Essential Go Libraries

Why This Matters - The Go Ecosystem Advantage

When building a house, you could craft every nail, screw, and tool by hand, but wouldn't you rather use a well-made toolbox? The Go ecosystem is exactly that—a comprehensive toolbox of battle-tested libraries that save you from reinventing the wheel.

Real-world Impact: Companies like Uber, Netflix, and Cloudflare don't succeed despite using third-party libraries—they succeed because of them. The right libraries accelerate development, prevent common bugs, and let teams focus on business logic rather than infrastructure code.

💡 Key Insight: Great Go developers don't just write code—they compose solutions from proven building blocks, just like master craftsmen use quality tools to build masterpieces.

In this article, you'll learn:

• How to evaluate and select the right libraries for your projects
• Production-ready patterns for web frameworks, databases, and testing
• Integration techniques that make libraries work together seamlessly
• Common pitfalls and how to avoid them

Learning Objectives

By the end of this article, you'll be able to:

✅ Evaluate libraries using systematic criteria for production readiness
✅ Select appropriate frameworks based on your specific requirements
✅ Integrate multiple libraries into cohesive applications
✅ Implement production patterns for common Go development scenarios
✅ Avoid common mistakes when adding third-party dependencies

Core Concepts - The Go Philosophy on Libraries

Standard Library First Approach

Go's philosophy emphasizes starting with the standard library and adding third-party libraries only when they provide clear value. This approach offers several advantages:

 1// Standard library approach - always available, well-documented
 2package main
 3
 4import (
 5    "encoding/json"
 6    "net/http"
 7    "log"
 8)
 9
10func main() {
11    // Simple HTTP server using only stdlib
12    http.HandleFunc("/api/users", func(w http.ResponseWriter, r *http.Request) {
13        users := []string{"Alice", "Bob", "Charlie"}
14        w.Header().Set("Content-Type", "application/json")
15        json.NewEncoder(w).Encode(users)
16    })
17
18    log.Fatal(http.ListenAndServe(":8080", nil))
19}

Why this matters: The standard library is stable, well-maintained, and has no external dependencies. Starting here ensures your application remains maintainable long-term.

When to Add Third-Party Libraries

Add external libraries when they provide:

• Significant productivity gains
• Missing functionality
• Performance optimizations
• Developer experience improvements

Practical Examples - Web Frameworks

Understanding the Web Framework Landscape

Web frameworks are like specialized vehicle chassis—they provide the structure, suspension, and engine mounting points, letting you focus on building the actual application rather than reinventing HTTP handling from scratch.

Key Decision Factors:

• Performance requirements
• Team expertise and learning curve
• Ecosystem and middleware support
• Compatibility with existing code

Gin: High-Performance HTTP Framework

Why choose Gin? It's built for speed—perfect when every millisecond counts and you need rich middleware ecosystem.

Basic Setup with Production Best Practices:

  1// run
  2package main
  3
  4import (
  5    "net/http"
  6    "time"
  7
  8    "github.com/gin-gonic/gin"
  9    "github.com/gin-gonic/gin/binding"
 10    "github.com/go-playground/validator/v10"
 11)
 12
 13// Custom validator struct for business logic
 14type UserValidator struct {
 15    validator *validator.Validate
 16}
 17
 18func NewUserValidator() *UserValidator {
 19    v := validator.New()
 20
 21    // Register custom validation
 22    v.RegisterValidation("future_date", validateFutureDate)
 23
 24    return &UserValidator{validator: v}
 25}
 26
 27// Custom validation function
 28func validateFutureDate(fl validator.FieldLevel) bool {
 29    date, ok := fl.Field().Interface().(time.Time)
 30    if !ok {
 31        return false
 32    }
 33    return date.After(time.Now())
 34}
 35
 36type User struct {
 37    ID       string    `json:"id" binding:"required,uuid"`
 38    Name     string    `json:"name" binding:"required,min=2,max=50"`
 39    Email    string    `json:"email" binding:"required,email"`
 40    Age      int       `json:"age" binding:"gte=0,lte=150"`
 41    ShipDate time.Time `json:"ship_date" binding:"required,future_date"`
 42}
 43
 44type UserService struct {
 45    users map[string]User
 46    validator *UserValidator
 47}
 48
 49func NewUserService() *UserService {
 50    return &UserService{
 51        users: make(map[string]User),
 52        validator: NewUserValidator(),
 53    }
 54}
 55
 56// Create user with comprehensive validation
 57func CreateUser(user *User) error {
 58    // Custom validation logic
 59    if err := s.validator.validator.Struct(user); err != nil {
 60        return err
 61    }
 62
 63    // Additional business rules
 64    if user.Age < 18 && !user.Email.Contains("@parent.") {
 65        return fmt.Errorf("users under 18 require parent email")
 66    }
 67
 68    user.ID = generateUUID()
 69    s.users[user.ID] = user
 70    return nil
 71}
 72
 73func main() {
 74    // Production configuration
 75    gin.SetMode(gin.ReleaseMode)
 76
 77    router := gin.New()
 78
 79    // Essential middleware stack
 80    router.Use(gin.Logger())
 81    router.Use(gin.Recovery())
 82    router.Use(corsMiddleware())
 83    router.Use(requestIDMiddleware())
 84
 85    userService := NewUserService()
 86
 87    // API routes with proper error handling
 88    api := router.Group("/api/v1")
 89    {
 90        api.POST("/users", userService.CreateUser)
 91        api.GET("/users/:id", userService.GetUser)
 92        api.PUT("/users/:id", userService.UpdateUser)
 93        api.DELETE("/users/:id", userService.DeleteUser)
 94    }
 95
 96    // Health check endpoint
 97    router.GET("/health", func(c *gin.Context) {
 98        c.JSON(http.StatusOK, gin.H{
 99            "status": "healthy",
100            "timestamp": time.Now(),
101            "version": "1.0.0",
102        })
103    })
104
105    server := &http.Server{
106        Addr:         ":8080",
107        Handler:      router,
108        ReadTimeout:  10 * time.Second,
109        WriteTimeout: 10 * time.Second,
110        IdleTimeout:  60 * time.Second,
111    }
112
113    log.Fatal(server.ListenAndServe())
114}
115
116// CORS middleware for API access
117func corsMiddleware() gin.HandlerFunc {
118    return func(c *gin.Context) {
119        c.Header("Access-Control-Allow-Origin", "*")
120        c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
121        c.Header("Access-Control-Allow-Headers", "Content-Type, Authorization")
122
123        if c.Request.Method == "OPTIONS" {
124            c.AbortWithStatus(204)
125            return
126        }
127
128        c.Next()
129    }
130}
131
132// Request ID middleware for tracing
133func requestIDMiddleware() gin.HandlerFunc {
134    return func(c *gin.Context) {
135        requestID := c.GetHeader("X-Request-ID")
136        if requestID == "" {
137            requestID = generateUUID()
138        }
139
140        c.Set("request_id", requestID)
141        c.Writer.Header().Set("X-Request-ID", requestID)
142        c.Next()
143    }
144}
145
146func generateUUID() string {
147    return fmt.Sprintf("%x", rand.New(rand.NewSource(time.Now().Unix())).Int63())
148}

Key Patterns Used:

• Structured error handling with proper HTTP status codes
• Middleware composition for cross-cutting concerns
• Custom validation for business logic
• Production configuration with timeouts and proper server setup

Chi: Idiomatic Go Router

Why choose Chi? When you want stdlib compatibility with enhanced routing capabilities.

  1// run
  2package main
  3
  4import (
  5    "context"
  6    "net/http"
  7    "time"
  8
  9    "github.com/go-chi/chi/v5"
 10    "github.com/go-chi/chi/v5/middleware"
 11)
 12
 13type ArticleService struct {
 14    articles map[string]Article
 15}
 16
 17type Article struct {
 18    ID       string    `json:"id"`
 19    Title    string    `json:"title"`
 20    Content  string    `json:"content"`
 21    Author   string    `json:"author"`
 22    CreatedAt time.Time `json:"created_at"`
 23}
 24
 25func NewArticleService() *ArticleService {
 26    articles := make(map[string]Article)
 27
 28    // Seed with sample data
 29    articles["1"] = Article{
 30        ID:        "1",
 31        Title:      "Getting Started with Go",
 32        Content:    "Go is a powerful language...",
 33        Author:     "John Doe",
 34        CreatedAt:  time.Now(),
 35    }
 36
 37    return &ArticleService{articles: articles}
 38}
 39
 40// Context-based middleware for authentication
 41func articleCtx(next http.Handler) http.Handler {
 42    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 43        articleID := chi.URLParam(r, "id")
 44        article, err := getArticle(articleID)
 45        if err != nil {
 46            http.Error(w, http.StatusText(404), 404)
 47            return
 48        }
 49
 50        // Add article to context
 51        ctx := context.WithValue(r.Context(), "article", article)
 52        next.ServeHTTP(w, r.WithContext(ctx))
 53    })
 54}
 55
 56func main() {
 57    r := chi.NewRouter()
 58
 59    // Standard middleware stack
 60    r.Use(middleware.RequestID)
 61    r.Use(middleware.RealIP)
 62    r.Use(middleware.Logger)
 63    r.Use(middleware.Recoverer)
 64    r.Use(middleware.Timeout(60 * time.Second))
 65    r.Use(middleware.AllowContentType("application/json"))
 66
 67    articleService := NewArticleService()
 68
 69    // API routes with nested routing
 70    r.Route("/api/v1", func(r chi.Router) {
 71        r.Route("/articles", func(r chi.Router) {
 72            // Public routes
 73            r.Get("/", articleService.ListArticles)
 74            r.With(articleCtx).Get("/{id}", articleService.GetArticle)
 75
 76            // Protected routes
 77            r.Group(func(r chi.Router) {
 78                r.Use(adminOnlyMiddleware)
 79                r.Post("/", articleService.CreateArticle)
 80                r.With(articleCtx).Put("/{id}", articleService.UpdateArticle)
 81                r.With(articleCtx).Delete("/{id}", articleService.DeleteArticle)
 82            })
 83        })
 84    })
 85
 86    // Health and metrics
 87    r.Get("/health", healthHandler)
 88    r.Get("/metrics", metricsHandler)
 89
 90    http.ListenAndServe(":8080", r)
 91}
 92
 93// Service methods with proper error handling
 94func ListArticles(w http.ResponseWriter, r *http.Request) {
 95    articles := make([]Article, 0, len(s.articles))
 96    for _, article := range s.articles {
 97        articles = append(articles, article)
 98    }
 99
100    respondWithJSON(w, http.StatusOK, map[string]interface{}{
101        "articles": articles,
102        "count": len(articles),
103    })
104}
105
106func GetArticle(w http.ResponseWriter, r *http.Request) {
107    article := r.Context().Value("article").(Article)
108    respondWithJSON(w, http.StatusOK, article)
109}
110
111func respondWithJSON(w http.ResponseWriter, code int, payload interface{}) {
112    w.Header().Set("Content-Type", "application/json")
113    w.WriteHeader(code)
114    json.NewEncoder(w).Encode(payload)
115}

Chi Advantages Demonstrated:

• Context-based request handling for clean data flow
• Composable middleware that integrates with stdlib patterns
• Nested routing for logical API organization
• Stdlib compatibility for maximum flexibility

Integration Patterns - Combining Libraries

Database + Web Framework Integration

Real-world Pattern: Building a REST API that demonstrates proper separation of concerns between web framework and database layers.

  1// run
  2package main
  3
  4import (
  5    "database/sql"
  6
  7    "github.com/gin-gonic/gin"
  8    "gorm.io/driver/postgres"
  9    "gorm.io/gorm"
 10)
 11
 12// Repository pattern for database abstraction
 13type UserRepository interface {
 14    Create(user *User) error
 15    FindByID(id uint)
 16    FindByEmail(email string)
 17    Update(user *User) error
 18    Delete(id uint) error
 19    List(limit, offset int)
 20}
 21
 22type User struct {
 23    ID        uint           `gorm:"primaryKey" json:"id"`
 24    Name      string         `gorm:"size:100;not null" json:"name" binding:"required,min=2,max=100"`
 25    Email     string         `gorm:"uniqueIndex;not null" json:"email" binding:"required,email"`
 26    CreatedAt time.Time      `json:"created_at"`
 27    UpdatedAt time.Time      `json:"updated_at"`
 28    DeletedAt gorm.DeletedAt `gorm:"index" json:"-"`
 29}
 30
 31type GormUserRepository struct {
 32    db *gorm.DB
 33}
 34
 35func NewGormUserRepository(db *gorm.DB) UserRepository {
 36    return &GormUserRepository{db: db}
 37}
 38
 39// Implementation with error handling and logging
 40func Create(user *User) error {
 41    if err := r.db.Create(user).Error; err != nil {
 42        // Log the error
 43        log.Printf("Failed to create user: %v", err)
 44
 45        // Return wrapped error with context
 46        if errors.Is(err, gorm.ErrDuplicatedKey) {
 47            return errors.New("user with this email already exists")
 48        }
 49        return errors.New("failed to create user")
 50    }
 51
 52    log.Printf("Created user: %d", user.ID)
 53    return nil
 54}
 55
 56// Service layer that combines repository with business logic
 57type UserService struct {
 58    repo UserRepository
 59}
 60
 61func NewUserService(repo UserRepository) *UserService {
 62    return &UserService{repo: repo}
 63}
 64
 65func CreateUser(req *CreateUserRequest) {
 66    // Validate business rules
 67    if err := s.validateCreateRequest(req); err != nil {
 68        return nil, err
 69    }
 70
 71    user := &User{
 72        Name:  req.Name,
 73        Email: req.Email,
 74    }
 75
 76    if err := s.repo.Create(user); err != nil {
 77        return nil, err
 78    }
 79
 80    return user, nil
 81}
 82
 83// Controller that handles HTTP concerns only
 84type UserController struct {
 85    service *UserService
 86}
 87
 88func NewUserController(service *UserService) *UserController {
 89    return &UserController{service: service}
 90}
 91
 92func CreateUser(ctx *gin.Context) {
 93    var req CreateUserRequest
 94    if err := ctx.ShouldBindJSON(&req); err != nil {
 95        ctx.JSON(http.StatusBadRequest, gin.H{
 96            "error": "invalid_request",
 97            "message": err.Error(),
 98        })
 99        return
100    }
101
102    user, err := c.service.CreateUser(&req)
103    if err != nil {
104        ctx.JSON(http.StatusInternalServerError, gin.H{
105            "error": "creation_failed",
106            "message": err.Error(),
107        })
108        return
109    }
110
111    ctx.JSON(http.StatusCreated, gin.H{
112        "user": user,
113        "message": "User created successfully",
114    })
115}

Integration Benefits:

• Separation of concerns: Each layer has a single responsibility
• Testability: Can mock each layer independently
• Flexibility: Can swap implementations
• Error handling: Proper error propagation and user feedback

Common Patterns and Pitfalls

Pattern: Dependency Injection

Instead of importing libraries directly throughout your code, use dependency injection:

 1// ❌ Anti-pattern: Direct coupling
 2type BadHandler struct {
 3    // Direct dependencies make testing difficult
 4}
 5
 6func HandleRequest(c *gin.Context) {
 7    db, _ := gorm.Open("postgres", dsn)
 8    // Use db directly...
 9}
10
11// ✅ Good pattern: Dependency injection
12type GoodHandler struct {
13    userService *UserService
14    logger      *Logger
15}
16
17func NewGoodHandler(userService *UserService, logger *Logger) *GoodHandler {
18    return &GoodHandler{
19        userService: userService,
20        logger:      logger,
21    }
22}
23
24func HandleRequest(c *gin.Context) {
25    user, err := h.userService.GetUser(1)
26    if err != nil {
27        h.logger.Error("Failed to get user", "error", err)
28        // Handle error...
29    }
30    // Use user...
31}

Pitfall: Over-engineering with Too Many Libraries

Common mistake: Adding libraries for every small task, creating complex dependency chains.

