go_blog/config/config.go

package config

import (
	"crypto/rand"
	"encoding/hex"
	"log"
	"os"
	"path/filepath"
	"runtime"

	"gopkg.in/yaml.v3"
)

// Config holds all application configuration.
type Config struct {
	Database DatabaseConfig `yaml:"database"`
	Web      WebConfig      `yaml:"web"`
	Path     string         `yaml:"path"`
	Secret   string         `yaml:"secret"`
}

// DatabaseConfig holds database-specific configuration.
type DatabaseConfig struct {
	Type string `yaml:"type"` // "sqlite" (default) or "mysql"
	DSN  string `yaml:"dsn"`  // MySQL connection string (required when type is "mysql")
}

// WebConfig holds web-server listening configuration.
type WebConfig struct {
	Port   string   `yaml:"port"`   // TCP port, "" or "0" to disable
	Socket string   `yaml:"socket"` // Unix socket path, "" to disable
	// TrustedProxies lists proxy IPs/CIDRs whose X-Forwarded-For /
	// X-Forwarded-Proto headers are trusted (e.g. the Caddy/nginx box in
	// front of the app). Defaults to loopback. If the app is exposed
	// directly to clients, leave the default so client-supplied
	// X-Forwarded-For cannot spoof the logged IP.
	TrustedProxies []string `yaml:"trusted_proxies"`
}

// defaultTrustedProxies is used when the config omits trusted_proxies.
var defaultTrustedProxies = []string{"127.0.0.1", "::1"}

const defaultPort = "8080"

// mysqlExampleDSN is written into new config files as a reference.
const mysqlExampleDSN = "user:password@tcp(127.0.0.1:3306)/blog_go?charset=utf8mb4&parseTime=True&loc=Local"

// getConfigPath returns the OS-aware config directory and config file path.
func getConfigPath() (dir, file string) {
	switch runtime.GOOS {
	case "windows":
		dir = filepath.Join(".", "win", "etc", "blog_go")
	case "darwin":
		dir = filepath.Join(".", "mac", "etc", "blog_go")
	default:
		dir = filepath.Join("/", "etc", "blog_go")
	}
	file = filepath.Join(dir, "config.yaml")
	return
}

// getDefaultStoragePath returns the OS-aware default storage path.
func getDefaultStoragePath() string {
	switch runtime.GOOS {
	case "windows":
		return filepath.Join(".", "win", "srv", "blog_go")
	case "darwin":
		return filepath.Join(".", "mac", "srv", "blog_go")
	default:
		return filepath.Join("/", "srv", "blog_go")
	}
}

// generateSecret returns a cryptographically random hex string for the
// session secret. A failure of crypto/rand is unrecoverable, so the program
// terminates instead of falling back to a predictable value.
func generateSecret() string {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		log.Fatalf("Failed to generate session secret: %v", err)
	}
	return hex.EncodeToString(b)
}

// getDefaultSocketPath returns the OS-aware default unix socket path.
func getDefaultSocketPath() string {
	if runtime.GOOS == "linux" {
		return "/run/blog_go/web.sock"
	}
	return ""
}
// LoadConfig reads the config file or creates one with defaults.
// If customPath is non-empty, it overrides the OS-aware config file path.
func LoadConfig(customPath string) *Config {
	configDir, configFile := getConfigPath()
	if customPath != "" {
		configFile = customPath
		configDir = filepath.Dir(configFile)
	}
	defaultPath := getDefaultStoragePath()

	// Check if config file exists; create with defaults if not.
	if _, err := os.Stat(configFile); os.IsNotExist(err) {
		log.Printf("Config file not found at %s, creating with defaults...", configFile)
		if err := os.MkdirAll(configDir, 0755); err != nil {
			log.Fatalf("Failed to create config directory %s: %v", configDir, err)
		}

		cfg := &Config{
			Database: DatabaseConfig{
				Type: "sqlite",
				DSN:  mysqlExampleDSN,
			},
			Web: WebConfig{
				Port:   defaultPort,
				Socket: getDefaultSocketPath(),
			},
			Path:   defaultPath,
			Secret: generateSecret(),
		}

		data, err := yaml.Marshal(cfg)
		if err != nil {
			log.Fatalf("Failed to marshal default config: %v", err)
		}

		if err := os.WriteFile(configFile, data, 0644); err != nil {
			log.Fatalf("Failed to write config file %s: %v", configFile, err)
		}
		log.Printf("Default config created at %s", configFile)
		return cfg
	}

	// Read existing config file.
	data, err := os.ReadFile(configFile)
	if err != nil {
		log.Fatalf("Failed to read config file %s: %v", configFile, err)
	}

	cfg := &Config{}
	if err := yaml.Unmarshal(data, cfg); err != nil {
		log.Printf("Warning: malformed config file %s: %v, using defaults", configFile, err)
	}

	return applyDefaults(cfg, defaultPath, configFile)
}

// applyDefaults fills zero-value fields with sensible defaults.
func applyDefaults(cfg *Config, defaultPath, configFile string) *Config {
	// If the entire web block is empty (old config without "web" key),
	// fill default port so the app still starts on 8080.
	if cfg.Web.Port == "" && cfg.Web.Socket == "" {
		cfg.Web.Port = defaultPort
	}
	if len(cfg.Web.TrustedProxies) == 0 {
		cfg.Web.TrustedProxies = defaultTrustedProxies
	}
	if cfg.Database.Type == "" {
		cfg.Database.Type = "sqlite"
	}
	if cfg.Path == "" {
		cfg.Path = defaultPath
	}
	if cfg.Secret == "" {
		// The config file exists but has no secret. Refuse to start: a
		// silently generated fallback would either be predictable (old
		// hostname+pid scheme) or invalidate all sessions on every restart.
		log.Fatalf("Config file %s is missing a session secret. "+
			"Add a random value, e.g. `secret: %s`, and restart.",
			configFile, generateSecret())
	}
	return cfg
}