PR6: harden repo source cache (URL-hashed mirrors + self-contained checkouts) by robbycochran · Pull Request #107 · stackrox/harness-openshell

robbycochran · 2026-08-28T03:54:56Z

What

Rework the on-disk repo cache that harness apply uses to stage a repo:
into the sandbox.

Before: ~/.cache/harness-openshell/repos/<repo-name>/ — keyed by
basename, mutated in place. Two repos sharing a basename collided on one
directory; two runs of the same repo raced on it.

After:

~/.cache/harness-openshell/
  mirrors/<sha256(canonical-url)>.git   bare, shallow, shared, updated in place
  checkouts/<run-id>/<repo-name>/       real repo (own .git), per run

Why it's shaped this way

URL-hashed mirrors — distinct repos that share a basename hash to
different mirrors; all spellings of one repo (.git suffix, trailing slash,
scheme/host case) canonicalize to a single mirror.
Self-contained per-run checkouts — built with git init + git fetch --depth 1 <mirror> <commit> + git checkout --detach FETCH_HEAD, not a
linked worktree. A linked worktree's .git is a file pointing at a host
path, which breaks once only the checkout is uploaded into the sandbox. A
self-contained checkout carries its own objects (no alternates), so the agent
can run git inside the sandbox. Because the fetch targets the local mirror
path, no repo URL or credentials leak into the checkout's .git/config.
One shared lock — the mirror is the only shared on-disk state; a
per-mirror flock is held across the mirror update and the local object copy,
so a concurrent run's shallow gc can't delete packs mid-read. Checkout and
submodule init run outside the lock (the checkout is independent by then), so
unrelated runs aren't serialized on network submodule fetches.

Hardening

Failed prepares (bad ref, network blip) remove their run dir instead of
leaking it under checkouts/.
Mirror creation is idempotent across a crash between init and remote setup.
Lock files are intentionally never unlinked — deleting an flock'd file
reintroduces the classic unlink race. One 0-byte file per repo, not per run.

Tests

internal/source/source_test.go — real-git file:// fixtures, no network.
Covers canonicalization, basename-collision isolation, self-contained checkout
(copies the checkout, deletes the whole cache, asserts git status/git log
still work), default-ref resolution, 6-goroutine concurrent same-repo prepare,
and bad-ref no-leak. go test ./... -race green; go vet and gofmt -l clean.

Summary by CodeRabbit

New Features
- Added isolated repository checkouts for each run.
- Improved caching to prevent naming collisions between repositories with the same basename.
- Preserved ref selection, shallow submodule initialization, and Git functionality.
- Added automatic cleanup of temporary checkouts.
Bug Fixes
- Prevented concurrent runs from interfering with one another.
- Removed credentials from stored repository URLs.
- Ensured failed preparations leave no temporary files.
Documentation
- Documented the updated repository cache and checkout behavior.

…ntained checkouts Replace the basename-keyed mutable repo cache (~/.cache/harness-openshell/repos/<repo-name>/) — which collided when two repos shared a basename and raced when two runs shared one repo — with: mirrors/<sha256(canonical-url)>.git bare, shallow, shared, updated in place checkouts/<run-id>/<repo-name>/ real repo (own .git), per run The mirror is the only shared on-disk state; every write to it is serialized under a per-mirror flock held across the mirror update and the local object copy, so a concurrent run's shallow gc can't delete packs mid-read. Distinct repos that share a basename now hash to different mirrors; concurrent runs of the same repo get independent checkouts. Each per-run checkout is built with `git init` + `git fetch --depth 1 <mirror> <commit>` + `git checkout --detach FETCH_HEAD` rather than a linked worktree. A linked worktree's .git is a *file* pointing at a host path, which breaks once only the checkout is uploaded into the sandbox; a self-contained checkout carries its own objects (no alternates), so git keeps working there. The fetch runs against the local mirror path, so no repo URL or credentials leak into the checkout's .git/config. Failed prepares (bad ref, network blip) clean up their run dir instead of leaking it under checkouts/. Mirror creation is idempotent across a crash between init and remote setup. Lock files are intentionally never unlinked (deleting an flock'd file reintroduces the unlink race); one 0-byte file per repo, not per run.

coderabbitai · 2026-08-28T03:56:01Z

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Reviewing files that changed from the base of the PR and between dacc054 and 60814b1.