 1// ❌ Over-engineered approach
 2import (
 3    "github.com/some/validation-lib"
 4    "github.com/another/string-util-lib"
 5    "github.com/yet-another/time-lib"
 6)
 7
 8func processUser(user User) error {
 9    // Using 3 different libraries for simple validation
10    if validationLib.IsNotEmpty(user.Name) &&
11       stringUtilLib.IsValidEmail(user.Email) &&
12       timeLib.IsFuture(user.Birthday) {
13        // Process user...
14    }
15}
16
17// ✅ Simplified approach using stdlib and focused libraries
18import (
19    "regexp"
20    "strings"
21    "time"
22)
23
24func processUser(user User) error {
25    if len(user.Name) == 0 {
26        return errors.New("name cannot be empty")
27    }
28
29    emailRegex := regexp.MustCompile(`^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`)
30    if !emailRegex.MatchString(user.Email) {
31        return errors.New("invalid email format")
32    }
33
34    if user.Birthday.After(time.Now()) {
35        return errors.New("birthday cannot be in the future")
36    }
37
38    // Process user...
39}

Integration and Mastery

Building a Production-Ready Service

Let's combine multiple libraries into a cohesive, production-ready service:

  1// run
  2package main
  3
  4import (
  5    "context"
  6    "fmt"
  7    "log"
  8    "os"
  9    "os/signal"
 10    "syscall"
 11    "time"
 12
 13    "github.com/gin-gonic/gin"
 14    "github.com/rs/zerolog"
 15    "github.com/spf13/viper"
 16    "gorm.io/driver/postgres"
 17    "gorm.io/gorm"
 18)
 19
 20type AppConfig struct {
 21    Server struct {
 22        Port         int           `mapstructure:"port"`
 23        ReadTimeout  time.Duration `mapstructure:"read_timeout"`
 24        WriteTimeout time.Duration `mapstructure:"write_timeout"`
 25    } `mapstructure:"server"`
 26
 27    Database struct {
 28        Host     string `mapstructure:"host"`
 29        Port     int    `mapstructure:"port"`
 30        User     string `mapstructure:"user"`
 31        Password string `mapstructure:"password"`
 32        DBName   string `mapstructure:"dbname"`
 33        SSLMode  string `mapstructure:"sslmode"`
 34    } `mapstructure:"database"`
 35
 36    Logging struct {
 37        Level  string `mapstructure:"level"`
 38        Format string `mapstructure:"format"`
 39    } `mapstructure:"logging"`
 40}
 41
 42type Application struct {
 43    config   *AppConfig
 44    logger   *zerolog.Logger
 45    server   *http.Server
 46    db       *gorm.DB
 47    router   *gin.Engine
 48}
 49
 50func NewApplication() {
 51    // Load configuration
 52    config, err := loadConfig()
 53    if err != nil {
 54        return nil, fmt.Errorf("failed to load config: %w", err)
 55    }
 56
 57    // Setup logger
 58    logger, err := setupLogger(config.Logging)
 59    if err != nil {
 60        return nil, fmt.Errorf("failed to setup logger: %w", err)
 61    }
 62
 63    // Connect to database
 64    db, err := setupDatabase(config.Database, logger)
 65    if err != nil {
 66        return nil, fmt.Errorf("failed to setup database: %w", err)
 67    }
 68
 69    // Setup router with middleware
 70    router := setupRouter(logger)
 71
 72    // Create HTTP server
 73    server := &http.Server{
 74        Addr:         fmt.Sprintf(":%d", config.Server.Port),
 75        Handler:      router,
 76        ReadTimeout:  config.Server.ReadTimeout,
 77        WriteTimeout: config.Server.WriteTimeout,
 78        IdleTimeout:  60 * time.Second,
 79    }
 80
 81    return &Application{
 82        config: config,
 83        logger: logger,
 84        server: server,
 85        db:     db,
 86        router: router,
 87    }, nil
 88}
 89
 90func Run() error {
 91    // Start server in goroutine
 92    go func() {
 93        app.logger.Info().
 94            Int("port", app.config.Server.Port).
 95            Msg("Starting HTTP server")
 96
 97        if err := app.server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
 98            app.logger.Error().Err(err).Msg("Server failed to start")
 99        }
100    }()
101
102    // Wait for interrupt signal
103    quit := make(chan os.Signal, 1)
104    signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
105    <-quit
106
107    app.logger.Info().Msg("Shutting down server...")
108
109    // Graceful shutdown
110    ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
111    defer cancel()
112
113    if err := app.server.Shutdown(ctx); err != nil {
114        app.logger.Error().Err(err).Msg("Server forced to shutdown")
115        return err
116    }
117
118    app.logger.Info().Msg("Server exited")
119    return nil
120}
121
122func loadConfig() {
123    viper.SetConfigName("config")
124    viper.SetConfigType("yaml")
125    viper.AddConfigPath(".")
126    viper.AddConfigPath("./config")
127
128    // Set environment variable support
129    viper.AutomaticEnv()
130    viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
131
132    // Set defaults
133    viper.SetDefault("server.port", 8080)
134    viper.SetDefault("server.read_timeout", "10s")
135    viper.SetDefault("server.write_timeout", "10s")
136    viper.SetDefault("logging.level", "info")
137    viper.SetDefault("logging.format", "json")
138
139    var config AppConfig
140    if err := viper.Unmarshal(&config); err != nil {
141        return nil, err
142    }
143
144    return &config, nil
145}
146
147func setupRouter(logger *zerolog.Logger) *gin.Engine {
148    gin.SetMode(gin.ReleaseMode)
149
150    r := gin.New()
151
152    // Add logging middleware
153    r.Use(gin.LoggerWithConfig(gin.LoggerConfig{
154        Formatter: func(param gin.LogFormatterParams) string {
155            logger.Info().
156                Str("client_ip", param.ClientIP).
157                Str("method", param.Method).
158                Str("path", param.Path).
159                Int("status", param.StatusCode).
160                Dur("latency", param.Latency).
161                Msg("HTTP Request")
162            return ""
163        },
164    }))
165
166    // Add recovery middleware
167    r.Use(gin.CustomRecovery(func(c *gin.Context, recovered interface{}) {
168        logger.Error().
169            Interface("panic", recovered).
170            Str("path", c.Request.URL.Path).
171            Msg("Recovered from panic")
172        c.JSON(500, gin.H{"error": "internal server error"})
173    }))
174
175    return r
176}
177
178func main() {
179    app, err := NewApplication()
180    if err != nil {
181        log.Fatalf("Failed to create application: %v", err)
182    }
183
184    if err := app.Run(); err != nil {
185        log.Fatalf("Application failed: %v", err)
186    }
187}

Mastery Pattern: This example shows how to:

• Integrate multiple libraries
• Handle configuration from files and environment
• Implement graceful shutdown for production
• Add proper logging and error handling
• Use dependency injection for testability

Database Libraries - Beyond GORM

SQL Drivers and Low-Level Access

When to use raw SQL: Complex queries, performance-critical operations, or fine-grained control.

  1// run
  2package main
  3
  4import (
  5    "database/sql"
  6    "fmt"
  7    "log"
  8    "time"
  9
 10    _ "github.com/lib/pq"
 11)
 12
 13// Connection pool configuration
 14type DatabaseConfig struct {
 15    Host            string
 16    Port            int
 17    User            string
 18    Password        string
 19    DBName          string
 20    MaxOpenConns    int
 21    MaxIdleConns    int
 22    ConnMaxLifetime time.Duration
 23}
 24
 25func NewDatabase(config DatabaseConfig) (*sql.DB, error) {
 26    dsn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
 27        config.Host, config.Port, config.User, config.Password, config.DBName)
 28
 29    db, err := sql.Open("postgres", dsn)
 30    if err != nil {
 31        return nil, fmt.Errorf("failed to open database: %w", err)
 32    }
 33
 34    // Configure connection pool for production
 35    db.SetMaxOpenConns(config.MaxOpenConns)
 36    db.SetMaxIdleConns(config.MaxIdleConns)
 37    db.SetConnMaxLifetime(config.ConnMaxLifetime)
 38
 39    // Verify connection
 40    if err := db.Ping(); err != nil {
 41        return nil, fmt.Errorf("failed to ping database: %w", err)
 42    }
 43
 44    return db, nil
 45}
 46
 47type Product struct {
 48    ID          int64
 49    Name        string
 50    Description string
 51    Price       float64
 52    Stock       int
 53    CreatedAt   time.Time
 54    UpdatedAt   time.Time
 55}
 56
 57type ProductRepository struct {
 58    db *sql.DB
 59}
 60
 61func NewProductRepository(db *sql.DB) *ProductRepository {
 62    return &ProductRepository{db: db}
 63}
 64
 65// Create with transaction and error handling
 66func (r *ProductRepository) Create(product *Product) error {
 67    tx, err := r.db.Begin()
 68    if err != nil {
 69        return fmt.Errorf("failed to begin transaction: %w", err)
 70    }
 71    defer tx.Rollback()
 72
 73    query := `
 74        INSERT INTO products (name, description, price, stock, created_at, updated_at)
 75        VALUES ($1, $2, $3, $4, $5, $6)
 76        RETURNING id
 77    `
 78
 79    now := time.Now()
 80    err = tx.QueryRow(
 81        query,
 82        product.Name,
 83        product.Description,
 84        product.Price,
 85        product.Stock,
 86        now,
 87        now,
 88    ).Scan(&product.ID)
 89
 90    if err != nil {
 91        return fmt.Errorf("failed to insert product: %w", err)
 92    }
 93
 94    // Update inventory table in same transaction
 95    _, err = tx.Exec(`
 96        INSERT INTO inventory_log (product_id, quantity, operation, timestamp)
 97        VALUES ($1, $2, 'create', $3)
 98    `, product.ID, product.Stock, now)
 99
100    if err != nil {
101        return fmt.Errorf("failed to log inventory: %w", err)
102    }
103
104    if err := tx.Commit(); err != nil {
105        return fmt.Errorf("failed to commit transaction: %w", err)
106    }
107
108    return nil
109}
110
111// Batch operations with prepared statements
112func (r *ProductRepository) BatchCreate(products []Product) error {
113    tx, err := r.db.Begin()
114    if err != nil {
115        return fmt.Errorf("failed to begin transaction: %w", err)
116    }
117    defer tx.Rollback()
118
119    stmt, err := tx.Prepare(`
120        INSERT INTO products (name, description, price, stock, created_at, updated_at)
121        VALUES ($1, $2, $3, $4, $5, $6)
122        RETURNING id
123    `)
124    if err != nil {
125        return fmt.Errorf("failed to prepare statement: %w", err)
126    }
127    defer stmt.Close()
128
129    now := time.Now()
130    for i := range products {
131        err := stmt.QueryRow(
132            products[i].Name,
133            products[i].Description,
134            products[i].Price,
135            products[i].Stock,
136            now,
137            now,
138        ).Scan(&products[i].ID)
139
140        if err != nil {
141            return fmt.Errorf("failed to insert product %s: %w", products[i].Name, err)
142        }
143    }
144
145    if err := tx.Commit(); err != nil {
146        return fmt.Errorf("failed to commit transaction: %w", err)
147    }
148
149    log.Printf("Successfully inserted %d products", len(products))
150    return nil
151}
152
153// Complex query with joins
154func (r *ProductRepository) FindWithCategory(categoryID int64) ([]Product, error) {
155    query := `
156        SELECT p.id, p.name, p.description, p.price, p.stock, p.created_at, p.updated_at
157        FROM products p
158        INNER JOIN product_categories pc ON p.id = pc.product_id
159        WHERE pc.category_id = $1
160        AND p.stock > 0
161        ORDER BY p.created_at DESC
162    `
163
164    rows, err := r.db.Query(query, categoryID)
165    if err != nil {
166        return nil, fmt.Errorf("failed to query products: %w", err)
167    }
168    defer rows.Close()
169
170    var products []Product
171    for rows.Next() {
172        var p Product
173        err := rows.Scan(
174            &p.ID,
175            &p.Name,
176            &p.Description,
177            &p.Price,
178            &p.Stock,
179            &p.CreatedAt,
180            &p.UpdatedAt,
181        )
182        if err != nil {
183            return nil, fmt.Errorf("failed to scan product: %w", err)
184        }
185        products = append(products, p)
186    }
187
188    if err := rows.Err(); err != nil {
189        return nil, fmt.Errorf("error iterating rows: %w", err)
190    }
191
192    return products, nil
193}
194
195func main() {
196    config := DatabaseConfig{
197        Host:            "localhost",
198        Port:            5432,
199        User:            "postgres",
200        Password:        "password",
201        DBName:          "store",
202        MaxOpenConns:    25,
203        MaxIdleConns:    5,
204        ConnMaxLifetime: 5 * time.Minute,
205    }
206
207    db, err := NewDatabase(config)
208    if err != nil {
209        log.Fatalf("Failed to connect to database: %v", err)
210    }
211    defer db.Close()
212
213    repo := NewProductRepository(db)
214
215    product := &Product{
216        Name:        "Laptop",
217        Description: "High-performance laptop",
218        Price:       1299.99,
219        Stock:       50,
220    }
221
222    if err := repo.Create(product); err != nil {
223        log.Fatalf("Failed to create product: %v", err)
224    }
225
226    log.Printf("Created product with ID: %d", product.ID)
227}

Key Patterns Demonstrated:

• Connection pooling for optimal performance
• Prepared statements for security and efficiency
• Transaction management for data consistency
• Error wrapping for better debugging

SQLx: Enhanced SQL Toolkit

Why choose SQLx? When you want the power of raw SQL with Go struct convenience.

  1// run
  2package main
  3
  4import (
  5    "fmt"
  6    "log"
  7    "time"
  8
  9    "github.com/jmoiron/sqlx"
 10    _ "github.com/lib/pq"
 11)
 12
 13type Order struct {
 14    ID          int64     `db:"id"`
 15    UserID      int64     `db:"user_id"`
 16    TotalAmount float64   `db:"total_amount"`
 17    Status      string    `db:"status"`
 18    CreatedAt   time.Time `db:"created_at"`
 19    UpdatedAt   time.Time `db:"updated_at"`
 20}
 21
 22type OrderItem struct {
 23    ID        int64   `db:"id"`
 24    OrderID   int64   `db:"order_id"`
 25    ProductID int64   `db:"product_id"`
 26    Quantity  int     `db:"quantity"`
 27    Price     float64 `db:"price"`
 28}
 29
 30type OrderRepository struct {
 31    db *sqlx.DB
 32}
 33
 34func NewOrderRepository(db *sqlx.DB) *OrderRepository {
 35    return &OrderRepository{db: db}
 36}
 37
 38// Named query with struct
 39func (r *OrderRepository) CreateOrder(order *Order, items []OrderItem) error {
 40    tx, err := r.db.Beginx()
 41    if err != nil {
 42        return fmt.Errorf("failed to begin transaction: %w", err)
 43    }
 44    defer tx.Rollback()
 45
 46    // Insert order using NamedExec
 47    query := `
 48        INSERT INTO orders (user_id, total_amount, status, created_at, updated_at)
 49        VALUES (:user_id, :total_amount, :status, :created_at, :updated_at)
 50        RETURNING id
 51    `
 52
 53    rows, err := tx.NamedQuery(query, order)
 54    if err != nil {
 55        return fmt.Errorf("failed to create order: %w", err)
 56    }
 57    defer rows.Close()
 58
 59    if rows.Next() {
 60        if err := rows.Scan(&order.ID); err != nil {
 61            return fmt.Errorf("failed to get order ID: %w", err)
 62        }
 63    }
 64
 65    // Batch insert order items
 66    for i := range items {
 67        items[i].OrderID = order.ID
 68    }
 69
 70    itemQuery := `
 71        INSERT INTO order_items (order_id, product_id, quantity, price)
 72        VALUES (:order_id, :product_id, :quantity, :price)
 73    `
 74
 75    if _, err := tx.NamedExec(itemQuery, items); err != nil {
 76        return fmt.Errorf("failed to create order items: %w", err)
 77    }
 78
 79    if err := tx.Commit(); err != nil {
 80        return fmt.Errorf("failed to commit transaction: %w", err)
 81    }
 82
 83    return nil
 84}
 85
 86// Complex query with joins using struct scanning
 87func (r *OrderRepository) GetOrderWithItems(orderID int64) (*Order, []OrderItem, error) {
 88    var order Order
 89    err := r.db.Get(&order, "SELECT * FROM orders WHERE id = $1", orderID)
 90    if err != nil {
 91        return nil, nil, fmt.Errorf("failed to get order: %w", err)
 92    }
 93
 94    var items []OrderItem
 95    err = r.db.Select(&items, "SELECT * FROM order_items WHERE order_id = $1", orderID)
 96    if err != nil {
 97        return nil, nil, fmt.Errorf("failed to get order items: %w", err)
 98    }
 99
100    return &order, items, nil
101}
102
103// IN clause query with slice parameter
104func (r *OrderRepository) GetOrdersByStatus(statuses []string) ([]Order, error) {
105    query, args, err := sqlx.In("SELECT * FROM orders WHERE status IN (?)", statuses)
106    if err != nil {
107        return nil, fmt.Errorf("failed to build query: %w", err)
108    }
109
110    query = r.db.Rebind(query)
111
112    var orders []Order
113    if err := r.db.Select(&orders, query, args...); err != nil {
114        return nil, fmt.Errorf("failed to query orders: %w", err)
115    }
116
117    return orders, nil
118}
119
120func main() {
121    db, err := sqlx.Connect("postgres", "host=localhost user=postgres password=password dbname=store sslmode=disable")
122    if err != nil {
123        log.Fatalf("Failed to connect: %v", err)
124    }
125    defer db.Close()
126
127    repo := NewOrderRepository(db)
128
129    order := &Order{
130        UserID:      1,
131        TotalAmount: 299.98,
132        Status:      "pending",
133        CreatedAt:   time.Now(),
134        UpdatedAt:   time.Now(),
135    }
136
137    items := []OrderItem{
138        {ProductID: 1, Quantity: 2, Price: 99.99},
139        {ProductID: 2, Quantity: 1, Price: 99.99},
140    }
141
142    if err := repo.CreateOrder(order, items); err != nil {
143        log.Fatalf("Failed to create order: %v", err)
144    }
145
146    log.Printf("Created order with ID: %d", order.ID)
147}

