Phase 2 enhancements to the policy decider, plus listing-level ETags
that benefit every deployment regardless of decider mode.
Reference Rego policy
---------------------
internal/policy/rego/access.rego mirrors InternalDecider's semantics
exactly — bottom-up walk, deny-first within a level, default-deny when
HasAnyFile=true, glob matching with @-boundary semantics (special-cased
bare "*" because OPA's glob.match treats empty delimiters
inconsistently for that pattern).
Embedded into the binary via go:embed; --print-rego dumps it to stdout
so federal customers standing up an external OPA can use it as a
parity-tested baseline:
zddc-server --print-rego > /etc/opa/policies/zddc-access.rego
Parity test runner
------------------
parity_test.go imports the OPA Go module as a TEST-ONLY dependency
(github.com/open-policy-agent/opa@v0.70.0). Every fixture from the
internal Go evaluator's test set runs through both implementations;
any divergence fails CI. The test-only import means production
binaries (built by `go build ./cmd/zddc-server`) stay OPA-free —
release-flag binary size unchanged at ~13 MB.
The parity test caught a real bug on first run: bare "*" patterns
didn't match through OPA's glob.match with empty delimiters. Fixed
in access.rego with a special-case rule. This is exactly the kind of
subtle drift the parity guard exists to catch.
External-mode decision cache
----------------------------
HTTPDecider is now wrapped in a cachingDecider with a default 1s TTL.
Bursty patterns like .archive listings (one OPA round-trip per entry
before, one per (email, decision-input) tuple per TTL window after)
amortize cleanly. Verified: 20 identical /D/ requests produce 1 OPA
hit with cache, 40 hits without (each listing makes 2 ACL queries).
ZDDC_OPA_CACHE_TTL knob (default 1s) lets operators tune. 0 disables.
1s matches the fsnotify watcher debounce window — staleness is
bounded the same way other policy-edit propagation already is.
Internal mode unchanged; the in-process Go evaluator is already
cheaper than a cache lookup would be.
Listing ETags
-------------
GET / (project list) and GET /<dir>/ (directory listing JSON) now
carry content-hash ETag + Cache-Control: private, max-age=0,
must-revalidate. SHA-256 of the rendered JSON, truncated to 16 hex
chars (64 bits — collision risk on a listing of any realistic size
is vanishingly small).
Server-side caching deliberately not added: it would require
mtime-based invalidation, and Azure Files SMB mounts (a common
deployment substrate) don't support fsnotify reliably. The
content-hash ETag delivers the bandwidth savings (304 on identical
fetches) without depending on watcher correctness — the hash is the
actual response, so it can't lie about staleness regardless of
underlying watcher behavior.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Add an internal access-decision boundary that all handlers go through
instead of calling zddc.AllowedWithChain directly. Two implementations
ship:
* InternalDecider — wraps the existing zddc.AllowedWithChain. The
default. No new dependencies, identical semantics to the legacy
code path. ZDDC_OPA_URL=internal (or unset).
* HTTPDecider — POSTs the canonical OPA wire format
(POST /v1/data/zddc/access/allow with {"input": {...}}, response
{"result": true|false}) over HTTP, HTTPS, or a Unix-domain socket.
For federal customers running their own audited Rego policies
alongside zddc-server. ZDDC_OPA_URL=http(s)://… or unix:///….
External-mode failure semantics: unreachable / non-2xx / malformed
response → fail closed (deny) by default with a WARN log. Operators
who prefer availability over correctness flip with ZDDC_OPA_FAIL_OPEN=1.
The decider is constructed once at startup, plumbed through ACLMiddleware
into the request context. Handlers retrieve it via DeciderFromContext;
non-request callers (fs.ListDirectory, EnumerateProjects, enumerateAccess)
take it as an explicit parameter.
zddc.ZddcFile and zddc.ACLRules gain JSON tags so external Rego authors
get idiomatic input shape (acl.allow, admins, …) instead of Go field
names (ACL.Allow, Admins, …).
Test coverage:
* InternalDecider parity tests against zddc.AllowedWithChain (every
documented cascade scenario: empty chain, leaf-allow-wins, leaf-
deny-beats-parent, leaf-allows-what-parent-denies, deepest-match-
wins, etc.)
* HTTPDecider happy-path test (canonical wire format)
* Fail-closed / fail-open / malformed-response tests
Production binary size unchanged (no new deps; HTTP transport is
stdlib net/http). 11 ACL call sites migrated. End-to-end verified
against the worked-example layout in zddc/README.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
