A from-scratch Rust implementation of Flatpak — the Linux application sandboxing and distribution framework. It provides a single flatpak binary that can install, run, build, sign, and distribute Flatpak applications without depending on the upstream C codebase or libostree.

Status#

All 24 implementation phases are complete. The test suite consists of:

124 sandbox-free Nix checks covering CLI surface, override management, config & history, build commands, metadata, install/uninstall/list/info, remote management, and miscellaneous commands.
75+ NixOS VM tests across 15 categories (sandbox execution, override effects, config, bundle roundtrip, build-update-repo, repair, info, history, seccomp, extensions, D-Bus proxy, documents/permissions, remote+network, metadata validation, misc/security).

Run the full suite with nix flake check.

Features#

Sandboxing — bubblewrap-based sandbox with full seccomp filter generation (BPF, blocks dangerous syscalls including new mount APIs, clone(CLONE_NEWUSER), TIOCSTI/TIOCLINUX ioctls, restricted socket families), capability handling, and instance tracking (ps, enter, kill, bwrapinfo.json parsing).
OSTree client — native implementation of OSTree commit/dirtree/dirmeta/ file objects, GVariant binary summary, content-addressed object storage, HTTPS pull (rustls + webpki-roots), local object cache, native deflate via miniz_oxide, parallel object fetching with connection reuse, HTTP redirect/chunked transfer support, and full static delta support including a complete bspatch implementation.
Build pipeline — build-init, build, build-finish, build-export, build-bundle/build-import-bundle (proper Flatpak bundle format with GVariant header + deflate-compressed payload), build-sign (GPG via gpg --detach-sign), build-update-repo (with --title, --redirect-url, --default-branch), build-commit-from, and repo info.
D-Bus proxy — integrates xdg-dbus-proxy to filter session, system, and accessibility buses based on [*Bus Policy] metadata sections.
Portals — native D-Bus client (via zbus) for the document portal (document-export, document-info, document-unexport) and the permission store (permission-set, permission-show, permission-remove, permission-reset), with on-disk fallback when the real portals are unreachable (useful for tests).
Extensions — parses [Extension *] groups, mounts extensions with add-ld-path/merge-dirs/subdirectories support, regenerates ld.so.cache via a sub-bwrap, and auto-installs missing extensions on flatpak run.
Sandbox fidelity — read-only /sys subdirectories, --new-session by default, memfd-based .flatpak-info/passwd/group, timezone symlinks, host font/icon bind-mounts, per-app shared /tmp, /run/host/{fonts,icons,container-manager}.
Security hardening — CVE-2024-32462 (run command escaping), CVE-2024-42472 (--persist symlink/path-traversal escapes), CVE-2021-43860 (NUL-byte rejection in metadata), --no-setuid, --no-world-writable, GPG signature verification of summaries and commits via gpgv.
CLI — install/uninstall/list/info/run/ps/kill/enter/override/config/ history/repair/search/mask/pin/make-current/remote-add/-delete/-modify/ -ls/-info/create-usb/documents/permissions/complete (tab completion). Supports --user/--system, --columns, --arch, --subpath, --require-version, --bundle, and many more upstream flags.

Building#

The project lives in a Nix flake-based monorepo. From the repository root:

# Debug build via Cargo:
cd rust/flatpak && cargo build

# Release build via Nix:
nix build .#rust-flatpak

# Run the full test suite (sandbox-free + VM tests):
nix flake check

The binary is produced at target/{debug,release}/flatpak (Cargo) or result/bin/flatpak (Nix).

Usage#

Drop-in compatible with the upstream flatpak CLI for the supported subcommands:

flatpak --user remote-add flathub https://flathub.org/repo/flathub.flatpakrepo
flatpak --user install flathub org.gnome.Calculator
flatpak run org.gnome.Calculator
flatpak --user list --app
flatpak --user info org.gnome.Calculator --show-permissions
flatpak --user override org.gnome.Calculator --filesystem=~/Documents

Project Layout#

Path	Contents
`src/main.rs`	CLI dispatch and command implementations
`src/sandbox.rs`	bubblewrap sandbox construction
`src/seccomp.rs`	BPF seccomp filter generation
`src/ostree.rs`	OSTree client (objects, summary, pull, checkout)
`src/deltas.rs`	OSTree static delta parser + bspatch
`src/gvariant.rs`	GVariant binary serializer
`src/dbus_proxy.rs`	`xdg-dbus-proxy` integration
`src/installation.rs`	Installation discovery and ref resolution
`src/portals.rs`	Document + permission portal client (`zbus`) + native D-Bus wire client
`src/build.rs`	`build-*` subcommand implementations
`src/metadata.rs`	INI-style metadata/override parser
`src/instance.rs`	Instance tracking (`ps`, `enter`, `kill`)
`src/extensions.rs`	Extension resolution and mounting
`tests/`	Sandbox-free shell test scripts (`testsuite.nix`)
`vmtests/`	NixOS VM test scripts (`vmtest.nix`)
`default.nix`	Nix package + checks attrset
`PLAN.md`	Detailed implementation plan and test parity tracker

Dependencies#

Runtime: bubblewrap, xdg-dbus-proxy (optional, for D-Bus filtering), gpg/gpgv (optional, for signing/verification).

Rust crates (see Cargo.toml): libc, serde, miniz_oxide (deflate), rustls + webpki-roots (HTTPS), zbus (D-Bus client).

License#

MIT

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