SQLx Benefits:

• Struct scanning reduces boilerplate
• Named queries improve readability
• IN clause handling simplifies array queries
• Maintains SQL control while adding convenience

NoSQL: Redis and MongoDB Clients

Redis for Caching and Sessions:

  1// run
  2package main
  3
  4import (
  5    "context"
  6    "encoding/json"
  7    "fmt"
  8    "time"
  9
 10    "github.com/redis/go-redis/v9"
 11)
 12
 13type CacheService struct {
 14    client *redis.Client
 15}
 16
 17func NewCacheService(addr, password string, db int) *CacheService {
 18    client := redis.NewClient(&redis.Options{
 19        Addr:         addr,
 20        Password:     password,
 21        DB:           db,
 22        PoolSize:     10,
 23        MinIdleConns: 5,
 24        DialTimeout:  5 * time.Second,
 25        ReadTimeout:  3 * time.Second,
 26        WriteTimeout: 3 * time.Second,
 27    })
 28
 29    return &CacheService{client: client}
 30}
 31
 32// Generic cache operations with JSON serialization
 33func (s *CacheService) Set(ctx context.Context, key string, value interface{}, expiration time.Duration) error {
 34    data, err := json.Marshal(value)
 35    if err != nil {
 36        return fmt.Errorf("failed to marshal value: %w", err)
 37    }
 38
 39    return s.client.Set(ctx, key, data, expiration).Err()
 40}
 41
 42func (s *CacheService) Get(ctx context.Context, key string, dest interface{}) error {
 43    data, err := s.client.Get(ctx, key).Bytes()
 44    if err != nil {
 45        return fmt.Errorf("failed to get value: %w", err)
 46    }
 47
 48    if err := json.Unmarshal(data, dest); err != nil {
 49        return fmt.Errorf("failed to unmarshal value: %w", err)
 50    }
 51
 52    return nil
 53}
 54
 55// Cache-aside pattern
 56func (s *CacheService) GetOrCompute(
 57    ctx context.Context,
 58    key string,
 59    dest interface{},
 60    compute func() (interface{}, error),
 61    expiration time.Duration,
 62) error {
 63    // Try to get from cache
 64    err := s.Get(ctx, key, dest)
 65    if err == nil {
 66        return nil // Cache hit
 67    }
 68
 69    // Cache miss - compute value
 70    value, err := compute()
 71    if err != nil {
 72        return fmt.Errorf("failed to compute value: %w", err)
 73    }
 74
 75    // Store in cache
 76    if err := s.Set(ctx, key, value, expiration); err != nil {
 77        // Log error but don't fail the request
 78        fmt.Printf("Failed to cache value: %v\n", err)
 79    }
 80
 81    // Return computed value
 82    data, _ := json.Marshal(value)
 83    return json.Unmarshal(data, dest)
 84}
 85
 86// Distributed lock pattern
 87func (s *CacheService) AcquireLock(ctx context.Context, key string, ttl time.Duration) (bool, error) {
 88    return s.client.SetNX(ctx, fmt.Sprintf("lock:%s", key), "1", ttl).Result()
 89}
 90
 91func (s *CacheService) ReleaseLock(ctx context.Context, key string) error {
 92    return s.client.Del(ctx, fmt.Sprintf("lock:%s", key)).Err()
 93}
 94
 95// Rate limiting using Redis
 96func (s *CacheService) RateLimit(ctx context.Context, key string, limit int, window time.Duration) (bool, error) {
 97    pipe := s.client.Pipeline()
 98
 99    incr := pipe.Incr(ctx, key)
100    pipe.Expire(ctx, key, window)
101
102    _, err := pipe.Exec(ctx)
103    if err != nil {
104        return false, err
105    }
106
107    count, err := incr.Result()
108    if err != nil {
109        return false, err
110    }
111
112    return count <= int64(limit), nil
113}
114
115func main() {
116    cache := NewCacheService("localhost:6379", "", 0)
117    ctx := context.Background()
118
119    // Example: Cache user data
120    type User struct {
121        ID    int    `json:"id"`
122        Name  string `json:"name"`
123        Email string `json:"email"`
124    }
125
126    user := User{ID: 1, Name: "Alice", Email: "alice@example.com"}
127
128    // Set with expiration
129    if err := cache.Set(ctx, "user:1", user, 10*time.Minute); err != nil {
130        fmt.Printf("Failed to cache user: %v\n", err)
131    }
132
133    // Get from cache
134    var cachedUser User
135    if err := cache.Get(ctx, "user:1", &cachedUser); err != nil {
136        fmt.Printf("Failed to get cached user: %v\n", err)
137    } else {
138        fmt.Printf("Cached user: %+v\n", cachedUser)
139    }
140
141    // Rate limiting example
142    allowed, err := cache.RateLimit(ctx, "api:user:1", 10, time.Minute)
143    if err != nil {
144        fmt.Printf("Rate limit check failed: %v\n", err)
145    }
146    fmt.Printf("Request allowed: %v\n", allowed)
147}

MongoDB for Document Storage:

  1// run
  2package main
  3
  4import (
  5    "context"
  6    "fmt"
  7    "log"
  8    "time"
  9
 10    "go.mongodb.org/mongo-driver/bson"
 11    "go.mongodb.org/mongo-driver/bson/primitive"
 12    "go.mongodb.org/mongo-driver/mongo"
 13    "go.mongodb.org/mongo-driver/mongo/options"
 14)
 15
 16type Document struct {
 17    ID        primitive.ObjectID `bson:"_id,omitempty"`
 18    Title     string             `bson:"title"`
 19    Content   string             `bson:"content"`
 20    Tags      []string           `bson:"tags"`
 21    Author    string             `bson:"author"`
 22    Version   int                `bson:"version"`
 23    CreatedAt time.Time          `bson:"created_at"`
 24    UpdatedAt time.Time          `bson:"updated_at"`
 25}
 26
 27type DocumentRepository struct {
 28    collection *mongo.Collection
 29}
 30
 31func NewDocumentRepository(db *mongo.Database) *DocumentRepository {
 32    return &DocumentRepository{
 33        collection: db.Collection("documents"),
 34    }
 35}
 36
 37// Create with MongoDB-specific features
 38func (r *DocumentRepository) Create(ctx context.Context, doc *Document) error {
 39    doc.ID = primitive.NewObjectID()
 40    doc.CreatedAt = time.Now()
 41    doc.UpdatedAt = time.Now()
 42    doc.Version = 1
 43
 44    _, err := r.collection.InsertOne(ctx, doc)
 45    if err != nil {
 46        return fmt.Errorf("failed to insert document: %w", err)
 47    }
 48
 49    return nil
 50}
 51
 52// Complex query with aggregation pipeline
 53func (r *DocumentRepository) GetPopularDocuments(ctx context.Context, limit int) ([]Document, error) {
 54    pipeline := mongo.Pipeline{
 55        {{"$match", bson.D{{"tags", bson.D{{"$exists", true}}}}}},
 56        {{"$addFields", bson.D{{"tag_count", bson.D{{"$size", "$tags"}}}}}},
 57        {{"$sort", bson.D{{"tag_count", -1}}}},
 58        {{"$limit", limit}},
 59    }
 60
 61    cursor, err := r.collection.Aggregate(ctx, pipeline)
 62    if err != nil {
 63        return nil, fmt.Errorf("failed to aggregate: %w", err)
 64    }
 65    defer cursor.Close(ctx)
 66
 67    var documents []Document
 68    if err := cursor.All(ctx, &documents); err != nil {
 69        return nil, fmt.Errorf("failed to decode documents: %w", err)
 70    }
 71
 72    return documents, nil
 73}
 74
 75// Update with optimistic locking
 76func (r *DocumentRepository) Update(ctx context.Context, doc *Document) error {
 77    filter := bson.M{
 78        "_id":     doc.ID,
 79        "version": doc.Version,
 80    }
 81
 82    update := bson.M{
 83        "$set": bson.M{
 84            "title":      doc.Title,
 85            "content":    doc.Content,
 86            "tags":       doc.Tags,
 87            "updated_at": time.Now(),
 88        },
 89        "$inc": bson.M{"version": 1},
 90    }
 91
 92    result, err := r.collection.UpdateOne(ctx, filter, update)
 93    if err != nil {
 94        return fmt.Errorf("failed to update document: %w", err)
 95    }
 96
 97    if result.MatchedCount == 0 {
 98        return fmt.Errorf("document was modified by another process")
 99    }
100
101    doc.Version++
102    return nil
103}
104
105// Full-text search
106func (r *DocumentRepository) Search(ctx context.Context, query string) ([]Document, error) {
107    filter := bson.M{
108        "$text": bson.M{
109            "$search": query,
110        },
111    }
112
113    opts := options.Find().SetProjection(bson.M{
114        "score": bson.M{"$meta": "textScore"},
115    }).SetSort(bson.M{
116        "score": bson.M{"$meta": "textScore"},
117    })
118
119    cursor, err := r.collection.Find(ctx, filter, opts)
120    if err != nil {
121        return nil, fmt.Errorf("failed to search: %w", err)
122    }
123    defer cursor.Close(ctx)
124
125    var documents []Document
126    if err := cursor.All(ctx, &documents); err != nil {
127        return nil, fmt.Errorf("failed to decode results: %w", err)
128    }
129
130    return documents, nil
131}
132
133func main() {
134    ctx := context.Background()
135
136    client, err := mongo.Connect(ctx, options.Client().ApplyURI("mongodb://localhost:27017"))
137    if err != nil {
138        log.Fatalf("Failed to connect to MongoDB: %v", err)
139    }
140    defer client.Disconnect(ctx)
141
142    db := client.Database("myapp")
143    repo := NewDocumentRepository(db)
144
145    doc := &Document{
146        Title:   "Introduction to Go",
147        Content: "Go is a statically typed, compiled programming language...",
148        Tags:    []string{"golang", "programming", "tutorial"},
149        Author:  "John Doe",
150    }
151
152    if err := repo.Create(ctx, doc); err != nil {
153        log.Fatalf("Failed to create document: %v", err)
154    }
155
156    log.Printf("Created document with ID: %s", doc.ID.Hex())
157}

Logging and Observability Libraries

Structured Logging with Zerolog

Why choose Zerolog? Zero-allocation JSON logging for high-performance applications.

  1// run
  2package main
  3
  4import (
  5    "context"
  6    "errors"
  7    "os"
  8    "time"
  9
 10    "github.com/rs/zerolog"
 11    "github.com/rs/zerolog/log"
 12)
 13
 14// Custom context key for request ID
 15type contextKey string
 16
 17const requestIDKey contextKey = "request_id"
 18
 19// Configure logger for different environments
 20func setupLogger(env string) zerolog.Logger {
 21    zerolog.TimeFieldFormat = zerolog.TimeFormatUnix
 22
 23    var logger zerolog.Logger
 24
 25    if env == "development" {
 26        // Pretty console output for development
 27        logger = zerolog.New(zerolog.ConsoleWriter{
 28            Out:        os.Stdout,
 29            TimeFormat: time.RFC3339,
 30        }).With().Timestamp().Caller().Logger()
 31    } else {
 32        // JSON output for production
 33        logger = zerolog.New(os.Stdout).
 34            With().
 35            Timestamp().
 36            Str("service", "myapp").
 37            Str("version", "1.0.0").
 38            Logger()
 39    }
 40
 41    // Set global log level
 42    switch env {
 43    case "development":
 44        zerolog.SetGlobalLevel(zerolog.DebugLevel)
 45    case "production":
 46        zerolog.SetGlobalLevel(zerolog.InfoLevel)
 47    default:
 48        zerolog.SetGlobalLevel(zerolog.WarnLevel)
 49    }
 50
 51    return logger
 52}
 53
 54// Log middleware for HTTP requests
 55func logMiddleware(logger zerolog.Logger) func(next http.Handler) http.Handler {
 56    return func(next http.Handler) http.Handler {
 57        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 58            start := time.Now()
 59
 60            // Generate request ID
 61            requestID := generateRequestID()
 62            ctx := context.WithValue(r.Context(), requestIDKey, requestID)
 63
 64            // Create sub-logger with request context
 65            reqLogger := logger.With().
 66                Str("request_id", requestID).
 67                Str("method", r.Method).
 68                Str("path", r.URL.Path).
 69                Str("remote_addr", r.RemoteAddr).
 70                Logger()
 71
 72            // Add logger to context
 73            ctx = reqLogger.WithContext(ctx)
 74
 75            // Wrap response writer to capture status code
 76            wrappedWriter := &responseWriter{ResponseWriter: w, statusCode: 200}
 77
 78            // Process request
 79            next.ServeHTTP(wrappedWriter, r.WithContext(ctx))
 80
 81            // Log request completion
 82            duration := time.Since(start)
 83            reqLogger.Info().
 84                Int("status", wrappedWriter.statusCode).
 85                Dur("duration", duration).
 86                Int64("bytes", wrappedWriter.bytesWritten).
 87                Msg("Request completed")
 88        })
 89    }
 90}
 91
 92type responseWriter struct {
 93    http.ResponseWriter
 94    statusCode   int
 95    bytesWritten int64
 96}
 97
 98func (rw *responseWriter) WriteHeader(statusCode int) {
 99    rw.statusCode = statusCode
100    rw.ResponseWriter.WriteHeader(statusCode)
101}
102
103func (rw *responseWriter) Write(b []byte) (int, error) {
104    n, err := rw.ResponseWriter.Write(b)
105    rw.bytesWritten += int64(n)
106    return n, err
107}
108
109// Business logic with contextual logging
110func processOrder(ctx context.Context, orderID string) error {
111    logger := zerolog.Ctx(ctx)
112
113    logger.Debug().
114        Str("order_id", orderID).
115        Msg("Processing order")
116
117    // Simulate processing steps
118    steps := []string{"validate", "charge", "fulfill", "notify"}
119
120    for i, step := range steps {
121        logger.Info().
122            Str("order_id", orderID).
123            Str("step", step).
124            Int("step_number", i+1).
125            Int("total_steps", len(steps)).
126            Msg("Executing step")
127
128        // Simulate work
129        time.Sleep(100 * time.Millisecond)
130
131        // Simulate error in fulfillment
132        if step == "fulfill" && orderID == "error-order" {
133            err := errors.New("inventory not available")
134            logger.Error().
135                Err(err).
136                Str("order_id", orderID).
137                Str("step", step).
138                Msg("Step failed")
139            return err
140        }
141    }
142
143    logger.Info().
144        Str("order_id", orderID).
145        Msg("Order processed successfully")
146
147    return nil
148}
149
150// Sampling for high-volume logs
151func setupSampledLogger() zerolog.Logger {
152    sampled := zerolog.New(os.Stdout).
153        Sample(&zerolog.BurstSampler{
154            Burst:       5,
155            Period:      1 * time.Second,
156            NextSampler: &zerolog.BasicSampler{N: 100},
157        })
158
159    return sampled.With().Timestamp().Logger()
160}
161
162func main() {
163    // Setup logger
164    logger := setupLogger("development")
165
166    // Set as global logger
167    log.Logger = logger
168
169    // Structured logging examples
170    logger.Info().
171        Str("environment", "development").
172        Int("port", 8080).
173        Msg("Application starting")
174
175    // Error logging with stack trace
176    err := errors.New("database connection failed")
177    logger.Error().
178        Err(err).
179        Str("database", "postgres").
180        Str("host", "localhost").
181        Stack().
182        Msg("Failed to connect to database")
183
184    // Contextual logging
185    ctx := logger.WithContext(context.Background())
186    if err := processOrder(ctx, "order-123"); err != nil {
187        logger.Error().Err(err).Msg("Order processing failed")
188    }
189
190    // Performance measurement
191    start := time.Now()
192    // ... operation ...
193    logger.Debug().
194        Dur("duration", time.Since(start)).
195        Msg("Operation completed")
196}
197
198func generateRequestID() string {
199    return fmt.Sprintf("%d", time.Now().UnixNano())
200}

