golang-safety
Defensive Golang coding against accidental bugs — nil panics, typed-nil interfaces, append backing-array aliasing, silent int64-to-int32 truncation, float == comparison, defer inside loops, defensive copies of slices and maps, and usable zero values. Use when a Go program panics on a nil map write or nil pointer dereference, when reviewing code for nil-safety, numeric conversion overflow, or resource lifecycle, or when designing a type whose zero value must be safe. Not for designing concurrent access with goroutines, channels, or sync primitives (→ See samber/cc-skills-golang@golang-concurrency skill), not for exploitable vulnerabilities such as injection, weak crypto, or leaked secrets (→ See samber/cc-skills-golang@golang-security skill), and not for debugging an already-failing program (→ See samber/cc-skills-golang@golang-troubleshooting skill).
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/samber/cc-skills-golang --skill golang-safety- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads golang-safety automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
Persona: You are a defensive Go engineer. You treat every untested assumption about nil, capacity, and numeric range as a latent crash waiting to happen.
Go Safety: Correctness & Defensive Coding
Prevents programmer mistakes — bugs, panics, and silent data corruption in normal (non-adversarial) code. Security handles attackers; safety handles ourselves.
Best Practices Summary
- Prefer generics over
anywhen the type set is known — compiler catches mismatches instead of runtime panics - Always use safe type assertions — for normal interfaces use comma-ok (
v, ok := x.(T)); for reflection in Go 1.25+ preferreflect.TypeAssert[T](value)overvalue.Interface().(T). - Typed nil pointer in an interface is not
== nil— the type descriptor makes it non-nil - Writing to a nil map panics — always initialize before use
appendmay reuse the backing array — both slices share memory if capacity allows, silently corrupting each other- Return defensive copies from exported functions — otherwise callers mutate your internals
deferruns at function exit, not loop iteration — extract loop body to a function- Integer conversions truncate silently —
int64toint32wraps without error - Float arithmetic is not exact — use epsilon comparison or
math/big - Design useful zero values — nil map fields panic on first write; use lazy init
- Use
sync.Oncefor lazy init — guarantees exactly-once even under concurrency
Nil Safety
Nil-related panics are the most common crash in Go.
The nil interface trap
Interfaces store (type, value). An interface is nil only when both are nil. Returning a typed nil pointer sets the type descriptor, making it non-nil:
// ✗ Dangerous — interface{type: *MyHandler, value: nil} is not == nil
func getHandler() http.Handler {
var h *MyHandler // nil pointer
if !enabled {
return h // interface{type: *MyHandler, value: nil} != nil
}
return h
}
// ✓ Good — return nil explicitly
func getHandler() http.Handler {
if !enabled {
return nil // interface{type: nil, value: nil} == nil
}
return &MyHandler{}
}
Nil map, slice, and channel behavior
| Type | Index into nil | Write to nil | Len/Cap of nil | Range over nil |
|---|---|---|---|---|
| Map | Zero value | panic | 0 | 0 iterations |
| Slice | panic | panic | 0 | 0 iterations |
| Channel | Blocks forever | Blocks forever | 0 | Blocks forever |
// ✗ Bad — nil map panics on write
var m map[string]int
m["key"] = 1
// ✓ Good — initialize or lazy-init in methods
m := make(map[string]int)
func (r *Registry) Add(name string, val int) {
if r.items == nil { r.items = make(map[string]int) }
r.items[name] = val
}
See Nil Safety Deep Dive for nil receivers, nil in generics, and nil interface performance.
Slice & Map Safety
Slice aliasing — the append trap
append reuses the backing array if capacity allows. Both slices then share memory:
// ✗ Dangerous — a and b share backing array
a := make([]int, 3, 5)
b := append(a, 4)
b[0] = 99 // also modifies a[0]
// ✓ Good — full slice expression forces new allocation
b := append(a[:len(a):len(a)], 4)
Map concurrent access
Maps MUST NOT be accessed concurrently — → see samber/cc-skills-golang@golang-concurrency for sync primitives.
See Slice and Map Deep Dive for range pitfalls, subslice memory retention, and slices.Clone/maps.Clone.
Numeric Safety
Implicit type conversions truncate silently
// ✗ Bad — silently wraps around if val > math.MaxInt32 (3B becomes -1.29B)
var val int64 = 3_000_000_000
i32 := int32(val) // -1294967296 (silent wraparound)
// ✓ Good — check before converting
if val > math.MaxInt32 || val < math.MinInt32 {
return fmt.Errorf("value %d overflows int32", val)
}
i32 := int32(val)
Float comparison
// ✗ Bad — floating point arithmetic is not exact
var a, b, c float64 = 0.1, 0.2, 0.3
a+b == c // false
// ✓ Good — use epsilon comparison
const epsilon = 1e-9
math.Abs((a+b)-c) < epsilon // true
Division by zero
Integer division by zero panics. Float division by zero produces +Inf, -Inf, or NaN.
func avg(total, count int) (int, error) {
if count == 0 {
return 0, errors.New("division by zero")
}
return total / count, nil
}
For integer overflow as a security vulnerability, see the samber/cc-skills-golang@golang-security skill section.
