zddc-server can now invoke podman as a CLIENT against a remote socket
instead of creating containers in its own process. The sidecar pattern
in tnd-zddc-chart will use this so zddc-server's own pod stays
unprivileged (only the podman-system-service sidecar runs privileged).
New surface:
--convert-podman-socket / ZDDC_CONVERT_PODMAN_SOCKET
e.g. unix:///var/run/podman/podman.sock
Empty (default) → local mode (podman creates containers in
zddc-server's own filesystem namespace).
Non-empty → remote mode: `podman --remote --url=<this> run …`
dispatches each container request to whatever process owns the
socket. Typically a `podman system service` sidecar in the same
Kubernetes pod.
--convert-scratch-dir / ZDDC_CONVERT_SCRATCH_DIR
Host-side directory for per-conversion intermediates (template,
HTML, PDF). In remote mode this MUST be a path the sidecar sees
at the same mountpoint — typically a shared emptyDir at /work
in both containers. Empty = $TMPDIR (local-mode default).
Runner behaviour:
local mode → unchanged. `podman run --userns=host --rm --pull=missing
--network=none --read-only …`. `--userns=host` stays so nested-podman
on a privileged host (the previous chart shape) keeps working for
anyone still using it.
remote mode → `podman --remote --url=<sock> run --rm --pull=missing
--network=none --read-only …`. `--userns=host` is dropped because
the sidecar is rootful inside its own privileged container and
doesn't need userns juggling.
Health probe gains a Mode field ("local" | "remote") and, in remote
mode, runs `podman --remote --url=<sock> version` to confirm the
sidecar's socket is reachable. Unreachable-socket → 503 with a clear
reason (sidecar may still be starting up); reachable → ready.
Capabilities log now includes engine_version + mode + remote_url for
easier debugging of "which podman is actually doing the work".
No tests removed — the existing fake-runner table covers both modes
since the runner's args are uniform (remote prefix is the only thing
that differs).
New endpoint GET /<path>/foo.md?convert=docx|html|pdf renders a markdown
source on demand. Surfaced as the Download buttons in browse's markdown
editor (separate commit).
Execution model — two upstream container images, lazy-pulled:
• docker.io/pandoc/latex:latest — MD→DOCX, MD→HTML (entrypoint pandoc)
• docker.io/zenika/alpine-chrome — HTML→PDF (entrypoint chromium-browser)
No custom image build. The runner passes --pull=missing on every podman/
docker invocation so the operator only needs the runtime installed —
first request pulls the image, subsequent requests use the local cache.
Overrides: --convert-pandoc-image / --convert-chromium-image (and the
matching ZDDC_CONVERT_* env vars). Engine: --convert-engine (podman
preferred, docker fallback). Resource caps: --convert-mem-mib (512),
--convert-cpus (2), --convert-pids (100), --convert-timeout (30s).
PDF flow is two-stage: pandoc renders the markdown through the embedded
viewer-template.html to standalone HTML, then chromium prints that HTML
via --print-to-pdf. Preserves the print-media CSS already authored in
viewer-template.html rather than going through pandoc's LaTeX template.
Each conversion runs in a throw-away container with --rm --network=none
--read-only --tmpfs=/tmp --cap-drop=ALL --security-opt=no-new-privileges
--env=HOME=/tmp plus a bind-mounted scratch dir for I/O. Pandoc reads
markdown from stdin / writes to stdout; the viewer template lives at
/tpl (ro). Chromium reads HTML from a read-write bind mount at /pdf
and writes the PDF to the same mount; the host reads it back. No shell
wrappers, no shell quoting — argv flows straight into each image's
entrypoint.
On-disk cache at <dir>/.converted/<base>.<ext> with mtime synced to the
source. Fast path is a stat-and-serve with no exec; slow path
singleflights concurrent requests for the same target. PUT/DELETE/MOVE
on the source .md purges the .converted/ sidecars.
Per-project template variables (client/project/contractor/project_number)
come from a new .zddc `convert:` cascade block, walked leaf→root with
per-key latest-wins. Filename-derived variables (title, tracking_number,
revision, status, is_draft) come from a new zddc.ParseFilename helper.
If neither podman nor docker is on PATH, the endpoint serves 503 with
a clear Retry-After. The rest of the server keeps working.
This is the first os/exec site in the codebase. The hardening in
internal/convert/runner.go — context.CancelFunc → process kill,
cmd.WaitDelay, platform-specific SysProcAttr (Setpgid + Pdeathsig on
Linux), minimal env, stdout cap via limitWriter, stderr ring buffer —
sets the pattern for any future shell-outs.
Public surface:
convert.ToDocx(ctx, source, meta) / .ToHTML / .ToPDF
convert.Probe(ctx, engineOverride) → install Runner if engine present
convert.SetImages(pandoc, chromium)
convert.ConfigureLimits(memMiB, cpus, pids, timeout)
convert.Available()
Container handler at internal/handler/converthandler.go; dispatcher
branch in cmd/zddc-server/main.go inserts the convert lookup after the
existing ACL gate, reusing the source file's read policy verbatim.