Application Metrics with Prometheus

  1// run
  2package main
  3
  4import (
  5    "net/http"
  6    "time"
  7
  8    "github.com/prometheus/client_golang/prometheus"
  9    "github.com/prometheus/client_golang/prometheus/promauto"
 10    "github.com/prometheus/client_golang/prometheus/promhttp"
 11)
 12
 13// Define metrics
 14var (
 15    httpRequestsTotal = promauto.NewCounterVec(
 16        prometheus.CounterOpts{
 17            Name: "http_requests_total",
 18            Help: "Total number of HTTP requests",
 19        },
 20        []string{"method", "endpoint", "status"},
 21    )
 22
 23    httpRequestDuration = promauto.NewHistogramVec(
 24        prometheus.HistogramOpts{
 25            Name:    "http_request_duration_seconds",
 26            Help:    "HTTP request latency in seconds",
 27            Buckets: prometheus.DefBuckets,
 28        },
 29        []string{"method", "endpoint"},
 30    )
 31
 32    activeConnections = promauto.NewGauge(
 33        prometheus.GaugeOpts{
 34            Name: "active_connections",
 35            Help: "Number of active connections",
 36        },
 37    )
 38
 39    orderProcessingDuration = promauto.NewSummary(
 40        prometheus.SummaryOpts{
 41            Name:       "order_processing_duration_seconds",
 42            Help:       "Order processing time in seconds",
 43            Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
 44        },
 45    )
 46)
 47
 48// Metrics middleware
 49func metricsMiddleware(next http.Handler) http.Handler {
 50    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 51        start := time.Now()
 52
 53        // Increment active connections
 54        activeConnections.Inc()
 55        defer activeConnections.Dec()
 56
 57        // Wrap response writer to capture status
 58        wrappedWriter := &statusRecorder{ResponseWriter: w, statusCode: 200}
 59
 60        // Process request
 61        next.ServeHTTP(wrappedWriter, r)
 62
 63        // Record metrics
 64        duration := time.Since(start).Seconds()
 65
 66        httpRequestsTotal.WithLabelValues(
 67            r.Method,
 68            r.URL.Path,
 69            http.StatusText(wrappedWriter.statusCode),
 70        ).Inc()
 71
 72        httpRequestDuration.WithLabelValues(
 73            r.Method,
 74            r.URL.Path,
 75        ).Observe(duration)
 76    })
 77}
 78
 79type statusRecorder struct {
 80    http.ResponseWriter
 81    statusCode int
 82}
 83
 84func (rec *statusRecorder) WriteHeader(code int) {
 85    rec.statusCode = code
 86    rec.ResponseWriter.WriteHeader(code)
 87}
 88
 89// Business metrics
 90func processOrderWithMetrics(orderID string) error {
 91    start := time.Now()
 92    defer func() {
 93        orderProcessingDuration.Observe(time.Since(start).Seconds())
 94    }()
 95
 96    // Process order...
 97    time.Sleep(100 * time.Millisecond)
 98
 99    return nil
100}
101
102func main() {
103    // Create router
104    mux := http.NewServeMux()
105
106    // Application endpoints
107    mux.HandleFunc("/api/orders", func(w http.ResponseWriter, r *http.Request) {
108        if err := processOrderWithMetrics("order-123"); err != nil {
109            http.Error(w, err.Error(), http.StatusInternalServerError)
110            return
111        }
112        w.WriteHeader(http.StatusOK)
113    })
114
115    // Metrics endpoint
116    mux.Handle("/metrics", promhttp.Handler())
117
118    // Health check
119    mux.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
120        w.WriteHeader(http.StatusOK)
121        w.Write([]byte("OK"))
122    })
123
124    // Apply metrics middleware
125    handler := metricsMiddleware(mux)
126
127    http.ListenAndServe(":8080", handler)
128}

Testing Libraries and Frameworks

Testify: Comprehensive Testing Toolkit

  1// run
  2package main
  3
  4import (
  5    "errors"
  6    "testing"
  7    "time"
  8
  9    "github.com/stretchr/testify/assert"
 10    "github.com/stretchr/testify/mock"
 11    "github.com/stretchr/testify/require"
 12    "github.com/stretchr/testify/suite"
 13)
 14
 15// Interface for dependency injection
 16type UserRepository interface {
 17    FindByID(id int) (*User, error)
 18    Create(user *User) error
 19    Delete(id int) error
 20}
 21
 22type User struct {
 23    ID        int
 24    Name      string
 25    Email     string
 26    CreatedAt time.Time
 27}
 28
 29// Mock implementation
 30type MockUserRepository struct {
 31    mock.Mock
 32}
 33
 34func (m *MockUserRepository) FindByID(id int) (*User, error) {
 35    args := m.Called(id)
 36    if args.Get(0) == nil {
 37        return nil, args.Error(1)
 38    }
 39    return args.Get(0).(*User), args.Error(1)
 40}
 41
 42func (m *MockUserRepository) Create(user *User) error {
 43    args := m.Called(user)
 44    return args.Error(0)
 45}
 46
 47func (m *MockUserRepository) Delete(id int) error {
 48    args := m.Called(id)
 49    return args.Error(0)
 50}
 51
 52// Service under test
 53type UserService struct {
 54    repo UserRepository
 55}
 56
 57func NewUserService(repo UserRepository) *UserService {
 58    return &UserService{repo: repo}
 59}
 60
 61func (s *UserService) GetUser(id int) (*User, error) {
 62    if id <= 0 {
 63        return nil, errors.New("invalid user ID")
 64    }
 65    return s.repo.FindByID(id)
 66}
 67
 68func (s *UserService) RegisterUser(name, email string) (*User, error) {
 69    if name == "" {
 70        return nil, errors.New("name is required")
 71    }
 72    if email == "" {
 73        return nil, errors.New("email is required")
 74    }
 75
 76    user := &User{
 77        Name:      name,
 78        Email:     email,
 79        CreatedAt: time.Now(),
 80    }
 81
 82    if err := s.repo.Create(user); err != nil {
 83        return nil, err
 84    }
 85
 86    return user, nil
 87}
 88
 89// Table-driven tests with testify
 90func TestUserService_GetUser(t *testing.T) {
 91    tests := []struct {
 92        name        string
 93        userID      int
 94        mockUser    *User
 95        mockError   error
 96        expectedErr string
 97    }{
 98        {
 99            name:   "valid user",
100            userID: 1,
101            mockUser: &User{
102                ID:    1,
103                Name:  "John Doe",
104                Email: "john@example.com",
105            },
106            mockError:   nil,
107            expectedErr: "",
108        },
109        {
110            name:        "invalid ID",
111            userID:      -1,
112            mockUser:    nil,
113            mockError:   nil,
114            expectedErr: "invalid user ID",
115        },
116        {
117            name:        "user not found",
118            userID:      999,
119            mockUser:    nil,
120            mockError:   errors.New("user not found"),
121            expectedErr: "user not found",
122        },
123    }
124
125    for _, tt := range tests {
126        t.Run(tt.name, func(t *testing.T) {
127            // Setup mock
128            mockRepo := new(MockUserRepository)
129            if tt.userID > 0 {
130                mockRepo.On("FindByID", tt.userID).Return(tt.mockUser, tt.mockError)
131            }
132
133            // Create service
134            service := NewUserService(mockRepo)
135
136            // Execute
137            user, err := service.GetUser(tt.userID)
138
139            // Assert
140            if tt.expectedErr != "" {
141                assert.Error(t, err)
142                assert.Contains(t, err.Error(), tt.expectedErr)
143                assert.Nil(t, user)
144            } else {
145                assert.NoError(t, err)
146                assert.NotNil(t, user)
147                assert.Equal(t, tt.mockUser.ID, user.ID)
148                assert.Equal(t, tt.mockUser.Name, user.Name)
149            }
150
151            // Verify mock expectations
152            if tt.userID > 0 {
153                mockRepo.AssertExpectations(t)
154            }
155        })
156    }
157}
158
159// Test suite for complex scenarios
160type UserServiceTestSuite struct {
161    suite.Suite
162    mockRepo *MockUserRepository
163    service  *UserService
164}
165
166func (suite *UserServiceTestSuite) SetupTest() {
167    suite.mockRepo = new(MockUserRepository)
168    suite.service = NewUserService(suite.mockRepo)
169}
170
171func (suite *UserServiceTestSuite) TearDownTest() {
172    suite.mockRepo.AssertExpectations(suite.T())
173}
174
175func (suite *UserServiceTestSuite) TestRegisterUser_Success() {
176    user := &User{
177        Name:  "Alice",
178        Email: "alice@example.com",
179    }
180
181    suite.mockRepo.On("Create", mock.AnythingOfType("*main.User")).Return(nil)
182
183    result, err := suite.service.RegisterUser(user.Name, user.Email)
184
185    require.NoError(suite.T(), err)
186    require.NotNil(suite.T(), result)
187    assert.Equal(suite.T(), user.Name, result.Name)
188    assert.Equal(suite.T(), user.Email, result.Email)
189    assert.False(suite.T(), result.CreatedAt.IsZero())
190}
191
192func (suite *UserServiceTestSuite) TestRegisterUser_ValidationErrors() {
193    testCases := []struct {
194        name          string
195        userName      string
196        email         string
197        expectedError string
198    }{
199        {"empty name", "", "test@example.com", "name is required"},
200        {"empty email", "John", "", "email is required"},
201    }
202
203    for _, tc := range testCases {
204        suite.Run(tc.name, func() {
205            result, err := suite.service.RegisterUser(tc.userName, tc.email)
206
207            assert.Error(suite.T(), err)
208            assert.Nil(suite.T(), result)
209            assert.Contains(suite.T(), err.Error(), tc.expectedError)
210        })
211    }
212}
213
214func TestUserServiceTestSuite(t *testing.T) {
215    suite.Run(t, new(UserServiceTestSuite))
216}

GoMock: Interface Mocking

 1// run
 2package main
 3
 4import (
 5    "context"
 6    "testing"
 7    "time"
 8
 9    "github.com/golang/mock/gomock"
10)
11
12// Generate mock with: mockgen -source=service.go -destination=mock_service.go
13
14type PaymentGateway interface {
15    ProcessPayment(ctx context.Context, amount float64, currency string) (string, error)
16    RefundPayment(ctx context.Context, transactionID string) error
17}
18
19type OrderService struct {
20    payment PaymentGateway
21}
22
23func NewOrderService(payment PaymentGateway) *OrderService {
24    return &OrderService{payment: payment}
25}
26
27func (s *OrderService) PlaceOrder(ctx context.Context, amount float64) (string, error) {
28    transactionID, err := s.payment.ProcessPayment(ctx, amount, "USD")
29    if err != nil {
30        return "", err
31    }
32
33    return transactionID, nil
34}
35
36// Example test using GoMock
37func TestOrderService_PlaceOrder(t *testing.T) {
38    ctrl := gomock.NewController(t)
39    defer ctrl.Finish()
40
41    mockPayment := NewMockPaymentGateway(ctrl)
42
43    // Set expectations
44    mockPayment.EXPECT().
45        ProcessPayment(gomock.Any(), 99.99, "USD").
46        Return("txn-12345", nil).
47        Times(1)
48
49    service := NewOrderService(mockPayment)
50    ctx := context.Background()
51
52    txnID, err := service.PlaceOrder(ctx, 99.99)
53
54    if err != nil {
55        t.Errorf("Expected no error, got %v", err)
56    }
57
58    if txnID != "txn-12345" {
59        t.Errorf("Expected txn-12345, got %s", txnID)
60    }
61}

HTTP Testing with httptest

 1// run
 2package main
 3
 4import (
 5    "encoding/json"
 6    "net/http"
 7    "net/http/httptest"
 8    "strings"
 9    "testing"
10
11    "github.com/stretchr/testify/assert"
12    "github.com/stretchr/testify/require"
13)
14
15type APIHandler struct {
16    service *UserService
17}
18
19func (h *APIHandler) CreateUser(w http.ResponseWriter, r *http.Request) {
20    var req struct {
21        Name  string `json:"name"`
22        Email string `json:"email"`
23    }
24
25    if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
26        http.Error(w, "Invalid request body", http.StatusBadRequest)
27        return
28    }
29
30    user, err := h.service.RegisterUser(req.Name, req.Email)
31    if err != nil {
32        http.Error(w, err.Error(), http.StatusBadRequest)
33        return
34    }
35
36    w.Header().Set("Content-Type", "application/json")
37    w.WriteHeader(http.StatusCreated)
38    json.NewEncoder(w).Encode(user)
39}
40
41func TestAPIHandler_CreateUser(t *testing.T) {
42    mockRepo := new(MockUserRepository)
43    mockRepo.On("Create", mock.AnythingOfType("*main.User")).Return(nil)
44
45    service := NewUserService(mockRepo)
46    handler := &APIHandler{service: service}
47
48    tests := []struct {
49        name           string
50        requestBody    string
51        expectedStatus int
52        checkResponse  func(t *testing.T, resp *http.Response)
53    }{
54        {
55            name:           "valid request",
56            requestBody:    `{"name":"John Doe","email":"john@example.com"}`,
57            expectedStatus: http.StatusCreated,
58            checkResponse: func(t *testing.T, resp *http.Response) {
59                var user User
60                err := json.NewDecoder(resp.Body).Decode(&user)
61                require.NoError(t, err)
62                assert.Equal(t, "John Doe", user.Name)
63                assert.Equal(t, "john@example.com", user.Email)
64            },
65        },
66        {
67            name:           "invalid JSON",
68            requestBody:    `{invalid json}`,
69            expectedStatus: http.StatusBadRequest,
70            checkResponse:  nil,
71        },
72        {
73            name:           "missing name",
74            requestBody:    `{"email":"john@example.com"}`,
75            expectedStatus: http.StatusBadRequest,
76            checkResponse:  nil,
77        },
78    }
79
80    for _, tt := range tests {
81        t.Run(tt.name, func(t *testing.T) {
82            req := httptest.NewRequest(http.MethodPost, "/api/users", strings.NewReader(tt.requestBody))
83            req.Header.Set("Content-Type", "application/json")
84
85            rr := httptest.NewRecorder()
86            handler.CreateUser(rr, req)
87
88            assert.Equal(t, tt.expectedStatus, rr.Code)
89
90            if tt.checkResponse != nil {
91                tt.checkResponse(t, rr.Result())
92            }
93        })
94    }
95}

Utility Libraries

Validation with go-playground/validator

 1// run
 2package main
 3
 4import (
 5    "fmt"
 6    "time"
 7
 8    "github.com/go-playground/validator/v10"
 9)
10
11type CreateUserRequest struct {
12    Name      string    `validate:"required,min=2,max=100"`
13    Email     string    `validate:"required,email"`
14    Age       int       `validate:"gte=0,lte=150"`
15    Password  string    `validate:"required,min=8,containsany=!@#$%^&*"`
16    BirthDate time.Time `validate:"required,past_date"`
17    Tags      []string  `validate:"dive,required,min=2"`
18}
19
20// Custom validator for past dates
21func validatePastDate(fl validator.FieldLevel) bool {
22    date, ok := fl.Field().Interface().(time.Time)
23    if !ok {
24        return false
25    }
26    return date.Before(time.Now())
27}
28
29func main() {
30    validate := validator.New()
31
32    // Register custom validation
33    validate.RegisterValidation("past_date", validatePastDate)
34
35    // Valid request
36    req := CreateUserRequest{
37        Name:      "John Doe",
38        Email:     "john@example.com",
39        Age:       30,
40        Password:  "SecureP@ss123",
41        BirthDate: time.Now().AddDate(-30, 0, 0),
42        Tags:      []string{"developer", "golang"},
43    }
44
45    err := validate.Struct(req)
46    if err != nil {
47        for _, err := range err.(validator.ValidationErrors) {
48            fmt.Printf("Field: %s, Failed validation: %s\n", err.Field(), err.Tag())
49        }
50    } else {
51        fmt.Println("Validation passed!")
52    }
53
54    // Invalid request
55    invalidReq := CreateUserRequest{
56        Name:     "J",  // Too short
57        Email:    "invalid-email",  // Not valid email
58        Age:      200,  // Too old
59        Password: "weak",  // Too short and missing special char
60    }
61
62    err = validate.Struct(invalidReq)
63    if err != nil {
64        fmt.Println("\nValidation errors:")
65        for _, err := range err.(validator.ValidationErrors) {
66            fmt.Printf("  - Field '%s' failed '%s' validation\n", err.Field(), err.Tag())
67        }
68    }
69}

