ZDDC/zddc/internal/convert/sysprocattr_windows.go
ZDDC b5aab81d31 feat(zddc): MD→{docx,html,pdf} server-side conversion via stock pandoc + chromium containers
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.
2026-05-13 10:33:56 -05:00

14 lines
467 B
Go

//go:build windows
package convert
import "syscall"
// sysProcAttr returns the platform-specific SysProcAttr for the
// container-engine child. Windows: no Setpgid / Pdeathsig analogue;
// process-group semantics differ. We rely on context cancel +
// cmd.Process.Kill() + WaitDelay for cleanup. In practice production
// deployments are Linux containers where the full hardening applies.
func sysProcAttr() *syscall.SysProcAttr {
return &syscall.SysProcAttr{}
}