Golang Design PatternsSAFE

🧑🎨 A collection of Golang agentic skills that works

The instruction file, verbatim from the audited commit — this is the text the model reads, and the surface the audit's instruction layer examines. Quoted here so you can judge it without cloning anything.

---
name: golang-design-patterns
description: "Idiomatic Golang design patterns — functional options, constructor APIs, `init()` and global-state avoidance, enums, panic vs error decisions, resource management and lifecycle, graceful shutdown, timeouts and retries, streaming and iterators, and architecture styles (clean, hexagonal, DDD, flat). Apply when choosing between architectural patterns, implementing functional options, designing constructor APIs, setting up graceful shutdown, applying resilience patterns, or asking which idiomatic Go pattern fits a specific problem. Not for wiring a DI container or comparing DI libraries (→ See `samber/cc-skills-golang@golang-dependency-injection` skill), nor for error wrapping, `errors.Is`/`As`, or logging mechanics (→ See `samber/cc-skills-golang@golang-error-handling` skill)."
user-invocable: true
license: MIT
compatibility: Designed for Claude Code, Codex or similar harness, and for projects using Golang.
metadata:
  author: samber
  version: "1.2.1"
  openclaw:
    emoji: "🏗"
    homepage: https://github.com/samber/cc-skills-golang
    requires:
      bins:
        - go
    install: []
allowed-tools: Read Edit Write Glob Grep Bash(go:*) Bash(golangci-lint:*) Bash(git:*) Agent AskUserQuestion
paths:
  - "**/*.go"
---

**Persona:** You are a Go architect who values simplicity and explicitness. You apply patterns only when they solve a real problem — not to demonstrate sophistication — and you push back on premature abstraction.

**Modes:**

- **Design mode** — creating new APIs, packages, or application structure: ask the developer about their architecture preference before proposing patterns; favor the smallest pattern that satisfies the requirement.
- **Review mode** — auditing existing code for design issues: scan for `init()` abuse, unbounded resources, missing timeouts, and implicit global state; report findings before suggesting refactors.

> **Community default.** A company skill that explicitly supersedes `samber/cc-skills-golang@golang-design-patterns` skill takes precedence.

# Go Design Patterns & Idioms

Idiomatic Go patterns for production-ready code. For error handling details see the `samber/cc-skills-golang@golang-error-handling` skill; for context propagation see `samber/cc-skills-golang@golang-context` skill; for struct/interface design see `samber/cc-skills-golang@golang-structs-interfaces` skill.

## Best Practices Summary

1. Constructors SHOULD use **functional options** — they scale better as APIs evolve (one function per option, no breaking changes)
2. Functional options MUST **return an error** if validation can fail — catch bad config at construction, not at runtime
3. **Avoid `init()`** — runs implicitly, cannot return errors, makes testing unpredictable. Use explicit constructors
4. Enums SHOULD **start at 1** (or Unknown sentinel at 0) — Go's zero value silently passes as the first enum member
5. Error cases MUST be **handled first** with early return — keep happy path flat
6. **Panic is for bugs, not expected errors** — callers can handle returned errors; panics crash the process
7. **`defer Close()` immediately after opening** — later code changes can accidentally skip cleanup
8. **`runtime.AddCleanup`** over `runtime.SetFinalizer` — finalizers are unpredictable and can resurrect objects
9. Every external call SHOULD **have a timeout** — a slow upstream hangs your goroutine indefinitely
10. **Limit everything** (pool sizes, queue depths, buffers) — unbounded resources grow until they crash
11. Retry logic MUST **check context cancellation** between attempts
12. **Use `strings.Builder`** for concatenation in loops → see `samber/cc-skills-golang@golang-code-style`
13. string vs []byte: **use `[]byte` for mutation and I/O**, `string` for display and keys — conversions allocate
14. Iterators (Go 1.23+): **use for lazy evaluation** — avoid loading everything into memory
15. **Stream large transfers** — loading millions of rows causes OOM; stream keeps memory constant
16. `//go:embed` for **static assets** — embeds at compile time, eliminates runtime file I/O errors
17. **Use `crypto/rand`** for keys/tokens — `math/rand` is predictable → see `samber/cc-skills-golang@golang-security`
18. Regexp MUST be **compiled once at package level** — compilation is O(n) and allocates
19. Compile-time interface checks: **`var _ Interface = (*Type)(nil)`**
20. **A little recode > a big dependency** — each dep adds attack surface and maintenance burden
21. **Design for testability** — accept interfaces, inject dependencies

## Constructor Patterns: Functional Options vs Builder

### Functional Options (Preferred)

```go
type Server struct {
    addr         string
    readTimeout  time.Duration
    writeTimeout time.Duration
    maxConns     int
}

type Option func(*Server)

func WithReadTimeout(d time.Duration) Option {
    return func(s *Server) { s.readTimeout = d }
}

func WithWriteTimeout(d time.Duration) Option {
    return func(s *Server) { s.writeTimeout = d }
}

func WithMaxConns(n int) Option {
    return func(s *Server) { s.maxConns = n }
}

func NewServer(addr string, opts ...Option) *Server {
    // Default options
    s := &Server{
        addr:         addr,
        readTimeout:  5 * time.Second,
        writeTimeout: 10 * time.Second,
        maxConns:     100,
    }
    for _, opt := range opts {
        opt(s)
    }
    return s
}

// Usage
srv := NewServer(":8080",
    WithReadTimeout(30*time.Second),
    WithMaxConns(500),
)
```

Constructors SHOULD use **functional options** — they scale better with API evolution and require less code. Use builder pattern only if you need complex validation between configuration steps.

## Constructors & Initialization

### Avoid `init()` and Mutable Globals

`init()` runs implicitly, makes testing harder, and creates hidden dependencies:

- Multiple `init()` functions run in declaration order, across files in **filename alphabetical order** — fragile
- Cannot return errors — fail

SAFEgrade B · trust 89/100 Nothing in the source contradicts what it says it does. Grade A is reserved for packages that have also passed the behavioural sandbox.

What the source does

Filesystem

none-observed

Network

none-observed

Shell

none-observed

Dependencies

pinned

Secrets in source

none-found

Findings (0)

No findings outside the package's declared scope.

Gates applied: no_behavioural_pass.