Configuration Management with Viper

  1// run
  2package main
  3
  4import (
  5    "fmt"
  6    "log"
  7    "time"
  8
  9    "github.com/spf13/viper"
 10)
 11
 12type AppConfig struct {
 13    Server   ServerConfig   `mapstructure:"server"`
 14    Database DatabaseConfig `mapstructure:"database"`
 15    Redis    RedisConfig    `mapstructure:"redis"`
 16    Features FeatureFlags   `mapstructure:"features"`
 17}
 18
 19type ServerConfig struct {
 20    Host         string        `mapstructure:"host"`
 21    Port         int           `mapstructure:"port"`
 22    ReadTimeout  time.Duration `mapstructure:"read_timeout"`
 23    WriteTimeout time.Duration `mapstructure:"write_timeout"`
 24}
 25
 26type DatabaseConfig struct {
 27    Host         string `mapstructure:"host"`
 28    Port         int    `mapstructure:"port"`
 29    User         string `mapstructure:"user"`
 30    Password     string `mapstructure:"password"`
 31    DBName       string `mapstructure:"dbname"`
 32    MaxOpenConns int    `mapstructure:"max_open_conns"`
 33}
 34
 35type RedisConfig struct {
 36    Host     string `mapstructure:"host"`
 37    Port     int    `mapstructure:"port"`
 38    Password string `mapstructure:"password"`
 39    DB       int    `mapstructure:"db"`
 40}
 41
 42type FeatureFlags struct {
 43    EnableNewUI     bool `mapstructure:"enable_new_ui"`
 44    EnableAnalytics bool `mapstructure:"enable_analytics"`
 45}
 46
 47func LoadConfig() (*AppConfig, error) {
 48    // Set config file details
 49    viper.SetConfigName("config")
 50    viper.SetConfigType("yaml")
 51    viper.AddConfigPath(".")
 52    viper.AddConfigPath("./config")
 53    viper.AddConfigPath("/etc/myapp/")
 54
 55    // Enable environment variable support
 56    viper.AutomaticEnv()
 57    viper.SetEnvPrefix("APP")
 58
 59    // Set defaults
 60    viper.SetDefault("server.host", "0.0.0.0")
 61    viper.SetDefault("server.port", 8080)
 62    viper.SetDefault("server.read_timeout", "10s")
 63    viper.SetDefault("server.write_timeout", "10s")
 64    viper.SetDefault("database.max_open_conns", 25)
 65    viper.SetDefault("redis.db", 0)
 66    viper.SetDefault("features.enable_new_ui", false)
 67
 68    // Read config file
 69    if err := viper.ReadInConfig(); err != nil {
 70        if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
 71            return nil, fmt.Errorf("failed to read config: %w", err)
 72        }
 73        log.Println("No config file found, using defaults and environment variables")
 74    }
 75
 76    // Unmarshal config into struct
 77    var config AppConfig
 78    if err := viper.Unmarshal(&config); err != nil {
 79        return nil, fmt.Errorf("failed to unmarshal config: %w", err)
 80    }
 81
 82    return &config, nil
 83}
 84
 85// Watch for config changes
 86func WatchConfig(onChange func(*AppConfig)) error {
 87    viper.WatchConfig()
 88    viper.OnConfigChange(func(e fsnotify.Event) {
 89        log.Printf("Config file changed: %s", e.Name)
 90
 91        var config AppConfig
 92        if err := viper.Unmarshal(&config); err != nil {
 93            log.Printf("Error reloading config: %v", err)
 94            return
 95        }
 96
 97        onChange(&config)
 98    })
 99
100    return nil
101}
102
103func main() {
104    config, err := LoadConfig()
105    if err != nil {
106        log.Fatalf("Failed to load config: %v", err)
107    }
108
109    fmt.Printf("Server: %s:%d\n", config.Server.Host, config.Server.Port)
110    fmt.Printf("Database: %s@%s:%d/%s\n",
111        config.Database.User,
112        config.Database.Host,
113        config.Database.Port,
114        config.Database.DBName)
115    fmt.Printf("Features: NewUI=%v, Analytics=%v\n",
116        config.Features.EnableNewUI,
117        config.Features.EnableAnalytics)
118}

JSON Processing with gjson/sjson

 1// run
 2package main
 3
 4import (
 5    "fmt"
 6
 7    "github.com/tidwall/gjson"
 8    "github.com/tidwall/sjson"
 9)
10
11func main() {
12    // Complex JSON document
13    json := `{
14        "user": {
15            "id": 123,
16            "name": "John Doe",
17            "email": "john@example.com",
18            "tags": ["developer", "golang", "devops"],
19            "metadata": {
20                "last_login": "2024-01-15T10:30:00Z",
21                "ip_address": "192.168.1.1"
22            }
23        },
24        "orders": [
25            {"id": 1, "total": 99.99, "status": "completed"},
26            {"id": 2, "total": 149.99, "status": "pending"},
27            {"id": 3, "total": 79.99, "status": "completed"}
28        ]
29    }`
30
31    // Fast JSON parsing with gjson
32    name := gjson.Get(json, "user.name")
33    fmt.Printf("User name: %s\n", name.String())
34
35    // Get nested values
36    lastLogin := gjson.Get(json, "user.metadata.last_login")
37    fmt.Printf("Last login: %s\n", lastLogin.String())
38
39    // Get array elements
40    firstOrder := gjson.Get(json, "orders.0.total")
41    fmt.Printf("First order total: %.2f\n", firstOrder.Float())
42
43    // Query arrays
44    completedOrders := gjson.Get(json, "orders.#(status==\"completed\")#.id")
45    fmt.Printf("Completed order IDs: %v\n", completedOrders.Array())
46
47    // Calculate total
48    totalAmount := gjson.Get(json, "orders.#.total")
49    var sum float64
50    for _, amount := range totalAmount.Array() {
51        sum += amount.Float()
52    }
53    fmt.Printf("Total amount: %.2f\n", sum)
54
55    // Modify JSON with sjson
56    updated, _ := sjson.Set(json, "user.name", "Jane Doe")
57    updated, _ = sjson.Set(updated, "user.tags.-1", "architect")
58    updated, _ = sjson.Set(updated, "orders.1.status", "completed")
59
60    newName := gjson.Get(updated, "user.name")
61    fmt.Printf("Updated name: %s\n", newName.String())
62
63    // Add new field
64    updated, _ = sjson.Set(updated, "user.verified", true)
65    fmt.Println("Updated JSON with new field")
66}

Web Frameworks Comparison Matrix

Feature Comparison

Feature	Gin	Echo	Fiber	Chi	stdlib
Performance	Excellent	Excellent	Best	Good	Good
Learning Curve	Low	Low	Low	Very Low	Medium
Middleware	Rich	Rich	Rich	Moderate	Manual
Validation	Built-in	Manual	Built-in	Manual	Manual
WebSocket	Plugin	Built-in	Built-in	Manual	stdlib
Context	Custom	Custom	Custom	stdlib	stdlib
HTTP/2	Yes	Yes	Yes	Yes	Yes
Documentation	Excellent	Excellent	Good	Good	Excellent
Community	Large	Large	Growing	Medium	Official
stdlib Compatible	No	No	No	Yes	Yes

When to Use Each Framework

Gin: Best for high-performance APIs with minimal setup

1// Strengths: Speed, rich middleware, good DX
2router := gin.Default()
3router.GET("/users/:id", getUser)

Echo: Best for feature-rich web applications

1// Strengths: WebSocket, middleware, validation helpers
2e := echo.New()
3e.GET("/users/:id", getUser)

Fiber: Best for Express.js-like experience in Go

1// Strengths: Fastest, Express-like API, great for Node developers
2app := fiber.New()
3app.Get("/users/:id", getUser)

Chi: Best for stdlib compatibility and gradual adoption

1// Strengths: Idiomatic Go, stdlib compatible, composable
2r := chi.NewRouter()
3r.Get("/users/{id}", getUser)

Performance Benchmark Summary

Based on real-world testing with 1000 concurrent connections:

Framework    Requests/sec    Latency p50    Latency p99    Memory
Fiber        125,000         0.8ms          3.2ms          45MB
Gin          118,000         0.9ms          3.5ms          52MB
Echo         115,000         0.9ms          3.8ms          54MB
Chi          98,000          1.2ms          4.5ms          48MB
stdlib       95,000          1.3ms          5.0ms          42MB

Note: Performance varies based on middleware, use case, and hardware.

Library Evaluation Criteria

Essential Evaluation Factors

 1// Evaluation checklist for production libraries
 2type LibraryEvaluation struct {
 3    // Maintenance and Activity
 4    LastCommitDays    int    // < 90 days is active
 5    OpenIssuesCount   int    // < 100 is manageable
 6    PRResponseTime    int    // < 7 days is good
 7    MaintainerCount   int    // > 2 is stable
 8
 9    // Quality Indicators
10    TestCoverage      float64  // > 80% is excellent
11    HasCI             bool     // Required
12    HasDocumentation  bool     // Required
13    HasExamples       bool     // Highly recommended
14
15    // Community and Adoption
16    GitHubStars       int      // > 1000 is popular
17    DependentProjects int      // > 100 is trusted
18    StackOverflowQs   int      // > 50 has community
19
20    // Compatibility
21    GoVersion         string   // Compatible with your version
22    BreakingChanges   int      // < 2 per year is stable
23    FollowsSemVer     bool     // Required
24
25    // Performance
26    BenchmarkResults  string   // Compare with alternatives
27    MemoryFootprint   int      // MB
28    AllocationCount   int      // Lower is better
29
30    // Security
31    KnownVulns        int      // 0 is required
32    SecurityAudits    bool     // Recommended for critical libs
33    DependencyCount   int      // < 10 is lightweight
34}

Decision Framework

  1// run
  2package main
  3
  4import (
  5    "fmt"
  6)
  7
  8type EvaluationResult struct {
  9    Score      int
 10    Recommendation string
 11    Concerns   []string
 12}
 13
 14func EvaluateLibrary(name string, eval LibraryEvaluation) EvaluationResult {
 15    score := 0
 16    var concerns []string
 17
 18    // Maintenance scoring
 19    if eval.LastCommitDays < 90 {
 20        score += 20
 21    } else if eval.LastCommitDays < 180 {
 22        score += 10
 23    } else {
 24        concerns = append(concerns, "Library may be inactive")
 25    }
 26
 27    // Quality scoring
 28    if eval.TestCoverage > 80 {
 29        score += 20
 30    } else if eval.TestCoverage > 60 {
 31        score += 10
 32    } else {
 33        concerns = append(concerns, "Low test coverage")
 34    }
 35
 36    if eval.HasCI && eval.HasDocumentation && eval.HasExamples {
 37        score += 15
 38    }
 39
 40    // Community scoring
 41    if eval.GitHubStars > 5000 {
 42        score += 15
 43    } else if eval.GitHubStars > 1000 {
 44        score += 10
 45    }
 46
 47    if eval.DependentProjects > 500 {
 48        score += 15
 49    } else if eval.DependentProjects > 100 {
 50        score += 10
 51    }
 52
 53    // Stability scoring
 54    if eval.FollowsSemVer && eval.BreakingChanges < 2 {
 55        score += 15
 56    }
 57
 58    // Security is critical
 59    if eval.KnownVulns > 0 {
 60        score = 0
 61        concerns = append(concerns, "HAS KNOWN VULNERABILITIES - DO NOT USE")
 62    }
 63
 64    // Generate recommendation
 65    var recommendation string
 66    switch {
 67    case score >= 80:
 68        recommendation = "Excellent choice for production"
 69    case score >= 60:
 70        recommendation = "Good choice with minor concerns"
 71    case score >= 40:
 72        recommendation = "Use with caution, address concerns"
 73    default:
 74        recommendation = "Not recommended for production"
 75    }
 76
 77    return EvaluationResult{
 78        Score:          score,
 79        Recommendation: recommendation,
 80        Concerns:       concerns,
 81    }
 82}
 83
 84func main() {
 85    // Example evaluation
 86    ginEval := LibraryEvaluation{
 87        LastCommitDays:    15,
 88        OpenIssuesCount:   45,
 89        PRResponseTime:    3,
 90        MaintainerCount:   5,
 91        TestCoverage:      85.0,
 92        HasCI:             true,
 93        HasDocumentation:  true,
 94        HasExamples:       true,
 95        GitHubStars:       70000,
 96        DependentProjects: 15000,
 97        StackOverflowQs:   500,
 98        BreakingChanges:   1,
 99        FollowsSemVer:     true,
100        KnownVulns:        0,
101        DependencyCount:   8,
102    }
103
104    result := EvaluateLibrary("gin-gonic/gin", ginEval)
105
106    fmt.Printf("Library Evaluation: gin-gonic/gin\n")
107    fmt.Printf("Score: %d/100\n", result.Score)
108    fmt.Printf("Recommendation: %s\n", result.Recommendation)
109    if len(result.Concerns) > 0 {
110        fmt.Println("Concerns:")
111        for _, concern := range result.Concerns {
112            fmt.Printf("  - %s\n", concern)
113        }
114    }
115}

Practice Exercises

Exercise 1: Multi-Library REST API

Build a production-ready REST API that integrates:

• Gin for routing and middleware
• GORM for database operations
• Viper for configuration management
• Zerolog for structured logging
• Resty for external API calls

Requirements:

• User CRUD operations with validation
• External API integration
• Structured logging for all operations
• Configuration from both files and environment variables
• Proper error handling and HTTP status codes

Starter Code:

 1// Your task: Complete this implementation
 2type User struct {
 3    // TODO: Define struct with GORM tags
 4}
 5
 6type UserService struct {
 7    db    *gorm.DB
 8    client *resty.Client
 9    logger zerolog.Logger
10}
11
12// TODO: Implement CRUD operations
13func CreateUser(user *User) error {
14    // TODO: Validate input
15    // TODO: Check external service
16    // TODO: Save to database
17    // TODO: Log operations
18}
19
20// TODO: Complete the main application
21func main() {
22    // TODO: Setup configuration with Viper
23    // TODO: Setup database with GORM
24    // TODO: Setup logger with Zerolog
25    // TODO: Setup Gin router with middleware
26    // TODO: Implement API endpoints
27}

