ring:defense-in-depth
Multi-layer validation pattern - validates data at EVERY layer it passes through to make bugs structurally impossible, not just caught.
Install
npx skillscat add lerianstudio/ring/ring-defense-in-depth Install via the SkillsCat registry.
This skill implements multi-layer validation by checking data at every layer it passes through, including entry points, business logic, environment guards, and debug instrumentation. It addresses bugs caused by invalid data reaching deep layers through single validation points that can be bypassed. Developers should use it when fixing bugs where invalid data causes failures, when validation exists at only one layer, or when preventing entire categories of bugs rather than individual instances.
Defense-in-Depth Validation
Overview
When you fix a bug caused by invalid data, adding validation at one place feels sufficient. But that single check can be bypassed by different code paths, refactoring, or mocks.
Core principle: Validate at EVERY layer data passes through. Make the bug structurally impossible.
Why Multiple Layers
Single validation: "We fixed the bug"
Multiple layers: "We made the bug impossible"
Different layers catch different cases:
- Entry validation catches most bugs
- Business logic catches edge cases
- Environment guards prevent context-specific dangers
- Debug logging helps when other layers fail
The Four Layers
| Layer | Purpose | Example |
|---|---|---|
| 1. Entry Point | Reject invalid input at API boundary | if (!workingDir || !existsSync(workingDir)) throw new Error(...) |
| 2. Business Logic | Ensure data makes sense for operation | if (!projectDir) throw new Error('projectDir required') |
| 3. Environment Guards | Prevent dangerous ops in contexts | if (NODE_ENV === 'test' && !path.startsWith(tmpdir())) throw... |
| 4. Debug Instrumentation | Capture context for forensics | logger.debug('About to git init', { directory, cwd, stack }) |
Applying the Pattern
Steps: (1) Trace data flow (origin → error) (2) Map all checkpoints (3) Add validation at each layer (4) Test each layer (try to bypass layer 1, verify layer 2 catches it)
Example
Bug: Empty projectDir caused git init in source code
Flow: Test setup ('') → Project.create(name, '') → WorkspaceManager.createWorkspace('') → git init in process.cwd()
Layers added: L1: Project.create() validates not empty/exists/writable | L2: WorkspaceManager validates not empty | L3: Refuse git init outside tmpdir in tests | L4: Stack trace logging
Result: 1847 tests passed, bug impossible to reproduce
Key Insight
All four layers necessary - each caught bugs others missed: different code paths bypassed entry validation | mocks bypassed business logic | edge cases needed environment guards | debug logging identified structural misuse.
Don't stop at one validation point. Add checks at every layer.
Install
npx skillscat add lerianstudio/ring/ring-defense-in-depth Install via the SkillsCat registry.