1. Project Structure

Organize your code in a way that makes it easy to understand and extend. A common structure includes separating your code into folders such as models, handlers, routes, middlewares, utils, and config.

Example structure:

go-rest-api/
|-- main.go
|-- config/
|   |-- config.go
|-- handlers/
|   |-- user.go
|-- models/
|   |-- user.go
|-- routes/
|   |-- routes.go
|-- middlewares/
|   |-- logging.go
|-- utils/
|   |-- helpers.go

2. Environment Configuration

Store configuration settings (like database credentials, port numbers, etc.) in environment variables or configuration files. Use a package like viper to manage configurations.

config/config.go:

package config

import (
    "github.com/spf13/viper"
    "log"
)

type Config struct {
    Port string
    DB   struct {
        Host     string
        Port     string
        User     string
        Password string
        Name     string
    }
}

var AppConfig Config

func LoadConfig() {
    viper.SetConfigName("config")
    viper.AddConfigPath(".")
    viper.AutomaticEnv()

    if err := viper.ReadInConfig(); err != nil {
        log.Fatalf("Error reading config file, %s", err)
    }

    err := viper.Unmarshal(&AppConfig)
    if err != nil {
        log.Fatalf("Unable to decode into struct, %v", err)
    }
}

3. Error Handling

Always handle errors appropriately. Return meaningful error messages and HTTP status codes.

handlers/user.go:

func GetUserHandler(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    id, err := strconv.Atoi(params["id"])
    if err != nil {
        http.Error(w, "Invalid user ID", http.StatusBadRequest)
        return
    }

    user, err := findUserByID(id)
    if err != nil {
        http.Error(w, "User not found", http.StatusNotFound)
        return
    }

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

4. Middlewares

Use middlewares for logging, authentication, and other cross-cutting concerns.

middlewares/logging.go:

package middlewares

import (
    "log"
    "net/http"
    "time"
)

func LoggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        start := time.Now()
        next.ServeHTTP(w, r)
        log.Printf("%s %s %s", r.Method, r.RequestURI, time.Since(start))
    })
}

In main.go or routes/routes.go:

r.Use(middlewares.LoggingMiddleware)

5. JSON Handling

Use proper JSON encoding and decoding. Validate incoming JSON data to ensure it meets the expected structure.

handlers/user.go:

func CreateUserHandler(w http.ResponseWriter, r *http.Request) {
    var user models.User
    if err := json.NewDecoder(r.Body).Decode(&user); err != nil {
        http.Error(w, "Invalid input", http.StatusBadRequest)
        return
    }

    // Validate user data...

    users = append(users, user)

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

6. Database Access

Use a database to store your data. Use a package like gorm for ORM or sqlx for raw SQL queries.

models/user.go:

package models

import "gorm.io/gorm"

type User struct {
    gorm.Model
    Name  string `json:"name"`
    Email string `json:"email"`
}

main.go:

package main

import (
    "github.com/yourusername/go-rest-api/config"
    "github.com/yourusername/go-rest-api/routes"
    "gorm.io/driver/postgres"
    "gorm.io/gorm"
    "log"
    "net/http"
)

func main() {
    config.LoadConfig()

    dsn := "host="   config.AppConfig.DB.Host  
        " user="   config.AppConfig.DB.User  
        " password="   config.AppConfig.DB.Password  
        " dbname="   config.AppConfig.DB.Name  
        " port="   config.AppConfig.DB.Port  
        " sslmode=disable"
    db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
    if err != nil {
        log.Fatalf("Could not connect to the database: %v", err)
    }

    r := routes.NewRouter(db)

    log.Println("Starting server on port", config.AppConfig.Port)
    log.Fatal(http.ListenAndServe(":" config.AppConfig.Port, r))
}

7. Logging

Use a structured logging library like logrus or zap for better logging.

middlewares/logging.go:

package middlewares

import (
    "github.com/sirupsen/logrus"
    "net/http"
    "time"
)

func LoggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        start := time.Now()
        next.ServeHTTP(w, r)
        logrus.WithFields(logrus.Fields{
            "method": r.Method,
            "url":    r.URL.Path,
            "time":   time.Since(start),
        }).Info("handled request")
    })
}

8. Security

Ensure your API is secure by using HTTPS, validating and sanitizing inputs, and implementing proper authentication and authorization.

9. Versioning

Version your API to handle changes without breaking existing clients. This can be done by including the version in the URL, such as /api/v1/users.

10. Documentation

Document your API using tools like Swagger or Postman to provide clear usage instructions for developers.

By following these best practices, you can create a robust, maintainable, and scalable RESTful API in Go.