Capture-set computation (INERT; Task 3-core, v0.133.0)
Pure appbackup.ComputeCaptureSet(binds, hasClassification, tier, hddPath) → CaptureSet
{HasClassification, Paths, Skipped}: legacy short-circuit → tier filter (§2) → structural
guards → equal-Abs collapse (mandatory>optional) → containment dedup → sort. Slash algebra,
no filepath/FS/log. Structural guards (traversal / bare HDD drive-root / reserved backups/)
are load-bearing (the compose parser does not reject ..). Pure CrossAppOverlaps advisory
(WARN wiring deferred to 3a/3b). INERT — no engine consumes it yet.
Tests: Groups A-F (appbackup) + F-S3 no-seam wiring (stacks); all 6 §10 red-proofs verified.
Docs: architecture §3 aligned (felhom.eu 8d85da7).
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package appbackup
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import (
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"path"
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"sort"
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"strings"
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)
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// Capture-set computation — Task 3-core of the backup-classification-redesign arc
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// (felhom.eu/documentation/architecture/07-backup-architecture.md §3; tier×class matrix §2; SQ2/SQ5
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// in SPIKE-backup-classification-2026-07-14.md). This is a PURE path-algebra layer: given an app's
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// classified binds, a tier, and the app's live hddPath, it returns the tier-filtered,
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// structurally-guarded, containment-deduped absolute capture set that the 3a (offsite) and 3b
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// (tier-2) engines will capture. Deliberately INERT — no engine consumes it yet.
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//
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// Purity contract: no os, no exec, no logging, no filepath. Reasons for refused captures are DATA
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// (SkippedPath.Reason); the engines log them (a skipped MANDATORY is a capture GAP the engines must
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// surface loudly). All resolution and prefix algebra uses path.Join/path.Clean and "/" string ops —
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// never filepath.* — because RelPath is defined forward-slash (classify.go) and every resolved Abs
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// is an in-container Linux path; filepath on the Windows `go test` host would flip separators and
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// break both expectations and the containment prefix checks.
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// CaptureTier selects the tier column of §2 that the filter applies.
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type CaptureTier string
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const (
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TierOffsite CaptureTier = "offsite" // §2: mandatory only (optional is the customer's local tier)
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TierSecondary CaptureTier = "secondary" // §2: mandatory + optional
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)
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// CapturePath is one resolved path in the capture set. Abs is the in-container Linux absolute path;
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// Root/RelPath preserve the bind's identity (the tier-2 layout and restore relpath-mirroring need it).
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type CapturePath struct {
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Abs string
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Root BindRoot
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RelPath string
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Class BindClass
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}
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// SkippedPath is a would-be capture the tier filter selected but a structural guard refused. Reason
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// is operator-English; the engines log it (a skipped mandatory path = a silent capture gap otherwise).
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type SkippedPath struct {
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Root BindRoot
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RelPath string
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Class BindClass
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Reason string
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}
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// CaptureSet is the result of ComputeCaptureSet. HasClassification mirrors the classifier's bool;
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// engines derive unit-only as (!HasClassification || len(Paths)==0). Paths is sorted by Abs.
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type CaptureSet struct {
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HasClassification bool
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Paths []CapturePath
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Skipped []SkippedPath
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}
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// Structural-guard reasons (distinct strings; each names the rule it enforces).
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const (
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reasonEscape = "path escapes the drive root"
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reasonBareRoot = "bare drive-root bind would capture the backups tree"
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reasonReserved = "path inside the reserved backups zone"
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)
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// ComputeCaptureSet resolves an app's classified binds into the tier-filtered absolute capture set.
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// Pipeline (fixed order, §8): legacy short-circuit → tier filter (§2 columns) → structural guards →
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// equal-Abs collapse (mandatory > optional) → containment dedup (keep ancestor) → sort by Abs.
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//
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// Tier columns (§2): TierOffsite carries mandatory only; TierSecondary carries mandatory + optional;
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// excluded is silently dropped at every tier (never in Paths, never in Skipped). A legacy app
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// (hasClassification=false) resolves NOTHING — {HasClassification:false} with nil Paths/Skipped —
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// so the engines' no-block branch stays byte-identical to today (the SQ5 cost-regression guard).
