Go Service

Go Service

Production-grade Go microservices using the standard library, sqlc for SQL, urfave/cli for commands, and slog for structured logging.

Core Principles

• Do one thing well: Single responsibility per component
• Simple over complex: Plain JSON, standard SQL, environment variables
• Compose: Design for piping and standard interfaces
• Explicit dependencies: No globals, no singletons, pass everything as parameters

Project Structure

.
├── cmd/
│   ├── server/          # Backend service entry point
│   └── client/          # CLI entry point
├── cli/                 # CLI implementation
├── client/              # Public client library
├── internal/            # Internal packages
│   └── db/             # Generated code (from sqlc)
├── migrations/          # SQL schema migrations
├── queries/             # SQL queries for sqlc
├── examples/            # Usage examples
├── testdata/            # Test fixtures
├── Makefile
├── .air.toml           # Air configuration
├── sqlc.yaml           # sqlc configuration
├── go.mod
├── README.md
└── CHANGELOG.md

Handler Functions Pattern

Write functions that return http.Handler (following Mat Ryer's approach):

func handleListWallets(store TransactionStore, logger *slog.Logger) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        ctx := r.Context()

        wallets, err := store.ListWallets(ctx)
        if err != nil {
            logger.ErrorContext(ctx, "failed to list wallets", "error", err)
            http.Error(w, "internal error", http.StatusInternalServerError)
            return
        }

        w.Header().Set("Content-Type", "application/json")
        json.NewEncoder(w).Encode(wallets)
    })
}

Middleware Composition

type adapter func(http.Handler) http.Handler

// adaptHandler applies adapters in reverse order so the first is outermost
func adaptHandler(h http.Handler, adapters ...adapter) http.Handler {
    for i := len(adapters) - 1; i >= 0; i-- {
        h = adapters[i](h)
    }
    return h
}

// Usage:
mux.Handle("GET /wallets", adaptHandler(
    handleListWallets(store, logger),
    withRequestID(),
    withLogging(logger),
    withMetrics(promRegistry),
    withJWTAuth(jwtSecret),
))

Dependency Injection

// Bad: hidden dependency on global
var db *sql.DB
func SaveTransaction(txn *Transaction) error {
    _, err := db.Exec("INSERT INTO transactions ...")
    return err
}

// Good: explicit dependencies
type TransactionStore interface {
    Save(ctx context.Context, txn *Transaction) error
}

type PostgresStore struct {
    db *sql.DB
}

func NewPostgresStore(db *sql.DB) *PostgresStore {
    return &PostgresStore{db: db}
}

// Dependencies are clear at construction time
store := NewPostgresStore(db)
poller := NewWalletPoller(solanaClient, store, natsConn)

Structured Logging with slog

func setupLogger(level slog.Level) *slog.Logger {
    opts := &slog.HandlerOptions{Level: level}
    return slog.New(slog.NewJSONHandler(os.Stderr, opts))
}

// Most logs at DEBUG level
logger.DebugContext(ctx, "polling wallet", "wallet", walletAddress, "last_slot", lastSlot)

// INFO for lifecycle events only
logger.InfoContext(ctx, "server started", "addr", addr, "version", version)

// ERROR for failures
logger.ErrorContext(ctx, "failed to store transaction", "error", err, "signature", sig)

Control verbosity via LOG_LEVEL env var. Default to WARN in production, DEBUG in development.

SQL with sqlc

Write SQL, get type-safe Go:

# sqlc.yaml
version: "2"
sql:
  - engine: "postgresql"
    queries: "queries/"
    schema: "migrations/"
    gen:
      go:
        package: "db"
        out: "internal/db"

Always regenerate after schema changes and commit the generated code.

Error Handling

// Always handle errors
txns, err := client.GetTransactions(ctx)
if err != nil {
    return fmt.Errorf("failed to get transactions: %w", err)
}

CLI with urfave/cli

Clean, composable command-line interfaces with automatic env var binding and built-in help.

Development Workflow

1. Plan: Design the interface first
2. Test first (TDD): Write the test, write minimal code, refactor
3. Server + Client: Every server feature gets a client method and CLI subcommand
4. Makefile: make test, make lint, make dev, make build-server
5. Hot reload: Use Air for development
6. Linting: golangci-lint with strict settings, fix all warnings

Unix Philosophy

• Be quiet by default: Only output on errors or significant events
• JSON on stdout: Machine-readable output, --format=table|json|csv for humans
• Errors to stderr: Keep stdout clean for piping
• Exit codes: 0 = success, non-zero = error