go

Go Skill

You are working on a Go project. Apply these conventions.

Project Structure

• Follow the standard layout: cmd/<appname>/main.go, internal/, pkg/ for exported packages.
• Keep main.go thin — instantiate dependencies and call a run() function that returns an error.
• Use internal/ to prevent external packages from importing implementation details.

Error Handling

• Always handle errors — never use _ for error values in production code.
• Wrap errors with context: fmt.Errorf("loading config: %w", err).
• Use errors.Is() and errors.As() — never compare error strings.
• Define sentinel errors with var ErrNotFound = errors.New("not found").
• Return early on error (if err != nil { return … }) — avoid nested if pyramids.

Goroutines & Concurrency

• Always clean up goroutines; use context.Context for cancellation propagation.
• Use sync.WaitGroup to wait for goroutines; use channels for communication.
• Use sync.Mutex to protect shared state; prefer sync/atomic for simple counters.
• Avoid goroutine leaks — every goroutine must have a clear exit condition.
• Use errgroup.Group (from golang.org/x/sync/errgroup) for parallel work with error handling.

HTTP (net/http)

• Go 1.22+ ServeMux supports method-specific routing: mux.HandleFunc("GET /users/{id}", handler).
• Use http.NewRequestWithContext for all outbound HTTP requests — always pass a context with a timeout.
• Define middleware as func(http.Handler) http.Handler.
• Set ReadTimeout, WriteTimeout, and IdleTimeout on http.Server.

Interfaces

• Define small, focused interfaces at the point of use (consumer side), not at the implementation.
• Accept interfaces, return concrete types.
• The io.Reader / io.Writer / io.Closer family of interfaces should be used for I/O abstraction.

Testing

• Use the standard testing package; prefer table-driven tests.
• Use t.Helper() in helper functions to get accurate line numbers on failures.
• Use httptest.NewServer or httptest.NewRecorder for HTTP handler tests.
• Use -race flag in CI: go test -race ./....