📒 Files selected for processing (3)

internal/source/cache.go
internal/source/mirror.go
internal/source/source_test.go

🚧 Files skipped from review as they are similar to previous changes (3)

internal/source/mirror.go
internal/source/cache.go
internal/source/source_test.go

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Walkthrough

The repository cache now uses URL-hashed bare mirrors and isolated per-run checkouts. The source package manages mirror locking, ref resolution, checkout creation, submodules, cleanup, and run IDs. The executor uses this package for repository preparation and upload.

Changes

Repository checkout cache

Layer / File(s)	Summary
Cache identity and path layout `internal/source/cache.go`	The cache canonicalizes URLs, removes embedded userinfo, derives repository names, hashes mirror paths, creates run-specific checkout paths, and generates cryptographically random run IDs.
Locked bare mirror management `internal/source/mirror.go`, `internal/source/source_test.go`	Git mirrors use persistent advisory locks. Mirror setup maintains credential-free `origin`, shallow-fetches refs, and resolves `FETCH_HEAD` to a commit. Tests cover URL variants and origin handling.
Self-contained per-run checkout `internal/source/checkout.go`, `internal/source/source_test.go`	`Cache.Prepare` creates an independent Git checkout, performs detached checkout and shallow submodule initialization, and removes failed or completed runs. Tests cover content, isolation, concurrency, default refs, cleanup, and basename collisions.
Executor upload and lifecycle integration `cmd/executor.go`, `CHANGELOG.md`	The executor generates a run ID, calls `source.Prepare`, uploads the prepared directory, and cleans it up after execution. The changelog documents the new layout.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 60814

This PR hardens repository caching and checkout isolation; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Executor
  participant CachePrepare
  participant BareMirror
  participant RunCheckout
  participant Sandbox
  Executor->>CachePrepare: Prepare repository ref
  CachePrepare->>BareMirror: lock, update, and resolve ref
  BareMirror-->>CachePrepare: resolved commit
  CachePrepare->>RunCheckout: create isolated checkout
  RunCheckout-->>Executor: checkout path and cleanup
  Executor->>Sandbox: upload checkout
  Executor->>RunCheckout: cleanup checkout

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Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 48.28% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the main change: hardening the repository source cache with URL-hashed mirrors and self-contained checkouts.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In `@internal/source/mirror.go`:
- Around line 104-115: Remove embedded userinfo from the origin URL in
ensureOrigin before updating or adding the remote, and rely on the configured
Git credential helper for authentication rather than persisting credentials in
the mirror configuration. Also update internal/source/cache.go lines 55-65 in
CanonicalizeURL to clear u.User so credential changes do not create separate
mirror keys.

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📥 Commits

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📒 Files selected for processing (6)

CHANGELOG.md
cmd/executor.go
internal/source/cache.go
internal/source/checkout.go
internal/source/mirror.go
internal/source/source_test.go

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coderabbitai Bot reviewed Aug 28, 2026

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Comment thread internal/source/mirror.go

robbycochran added 2 commits August 31, 2026 09:35

Merge remote-tracking branch 'origin/main' into rc-pr6-source-hardening

22b33cb

fix(source): exclude credentials from mirror state

60814b1

robbycochran merged commit 58a0bfc into main Aug 31, 2026
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PR6: harden repo source cache (URL-hashed mirrors + self-contained checkouts) - #107

PR6: harden repo source cache (URL-hashed mirrors + self-contained checkouts)#107
robbycochran merged 3 commits into
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rc-pr6-source-hardening

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What

Why it's shaped this way

Hardening

Tests

Summary by CodeRabbit

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Walkthrough

Changes

Sequence Diagram(s)

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robbycochran commented Aug 28, 2026 •

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