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//
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// Resolution: RootHDD → path.Join(hddPath, relPath); RootUserdata → path.Join(hddPath, "userdata",
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// relPath). Guards run AFTER the tier filter, so Skipped means exactly "would have been captured by
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// this tier, refused for structural safety".
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func ComputeCaptureSet(binds []ClassifiedBind, hasClassification bool, tier CaptureTier, hddPath string) CaptureSet {
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if !hasClassification {
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return CaptureSet{HasClassification: false}
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}
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cs := CaptureSet{HasClassification: true}
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// Stage 1+2: tier filter, then structural guards. Survivors are resolved to CapturePath.
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var resolved []CapturePath
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for _, b := range binds {
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if !tierKeeps(tier, b.Class) {
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continue // excluded (any tier) or optional@offsite — silently filtered, not skipped
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}
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if reason, bad := structuralGuard(b.Root, b.RelPath); bad {
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cs.Skipped = append(cs.Skipped, SkippedPath{
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Root: b.Root, RelPath: b.RelPath, Class: b.Class, Reason: reason,
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})
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continue
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}
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resolved = append(resolved, CapturePath{
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Abs: resolveAbs(hddPath, b.Root, b.RelPath), Root: b.Root, RelPath: b.RelPath, Class: b.Class,
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})
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}
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// Stage 3: equal-Abs collapse — one entry per Abs, mandatory beats optional (mandatory semantics
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// must never degrade). Deterministic on ties: keep the lexicographically-smaller (Root, RelPath).
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byAbs := make(map[string]CapturePath, len(resolved))
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for _, cp := range resolved {
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if cur, ok := byAbs[cp.Abs]; ok {
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byAbs[cp.Abs] = strongerCapture(cur, cp)
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continue
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}
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byAbs[cp.Abs] = cp
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}
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uniq := make([]CapturePath, 0, len(byAbs))
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for _, cp := range byAbs {
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uniq = append(uniq, cp)
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}
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// Stage 4: containment dedup — drop any path whose ancestor is already present (keep the ancestor).
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for _, cp := range uniq {
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if hasStrictAncestor(cp.Abs, uniq) {
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continue
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}
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cs.Paths = append(cs.Paths, cp)
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}
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// Stage 5: deterministic order.
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sort.Slice(cs.Paths, func(i, j int) bool { return cs.Paths[i].Abs < cs.Paths[j].Abs })
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sort.Slice(cs.Skipped, func(i, j int) bool {
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if cs.Skipped[i].Root != cs.Skipped[j].Root {
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return cs.Skipped[i].Root < cs.Skipped[j].Root
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}
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return cs.Skipped[i].RelPath < cs.Skipped[j].RelPath
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})
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return cs
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}
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// tierKeeps applies the §2 tier column: mandatory everywhere, optional only for secondary, excluded
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// never.
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func tierKeeps(tier CaptureTier, class BindClass) bool {
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switch class {
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case ClassMandatory:
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return true
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case ClassOptional:
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return tier == TierSecondary
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default: // ClassExcluded (and any unexpected value) — never captured automatically
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return false
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}
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}
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// structuralGuard refuses a (root, relPath) that would capture an unsafe location. Evaluated after
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// the tier filter. RelPath arrives path.Clean'd from the compose parser but is NOT traversal-checked
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// there (ParseComposeClassifiableBinds path.Cleans; ValidateBackupSpec vets only SPEC entries), so an
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// unlisted writable "${HDD_PATH}/../x" bind reaches here classed mandatory — this guard is
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// load-bearing security, not defence-in-depth.
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func structuralGuard(root BindRoot, relPath string) (reason string, bad bool) {
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if relPathEscapes(relPath) {
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return reasonEscape, true
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}
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if root == RootHDD {
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if relPath == "" {
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return reasonBareRoot, true // bare ${HDD_PATH} would nest <hddPath>/backups into the capture
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}
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if relPath == "backups" || strings.HasPrefix(relPath, "backups/") {
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return reasonReserved, true
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}
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}
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// RootUserdata + "" is allowed: resolves to <hddPath>/userdata, which does not nest backups/.
