Agent skill

go-best-practices

Go development best practices, patterns, and conventions. Use when writing Go code, reviewing .go files, discussing goroutines, channels, error handling, or Go project structure. Triggers on mentions of Go, Golang, goroutines, channels, defer, interfaces, go mod.

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SKILL.md

Go Best Practices

Project Structure

project/
├── cmd/
│   └── myapp/
│       └── main.go
├── internal/
│   ├── handler/
│   ├── service/
│   └── repository/
├── pkg/
│   └── shared/
├── go.mod
└── go.sum

Error Handling

Always Check Errors

go
// Bad
result, _ := doSomething()

// Good
result, err := doSomething()
if err != nil {
    return fmt.Errorf("doSomething failed: %w", err)
}

Wrap Errors with Context

go
func fetchUser(id string) (*User, error) {
    user, err := db.Query(id)
    if err != nil {
        return nil, fmt.Errorf("fetch user %s: %w", id, err)
    }
    return user, nil
}

Sentinel Errors

go
var (
    ErrNotFound     = errors.New("not found")
    ErrUnauthorized = errors.New("unauthorized")
)

// Check with errors.Is
if errors.Is(err, ErrNotFound) {
    return http.StatusNotFound
}

Custom Error Types

go
type ValidationError struct {
    Field   string
    Message string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("%s: %s", e.Field, e.Message)
}

// Check with errors.As
var validErr *ValidationError
if errors.As(err, &validErr) {
    log.Printf("validation failed on %s", validErr.Field)
}

Concurrency

Goroutines with WaitGroups

go
var wg sync.WaitGroup
for _, item := range items {
    wg.Add(1)
    go func(item Item) {
        defer wg.Done()
        process(item)
    }(item)
}
wg.Wait()

Channels

go
// Buffered channel for bounded work
jobs := make(chan Job, 100)

// Signal-only channel
done := make(chan struct{})

// Close to broadcast
close(done)

Context for Cancellation

go
func fetchData(ctx context.Context, url string) error {
    req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
    if err != nil {
        return err
    }

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return err
    }
    defer resp.Body.Close()

    return nil
}

Worker Pools

go
func worker(id int, jobs <-chan Job, results chan<- Result) {
    for job := range jobs {
        results <- process(job)
    }
}

func main() {
    jobs := make(chan Job, 100)
    results := make(chan Result, 100)

    // Start workers
    for w := 0; w < 3; w++ {
        go worker(w, jobs, results)
    }

    // Send jobs
    for _, job := range allJobs {
        jobs <- job
    }
    close(jobs)
}

Interfaces

Small Interfaces

go
// Good - single method
type Reader interface {
    Read(p []byte) (n int, err error)
}

// Accept interfaces, return structs
func Process(r Reader) (*Result, error) {
    // ...
}

Interface Composition

go
type ReadWriter interface {
    Reader
    Writer
}

Testing

Table-Driven Tests

go
func TestAdd(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        expected int
    }{
        {"positive", 2, 3, 5},
        {"negative", -1, -2, -3},
        {"zero", 0, 0, 0},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            got := Add(tt.a, tt.b)
            if got != tt.expected {
                t.Errorf("Add(%d, %d) = %d; want %d", tt.a, tt.b, got, tt.expected)
            }
        })
    }
}

Test Helpers

go
func setupTestDB(t *testing.T) *DB {
    t.Helper()
    db, err := NewDB(":memory:")
    if err != nil {
        t.Fatalf("setup db: %v", err)
    }
    t.Cleanup(func() { db.Close() })
    return db
}

Resource Management

Defer for Cleanup

go
func readFile(path string) ([]byte, error) {
    f, err := os.Open(path)
    if err != nil {
        return nil, err
    }
    defer f.Close()

    return io.ReadAll(f)
}

Mutex Patterns

go
type SafeCounter struct {
    mu    sync.RWMutex
    value int
}

func (c *SafeCounter) Inc() {
    c.mu.Lock()
    defer c.mu.Unlock()
    c.value++
}

func (c *SafeCounter) Value() int {
    c.mu.RLock()
    defer c.mu.RUnlock()
    return c.value
}

Naming Conventions

  • Packages: short, lowercase, no underscores (http, json)
  • Exported: PascalCase (NewServer, UserID)
  • Unexported: camelCase (userID, conn)
  • Acronyms: consistent case (URL, userID)
  • Getters: no Get prefix (user.Name() not user.GetName())

Common Patterns

Functional Options

go
type Server struct {
    port    int
    timeout time.Duration
}

type Option func(*Server)

func WithPort(p int) Option {
    return func(s *Server) { s.port = p }
}

func NewServer(opts ...Option) *Server {
    s := &Server{port: 8080, timeout: 30 * time.Second}
    for _, opt := range opts {
        opt(s)
    }
    return s
}

Constructor Pattern

go
func NewUser(name string) (*User, error) {
    if name == "" {
        return nil, errors.New("name required")
    }
    return &User{Name: name, CreatedAt: time.Now()}, nil
}

Anti-Patterns to Avoid

  • Naked returns in long functions
  • Ignoring errors with _
  • Passing large structs by value
  • Using init() for complex logic
  • Global mutable state
  • Goroutine leaks (always ensure cleanup)

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