Adds the foundation for external file mounts: admin-configured backends
(raw host filesystem in v1; sftp/webdav/… as future provider kinds) surfaced
as a folder inside a user's drive. Mount contents are virtual/live-passthrough
— read straight from the backend, never stored in storage.files — and are a
deliberately separate, limited storage type (no dedup/sharing/trash/search).
The feature is dark by default (OXICLOUD_ENABLE_EXTERNAL_MOUNTS=false).
P1 scope (this PR): data model, the pluggable provider abstraction, and the
read-only REST surface (mount listing + download). Read-write (P2),
WebDAV/NextCloud path resolution (P3), and the admin UI (P4) follow.
Core model
- Mount root = a real storage.folders row; authorization for everything inside
collapses onto that folder UUID (ltree-ancestry grant cascade).
- Children are virtual, addressed by ext:<mount_id>:<base64url(node_id)> where
node_id is provider-owned and opaque to the rest of the system.
- A lock-free (arc-swap) MountRegistry maps mount-root UUID -> provider; a thin
MountRouter::classify() is the single cheap hook handlers call before parsing
an id as a UUID. With no mounts configured it always returns Regular, so
existing code paths are unchanged.
Added
- migrations/20260805000000_external_mounts.sql (storage.external_mounts, kind + config JSONB)
- domain/services/external_mount_id (id envelope + virtual etags)
- application/ports/external_mount_ports (ExternalMountProvider, MountProviderFactory, repo port)
- infrastructure local_fs_mount_provider (tokio::fs, symlink-escape-safe) + factory
- application MountRegistry + MountRouter, pg ExternalMountRepository
- DI wiring (AppState.mount_router), FeaturesConfig.enable_external_mounts
- listing branch (FolderService::list_mount_dir_with_perms + folder_handler) and
download branch (FileRetrievalService stat/open mount methods + file_handler)
Authorization stays in the service layer (authz.require(Resource::Folder(mount_id)));
handlers only classify. Cross-backend operations are out of scope for P1.
Tests: 529 unit tests + 5 testcontainers integration tests (real Postgres 17),
including end-to-end authorization (owner allowed, stranger denied). Line
coverage of the new modules is 84–100% (cargo-llvm-cov). Known gap:
file_handler::download_mount_file (HTTP glue) needs a full-app test (P4).
Bradley Nelson