Solution

  1// Complete solution implementation
  2package main
  3
  4import (
  5    "fmt"
  6    "net/http"
  7    "time"
  8
  9    "github.com/gin-gonic/gin"
 10    "github.com/go-resty/resty/v2"
 11    "github.com/rs/zerolog"
 12    "github.com/spf13/viper"
 13    "gorm.io/driver/postgres"
 14    "gorm.io/gorm"
 15)
 16
 17type User struct {
 18    ID        uint           `gorm:"primaryKey" json:"id"`
 19    Name      string         `gorm:"size:100;not null" json:"name" binding:"required,min=2,max=100"`
 20    Email     string         `gorm:"uniqueIndex;not null" json:"email" binding:"required,email"`
 21    ExternalID string        `gorm:"size:50" json:"external_id"`
 22    CreatedAt time.Time      `json:"created_at"`
 23    UpdatedAt time.Time      `json:"updated_at"`
 24}
 25
 26type ExternalUserData struct {
 27    ID    string `json:"id"`
 28    Name  string `json:"name"`
 29    Email string `json:"email"`
 30    Score int    `json:"score"`
 31}
 32
 33type UserService struct {
 34    db     *gorm.DB
 35    client *resty.Client
 36    logger zerolog.Logger
 37}
 38
 39func NewUserService(db *gorm.DB, client *resty.Client, logger zerolog.Logger) *UserService {
 40    return &UserService{
 41        db:     db,
 42        client: client,
 43        logger: logger,
 44    }
 45}
 46
 47func CreateUser(user *User) error {
 48    s.logger.Info().
 49        Str("email", user.Email).
 50        Msg("Creating user")
 51
 52    // Validate user doesn't exist
 53    var existingUser User
 54    if err := s.db.Where("email = ?", user.Email).First(&existingUser).Error; err == nil {
 55        s.logger.Error().
 56            Str("email", user.Email).
 57            Msg("User already exists")
 58        return fmt.Errorf("user with email %s already exists", user.Email)
 59    }
 60
 61    // Fetch external data
 62    externalData, err := s.fetchExternalUserData(user.Email)
 63    if err != nil {
 64        s.logger.Warn().
 65            Str("email", user.Email).
 66            Err(err).
 67            Msg("Failed to fetch external user data")
 68        // Continue without external data
 69    } else {
 70        user.ExternalID = externalData.ID
 71        s.logger.Info().
 72            Str("external_id", externalData.ID).
 73            Str("email", user.Email).
 74            Msg("Fetched external user data")
 75    }
 76
 77    // Create user
 78    if err := s.db.Create(user).Error; err != nil {
 79        s.logger.Error().
 80            Str("email", user.Email).
 81            Err(err).
 82            Msg("Failed to create user")
 83        return fmt.Errorf("failed to create user: %w", err)
 84    }
 85
 86    s.logger.Info().
 87        Uint("id", user.ID).
 88        Str("email", user.Email).
 89        Msg("User created successfully")
 90
 91    return nil
 92}
 93
 94func fetchExternalUserData(email string) {
 95    resp, err := s.client.R().
 96        SetQueryParam("email", email).
 97        Get("https://jsonplaceholder.typicode.com/users")
 98
 99    if err != nil {
100        return nil, err
101    }
102
103    if resp.StatusCode() != 200 {
104        return nil, fmt.Errorf("external API returned status %d", resp.StatusCode())
105    }
106
107    var users []ExternalUserData
108    if err := resp.Unmarshal(&users); err != nil {
109        return nil, err
110    }
111
112    // Find user by email
113    for _, user := range users {
114        if user.Email == email {
115            return &user, nil
116        }
117    }
118
119    return nil, fmt.Errorf("user not found in external service")
120}
121
122// Complete main application
123func main() {
124    // Setup configuration
125    viper.SetConfigName("config")
126    viper.SetConfigType("yaml")
127    viper.AddConfigPath(".")
128    viper.AutomaticEnv()
129
130    viper.SetDefault("server.port", 8080)
131    viper.SetDefault("database.host", "localhost")
132    viper.SetDefault("database.port", 5432)
133
134    if err := viper.ReadInConfig(); err != nil {
135        fmt.Printf("Config file not found, using defaults\n")
136    }
137
138    // Setup logger
139    logger := zerolog.New(zerolog.ConsoleWriter{Out: os.Stderr}).With().Timestamp().Logger()
140    level, _ := zerolog.ParseLevel(viper.GetString("logging.level"))
141    logger = logger.Level(level)
142
143    // Setup database
144    dsn := fmt.Sprintf("host=%s user=%s password=%s dbname=%s port=%d sslmode=%s",
145        viper.GetString("database.host"),
146        viper.GetString("database.user"),
147        viper.GetString("database.password"),
148        viper.GetString("database.dbname"),
149        viper.GetInt("database.port"),
150        viper.GetString("database.sslmode"),
151    )
152
153    db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
154    if err != nil {
155        logger.Fatal().Err(err).Msg("Failed to connect to database")
156    }
157
158    db.AutoMigrate(&User{})
159
160    // Setup HTTP client
161    client := resty.New().SetTimeout(10 * time.Second)
162
163    // Setup services
164    userService := NewUserService(db, client, logger)
165
166    // Setup router
167    router := gin.New()
168    router.Use(gin.Logger())
169    router.Use(gin.Recovery())
170
171    // API endpoints
172    router.POST("/api/users", func(c *gin.Context) {
173        var user User
174        if err := c.ShouldBindJSON(&user); err != nil {
175            c.JSON(400, gin.H{"error": err.Error()})
176            return
177        }
178
179        if err := userService.CreateUser(&user); err != nil {
180            c.JSON(500, gin.H{"error": err.Error()})
181            return
182        }
183
184        c.JSON(201, user)
185    })
186
187    router.GET("/api/users/:id", func(c *gin.Context) {
188        var user User
189        if err := db.First(&user, c.Param("id")).Error; err != nil {
190            c.JSON(404, gin.H{"error": "User not found"})
191            return
192        }
193        c.JSON(200, user)
194    })
195
196    port := viper.GetInt("server.port")
197    logger.Info().Int("port", port).Msg("Starting server")
198
199    if err := router.Run(fmt.Sprintf(":%d", port)); err != nil {
200        logger.Fatal().Err(err).Msg("Failed to start server")
201    }
202}

Exercise 2: Caching Layer with Redis

Build a production-ready caching system that:

• Implements cache-aside pattern
• Supports TTL and cache invalidation
• Includes distributed locking
• Provides metrics for hit/miss rates
• Handles cache stampede scenarios

Requirements:

• Redis client integration
• Generic caching for multiple data types
• Graceful degradation when Redis is unavailable
• Prometheus metrics for monitoring
• Proper error handling and logging

Starter Code:

 1// Your task: Complete this implementation
 2type CacheManager struct {
 3    redis  *redis.Client
 4    logger zerolog.Logger
 5    hits   prometheus.Counter
 6    misses prometheus.Counter
 7}
 8
 9// TODO: Implement cache-aside pattern
10func GetOrSet[T any](ctx context.Context, key string, ttl time.Duration, fetcher func() (T, error)) (T, error) {
11    // TODO: Try cache first
12    // TODO: If miss, fetch from source
13    // TODO: Handle cache stampede with distributed lock
14    // TODO: Update metrics
15}
16
17// TODO: Implement cache invalidation
18func InvalidatePattern(ctx context.Context, pattern string) error {
19    // TODO: Find keys matching pattern
20    // TODO: Delete keys in batches
21}
22
23// TODO: Implement distributed lock
24func WithLock(ctx context.Context, key string, ttl time.Duration, fn func() error) error {
25    // TODO: Acquire lock
26    // TODO: Execute function
27    // TODO: Release lock
28}

Solution

  1// Complete solution implementation
  2package main
  3
  4import (
  5    "context"
  6    "encoding/json"
  7    "fmt"
  8    "sync"
  9    "time"
 10
 11    "github.com/prometheus/client_golang/prometheus"
 12    "github.com/prometheus/client_golang/prometheus/promauto"
 13    "github.com/redis/go-redis/v9"
 14    "github.com/rs/zerolog"
 15)
 16
 17var (
 18    cacheHits = promauto.NewCounter(prometheus.CounterOpts{
 19        Name: "cache_hits_total",
 20        Help: "Total number of cache hits",
 21    })
 22
 23    cacheMisses = promauto.NewCounter(prometheus.CounterOpts{
 24        Name: "cache_misses_total",
 25        Help: "Total number of cache misses",
 26    })
 27
 28    cacheErrors = promauto.NewCounter(prometheus.CounterOpts{
 29        Name: "cache_errors_total",
 30        Help: "Total number of cache errors",
 31    })
 32)
 33
 34type CacheManager struct {
 35    redis      *redis.Client
 36    logger     zerolog.Logger
 37    fallback   bool
 38    inFlight   sync.Map // Prevent cache stampede
 39}
 40
 41func NewCacheManager(redis *redis.Client, logger zerolog.Logger) *CacheManager {
 42    return &CacheManager{
 43        redis:    redis,
 44        logger:   logger,
 45        fallback: true,
 46    }
 47}
 48
 49// Generic cache-aside pattern with stampede prevention
 50func (c *CacheManager) GetOrSet(
 51    ctx context.Context,
 52    key string,
 53    ttl time.Duration,
 54    fetcher func() (interface{}, error),
 55) (interface{}, error) {
 56    // Try to get from cache
 57    data, err := c.redis.Get(ctx, key).Bytes()
 58    if err == nil {
 59        cacheHits.Inc()
 60        c.logger.Debug().Str("key", key).Msg("Cache hit")
 61
 62        var result interface{}
 63        if err := json.Unmarshal(data, &result); err != nil {
 64            return nil, fmt.Errorf("failed to unmarshal cached data: %w", err)
 65        }
 66        return result, nil
 67    }
 68
 69    // Cache miss
 70    cacheMisses.Inc()
 71    c.logger.Debug().Str("key", key).Msg("Cache miss")
 72
 73    // Prevent cache stampede - only one goroutine fetches data
 74    actual, loaded := c.inFlight.LoadOrStore(key, &sync.Mutex{})
 75    mu := actual.(*sync.Mutex)
 76
 77    if loaded {
 78        // Another goroutine is fetching, wait for it
 79        c.logger.Debug().Str("key", key).Msg("Waiting for in-flight request")
 80        mu.Lock()
 81        mu.Unlock()
 82
 83        // Try cache again after other goroutine finished
 84        return c.GetOrSet(ctx, key, ttl, fetcher)
 85    }
 86
 87    // This goroutine will fetch the data
 88    mu.Lock()
 89    defer func() {
 90        mu.Unlock()
 91        c.inFlight.Delete(key)
 92    }()
 93
 94    // Fetch data
 95    result, err := fetcher()
 96    if err != nil {
 97        return nil, fmt.Errorf("failed to fetch data: %w", err)
 98    }
 99
100    // Store in cache
101    data, err = json.Marshal(result)
102    if err != nil {
103        c.logger.Error().Err(err).Str("key", key).Msg("Failed to marshal data")
104        return result, nil // Return result even if caching fails
105    }
106
107    if err := c.redis.Set(ctx, key, data, ttl).Err(); err != nil {
108        cacheErrors.Inc()
109        c.logger.Error().Err(err).Str("key", key).Msg("Failed to cache data")
110        // Continue - data is still valid
111    }
112
113    return result, nil
114}
115
116// Invalidate keys matching pattern
117func (c *CacheManager) InvalidatePattern(ctx context.Context, pattern string) error {
118    var cursor uint64
119    var deletedCount int
120
121    for {
122        keys, nextCursor, err := c.redis.Scan(ctx, cursor, pattern, 100).Result()
123        if err != nil {
124            return fmt.Errorf("failed to scan keys: %w", err)
125        }
126
127        if len(keys) > 0 {
128            pipe := c.redis.Pipeline()
129            for _, key := range keys {
130                pipe.Del(ctx, key)
131            }
132
133            if _, err := pipe.Exec(ctx); err != nil {
134                c.logger.Error().Err(err).Msg("Failed to delete keys")
135            } else {
136                deletedCount += len(keys)
137            }
138        }
139
140        cursor = nextCursor
141        if cursor == 0 {
142            break
143        }
144    }
145
146    c.logger.Info().
147        Str("pattern", pattern).
148        Int("deleted", deletedCount).
149        Msg("Invalidated cache keys")
150
151    return nil
152}
153
154// Distributed lock implementation
155func (c *CacheManager) WithLock(
156    ctx context.Context,
157    key string,
158    ttl time.Duration,
159    fn func() error,
160) error {
161    lockKey := fmt.Sprintf("lock:%s", key)
162    lockValue := fmt.Sprintf("%d", time.Now().UnixNano())
163
164    // Try to acquire lock
165    acquired := false
166    for i := 0; i < 10; i++ {
167        ok, err := c.redis.SetNX(ctx, lockKey, lockValue, ttl).Result()
168        if err != nil {
169            return fmt.Errorf("failed to acquire lock: %w", err)
170        }
171
172        if ok {
173            acquired = true
174            break
175        }
176
177        // Wait before retry
178        time.Sleep(100 * time.Millisecond)
179    }
180
181    if !acquired {
182        return fmt.Errorf("failed to acquire lock after retries")
183    }
184
185    // Ensure lock is released
186    defer func() {
187        // Only delete if we still own the lock
188        script := `
189            if redis.call("get", KEYS[1]) == ARGV[1] then
190                return redis.call("del", KEYS[1])
191            else
192                return 0
193            end
194        `
195        c.redis.Eval(ctx, script, []string{lockKey}, lockValue)
196    }()
197
198    // Execute function
199    return fn()
200}
201
202// Example usage
203func main() {
204    logger := zerolog.New(os.Stdout).With().Timestamp().Logger()
205
206    client := redis.NewClient(&redis.Options{
207        Addr: "localhost:6379",
208    })
209
210    cache := NewCacheManager(client, logger)
211    ctx := context.Background()
212
213    // Example: Cache user data
214    type User struct {
215        ID    int    `json:"id"`
216        Name  string `json:"name"`
217        Email string `json:"email"`
218    }
219
220    // Fetch with caching
221    result, err := cache.GetOrSet(ctx, "user:123", 5*time.Minute, func() (interface{}, error) {
222        // Simulate database fetch
223        time.Sleep(100 * time.Millisecond)
224        return User{ID: 123, Name: "John Doe", Email: "john@example.com"}, nil
225    })
226
227    if err != nil {
228        logger.Error().Err(err).Msg("Failed to get user")
229    } else {
230        logger.Info().Interface("user", result).Msg("Got user")
231    }
232
233    // Invalidate pattern
234    if err := cache.InvalidatePattern(ctx, "user:*"); err != nil {
235        logger.Error().Err(err).Msg("Failed to invalidate cache")
236    }
237
238    // Use distributed lock
239    err = cache.WithLock(ctx, "process-orders", 30*time.Second, func() error {
240        // Critical section - only one process can execute this
241        logger.Info().Msg("Processing orders with lock")
242        time.Sleep(1 * time.Second)
243        return nil
244    })
245
246    if err != nil {
247        logger.Error().Err(err).Msg("Failed to execute with lock")
248    }
249}

Exercise 3: Testing Framework Integration

Build a comprehensive test suite that demonstrates:

• Unit testing with testify
• Mocking with testify/mock
• HTTP testing with httptest
• Table-driven tests
• Test suites with setup/teardown

Requirements:

• Test a service with multiple dependencies
• Mock external API calls
• Test HTTP handlers
• Achieve >80% test coverage
• Include integration tests

Starter Code:

 1// Your task: Complete this implementation
 2type OrderService struct {
 3    repo    OrderRepository
 4    payment PaymentGateway
 5    notify  NotificationService
 6    logger  zerolog.Logger
 7}
 8
 9// TODO: Implement PlaceOrder method
10func PlaceOrder(ctx context.Context, order *Order) error {
11    // TODO: Validate order
12    // TODO: Process payment
13    // TODO: Save to database
14    // TODO: Send notification
15}
16
17// TODO: Write comprehensive tests
18func TestOrderService_PlaceOrder(t *testing.T) {
19    // TODO: Setup mocks
20    // TODO: Test success case
21    // TODO: Test payment failure
22    // TODO: Test database failure
23    // TODO: Test notification failure
24}

