157 lines
8.1 KiB
Markdown
157 lines
8.1 KiB
Markdown
# lixenwraith/config LLM Usage Guide
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This guide details the `lixenwraith/config` package for thread-safe Go configuration. It supports multiple sources (files, environment, CLI), type-safe struct population, and live reconfiguration.
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## Quick Start: Recommended Usage
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The recommended pattern uses the **Builder** with a **target struct**. This provides compile-time type safety and eliminates the need for runtime type assertions.
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```go
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package main
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import (
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"fmt"
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"log"
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"os"
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"github.com/lixenwraith/config"
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)
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// 1. Define your application's configuration struct.
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type AppConfig struct {
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Server struct {
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Host string `toml:"host"`
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Port int `toml:"port"`
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} `toml:"server"`
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Debug bool `toml:"debug"`
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}
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func main() {
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// 2. Create a target instance with defaults.
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// Method A: Direct initialization (cleaner for simple defaults)
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target := &AppConfig{}
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target.Server.Host = "localhost"
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target.Server.Port = 8080
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// Method B: Use WithDefaults() for explicit separation (shown below)
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// 3. Use the builder to configure and load all sources.
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cfg, err := config.NewBuilder().
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WithTarget(target). // Enable type-safe mode and register struct fields.
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// WithDefaults(&AppConfig{...}), // Optional: Override defaults from WithTarget.
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WithFile("config.toml"). // Load from file (supports .toml, .json, .yaml).
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WithEnvPrefix("APP_"). // Load from environment (e.g., APP_SERVER_PORT).
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WithArgs(os.Args[1:]). // Load from command-line flags (e.g., --server.port=9090).
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Build() // Build the final config object.
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if err != nil {
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log.Fatalf("Config build failed: %v", err)
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}
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// 4. Access the fully populated, type-safe struct.
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// The `target` variable is now populated with the final merged values.
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fmt.Printf("Running on %s:%d\n", target.Server.Host, target.Server.Port)
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// Or, retrieve the updated struct at any time (e.g., after a live reload).
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latest, _ := cfg.AsStruct()
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latestConfig := latest.(*AppConfig)
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fmt.Printf("Debug mode: %v\n", latestConfig.Debug)
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}
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```
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## Supported Formats: TOML, JSON, YAML
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The package supports multiple file formats. The format is auto-detected from the file extension (`.toml`, `.json`, `.yaml`, `.yml`) or file content.
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* To specify a format explicitly, use `Builder.WithFileFormat("json")`.
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* The default struct tag for field mapping is `toml`, but can be changed with `Builder.WithTagName("json")`.
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## Builder Pattern
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The `Builder` is the primary way to construct a `Config` instance.
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```go
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// NewBuilder creates a new configuration builder.
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func NewBuilder() *Builder
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// Build finalizes configuration; returns the first of any accumulated errors.
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func (b *Builder) Build() (*Config, error)
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// MustBuild is like Build but panics on fatal errors.
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func (b *Builder) MustBuild() *Config
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```
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### Builder Methods
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* `WithTarget(target any)`: **(Recommended)** Enables type-safe mode. Registers fields from the target struct and allows access via `AsStruct()`. The target's initial values are used as defaults unless `WithDefaults` is also called.
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* `WithDefaults(defaults any)`: Explicitly sets a struct containing default values. Overrides any defaults from `WithTarget`.
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* `WithFile(path string)`: Sets the configuration file path.
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* `WithFileDiscovery(opts FileDiscoveryOptions)`: Enables automatic config file discovery (searches CLI flags, env vars, XDG paths, and current directory).
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* `WithArgs(args []string)`: Sets the command-line arguments to parse (e.g., `--server.port=9090`).
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* `WithEnvPrefix(prefix string)`: Sets the global environment variable prefix (e.g., `MYAPP_`).
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* `WithSources(sources ...Source)`: Overrides the default source precedence order.
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* `WithTypedValidator(fn any)`: **(Recommended for validation)** Adds a type-safe validation function that runs *after* the target struct is populated. The function signature must be `func(c *YourConfigType) error`.
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* `WithValidator(fn ValidatorFunc)`: Adds a validation function that runs *before* type-safe population, operating on the raw `*Config` object.