Resource Safety
defer in loops — resource accumulation
defer runs at function exit, not loop iteration. Resources accumulate until the function returns:
// ✗ Bad — all files stay open until function returns
for _, path := range paths {
f, _ := os.Open(path)
defer f.Close() // deferred until function exits
process(f)
}
// ✓ Good — extract to function so defer runs per iteration
for _, path := range paths {
if err := processOne(path); err != nil { return err }
}
func processOne(path string) error {
f, err := os.Open(path)
if err != nil { return err }
defer f.Close()
return process(f)
}
Goroutine leaks
→ See samber/cc-skills-golang@golang-concurrency for goroutine lifecycle and leak prevention.
Immutability & Defensive Copying
Exported functions returning slices/maps SHOULD return defensive copies.
Protecting struct internals
// ✗ Bad — exported slice field, anyone can mutate
type Config struct {
Hosts []string
}
// ✓ Good — unexported field with accessor returning a copy
type Config struct {
hosts []string
}
func (c *Config) Hosts() []string {
return slices.Clone(c.hosts)
}
Initialization Safety
Zero-value design
Design types so var x MyType is safe — prevents "forgot to initialize" bugs:
var mu sync.Mutex // ✓ usable at zero value
var buf bytes.Buffer // ✓ usable at zero value
// ✗ Bad — nil map panics on write
type Cache struct { data map[string]any }
sync.Once for lazy initialization
type DB struct {
once sync.Once
conn *sql.DB
}
func (db *DB) connection() *sql.DB {
db.once.Do(func() {
db.conn, _ = sql.Open("postgres", connStr)
})
return db.conn
}
init() function pitfalls
→ See samber/cc-skills-golang@golang-design-patterns for why init() should be avoided in favor of explicit constructors.
Enforce with Linters
Many safety pitfalls are caught automatically by linters: errcheck, forcetypeassert, nilerr, govet, staticcheck. See the samber/cc-skills-golang@golang-lint skill for configuration and usage.
Go 1.25+ reflection type assertions
For reflection code, prefer reflect.TypeAssert[T] over value.Interface().(T).
v := reflect.ValueOf(x)
if s, ok := reflect.TypeAssert[string](v); ok {
use(s)
}
Common Mistakes
| Mistake | Fix |
|---|---|
Bare type assertion v := x.(T) | Panics on type mismatch, crashing the program. Use v, ok := x.(T) to handle gracefully |
| Returning typed nil in interface function | Interface holds (type, nil) which is != nil. Return untyped nil for the nil case |
| Writing to a nil map | Nil maps have no backing storage — write panics. Initialize with make(map[K]V) or lazy-init |
Assuming append always copies | If capacity allows, both slices share the backing array. Use s[:len(s):len(s)] to force a copy |
defer in a loop | defer runs at function exit, not loop iteration — resources accumulate. Extract body to a separate function |
int64 to int32 without bounds check | Values wrap silently (3B → -1.29B). Check against math.MaxInt32/math.MinInt32 first |
Comparing floats with == | IEEE 754 representation is not exact (0.1+0.2 != 0.3). Use math.Abs(a-b) < epsilon |
| Integer division without zero check | Integer division by zero panics. Guard with if divisor == 0 before dividing |
| Returning internal slice/map reference | Callers can mutate your struct's internals through the shared backing array. Return a defensive copy |
Multiple init() with ordering assumptions | init() execution order across files is unspecified. → See samber/cc-skills-golang@golang-design-patterns — use explicit constructors |
| Blocking forever on nil channel | Nil channels block on both send and receive. Always initialize before use |
Cross-References
- → See
samber/cc-skills-golang@golang-concurrencyskill for concurrent access patterns and sync primitives - → See
samber/cc-skills-golang@golang-data-structuresskill for slice/map internals, capacity growth, and container/ packages - → See
samber/cc-skills-golang@golang-error-handlingskill for nil error interface trap - → See
samber/cc-skills-golang@golang-securityskill for security-relevant safety issues (memory safety, integer overflow) - → See
samber/cc-skills-golang@golang-troubleshootingskill for debugging panics and race conditions - → See
samber/cc-skills-golang@golang-continuous-integrationskill for automated AI-driven code review in CI using these guidelines
FAQ
What does the golang-safety skill do?
Defensive Golang coding against accidental bugs — nil panics, typed-nil interfaces, append backing-array aliasing, silent int64-to-int32 truncation, float == comparison, defer inside loops, defensive copies of slices and maps, and usable zero values. Use when a Go program panics on a nil map write or nil pointer dereference, when reviewing code for nil-safety, numeric conversion overflow, or resource lifecycle, or when designing a type whose zero value must be safe. Not for designing concurrent access with goroutines, channels, or sync primitives (→ See samber/cc-skills-golang@golang-concurrency skill), not for exploitable vulnerabilities such as injection, weak crypto, or leaked secrets (→ See samber/cc-skills-golang@golang-security skill), and not for debugging an already-failing program (→ See samber/cc-skills-golang@golang-troubleshooting skill).
How do I install golang-safety?
Run npx skills add https://github.com/samber/cc-skills-golang --skill golang-safety in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/golang-safety/ (personal) or .claude/skills/golang-safety/ (project).
Which AI agents can use golang-safety?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is golang-safety safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains golang-safety?
It is published by samber in samber/cc-skills-golang. It has 40,740 recorded installs.
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