Gzip Campfire HTML outside the lock; skip fragment dups on CRuby

[thomasklemm]

Stacked on #424. CRuby first; Spinel gzip path included because the same lock was the measured cliff there.

What

• CRuby GzipCache: still keys by the identity body (MRI string hash of 420 KB is cheaper than SHA-256 — measured: digest key dropped /rooms/1 from ~1725 to ~1140 req/s). Gzip itself now runs outside the Mutex. Two threads that miss both gzip; one write wins.
• CRuby Rails.cache.read_str: no longer dups the stored fragment. A <% cache %> hit only appends it; DupCoder's write-side copy already isolates the store. read (untyped) still dups. write_str freezes the stored copy.
• Spinel tep: keys gzip by SHA-256 of the identity body so the lock only covers a 64-char lookup, and gzip runs outside the lock. Spinel Hash hashes the whole key and has no GVL — this is the lane that still needed the digest.

Does not touch #426 (compile walls / param_rebind).

Bench (this orb, gzip, c=16, 2×8s)

CRuby vs the #424 head on the same box:

route	#424 ruby	now ruby	vs #424
/rooms/1	1725	1886	1.09×
messages page	3303	3601	1.09×
sidebar	2242	2436	1.09×
search	2851	3271	1.15×
POST message	797	878	1.10×

Spinel /rooms/1 869 → 1210 (1.39×) with the digest key. Rust on the same run: 11992. Still ~6× CRuby on the room page — language + architecture, not one missing SQL.

Campfire (issues only)

Already filed: #307 sidebar split, #308 page_updated_since, #309 bot COUNT. New: basecamp/once-campfire#313 WAL auto-checkpoint on the writer thread (Rust attribution item 3; no existing issue/PR). #310 already covers direct-room lookup.

Tests

cargo test --test gzip_cache: 4 passed (identical bodies once, distinct bodies, tep digest hit, overlay read_str no-dup).

Summary by CodeRabbit

• Bug Fixes
  • Compressed responses are cached by content, preventing different response bodies from receiving the wrong compressed result. Identical content can reuse cached compression, and compression runs outside the cache lock.
  • String-cache reads now reject expired or invalid entries. Cached values remain protected from modification; ordinary reads still return a separate copy.
• Documentation
  • Clarified how compressed-response cache keys differ between runtime implementations.

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Reviewing files that changed from the base of the PR and between 89e6ca8 and da1c6c1.

📒 Files selected for processing (2)

• runtime/spinel/scaffold/ruby_overlay/runtime/rails_cache.rb
• tests/gzip_cache.rs

🚧 Files skipped from review as they are similar to previous changes (2)

• tests/gzip_cache.rs
• runtime/spinel/scaffold/ruby_overlay/runtime/rails_cache.rb

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📝 Walkthrough

Walkthrough

The gzip caches now use lane-specific keys and perform compression outside the lock. Rails string-cache methods return stored strings directly or store frozen copies. Integration tests cover gzip cache results and Rails string-cache behavior.

Changes

Runtime cache behavior

Layer / File(s)	Summary
Gzip cache keying and compression runtime/spinel/tep/tep_core.rb, runtime/spinel/tep/tep.rb, runtime/spinel/scaffold/ruby_overlay/runtime/gzip_cache.rb, docs/pipeline/runtime.md, tests/gzip_cache.rs	Spinel keys compressed bodies by SHA-256, while CRuby keys them by raw body bytes. Both compress cache misses outside the lock. Documentation and integration tests describe or verify these behaviors.
Rails string-cache reads and writes runtime/spinel/scaffold/ruby_overlay/runtime/rails_cache.rb, tests/gzip_cache.rs	read_str returns stored strings without duplication. String writes and counter values are frozen. Ordinary read continues to return a duplicate. Tests cover frozen entries and read behavior.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to da1c6

No actionable issue remains from the inspected cache changes; the PR is mergeable after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 89e6c

The main request paths preserve response identity and synchronized cache updates. One ownership gap remains: cached Strings written through the general API can now be modified through a typed read. The inspected fragment consumers only append those values, so no remotely exploitable corruption path was established.

Retained concerns

• Low · architecture · observed: read_str now exposes the stored String regardless of which API wrote it. write_str freezes its stored copy, but write and increment_str retain mutable Strings in the same store. Application code that mutates a typed read of those entries can therefore alter shared state outside the mutex and affect later reads; the base returned a duplicate. The inspected generated fragment consumers are append-only, so direct attacker reachability and actual cross-request corruption were not established.

Security review details

Security Blast Radius

• inferred — The demonstrated ownership gap is scoped to entries in one MemoryStore instance, including the process-shared Rails cache. It requires application code to mutate a typed read of a mutable entry. Production tenant relationships and such callers were not established, so cross-tenant exposure cannot be asserted.

Security Findings and Attack Paths

• inferred — A mixed-use sequence of write, read_str, and in-place mutation can alter the stored String and affect subsequent reads. Unlike the base, no defensive duplicate separates that reader from storage. No inspected HTTP-controlled path performs the required mutation, and the generated fragment path is append-only; this is an ownership regression, not a verified remote attack.

Trust Boundaries and Controls

• observed — Request-controlled Accept-Encoding selects compression only after the application produces its response. Existing skips remain for HEAD, bodyless statuses, already encoded responses, small bodies, and listed binary types; Tep also excludes streaming, files, and WebSocket upgrades. CRuby wraps the ordinary Rack response path rather than the Cable upgrade path.

Resilience and Maintainability Implications

• inferred — The gzip storage cap does not bound in-flight compression buffers. Moving compression outside the lock permits simultaneous work and duplicate same-body misses in parallel serving lanes. Puma thread configuration provides a concrete limit there; practical Spinel amplification depends on scheduling, response sizes, and deployment controls not established by this review.

Hardening Proposals

• proposed — Make typed-read ownership consistent across writers: either ensure every stored String is immutable, including counter values, or return a defensive copy when read_str encounters a mutable entry. Validate mixed writer/read sequences so append-only fragment optimization does not weaken the general store boundary.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 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 summarizes the main changes: gzip runs outside the lock, and CRuby avoids duplicating cached fragments.
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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Inline comments:
Review comments at @runtime/spinel/scaffold/ruby_overlay/runtime/rails_cache.rb:
- Line 90: Update `write` or `read_str` so callers cannot mutate cached String
entries: freeze Strings stored by `write`, or return a duplicate when `read_str`
encounters an unfrozen String. Preserve the existing behavior for non-String
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📒 Files selected for processing (6)

• docs/pipeline/runtime.md
• runtime/spinel/scaffold/ruby_overlay/runtime/gzip_cache.rb
• runtime/spinel/scaffold/ruby_overlay/runtime/rails_cache.rb
• runtime/spinel/tep/tep.rb
• runtime/spinel/tep/tep_core.rb
• tests/gzip_cache.rs

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