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* `WithTagName(tagName string)`: Sets the primary struct tag for field mapping (`"toml"`, `"json"`, `"yaml"`).
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* `WithPrefix(prefix string)`: Adds a prefix to all registered paths from a struct.
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* `WithFileFormat(format string)`: Explicitly sets the file format (`"toml"`, `"json"`, `"yaml"`, `"auto"`).
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* `WithSecurityOptions(opts SecurityOptions)`: Sets security options for file loading (path traversal, file size limits).
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* `WithEnvTransform(fn EnvTransformFunc)`: Sets a custom environment variable mapping function.
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* `WithEnvWhitelist(paths ...string)`: Limits environment variable loading to a specific set of paths.
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## Type-Safe Access & Population
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These are the **preferred methods** for accessing configuration data.
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* `AsStruct() (any, error)`: After using `Builder.WithTarget()`, this method returns the populated, type-safe target struct. This is the primary way to access config after initialization or live reload.
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* `Scan(basePath string, target any)`: Populates a struct with values from a specific config path (e.g., `cfg.Scan("server", &serverConf)`).
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* `GetTyped[T](c *Config, path string) (T, error)`: Retrieves a single value and decodes it to type `T`, handling type conversion automatically.
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* `ScanTyped[T](c *Config, basePath ...string) (*T, error)`: A generic wrapper around `Scan` that allocates, populates, and returns a pointer to a struct of type `T`.
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## Live Reconfiguration
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Enable automatic reloading of configuration when the source file changes.
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* `AutoUpdate()`: Enables file watching and automatic reloading with default options.
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* `AutoUpdateWithOptions(opts WatchOptions)`: Enables reloading with custom options (e.g., poll interval, debounce).
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* `StopAutoUpdate()`: Stops the file watcher.
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* `Watch() <-chan string`: Returns a channel that receives the paths of changed values.
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* `WatchFile(filePath string, formatHint ...string)`: Switches the watcher to a new file at runtime.
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* `IsWatching() bool`: Returns `true` if the file watcher is active.
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The watch channel also receives special notifications: `"file_deleted"`, `"permissions_changed"`, `"reload_error:..."`.
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## Source Precedence
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The default order of precedence (highest to lowest) is:
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1. **CLI**: Command-line arguments (`--server.port=9090`)
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2. **Env**: Environment variables (`MYAPP_SERVER_PORT=8888`)
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3. **File**: Configuration file (`config.toml`)
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4. **Default**: Values registered from a struct.
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This order can be changed via `Builder.WithSources()` or `Config.SetPrecedence()`.
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## Dynamic / Legacy Value Access
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These methods are for dynamic key-value access and should be **avoided when a type-safe struct can be used**. They require runtime type assertions.
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* `Get(path string) (any, bool)`: Retrieves the final merged value. The `bool` indicates if the path was registered. Requires a type assertion, e.g., `port := val.(int64)`.
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* `Set(path string, value any)`: Updates a value in the highest priority source. The path must be registered first.
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* `GetSource(path string, source Source) (any, bool)`: Retrieves a value from a specific source layer.
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* `SetSource(path string, source Source, value any)`: Sets a value for a specific source layer.
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## API Reference Summary
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### Core Types
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* `Config`: The primary thread-safe configuration manager.
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* `Source`: A configuration source (`SourceCLI`, `SourceEnv`, `SourceFile`, `SourceDefault`).
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* `LoadOptions`: Options for loading configuration from multiple sources.
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* `Builder`: Fluent API for constructing a `Config` instance.
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### Core Methods
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* `New() *Config`: Creates a new `Config` instance.
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* `Register(path string, defaultValue any)`: Registers a path with a default value.
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* `RegisterStruct(prefix string, structWithDefaults any)`: Recursively registers fields from a struct using `toml` tags.
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* `Validate(required ...string)`: Checks that all specified required paths have been set from a non-default source.
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* `Save(path string)`: Atomically saves the current merged configuration state to a file.
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* `Clone() *Config`: Creates a deep copy of the configuration state.
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* `Debug() string`: Returns a formatted string of all values for debugging. |