Go Conventions

Go Conventions

Intro

Idiomatic Go is small interfaces, explicit error wrapping, clear goroutine ownership, and domain-oriented packages. Follow gofmt, respect context.Context, and never start a goroutine without knowing how it stops.

Overview

Error handling

Return errors as the last return value; never panic in library code. Wrap with context using fmt.Errorf("loading config: %w", err) so callers can unwrap with errors.Is (sentinel errors) or errors.As (typed errors). Define sentinel errors at package level: var ErrNotFound = errors.New("not found"). Use custom error types only when callers need structured fields. Never silently ignore an error — assigning to _ requires a comment explaining why.

Interfaces

Accept interfaces, return concrete types. Keep interfaces small — 1–3 methods is ideal ("the bigger the interface, the weaker the abstraction"). Define interfaces where they are consumed, not where they are implemented. Reach for stdlib interfaces (io.Reader, io.Writer, fmt.Stringer) before inventing new ones. Name single-method interfaces with the -er suffix.

Goroutine patterns

Pass context.Context as the first parameter to any function that blocks or does I/O. Use errgroup.Group for fan-out/fan-in — it handles error propagation and cancellation. Every goroutine must have a clear owner responsible for its lifecycle. Always select on ctx.Done() alongside channel operations.

Package layout

Organize by domain, not by layer: user/, order/, not models/, handlers/. Package names are short, lowercase, and singular (http, user, config). Avoid catch-all util, common, and helpers packages. Keep main.go minimal — parse flags, wire dependencies, call run(ctx). Put implementation details under internal/ to block external imports.

Testing

Use table-driven tests with named subtests for multi-case coverage. testify/assert for readable checks, testify/require for fatal ones. Use httptest.NewServer for client tests, NewRecorder for handler tests. Call t.Helper() in helpers so failures point at the caller. Run go test -race ./... in CI. Use t.Parallel() for independent tests.

Code style

gofmt is non-negotiable; goimports handles import grouping (stdlib, blank line, third-party, blank line, internal). Exported names get doc comments that start with the name. Use named return values sparingly. Prefer early returns and guard clauses over deep nesting.

Gotchas

Agent-specific failure modes — provider-neutral pause-and-self-check items:

• Goroutines with no visible stop condition. Starting a goroutine without a context.Context cancellation path or a done channel means it may run forever after the caller is gone. Every goroutine must have an owner and a clear termination path.
• panic in library code for non-programmer-error conditions. Library code must return errors, not panic, for any condition a caller might encounter in normal use. Reserve panic for programmer errors: nil pointers being dereferenced, impossible state. In application code panic is still rare; prefer log.Fatal + os.Exit at the main level.
• Large interfaces defined alongside their only implementation. Interfaces should be defined where they are consumed, not where they are produced. A 10-method interface defined next to its sole implementation is not an abstraction — it is added complexity with no benefit.
• util, common, and helpers packages. These names say nothing about what the code does and attract unrelated functions. Name packages by their domain and responsibility; if something doesn't fit a named package, question whether it belongs in the codebase.
• Silently ignoring errors with _ =. Discarding an error without even a comment is a bug waiting to happen. When an error genuinely cannot matter, document why: _ = f.Close() // best-effort cleanup after write; error already reported.
• Implementing the same interface in the same file as the interface definition. Go's interface satisfaction is implicit; coupling the interface definition to the implementation defeats the decoupling purpose. Keep them in separate packages.
• context.Background() deep inside a call stack. Creating a fresh context.Background() inside a called function discards cancellation and deadline signals from the caller. Accept ctx context.Context as the first parameter and propagate it.

Full reference

Functional options

Extensible constructors that stay backward compatible:

type Server struct {
    addr    string
    timeout time.Duration
    logger  *slog.Logger
}

type Option func(*Server)

func WithTimeout(d time.Duration) Option {
    return func(s *Server) { s.timeout = d }
}

func NewServer(addr string, opts ...Option) *Server {
    s := &Server{addr: addr, timeout: 30 * time.Second, logger: slog.Default()}
    for _, opt := range opts {
        opt(s)
    }
    return s
}

Use when a constructor has 3+ optional parameters or when backward compatibility matters on a public API.

Worker pool with errgroup

func ProcessItems(ctx context.Context, items []Item, workers int) error {
    g, ctx := errgroup.WithContext(ctx)
    jobs := make(chan Item, workers)

    g.Go(func() error {
        defer close(jobs)
        for _, item := range items {
            select {
            case jobs <- item:
            case <-ctx.Done():
                return ctx.Err()
            }
        }
        return nil
    })

    for range workers {
        g.Go(func() error {
            for item := range jobs {
                if err := process(ctx, item); err != nil {
                    return fmt.Errorf("processing %s: %w", item.ID, err)
                }
            }
            return nil
        })
    }
    return g.Wait()
}

errgroup.WithContext cancels all goroutines on first error. Size the buffer to the worker count. Always select on ctx.Done() in the producer.

Graceful shutdown

func run(ctx context.Context) error {
    srv := &http.Server{Addr: ":8080", Handler: mux}
    errCh := make(chan error, 1)
    go func() { errCh <- srv.ListenAndServe() }()

    select {
    case err := <-errCh:
        return err
    case <-ctx.Done():
    }

    shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
    defer cancel()
    return srv.Shutdown(shutdownCtx)
}

func main() {
    ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
    defer stop()
    if err := run(ctx); err != nil && !errors.Is(err, http.ErrServerClosed) {
        slog.Error("server failed", "error", err)
        os.Exit(1)
    }
}

signal.NotifyContext for OS signals, srv.Shutdown to drain in-flight requests, timeout on shutdown so it never hangs forever.

Middleware chain

type Middleware func(http.Handler) http.Handler

func Chain(h http.Handler, mw ...Middleware) http.Handler {
    for i := len(mw) - 1; i >= 0; i-- {
        h = mw[i](h)
    }
    return h
}

First listed is outermost. See references/go-patterns.md for complete logging and recovery middleware examples.

Table-driven tests

func TestParseSize(t *testing.T) {
    tests := []struct {
        name    string
        input   string
        want    int64
        wantErr bool
    }{
        {name: "bytes", input: "100B", want: 100},
        {name: "kilobytes", input: "2KB", want: 2048},
        {name: "empty string", input: "", wantErr: true},
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            t.Parallel()
            got, err := ParseSize(tt.input)
            if tt.wantErr {
                require.Error(t, err)
                return
            }
            require.NoError(t, err)
            assert.Equal(t, tt.want, got)
        })
    }
}

Always use t.Run with named subtests. Put expected-error cases last for readability.

Go proverbs worth tattooing

• Don't communicate by sharing memory; share memory by communicating.
• A little copying is better than a little dependency.
• Clear is better than clever.
• Make the zero value useful.
• Errors are values — handle them, don't just check them.
• The empty interface says nothing.

Anti-patterns

• Goroutines with no visible stop condition.
• panic in library code for non-programmer-error conditions.
• Large interfaces defined alongside their sole implementation.
• util/common/helpers packages that accrete unrelated code.
• Ignoring errors without a _ = plus justification comment.
• Naked returns in long functions where named returns obscure flow.

Further reading

• references/go-patterns.md — full functional options, middleware, worker pool, and graceful shutdown examples.