Implements #51 per the issue DoD and the owner direction comment (issuecomment-44068).
## Behavior
**Config: `cache_max_bytes`** (integrates with the #52/#53 validation framework)
- Strict int64 parsing via a new `getInt64`/`int64Val` getter in the existing strict-loader pattern; the key is registered in the known-keys list. A SET but invalid value — negative, float, null, non-numeric string, boolean, list — aborts startup with exit 1 naming the key and the offending value.
- Explicit values are used exactly as given, any non-negative amount, no floor. `cache_max_bytes: 0` is a valid value that disables the disk cache entirely.
- Omitted: after `state_dir` validation, the default resolves to `max(75% of free bytes on the filesystem containing <state_dir>/cache/, 500 MiB)`. The cache directory is created first and statfs runs on that actual path, so the measurement hits the right filesystem. The probe is injectable (`FreeSpaceProbeFunc`) so tests do not depend on the host disk. The effective limit (and disabled state) is logged at startup.
**Size accounting** (no directory scans on the hot path)
- Migration `002` adds a `variant_content` table — processed variants were previously untracked anywhere — and a `last_accessed_at` column on `source_content`, both indexed. Total usage is two SUM queries.
- Stores record accounting rows; cache hits touch the LRU timestamps (same cost class as the existing per-request stats UPDATEs). The variant accounting insert is best-effort with a warning: the reconciliation pass (below) adopts any file that missed its row, and this keeps the pre-migration inline test schema working.
**Eviction policy: global LRU across both content classes**
- Candidates are the least-recently-used entries from `variant_content` and `source_content` (batched, 100 per class per pass, merged oldest-first by `COALESCE(last_accessed_at, fetched_at)`), evicted until usage is at or below the limit.
- Why global LRU: recency of actual use is the best cheap predictor of future use for a CDN-style cache, and treating both classes in one ordering avoids pathologies of class-priority schemes (e.g. evicting every variant before any cold source blob, which would tank hit rate, or the reverse, which would hoard stale sources). Byte-for-byte, the coldest data goes first regardless of what kind it is. LFU-style schemes need more bookkeeping for marginal gain at this scale.
- Reference safety (the multi-reference DoD case): evicting a source blob deletes ALL `source_metadata` rows referencing it plus its `source_content` row in a single transaction BEFORE the file is unlinked. A blob referenced by multiple source paths is only ever removed together with all of its references, and DB rows never point at deleted files (the crash window leaves at worst an orphaned file, which reconciliation sweeps). The JSON metadata sidecars for removed rows are deleted as well.
**Triggers, off the request path**
- A background goroutine (started in the handlers OnStart hook, stopped in OnStop) runs an eviction pass on a periodic ticker (5 min) and on write pressure: every store sends a non-blocking notification on a capacity-1 channel. Requests never wait on eviction.
- On startup the goroutine first reconciles accounting with the disk (off the hot path): adopts untracked variant files (size/mtime from disk, content type from the `.meta` sidecar), drops accounting rows whose files are missing, removes source blob files the DB does not know (unreachable, since lookups go through `source_metadata`), removes rows whose files are gone, and sweeps `.tmp-*` files older than an hour.
**`cache_max_bytes: 0` disables the disk cache**
- No cache directories are created, lookups always miss, `StoreSource`/`StoreVariant` are no-ops, no evictor runs; every request fetches and processes uncached. Verified end-to-end (below).
## Notes for review
- At the `imgcache.CacheConfig` layer, disabling is an explicit `DisableDiskCache` flag rather than `MaxBytes == 0`, because existing test fixtures construct `CacheConfig` without `MaxBytes` and rely on the legacy "no limit" behavior; per repo rules those tests were not touched. The config layer maps `cache_max_bytes: 0` to the flag in `handlers`. `MaxBytes == 0` at that layer means "no limit enforced" and is unreachable from production config (the computed default is always at least 500 MiB).
- The negative cache stays active in disabled mode: it is DB-backed (TTL-expired rows in SQLite), not part of the disk cache this issue bounds, and it protects against hammering failing upstreams. Flagging explicitly since the direction said "no cache reads, no cache writes" — I read that as the disk cache; happy to disable it too if intended.
- One deviation from pure red/green: after the red commit I extended the new-test fixture helper (`newEvictionTestCache`) to pass `DisableDiskCache: maxBytes == 0`, mirroring the production mapping, when the flag design emerged. Assertions were not touched; no pre-existing tests were modified.
- Sidecar files (`.meta`, metadata JSON) are not counted in usage; they are bounded by entry counts and small (tens of bytes to ~1 KiB per entry) while content bytes dominate. Documented here for transparency.
- Discovered while working: `Cache.Stats` reads the never-populated `output_content`/`request_cache` tables, so `TotalItems`/`TotalSizeBytes` are always 0. Out of scope here; filing as a separate issue.
## Verification
- TDD: commit `3963ec3` adds the failing tests first (18 new tests covering strict parsing, default computation with injected probe including floor and 75% branches, explicit-no-floor, zero-disables, size accounting, dedup accounting, LRU order, multi-reference blob eviction with the no-dangling-references invariant, under-limit no-op, write-pressure trigger, periodic trigger, reconciliation); implementation follows in `8cb09b6`/`bdd86a4` until green.
- `make check` green (all tests, lint 0 issues, fmt-check) at HEAD.
