config

Overview ¶

Package config loads application configuration from environment variables, .env files, and JSON config files into typed Go structs.

It uses struct tags to map fields to environment variables and supports default values, type coercion, and validation via the request package's existing tag validators.

Quick Start ¶

type AppConfig struct {
    Host     string `env:"HOST"      default:"localhost"  validate:"required"`
    Port     int    `env:"PORT"      default:"8080"       validate:"required,min=1,max=65535"`
    Debug    bool   `env:"DEBUG"     default:"false"`
    DBUrl    string `env:"DB_URL"    validate:"required,url"`
    LogLevel string `env:"LOG_LEVEL" default:"info"       validate:"oneof=debug info warn error"`
}

var cfg AppConfig
if err := config.Load(&cfg); err != nil {
    log.Fatal(err)
}

Struct Tags ¶

• env:"VAR_NAME" — maps the field to the named environment variable
• default:"value" — fallback if env var and config file both miss
• validate:"..." — reuses request package validators (required, min, max, url, etc.)

Source Priority (high to low) ¶

1. Environment variables (always win)
2. .env file (loaded into process env, doesn't override existing)
3. JSON config file (base config layer)
4. default:"..." tags (fallback)

Options ¶

config.Load(&cfg,
    config.WithPrefix("APP"),           // APP_PORT instead of PORT
    config.WithEnvFile(".env"),          // Load .env file
    config.WithJSONFile("config.json"), // Load JSON config as base
    config.WithRequired(),              // Error if files don't exist
)

Supported Types ¶

• string, bool, int/int8/16/32/64, uint variants, float32/64
• time.Duration (parses "5s", "1m30s")
• []string, []int (comma-separated: "a,b,c")
• Nested structs (flattened env: DB_HOST for field DB.Host)

Nested Structs ¶

type Config struct {
    DB struct {
        Host string `env:"HOST" default:"localhost"`
        Port int    `env:"PORT" default:"5432"`
    }
}

// With prefix "APP": reads APP_DB_HOST, APP_DB_PORT
config.Load(&cfg, config.WithPrefix("APP"))

MustLoad ¶

For use in main() or init(), MustLoad panics on error:

var cfg AppConfig
config.MustLoad(&cfg, config.WithEnvFile(".env"))