Solution

  1// Complete solution implementation
  2package main
  3
  4import (
  5    "context"
  6    "errors"
  7    "testing"
  8    "time"
  9
 10    "github.com/rs/zerolog"
 11    "github.com/stretchr/testify/assert"
 12    "github.com/stretchr/testify/mock"
 13    "github.com/stretchr/testify/require"
 14    "github.com/stretchr/testify/suite"
 15)
 16
 17// Domain models
 18type Order struct {
 19    ID          string
 20    UserID      string
 21    Amount      float64
 22    Status      string
 23    PaymentID   string
 24    CreatedAt   time.Time
 25}
 26
 27// Interfaces for dependencies
 28type OrderRepository interface {
 29    Create(ctx context.Context, order *Order) error
 30    UpdateStatus(ctx context.Context, orderID string, status string) error
 31}
 32
 33type PaymentGateway interface {
 34    ProcessPayment(ctx context.Context, amount float64) (string, error)
 35}
 36
 37type NotificationService interface {
 38    SendOrderConfirmation(ctx context.Context, userID string, orderID string) error
 39}
 40
 41// Mocks
 42type MockOrderRepository struct {
 43    mock.Mock
 44}
 45
 46func (m *MockOrderRepository) Create(ctx context.Context, order *Order) error {
 47    args := m.Called(ctx, order)
 48    return args.Error(0)
 49}
 50
 51func (m *MockOrderRepository) UpdateStatus(ctx context.Context, orderID string, status string) error {
 52    args := m.Called(ctx, orderID, status)
 53    return args.Error(0)
 54}
 55
 56type MockPaymentGateway struct {
 57    mock.Mock
 58}
 59
 60func (m *MockPaymentGateway) ProcessPayment(ctx context.Context, amount float64) (string, error) {
 61    args := m.Called(ctx, amount)
 62    return args.String(0), args.Error(1)
 63}
 64
 65type MockNotificationService struct {
 66    mock.Mock
 67}
 68
 69func (m *MockNotificationService) SendOrderConfirmation(ctx context.Context, userID string, orderID string) error {
 70    args := m.Called(ctx, userID, orderID)
 71    return args.Error(0)
 72}
 73
 74// Service implementation
 75type OrderService struct {
 76    repo    OrderRepository
 77    payment PaymentGateway
 78    notify  NotificationService
 79    logger  zerolog.Logger
 80}
 81
 82func NewOrderService(
 83    repo OrderRepository,
 84    payment PaymentGateway,
 85    notify NotificationService,
 86    logger zerolog.Logger,
 87) *OrderService {
 88    return &OrderService{
 89        repo:    repo,
 90        payment: payment,
 91        notify:  notify,
 92        logger:  logger,
 93    }
 94}
 95
 96func (s *OrderService) PlaceOrder(ctx context.Context, order *Order) error {
 97    // Validate order
 98    if order.Amount <= 0 {
 99        return errors.New("invalid order amount")
100    }
101    if order.UserID == "" {
102        return errors.New("user ID is required")
103    }
104
105    order.Status = "pending"
106    order.CreatedAt = time.Now()
107
108    // Process payment
109    paymentID, err := s.payment.ProcessPayment(ctx, order.Amount)
110    if err != nil {
111        s.logger.Error().Err(err).Msg("Payment failed")
112        return fmt.Errorf("payment processing failed: %w", err)
113    }
114
115    order.PaymentID = paymentID
116    order.Status = "paid"
117
118    // Save order
119    if err := s.repo.Create(ctx, order); err != nil {
120        s.logger.Error().Err(err).Msg("Failed to create order")
121        return fmt.Errorf("failed to save order: %w", err)
122    }
123
124    order.Status = "confirmed"
125    if err := s.repo.UpdateStatus(ctx, order.ID, "confirmed"); err != nil {
126        s.logger.Error().Err(err).Msg("Failed to update order status")
127        // Continue - order is saved
128    }
129
130    // Send notification (non-blocking)
131    go func() {
132        if err := s.notify.SendOrderConfirmation(context.Background(), order.UserID, order.ID); err != nil {
133            s.logger.Error().Err(err).Msg("Failed to send notification")
134        }
135    }()
136
137    s.logger.Info().
138        Str("order_id", order.ID).
139        Str("user_id", order.UserID).
140        Float64("amount", order.Amount).
141        Msg("Order placed successfully")
142
143    return nil
144}
145
146// Table-driven tests
147func TestOrderService_PlaceOrder(t *testing.T) {
148    tests := []struct {
149        name          string
150        order         *Order
151        setupMocks    func(*MockOrderRepository, *MockPaymentGateway, *MockNotificationService)
152        expectedError string
153    }{
154        {
155            name: "successful order",
156            order: &Order{
157                ID:     "order-123",
158                UserID: "user-456",
159                Amount: 99.99,
160            },
161            setupMocks: func(repo *MockOrderRepository, payment *MockPaymentGateway, notify *MockNotificationService) {
162                payment.On("ProcessPayment", mock.Anything, 99.99).
163                    Return("payment-789", nil)
164                repo.On("Create", mock.Anything, mock.AnythingOfType("*main.Order")).
165                    Return(nil)
166                repo.On("UpdateStatus", mock.Anything, "order-123", "confirmed").
167                    Return(nil)
168                notify.On("SendOrderConfirmation", mock.Anything, "user-456", "order-123").
169                    Return(nil)
170            },
171            expectedError: "",
172        },
173        {
174            name: "invalid amount",
175            order: &Order{
176                ID:     "order-123",
177                UserID: "user-456",
178                Amount: -10,
179            },
180            setupMocks:    func(repo *MockOrderRepository, payment *MockPaymentGateway, notify *MockNotificationService) {},
181            expectedError: "invalid order amount",
182        },
183        {
184            name: "payment failure",
185            order: &Order{
186                ID:     "order-123",
187                UserID: "user-456",
188                Amount: 99.99,
189            },
190            setupMocks: func(repo *MockOrderRepository, payment *MockPaymentGateway, notify *MockNotificationService) {
191                payment.On("ProcessPayment", mock.Anything, 99.99).
192                    Return("", errors.New("insufficient funds"))
193            },
194            expectedError: "payment processing failed",
195        },
196        {
197            name: "database failure",
198            order: &Order{
199                ID:     "order-123",
200                UserID: "user-456",
201                Amount: 99.99,
202            },
203            setupMocks: func(repo *MockOrderRepository, payment *MockPaymentGateway, notify *MockNotificationService) {
204                payment.On("ProcessPayment", mock.Anything, 99.99).
205                    Return("payment-789", nil)
206                repo.On("Create", mock.Anything, mock.AnythingOfType("*main.Order")).
207                    Return(errors.New("database connection failed"))
208            },
209            expectedError: "failed to save order",
210        },
211    }
212
213    for _, tt := range tests {
214        t.Run(tt.name, func(t *testing.T) {
215            // Setup
216            mockRepo := new(MockOrderRepository)
217            mockPayment := new(MockPaymentGateway)
218            mockNotify := new(MockNotificationService)
219            logger := zerolog.Nop()
220
221            tt.setupMocks(mockRepo, mockPayment, mockNotify)
222
223            service := NewOrderService(mockRepo, mockPayment, mockNotify, logger)
224
225            // Execute
226            err := service.PlaceOrder(context.Background(), tt.order)
227
228            // Assert
229            if tt.expectedError != "" {
230                require.Error(t, err)
231                assert.Contains(t, err.Error(), tt.expectedError)
232            } else {
233                require.NoError(t, err)
234                assert.Equal(t, "confirmed", tt.order.Status)
235                assert.NotEmpty(t, tt.order.PaymentID)
236            }
237
238            // Verify mocks
239            mockRepo.AssertExpectations(t)
240            mockPayment.AssertExpectations(t)
241        })
242    }
243}
244
245// Test suite with setup/teardown
246type OrderServiceTestSuite struct {
247    suite.Suite
248    repo    *MockOrderRepository
249    payment *MockPaymentGateway
250    notify  *MockNotificationService
251    service *OrderService
252    logger  zerolog.Logger
253}
254
255func (suite *OrderServiceTestSuite) SetupTest() {
256    suite.repo = new(MockOrderRepository)
257    suite.payment = new(MockPaymentGateway)
258    suite.notify = new(MockNotificationService)
259    suite.logger = zerolog.Nop()
260    suite.service = NewOrderService(suite.repo, suite.payment, suite.notify, suite.logger)
261}
262
263func (suite *OrderServiceTestSuite) TearDownTest() {
264    suite.repo.AssertExpectations(suite.T())
265    suite.payment.AssertExpectations(suite.T())
266}
267
268func (suite *OrderServiceTestSuite) TestPlaceOrder_Success() {
269    order := &Order{
270        ID:     "order-123",
271        UserID: "user-456",
272        Amount: 99.99,
273    }
274
275    suite.payment.On("ProcessPayment", mock.Anything, 99.99).
276        Return("payment-789", nil)
277    suite.repo.On("Create", mock.Anything, order).
278        Return(nil)
279    suite.repo.On("UpdateStatus", mock.Anything, "order-123", "confirmed").
280        Return(nil)
281
282    err := suite.service.PlaceOrder(context.Background(), order)
283
284    suite.NoError(err)
285    suite.Equal("confirmed", order.Status)
286    suite.Equal("payment-789", order.PaymentID)
287}
288
289func (suite *OrderServiceTestSuite) TestPlaceOrder_ValidationErrors() {
290    testCases := []struct {
291        name  string
292        order *Order
293        error string
294    }{
295        {
296            name:  "negative amount",
297            order: &Order{ID: "1", UserID: "user", Amount: -10},
298            error: "invalid order amount",
299        },
300        {
301            name:  "missing user ID",
302            order: &Order{ID: "1", Amount: 100},
303            error: "user ID is required",
304        },
305    }
306
307    for _, tc := range testCases {
308        suite.Run(tc.name, func() {
309            err := suite.service.PlaceOrder(context.Background(), tc.order)
310            suite.Error(err)
311            suite.Contains(err.Error(), tc.error)
312        })
313    }
314}
315
316func TestOrderServiceTestSuite(t *testing.T) {
317    suite.Run(t, new(OrderServiceTestSuite))
318}

Exercise 4: Observability Stack Integration

Build a production observability system that:

• Implements structured logging with Zerolog
• Collects metrics with Prometheus
• Provides distributed tracing context
• Includes health checks and readiness probes
• Creates operational dashboards

Requirements:

• Request/response logging with correlation IDs
• Business and system metrics
• Error rate and latency tracking
• Resource utilization metrics
• Exportable metrics endpoint

Starter Code:

 1// Your task: Complete this implementation
 2type ObservabilityMiddleware struct {
 3    logger  zerolog.Logger
 4    metrics *MetricsCollector
 5}
 6
 7// TODO: Implement logging middleware
 8func LoggingMiddleware() func(http.Handler) http.Handler {
 9    // TODO: Add request ID
10    // TODO: Log request details
11    // TODO: Measure latency
12    // TODO: Log response status
13}
14
15// TODO: Implement metrics collection
16type MetricsCollector struct {
17    // TODO: Define metrics
18}
19
20// TODO: Implement health checks
21func HealthCheckHandler(w http.ResponseWriter, r *http.Request) {
22    // TODO: Check database
23    // TODO: Check Redis
24    // TODO: Check external services
25    // TODO: Return aggregated health
26}

Solution

  1// Complete solution implementation
  2package main
  3
  4import (
  5    "context"
  6    "encoding/json"
  7    "fmt"
  8    "net/http"
  9    "time"
 10
 11    "github.com/prometheus/client_golang/prometheus"
 12    "github.com/prometheus/client_golang/prometheus/promauto"
 13    "github.com/prometheus/client_golang/prometheus/promhttp"
 14    "github.com/rs/zerolog"
 15)
 16
 17// Metrics collector
 18type MetricsCollector struct {
 19    requestsTotal   *prometheus.CounterVec
 20    requestDuration *prometheus.HistogramVec
 21    activeRequests  prometheus.Gauge
 22    errorRate       *prometheus.CounterVec
 23    dbConnections   prometheus.Gauge
 24    cacheHitRate    *prometheus.CounterVec
 25}
 26
 27func NewMetricsCollector() *MetricsCollector {
 28    return &MetricsCollector{
 29        requestsTotal: promauto.NewCounterVec(
 30            prometheus.CounterOpts{
 31                Name: "http_requests_total",
 32                Help: "Total number of HTTP requests",
 33            },
 34            []string{"method", "endpoint", "status"},
 35        ),
 36        requestDuration: promauto.NewHistogramVec(
 37            prometheus.HistogramOpts{
 38                Name:    "http_request_duration_seconds",
 39                Help:    "HTTP request latency",
 40                Buckets: []float64{.001, .005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10},
 41            },
 42            []string{"method", "endpoint"},
 43        ),
 44        activeRequests: promauto.NewGauge(
 45            prometheus.GaugeOpts{
 46                Name: "http_active_requests",
 47                Help: "Number of active HTTP requests",
 48            },
 49        ),
 50        errorRate: promauto.NewCounterVec(
 51            prometheus.CounterOpts{
 52                Name: "http_errors_total",
 53                Help: "Total number of HTTP errors",
 54            },
 55            []string{"method", "endpoint", "error_type"},
 56        ),
 57        dbConnections: promauto.NewGauge(
 58            prometheus.GaugeOpts{
 59                Name: "database_connections_active",
 60                Help: "Number of active database connections",
 61            },
 62        ),
 63        cacheHitRate: promauto.NewCounterVec(
 64            prometheus.CounterOpts{
 65                Name: "cache_operations_total",
 66                Help: "Total cache operations",
 67            },
 68            []string{"operation", "result"},
 69        ),
 70    }
 71}
 72
 73// Observability middleware
 74type ObservabilityMiddleware struct {
 75    logger  zerolog.Logger
 76    metrics *MetricsCollector
 77}
 78
 79func NewObservabilityMiddleware(logger zerolog.Logger, metrics *MetricsCollector) *ObservabilityMiddleware {
 80    return &ObservabilityMiddleware{
 81        logger:  logger,
 82        metrics: metrics,
 83    }
 84}
 85
 86// Logging and metrics middleware
 87func (o *ObservabilityMiddleware) Handler(next http.Handler) http.Handler {
 88    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 89        start := time.Now()
 90
 91        // Generate correlation ID
 92        requestID := r.Header.Get("X-Request-ID")
 93        if requestID == "" {
 94            requestID = fmt.Sprintf("%d", time.Now().UnixNano())
 95        }
 96
 97        // Create request logger
 98        reqLogger := o.logger.With().
 99            Str("request_id", requestID).
100            Str("method", r.Method).
101            Str("path", r.URL.Path).
102            Str("remote_addr", r.RemoteAddr).
103            Str("user_agent", r.UserAgent()).
104            Logger()
105
106        // Add to context
107        ctx := reqLogger.WithContext(r.Context())
108        r = r.WithContext(ctx)
109
110        // Track active requests
111        o.metrics.activeRequests.Inc()
112        defer o.metrics.activeRequests.Dec()
113
114        // Wrap response writer
115        wrappedWriter := &responseWriter{
116            ResponseWriter: w,
117            statusCode:     200,
118        }
119
120        // Log request start
121        reqLogger.Info().Msg("Request started")
122
123        // Process request
124        next.ServeHTTP(wrappedWriter, r)
125
126        // Calculate duration
127        duration := time.Since(start)
128
129        // Record metrics
130        o.metrics.requestsTotal.WithLabelValues(
131            r.Method,
132            r.URL.Path,
133            fmt.Sprintf("%d", wrappedWriter.statusCode),
134        ).Inc()
135
136        o.metrics.requestDuration.WithLabelValues(
137            r.Method,
138            r.URL.Path,
139        ).Observe(duration.Seconds())
140
141        // Track errors
142        if wrappedWriter.statusCode >= 400 {
143            errorType := "client_error"
144            if wrappedWriter.statusCode >= 500 {
145                errorType = "server_error"
146            }
147
148            o.metrics.errorRate.WithLabelValues(
149                r.Method,
150                r.URL.Path,
151                errorType,
152            ).Inc()
153        }
154
155        // Log request completion
156        logEvent := reqLogger.Info()
157        if wrappedWriter.statusCode >= 400 {
158            logEvent = reqLogger.Warn()
159        }
160        if wrappedWriter.statusCode >= 500 {
161            logEvent = reqLogger.Error()
162        }
163
164        logEvent.
165            Int("status", wrappedWriter.statusCode).
166            Dur("duration", duration).
167            Int64("bytes_written", wrappedWriter.bytesWritten).
168            Msg("Request completed")
169    })
170}
171
172type responseWriter struct {
173    http.ResponseWriter
174    statusCode   int
175    bytesWritten int64
176}
177
178func (rw *responseWriter) WriteHeader(statusCode int) {
179    rw.statusCode = statusCode
180    rw.ResponseWriter.WriteHeader(statusCode)
181}
182
183func (rw *responseWriter) Write(b []byte) (int, error) {
184    n, err := rw.ResponseWriter.Write(b)
185    rw.bytesWritten += int64(n)
186    return n, err
187}
188
189// Health check system
190type HealthChecker struct {
191    checks  map[string]HealthCheck
192    timeout time.Duration
193}
194
195type HealthCheck func(ctx context.Context) error
196
197type HealthStatus struct {
198    Status string                       `json:"status"`
199    Checks map[string]ComponentHealth   `json:"checks"`
200    Time   time.Time                    `json:"timestamp"`
201}
202
203type ComponentHealth struct {
204    Status  string `json:"status"`
205    Message string `json:"message,omitempty"`
206}
207
208func NewHealthChecker(timeout time.Duration) *HealthChecker {
209    return &HealthChecker{
210        checks:  make(map[string]HealthCheck),
211        timeout: timeout,
212    }
213}
214
215func (h *HealthChecker) RegisterCheck(name string, check HealthCheck) {
216    h.checks[name] = check
217}
218
219func (h *HealthChecker) Check(ctx context.Context) HealthStatus {
220    ctx, cancel := context.WithTimeout(ctx, h.timeout)
221    defer cancel()
222
223    status := HealthStatus{
224        Status: "healthy",
225        Checks: make(map[string]ComponentHealth),
226        Time:   time.Now(),
227    }
228
229    for name, check := range h.checks {
230        err := check(ctx)
231        if err != nil {
232            status.Status = "unhealthy"
233            status.Checks[name] = ComponentHealth{
234                Status:  "unhealthy",
235                Message: err.Error(),
236            }
237        } else {
238            status.Checks[name] = ComponentHealth{
239                Status: "healthy",
240            }
241        }
242    }
243
244    return status
245}
246
247func (h *HealthChecker) Handler(w http.ResponseWriter, r *http.Request) {
248    status := h.Check(r.Context())
249
250    w.Header().Set("Content-Type", "application/json")
251    if status.Status != "healthy" {
252        w.WriteHeader(http.StatusServiceUnavailable)
253    }
254
255    json.NewEncoder(w).Encode(status)
256}
257
258// Example usage
259func main() {
260    // Setup logger
261    logger := zerolog.New(os.Stdout).With().Timestamp().Logger()
262
263    // Setup metrics
264    metrics := NewMetricsCollector()
265
266    // Setup middleware
267    obs := NewObservabilityMiddleware(logger, metrics)
268
269    // Setup health checks
270    health := NewHealthChecker(5 * time.Second)
271
272    // Register health checks
273    health.RegisterCheck("database", func(ctx context.Context) error {
274        // Check database connection
275        return nil
276    })
277
278    health.RegisterCheck("redis", func(ctx context.Context) error {
279        // Check Redis connection
280        return nil
281    })
282
283    // Setup router
284    mux := http.NewServeMux()
285
286    // Application endpoints
287    mux.HandleFunc("/api/users", func(w http.ResponseWriter, r *http.Request) {
288        logger := zerolog.Ctx(r.Context())
289        logger.Info().Msg("Processing users request")
290
291        // Simulate work
292        time.Sleep(50 * time.Millisecond)
293
294        w.WriteHeader(http.StatusOK)
295        json.NewEncoder(w).Encode(map[string]string{
296            "message": "Users endpoint",
297        })
298    })
299
300    // Observability endpoints
301    mux.HandleFunc("/health", health.Handler)
302    mux.Handle("/metrics", promhttp.Handler())
303
304    // Apply middleware
305    handler := obs.Handler(mux)
306
307    logger.Info().Int("port", 8080).Msg("Starting server")
308    http.ListenAndServe(":8080", handler)
309}

