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91 lines
4.5 KiB
Markdown
91 lines
4.5 KiB
Markdown
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# Karapace Architecture
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## Overview
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Karapace is a deterministic container environment engine organized as a Cargo workspace of 9 crates. Each crate has a single responsibility and clean dependency boundaries.
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## Crate Dependency Graph
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```
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karapace-cli ─────┬──▶ karapace-core ──┬──▶ karapace-schema
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│ ├──▶ karapace-store
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│ ├──▶ karapace-runtime
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│ └──▶ karapace-remote
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├──▶ karapace-remote ──▶ karapace-store
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└──▶ karapace-tui ────▶ karapace-core
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karapace-dbus ────────▶ karapace-core
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karapace-server ──────▶ karapace-store (standalone HTTP server)
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```
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## Crate Responsibilities
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### `karapace-schema`
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Manifest v1 parsing (TOML), normalization, canonical JSON serialization, environment identity hashing, lock file v2 (resolved packages, integrity/intent verification), and built-in presets.
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### `karapace-store`
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Content-addressable object store (blake3), layer manifests, environment metadata (with naming, ref-counting, state machine), garbage collection with signal cancellation, and store integrity verification. All writes are atomic via `NamedTempFile` + `persist`.
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### `karapace-runtime`
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Container runtime abstraction (`RuntimeBackend` trait) with three backends:
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- **Namespace** — `unshare` + `fuse-overlayfs` + `chroot` (unprivileged)
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- **OCI** — `crun`/`runc`/`youki`
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- **Mock** — deterministic test backend
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Also handles image downloading, sandbox scripting, host integration (Wayland, GPU, audio, D-Bus), security policy enforcement, and desktop app export.
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### `karapace-core`
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The `Engine` struct orchestrates the full lifecycle: init → resolve → lock → build → enter/exec → freeze → archive → destroy. Caches `MetadataStore`, `ObjectStore`, and `LayerStore` as fields. Handles drift detection (diff/commit/export via overlay upper_dir scanning) and garbage collection delegation.
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### `karapace-cli`
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23 CLI commands, each in its own file under `commands/`. Shared helpers in `commands/mod.rs` (spinners, colored output, environment resolution, JSON formatting). `main.rs` is a thin dispatcher. Exit codes: 0 (success), 1 (failure), 2 (manifest error), 3 (store error).
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### `karapace-dbus`
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Socket-activated D-Bus service (`org.karapace.Manager1`) with 11 methods. Typed serde response structs. Desktop notifications via `notify-rust`. 30-second idle timeout for socket activation. Hardened systemd unit file.
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### `karapace-remote`
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Remote content-addressable store with `RemoteBackend` trait, HTTP backend (ureq), push/pull transfer with blake3 integrity verification on pull, and a JSON registry for name@tag references.
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### `karapace-tui`
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Interactive terminal UI (ratatui + crossterm) with list/detail/help views, vim-style keybindings, search/filter, sort cycling, freeze/archive/rename actions, and confirmation dialogs.
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## Key Design Decisions
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1. **Content-addressed identity** — `env_id` is computed from the *resolved* lock file (pinned versions + base image content digest), not from unresolved manifest data.
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2. **Atomic operations** — All store writes use `NamedTempFile` + `persist` for crash safety. Rebuild builds the new environment before destroying the old one.
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3. **No `unwrap()` in production** — All error paths are handled with proper error types (`StoreError`, `CoreError`, `RemoteError`, `RuntimeError`).
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4. **Store locking** — `StoreLock` file lock on all mutating operations (CLI + D-Bus). GC respects active/archived environments.
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5. **Layered security** — Mount whitelist, device policy, env var allow/deny, resource limits. No privilege escalation.
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## Data Flow
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```
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Manifest (TOML)
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│
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▼
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NormalizedManifest (canonical JSON)
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│
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▼ resolve (RuntimeBackend)
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ResolutionResult (base_image_digest + resolved_packages)
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│
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▼
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LockFile v2 (pinned, verifiable)
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│
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▼ compute_identity()
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EnvIdentity (env_id = blake3 of canonical lock)
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│
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▼ build (store objects + layers + metadata)
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Built Environment (overlay filesystem)
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```
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### `karapace-server`
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Reference remote server implementing protocol v1 over HTTP (tiny_http). Provides blob storage, registry, and list endpoints. Used for testing push/pull workflows.
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## Test Coverage
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417 tests across all crates. 24 ignored tests require privileged operations (real `unshare`, `fuse-overlayfs`, ENOSPC simulation, namespace access).
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