- Pinned CI lint gate: `docker build --target lint .` green (golangci-lint v2.10.1).
- End-to-end with the built binary:
- omitted key: startup logs `computed default cache size limit from free space` and `effective cache size limit` (75% of the test host's free space);
- `cache_max_bytes: banana`: exit 1 with `config key "cache_max_bytes": value "banana" is not an integer`;
- `cache_max_bytes: 0`: `cache_disabled=true` logged, two identical requests both fetch upstream (2 upstream fetches logged), 200 `image/jpeg` responses, no `cache/` directory created, only `state.sqlite3` in the state dir;
- enabled: second request served from cache (1 upstream fetch), `variant_content` and `source_content` rows match the on-disk file sizes.
Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #55
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
Extracts HMAC-SHA256 request signing out of `internal/imgcache/` into its own `internal/signature/` package, per the plan in [issue #39](#39).
This is one of the remaining "easily separable" extractions (`imageprocessor`, `allowlist`, `magic`, and `httpfetcher` already landed). Only the signer is moved here so the diff stays reviewable.
## What moved
From `internal/imgcache/signature.go` and its tests into `internal/signature/`:
- `Signer` type, its `New` constructor, `Sign`, `Verify`, `GenerateSignedURL`
- `ParseParams` (query-string signature/expiration parsing)
- Signature error sentinels
## One-way import edge
To keep the import edge one-way (`imgcache` depends on `signature`, never the reverse), the package defines a standalone `Request` type carrying just the fields the signature covers, instead of importing `imgcache.ImageRequest`. `imgcache` projects its `ImageRequest` onto `signature.Request` via a small unexported `signatureRequest` helper. This mirrors how the `magic` extraction defined its own `ImageFormat` type.
## Renames (no stuttering)
- `NewSigner` -> `signature.New`
- `ParseSignatureParams` -> `signature.ParseParams`
- `ErrSignatureRequired`/`Invalid`/`Expired` -> `signature.ErrRequired`/`Invalid`/`Expired`
The `ErrRequired` message is updated from "non-whitelisted host" to "non-allowlisted host" for inclusive terminology, consistent with the `allowlist` rename.
## Rework (post-review)
Three commits added after review feedback:
- `d69019b` — golden known-answer test pinning the exact HMAC signatures and signed URL paths for three fixed vectors (resized, resized+query, orig size), cross-validated against an independent HMAC implementation. Any change to the signed byte format now fails loudly.
- `43b9f1c` — whitelist→allowlist rename completed across `internal/imgcache` and `internal/handlers` (`ServiceConfig.Allowlist`, `Allowlist` interface, `IsAllowlisted`, test helpers and test names).
- `3dc1999` — one-pass config surface rename, no back-compat alias: YAML key `whitelist_hosts` → `allowlist_hosts`, `Config.WhitelistHosts` → `Config.AllowlistHosts`, `config.example.yml`, `scripts/manual-test.sh`, and `README.md` (which also documented a nonexistent `source_host_whitelist` key — now fixed to the real one).
## Behavior
Pure refactor apart from the config key rename above. The bytes fed to the HMAC are unchanged (`host:path:query:width:height:format:expiration`), so previously issued signatures remain valid — now enforced by the golden test. All existing tests move with the package. `script/cibuild` passes at head `3dc1999` (fmt-check, lint, test, build).
refs #39
Co-authored-by: sneak <sneak@sneak.berlin>
Co-authored-by: Jeffrey Paul <sneak@noreply.example.org>
Reviewed-on: #46
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
Closes #27
Signatures are per-URL only — this PR adds explicit tests and documentation enforcing that HMAC-SHA256 signatures verify against exact URLs only. No suffix matching, wildcard matching, or partial matching is supported.
## What this does NOT touch
**The host whitelist code (`whitelist.go`) is not modified.** This PR is exclusively about signature verification, per sneak's instructions on [issue #27](#27), [PR #32](#32), and [PR #35](#35).
## Changes
### `internal/imgcache/signature.go`
- Added documentation comments on `Verify()` and `buildSignatureData()` explicitly specifying that signatures are exact-match only — no suffix, wildcard, or partial matching
### `internal/imgcache/signature_test.go`
- **`TestSigner_Verify_ExactMatchOnly`**: 14 tamper cases verifying that modifying any signed component (host, path, query, dimensions, format) causes verification to fail. Host-specific cases include:
- Parent domain (`example.com`) does not match subdomain signature (`cdn.example.com`)
- Sibling subdomain (`images.example.com`) does not match
- Deeper subdomain (`images.cdn.example.com`) does not match
- Evil suffix domain (`cdn.example.com.evil.com`) does not match
- Prefixed host (`evilcdn.example.com`) does not match
- **`TestSigner_Sign_ExactHostInData`**: Verifies that suffix-related hosts (`cdn.example.com`, `example.com`, `images.example.com`, etc.) all produce distinct signatures
### `internal/imgcache/service_test.go`
- **`TestService_ValidateRequest_SignatureExactHostMatch`**: Integration test through `ValidateRequest` verifying that a valid signature for `cdn.example.com` is rejected when presented with a different host (parent domain, sibling subdomain, deeper subdomain, evil suffix, prefixed host)
### `README.md`
- Updated Signature Specification section to explicitly document exact-match-only semantics
Co-authored-by: user <user@Mac.lan guest wan>
Reviewed-on: #40
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
