Replaces the always-spawn-an-OCI-container model with a per-call
bubblewrap sandbox. Pandoc and chromium binaries are baked into the
zddc-server runtime image; each conversion runs them under bwrap's
Linux-namespace isolation. No daemon, no socket, no privileged outer
container, no OCI image pull at conversion time.
Why: the OCI engine paid ≈ 350 MB image pulls + 400 MB persistent
storage + ~300 ms per-conversion startup, plus required either an
on-host daemon socket (zddc-RCE → host-RCE in one hop) or nested
container privileges. bwrap gets the same sandbox properties
(--unshare-all, ro-bind /usr, tmpfs /tmp, clearenv, no-network) at
~5 ms per call and zero external dependencies. This is the same
primitive Flatpak uses for every app launch — battle-tested at scale
for "untrusted-input, short-lived, isolated."
Runner abstraction:
- `Runner.Run` signature: image string → ToolSpec{Image, Binary}.
Both fields populated by entry points; whichever engine is
installed reads the one it needs.
- `bwrapRunner` (new): assembles bwrap argv via `buildBwrapArgs`
helper (testable in isolation), spawns bwrap with the binary.
- `containerRunner` (renamed conceptually to "legacy fallback"):
unchanged behavior, still reachable for hosts that prefer OCI
containers per conversion.
Probe order in health.Probe: bwrap → podman → docker. First hit wins.
Engine kinds in Capabilities: "bwrap" | "podman" | "docker". The
no-engine error message now lists all three.
Config (cmd/zddc-server):
- new --convert-pandoc-binary / ZDDC_CONVERT_PANDOC_BINARY (default "pandoc")
- new --convert-chromium-binary / ZDDC_CONVERT_CHROMIUM_BINARY (default "chromium-browser")
- existing --convert-pandoc-image / --convert-chromium-image kept
for the OCI engine, doc updated to clarify they only apply there.
- --convert-engine helptext lists bwrap first.
Images:
- New `zddc/runtime.Containerfile` — alpine + bubblewrap + pandoc-cli +
chromium + font-noto. Documents build/publish workflow.
- helm/zddc-server-prod/values.yaml.example: runtimeImage default
switched to a placeholder for the new bundled runtime image; bare
alpine NO LONGER works for /.convert (clearly called out in the
comment).
- bitnest dev: /var/lib/zddc-dev-build/Containerfile mirrors the
production runtime image. Quadlet at /etc/containers/systemd/
zddc.container drops the podman-socket mount (no longer needed)
and sets ZDDC_CONVERT_ENGINE=bwrap explicitly to avoid silent
downgrades if a stray podman ends up on PATH.
Tests:
- convert_test.go: fakeRunner / recordingRunner now record ToolSpec.
- New TestToolSpecPopulation pins that both Image and Binary are
filled by every entry point.
- New TestBwrapArgs_SandboxFlagsPresent / MountTranslation /
RejectsBadMountSpec lock in the bwrap argv shape — a refactor that
drops a hardening flag or misroutes a mount fails this loud.
Docs:
- AGENTS.md § "Server-side document conversion" rewritten around
the bwrap-first model with podman/docker as legacy fallbacks.
- ARCHITECTURE.md convert reference updated.
- internal/convert package doc reflects the two-engine probe order.
Verified end-to-end on bitnest: probe reports
engine=bwrap pandoc_binary=pandoc chromium_binary=chromium-browser
on startup. All 15 Go test packages green.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
ZDDC
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