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return "", false
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}
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// relPathEscapes reports whether relPath is absolute or contains a ".." path segment. Detection is
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// SEGMENT-WISE on the slash-split path (".." as a whole component), so a legit dir literally named
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// "a..b" passes.
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func relPathEscapes(relPath string) bool {
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if path.IsAbs(relPath) {
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return true
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}
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for _, seg := range strings.Split(relPath, "/") {
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if seg == ".." {
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return true
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}
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}
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return false
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}
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// resolveAbs maps a guarded (root, relPath) to its in-container absolute path via slash algebra.
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func resolveAbs(hddPath string, root BindRoot, relPath string) string {
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if root == RootUserdata {
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return path.Join(hddPath, "userdata", relPath)
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}
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return path.Join(hddPath, relPath)
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}
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// strongerCapture picks the winner of an equal-Abs collision: mandatory beats optional; on equal
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// class strength, the lexicographically-smaller (Root, RelPath) wins (determinism).
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func strongerCapture(a, b CapturePath) CapturePath {
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sa, sb := classStrength(a.Class), classStrength(b.Class)
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if sa != sb {
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if sa > sb {
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return a
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}
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return b
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}
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if a.Root != b.Root {
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if a.Root < b.Root {
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return a
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}
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return b
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}
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if a.RelPath <= b.RelPath {
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return a
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}
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return b
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}
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// classStrength ranks capture classes for the equal-Abs collapse (mandatory must never degrade).
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func classStrength(c BindClass) int {
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switch c {
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case ClassMandatory:
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return 2
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case ClassOptional:
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return 1
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default:
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return 0
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}
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}
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// hasStrictAncestor reports whether some OTHER path in set is a strict directory ancestor of abs
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// (abs == ancestor+"/"+…). Slash-aware prefix so "/x/paper" does not "contain" "/x/paperless".
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func hasStrictAncestor(abs string, set []CapturePath) bool {
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for _, o := range set {
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if o.Abs == abs {
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continue
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}
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if strings.HasPrefix(abs, o.Abs+"/") {
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return true
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}
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}
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return false
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}
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// Overlap is one absolute path claimed non-excluded by more than one app's capture set (§4.2). Apps
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// is sorted.
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type Overlap struct {
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Abs string
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Apps []string
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}
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// CrossAppOverlaps reports absolute paths that appear in ≥2 apps' Paths — the catalog-convention
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// tripwire (§4: at most one app may class a host path non-excluded). Pure and advisory here; the
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// WARN wiring lands in 3a/3b, not in 3-core. Match is EXACT-Abs only: cross-app CONTAINMENT
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// (calibre-web's mandatory media/books sitting inside plex's excluded reader bind) is legitimate per
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// §4 and must NOT report. Deterministic despite the map input: app names are scanned in sorted order
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// and the output is sorted by Abs. Empty input / no overlap → empty (non-nil) slice.
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func CrossAppOverlaps(sets map[string]CaptureSet) []Overlap {
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apps := make([]string, 0, len(sets))
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for app := range sets {
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apps = append(apps, app)
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}
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sort.Strings(apps)
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byAbs := make(map[string][]string)
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for _, app := range apps {
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seen := make(map[string]bool) // guard against an app listing the same Abs twice
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for _, cp := range sets[app].Paths {
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if seen[cp.Abs] {
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continue
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}
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seen[cp.Abs] = true
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byAbs[cp.Abs] = append(byAbs[cp.Abs], app)
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}
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}
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out := make([]Overlap, 0)
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for abs, owners := range byAbs {
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if len(owners) < 2 {
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continue
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}
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sorted := append([]string(nil), owners...)
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sort.Strings(sorted)
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out = append(out, Overlap{Abs: abs, Apps: sorted})
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}
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sort.Slice(out, func(i, j int) bool { return out[i].Abs < out[j].Abs })
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return out
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}
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