isle/go/daemon/daemon.go

// Package daemon contains types and functions related specifically to the
// isle daemon.
package daemon

import (
	"fmt"
	"io"
	"isle/yamlutil"
	"os"
	"path/filepath"

	"github.com/imdario/mergo"
	"gopkg.in/yaml.v3"
)

func defaultConfigPath(appDirPath string) string {
	return filepath.Join(appDirPath, "etc", "daemon.yml")
}

// CopyDefaultConfig copies the daemon config file embedded in the AppDir into
// the given io.Writer.
func CopyDefaultConfig(into io.Writer, appDirPath string) error {

	defaultConfigPath := defaultConfigPath(appDirPath)

	f, err := os.Open(defaultConfigPath)
	if err != nil {
		return fmt.Errorf("opening daemon config at %q: %w", defaultConfigPath, err)
	}

	defer f.Close()

	if _, err := io.Copy(into, f); err != nil {
		return fmt.Errorf("copying daemon config from %q: %w", defaultConfigPath, err)
	}

	return nil
}

// LoadConfig loads the daemon config from userConfigPath, merges it with
// the default found in the appDirPath, and returns the result.
//
// If userConfigPath is not given then the default is loaded and returned.
func LoadConfig(
	appDirPath, userConfigPath string,
) (
	Config, error,
) {

	defaultConfigPath := defaultConfigPath(appDirPath)

	var fullDaemon map[string]interface{}

	if err := yamlutil.LoadYamlFile(&fullDaemon, defaultConfigPath); err != nil {
		return Config{}, fmt.Errorf("parsing default daemon config file: %w", err)
	}

	if userConfigPath != "" {

		var daemonConfig map[string]interface{}
		if err := yamlutil.LoadYamlFile(&daemonConfig, userConfigPath); err != nil {
			return Config{}, fmt.Errorf("parsing %q: %w", userConfigPath, err)
		}

		err := mergo.Merge(&fullDaemon, daemonConfig, mergo.WithOverride)
		if err != nil {
			return Config{}, fmt.Errorf("merging contents of file %q: %w", userConfigPath, err)
		}
	}

	fullDaemonB, err := yaml.Marshal(fullDaemon)

	if err != nil {
		return Config{}, fmt.Errorf("yaml marshaling: %w", err)
	}

	var config Config
	if err := yaml.Unmarshal(fullDaemonB, &config); err != nil {
		return Config{}, fmt.Errorf("yaml unmarshaling back into Config struct: %w", err)
	}

	config.fillDefaults()

	return config, nil
}