Exercise 5: Configuration Management System

Build a comprehensive configuration system that:

• Supports multiple config sources (files, env vars, remote)
• Provides type-safe configuration access
• Enables hot-reloading of configuration
• Validates configuration on startup
• Supports feature flags

Requirements:

• Viper for configuration management
• Environment-specific configs (dev/staging/prod)
• Secret management integration
• Configuration validation
• Feature flag system

Starter Code:

 1// Your task: Complete this implementation
 2type AppConfig struct {
 3    Server   ServerConfig
 4    Database DatabaseConfig
 5    Features FeatureFlags
 6}
 7
 8// TODO: Implement config loading
 9func LoadConfig(env string) (*AppConfig, error) {
10    // TODO: Load from file
11    // TODO: Override with environment variables
12    // TODO: Validate configuration
13    // TODO: Set up watchers
14}
15
16// TODO: Implement validation
17func ValidateConfig(config *AppConfig) error {
18    // TODO: Validate required fields
19    // TODO: Check value ranges
20    // TODO: Verify dependencies
21}
22
23// TODO: Implement feature flags
24func IsFeatureEnabled(flag string) bool {
25    // TODO: Check feature flag
26    // TODO: Support percentage rollout
27}

Solution

  1// Complete solution implementation
  2package main
  3
  4import (
  5    "errors"
  6    "fmt"
  7    "os"
  8    "strings"
  9    "time"
 10
 11    "github.com/fsnotify/fsnotify"
 12    "github.com/go-playground/validator/v10"
 13    "github.com/rs/zerolog"
 14    "github.com/rs/zerolog/log"
 15    "github.com/spf13/viper"
 16)
 17
 18// Configuration structures
 19type AppConfig struct {
 20    Environment string         `mapstructure:"environment" validate:"required,oneof=development staging production"`
 21    Server      ServerConfig   `mapstructure:"server" validate:"required"`
 22    Database    DatabaseConfig `mapstructure:"database" validate:"required"`
 23    Redis       RedisConfig    `mapstructure:"redis" validate:"required"`
 24    Features    FeatureFlags   `mapstructure:"features"`
 25    Logging     LoggingConfig  `mapstructure:"logging" validate:"required"`
 26}
 27
 28type ServerConfig struct {
 29    Host            string        `mapstructure:"host" validate:"required"`
 30    Port            int           `mapstructure:"port" validate:"required,min=1,max=65535"`
 31    ReadTimeout     time.Duration `mapstructure:"read_timeout" validate:"required"`
 32    WriteTimeout    time.Duration `mapstructure:"write_timeout" validate:"required"`
 33    ShutdownTimeout time.Duration `mapstructure:"shutdown_timeout" validate:"required"`
 34    TLS             TLSConfig     `mapstructure:"tls"`
 35}
 36
 37type TLSConfig struct {
 38    Enabled  bool   `mapstructure:"enabled"`
 39    CertFile string `mapstructure:"cert_file"`
 40    KeyFile  string `mapstructure:"key_file"`
 41}
 42
 43type DatabaseConfig struct {
 44    Host            string        `mapstructure:"host" validate:"required"`
 45    Port            int           `mapstructure:"port" validate:"required,min=1,max=65535"`
 46    User            string        `mapstructure:"user" validate:"required"`
 47    Password        string        `mapstructure:"password" validate:"required"`
 48    DBName          string        `mapstructure:"dbname" validate:"required"`
 49    MaxOpenConns    int           `mapstructure:"max_open_conns" validate:"required,min=1,max=100"`
 50    MaxIdleConns    int           `mapstructure:"max_idle_conns" validate:"required,min=1,max=100"`
 51    ConnMaxLifetime time.Duration `mapstructure:"conn_max_lifetime" validate:"required"`
 52}
 53
 54type RedisConfig struct {
 55    Host     string `mapstructure:"host" validate:"required"`
 56    Port     int    `mapstructure:"port" validate:"required,min=1,max=65535"`
 57    Password string `mapstructure:"password"`
 58    DB       int    `mapstructure:"db" validate:"min=0,max=15"`
 59}
 60
 61type FeatureFlags struct {
 62    EnableNewUI      bool              `mapstructure:"enable_new_ui"`
 63    EnableAnalytics  bool              `mapstructure:"enable_analytics"`
 64    EnableBetaAPI    bool              `mapstructure:"enable_beta_api"`
 65    RolloutPercentage map[string]int   `mapstructure:"rollout_percentage"`
 66}
 67
 68type LoggingConfig struct {
 69    Level  string `mapstructure:"level" validate:"required,oneof=debug info warn error"`
 70    Format string `mapstructure:"format" validate:"required,oneof=json console"`
 71}
 72
 73// Config manager
 74type ConfigManager struct {
 75    config    *AppConfig
 76    viper     *viper.Viper
 77    validator *validator.Validate
 78    logger    zerolog.Logger
 79    callbacks []func(*AppConfig)
 80}
 81
 82func NewConfigManager(logger zerolog.Logger) *ConfigManager {
 83    return &ConfigManager{
 84        viper:     viper.New(),
 85        validator: validator.New(),
 86        logger:    logger,
 87        callbacks: make([]func(*AppConfig), 0),
 88    }
 89}
 90
 91// Load configuration with multiple sources
 92func (cm *ConfigManager) Load(env string) error {
 93    // Set config file
 94    cm.viper.SetConfigName(fmt.Sprintf("config.%s", env))
 95    cm.viper.SetConfigType("yaml")
 96    cm.viper.AddConfigPath(".")
 97    cm.viper.AddConfigPath("./config")
 98    cm.viper.AddConfigPath("/etc/myapp/")
 99
100    // Enable environment variable override
101    cm.viper.AutomaticEnv()
102    cm.viper.SetEnvPrefix("APP")
103    cm.viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
104
105    // Set defaults
106    cm.setDefaults(env)
107
108    // Read config file
109    if err := cm.viper.ReadInConfig(); err != nil {
110        if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
111            return fmt.Errorf("failed to read config file: %w", err)
112        }
113        cm.logger.Warn().Msg("No config file found, using defaults and environment variables")
114    } else {
115        cm.logger.Info().Str("file", cm.viper.ConfigFileUsed()).Msg("Loaded config file")
116    }
117
118    // Unmarshal config
119    var config AppConfig
120    if err := cm.viper.Unmarshal(&config); err != nil {
121        return fmt.Errorf("failed to unmarshal config: %w", err)
122    }
123
124    // Validate config
125    if err := cm.ValidateConfig(&config); err != nil {
126        return fmt.Errorf("config validation failed: %w", err)
127    }
128
129    cm.config = &config
130    return nil
131}
132
133// Set default values
134func (cm *ConfigManager) setDefaults(env string) {
135    cm.viper.SetDefault("environment", env)
136
137    // Server defaults
138    cm.viper.SetDefault("server.host", "0.0.0.0")
139    cm.viper.SetDefault("server.port", 8080)
140    cm.viper.SetDefault("server.read_timeout", "10s")
141    cm.viper.SetDefault("server.write_timeout", "10s")
142    cm.viper.SetDefault("server.shutdown_timeout", "30s")
143    cm.viper.SetDefault("server.tls.enabled", false)
144
145    // Database defaults
146    cm.viper.SetDefault("database.host", "localhost")
147    cm.viper.SetDefault("database.port", 5432)
148    cm.viper.SetDefault("database.max_open_conns", 25)
149    cm.viper.SetDefault("database.max_idle_conns", 5)
150    cm.viper.SetDefault("database.conn_max_lifetime", "5m")
151
152    // Redis defaults
153    cm.viper.SetDefault("redis.host", "localhost")
154    cm.viper.SetDefault("redis.port", 6379)
155    cm.viper.SetDefault("redis.db", 0)
156
157    // Feature flag defaults
158    cm.viper.SetDefault("features.enable_new_ui", false)
159    cm.viper.SetDefault("features.enable_analytics", true)
160    cm.viper.SetDefault("features.enable_beta_api", false)
161
162    // Logging defaults
163    cm.viper.SetDefault("logging.level", "info")
164    cm.viper.SetDefault("logging.format", "json")
165
166    // Environment-specific defaults
167    if env == "development" {
168        cm.viper.SetDefault("logging.level", "debug")
169        cm.viper.SetDefault("logging.format", "console")
170    }
171}
172
173// Validate configuration
174func (cm *ConfigManager) ValidateConfig(config *AppConfig) error {
175    if err := cm.validator.Struct(config); err != nil {
176        return fmt.Errorf("validation error: %w", err)
177    }
178
179    // Custom validation
180    if config.Database.MaxIdleConns > config.Database.MaxOpenConns {
181        return errors.New("max_idle_conns cannot exceed max_open_conns")
182    }
183
184    if config.Server.TLS.Enabled {
185        if config.Server.TLS.CertFile == "" || config.Server.TLS.KeyFile == "" {
186            return errors.New("TLS cert_file and key_file are required when TLS is enabled")
187        }
188    }
189
190    // Check secret values from environment
191    if config.Database.Password == "" {
192        return errors.New("database password is required")
193    }
194
195    return nil
196}
197
198// Watch for config changes
199func (cm *ConfigManager) Watch() {
200    cm.viper.WatchConfig()
201    cm.viper.OnConfigChange(func(e fsnotify.Event) {
202        cm.logger.Info().Str("file", e.Name).Msg("Config file changed")
203
204        // Reload config
205        var newConfig AppConfig
206        if err := cm.viper.Unmarshal(&newConfig); err != nil {
207            cm.logger.Error().Err(err).Msg("Failed to unmarshal config")
208            return
209        }
210
211        // Validate new config
212        if err := cm.ValidateConfig(&newConfig); err != nil {
213            cm.logger.Error().Err(err).Msg("New config validation failed")
214            return
215        }
216
217        // Update config
218        cm.config = &newConfig
219
220        // Notify callbacks
221        for _, callback := range cm.callbacks {
222            callback(&newConfig)
223        }
224
225        cm.logger.Info().Msg("Config reloaded successfully")
226    })
227}
228
229// Register callback for config changes
230func (cm *ConfigManager) OnConfigChange(callback func(*AppConfig)) {
231    cm.callbacks = append(cm.callbacks, callback)
232}
233
234// Get current config
235func (cm *ConfigManager) Config() *AppConfig {
236    return cm.config
237}
238
239// Feature flag checks
240func (cm *ConfigManager) IsFeatureEnabled(feature string) bool {
241    switch feature {
242    case "new_ui":
243        return cm.config.Features.EnableNewUI
244    case "analytics":
245        return cm.config.Features.EnableAnalytics
246    case "beta_api":
247        return cm.config.Features.EnableBetaAPI
248    default:
249        return false
250    }
251}
252
253// Check feature with percentage rollout
254func (cm *ConfigManager) IsFeatureEnabledForUser(feature string, userID string) bool {
255    // Check if feature is globally enabled
256    if !cm.IsFeatureEnabled(feature) {
257        return false
258    }
259
260    // Check rollout percentage
261    if percentage, ok := cm.config.Features.RolloutPercentage[feature]; ok {
262        // Simple hash-based rollout
263        hash := 0
264        for _, c := range userID {
265            hash = (hash * 31) + int(c)
266        }
267        return (hash % 100) < percentage
268    }
269
270    return true
271}
272
273// Example usage
274func main() {
275    logger := zerolog.New(os.Stdout).With().Timestamp().Logger()
276
277    // Get environment
278    env := os.Getenv("APP_ENV")
279    if env == "" {
280        env = "development"
281    }
282
283    // Create config manager
284    configMgr := NewConfigManager(logger)
285
286    // Load configuration
287    if err := configMgr.Load(env); err != nil {
288        log.Fatal().Err(err).Msg("Failed to load configuration")
289    }
290
291    config := configMgr.Config()
292
293    logger.Info().
294        Str("environment", config.Environment).
295        Int("port", config.Server.Port).
296        Str("log_level", config.Logging.Level).
297        Msg("Configuration loaded")
298
299    // Register config change handler
300    configMgr.OnConfigChange(func(newConfig *AppConfig) {
301        logger.Info().Msg("Configuration changed, updating application")
302        // Update application components
303    })
304
305    // Start config watcher
306    configMgr.Watch()
307
308    // Check feature flags
309    if configMgr.IsFeatureEnabled("new_ui") {
310        logger.Info().Msg("New UI is enabled")
311    }
312
313    if configMgr.IsFeatureEnabledForUser("beta_api", "user-123") {
314        logger.Info().Str("user", "user-123").Msg("Beta API enabled for user")
315    }
316
317    // Print configuration
318    fmt.Printf("\n=== Configuration ===\n")
319    fmt.Printf("Environment: %s\n", config.Environment)
320    fmt.Printf("Server: %s:%d\n", config.Server.Host, config.Server.Port)
321    fmt.Printf("Database: %s@%s:%d/%s\n",
322        config.Database.User,
323        config.Database.Host,
324        config.Database.Port,
325        config.Database.DBName)
326    fmt.Printf("Redis: %s:%d (DB %d)\n",
327        config.Redis.Host,
328        config.Redis.Port,
329        config.Redis.DB)
330    fmt.Printf("Features:\n")
331    fmt.Printf("  - New UI: %v\n", config.Features.EnableNewUI)
332    fmt.Printf("  - Analytics: %v\n", config.Features.EnableAnalytics)
333    fmt.Printf("  - Beta API: %v\n", config.Features.EnableBetaAPI)
334}

Further Reading

• Go Package Discovery - Official package repository
• Awesome Go - Curated list of Go libraries
• Gin Documentation - Comprehensive Gin guide
• GORM Guide - ORM documentation and patterns
• Go Modules Reference - Dependency management

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Previous: 15 Testing and Quality Assurance | Next: 17 Debugging Go Applications

Summary

Key Takeaways

🎯 Library Selection Strategy:

• Start with standard library
• Add libraries only when they solve specific problems
• Evaluate based on maintenance, community, and compatibility
• Prefer libraries that integrate well with Go idioms

🔧 Integration Patterns:

• Use dependency injection for testability
• Implement proper error handling and logging
• Create abstraction layers for major components
• Follow the repository pattern for data access

⚡ Performance Considerations:

• Profile before optimizing
• Consider the trade-offs between convenience and performance
• Use libraries appropriate for your scale requirements
• Monitor resource usage in production

Next Steps in Your Learning Journey

📚 Recommended Learning Path:

1. Practice the exercises - Build hands-on experience with library integration
2. Study production patterns - Look at open-source Go projects for real-world examples
3. Experiment with different libraries - Try alternatives to find what works best for you
4. Contribute to open source - Understand library maintenance and best practices

🛠️ Advanced Topics to Explore:

• Custom middleware development - Build your own Gin/Echo middleware
• Database optimization - Advanced GORM/sqlx patterns and connection pooling
• Testing strategies - Comprehensive testing with testify and mocking
• Performance tuning - Profiling and optimization techniques

🚀 Production Readiness:

• Study deployment patterns for Go applications
• Learn about observability and monitoring
• Understand security best practices for web services
• Explore containerization and orchestration

Remember: The best Go developers don't know all libraries—they know how to evaluate, integrate, and use the right libraries for each specific problem.