Inside a sandbox with no
`--filesystem=`, `$HOME` still resolves to the real home *path* but that
directory holds only the application's own `.var/app/…` tree, so a typed
`~/Pictures` failed the `exists()` check and the launch screen said so — a
truthful message about a situation the user could not fix from inside the
application.

**Every folder the desktop asks for is now chosen in the platform's
dialogue** (FR-EXP-6): the library folder on the launch screen (`Choose
folder…`), an import's source and second copy, a folder or file of
Lightroom presets, and an album's folder on this device.
`ui/dr-ui/src/folder_dialog.rs` asks through `rfd` with its `xdg-portal`
backend — `org.freedesktop.portal.FileChooser` over D-Bus, which Flatpak
always permits without a `--talk-name` — and the common item dialogue on
Windows. No path is typed anywhere on the desktop any more; Android keeps
its fields (`Pickers.local-paths`), because SAF returns document trees rather
than paths.

What the portal hands back inside a sandbox is a path under
`/run/user/$UID/doc/` that the document portal has exported, and the chosen
library goes through the same `normalise_endpoint` a typed one did, which
checks it with `std::fs`. That is the route this section used to ask for —
`rfd` drives `ashpd` underneath, the crate it named. Two things differ from
the plan, and both are stated rather than smoothed over:

- **It is not behind a platform seam.** The plan put the chooser beside
  `LocalStorage::grant` in `dr-plat`, the one place a `Path` enters the
  application. It is in `ui/`, and the path it returns reaches the folder
  connector as a string, as a typed one did.
- **Nothing has confirmed the sandbox half.** Whether the exported path
  still resolves after a restart — a library is remembered across launches,
  so it has to — and whether the export is writable, so a sidecar can be
  written beside a photograph, are the first two things a Flatpak build has
  to check.

Import is still blocked one step earlier. `dr_plat::volumes()` finds a camera
card by reading `/proc/self/mountinfo` and the `removable` flag under `/sys`. A
sandboxed process is in its own mount namespace, so the table it reads
describes the sandbox; a card mounted at `/run/media/…` on the host is not in
it. `volumes()` correctly returns an empty list, which the interface presents
as "no card found" — but the import page now offers `Browse…` beside that
message, and the dialogue it opens is the portal's, which can reach the card.

### The permission that would hide this, and why it is not in the manifest

`--filesystem=host` makes both work immediately and is the thing FR-PLAT-LIN-3
names as the alternative to portals. Granting it would mean the sandboxed build
never exercises the sandbox, which removes the entire reason for shipping one
(§2). `--filesystem=xdg-pictures` is narrower and would be tempting, but it is
still a static grant that lets a path resolve without the portal — it makes
the same design work by not testing it, only in a smaller directory.

So the manifest grants no filesystem access at all, and a Flatpak built from
it reaches the user's photographs only through what the portal hands it.

### What closes it

1. **Build it and run it.** `flatpak-builder` is not installed on the machine
   this is developed on, so the manifest has never produced a package.
2. **Removable volumes.** There is no portal for "list the mounted cards".
   Under a sandbox `imports_supported()` should report the same `false` it
   reports on Android, for the same reason — the volume list cannot be right
   however hard the user tries — and leave `Browse…` as the way to a card.

**Done when:** a Flatpak built from
[`packaging/flatpak/paris.tourolle.darkroom.yml`](../../packaging/flatpak/paris.tourolle.darkroom.yml),
with its `finish-args` unchanged and no `flatpak override` applied, can select a
library root, scan it, write a sidecar back into it, and open it again after a
restart.

### Running a Flatpak build before then

If the portal's path turns out not to hold across a restart, the rest of the
application can still be tested inside the sandbox by granting the access
per-installation rather than in the manifest, so the file that describes the
application keeps telling the truth:

```bash
flatpak override --user --filesystem=~/Pictures paris.tourolle.darkroom
```

---

## 5. AppImage

A v1 channel, and the recipe is outstanding work rather than a decision to be
made. What it will have to account for, none of which is a surprise:

- **glibc.** An AppImage links against the oldest glibc it must run on, so it
  is built in a container with an old base rather than on a rolling-release
  developer machine. A release binary built on a current rolling-release host carries
  `GLIBC_2.44` references and would run on almost nothing else.
- **What to bundle and what not to.** The binary links fontconfig, freetype,
  expat, libpng, zlib, brotli and bzip2 — bundle those. It does *not* link
  Vulkan, libxkbcommon or either display-server library: wgpu `dlopen`s
  `libvulkan.so.1`, and `x11rb` and `wayland-client` speak the wire protocols
  in Rust. The Vulkan loader and the ICD must come from the host, and bundling
  a loader is the classic way to break an AppImage on a driver it did not
  expect.
- **The models.** ~15 MB of ONNX weights inside the image, or a first-run
  download. In-tree is consistent with how the Lensfun database ships and with
  NFR-SEC-5's local-first posture; the licence question (D13) is the same one
  it is everywhere else and is not made easier or harder by this channel.
- **No sandbox.** An AppImage tests nothing about FR-PLAT-LIN-3. It is a
  convenience channel for distributions the PKGBUILD does not serve, and should
  never be the channel a portal problem is discovered on.

---

## 6. Android: F-Droid in v1, Play deferred

NFR-COMPAT-2 says Play distribution is what makes ARCH §6.9's constraints
binding, and that is worth reading precisely, because the constraint is already
met and would be met whatever the channel.

§6.9 is *verified*, not assumed: `MANAGE_EXTERNAL_STORAGE` is not grantable
under Play policy, and `READ_MEDIA_IMAGES` would not help because proprietary
RAW is not typed `image/*` by the platform scanner and does not appear in
`MediaStore.Images`. SAF is the only route that works, so FR-PLAT-AND-1 asks
for it unconditionally and `SourceRef` (ARCH §3.1) exists to make it possible.
A sideloaded or F-Droid build *could* ask for broader permissions; it would
gain nothing by doing so.

So the coupling runs the opposite way from how it is usually described. Play is
deferred for a reason that has nothing to do with storage: GPLv3 distribution
through Play is generally workable but has not been confirmed for this project
(ARCH §14), and F-Droid has no such question. Confirming it is a licence-reading
exercise; nothing in the storage design waits on the answer.

---

## 7. Where the recipes live

```
packaging/
  PKGBUILD                                  Arch source package
  paris.tourolle.darkroom.desktop           the desktop entry, installed by every channel
  paris.tourolle.darkroom.metainfo.xml      AppStream, installed by every channel
  flatpak/
    paris.tourolle.darkroom.yml             the manifest, and where the permissions are argued
  windows/
    darkroom.nsi                            the installer; docker/windows/package.sh drives it
```

`packaging/` also accumulates built `.pkg.tar.zst` artefacts from local
`makepkg` runs. Those are not part of any channel and should not be committed.