go-http-server-with-otel/pkg/config/config.go

package config

import (
	"context"
	"flag"
	"fmt"
	"os"
	"runtime/debug"

	"github.com/caarlos0/env/v9"
	"gopkg.in/yaml.v3"
)

// To be set by ldflags in go build command or
// retrieved from build meta below
var Version = "(devel)"

// Calling this will try to load from config if -config is
// provided as a file, and will apply any environment overrides
// on-top of configuration defaults.
// Config is stored in returned context, and can be retrieved
// using config.FromCtx(ctx)
func LoadConfig(ctx context.Context) (context.Context, error) {
	configPath := flag.String("config", "", "Path to the configuration file")
	flag.Parse()

	// Start with defaults
	// Load from config if provided
	// Layer on environment
	cfg, err := loadConfig(*configPath)
	if err != nil {
		return ctx, err
	}

	// Add config to context, and return
	// an updated context
	ctx = cfg.AddToCtx(ctx)
	return ctx, nil
}

func loadConfig(configPath string) (*AppConfig, error) {
	cfg := newAppConfig()

	if configPath != "" {
		file, err := os.Open(configPath)
		if err != nil {
			return nil, fmt.Errorf("could not open config file: %w", err)
		}
		defer file.Close()

		decoder := yaml.NewDecoder(file)
		if err := decoder.Decode(cfg); err != nil {
			return nil, fmt.Errorf("could not decode config file: %w", err)
		}
	}

	if err := env.Parse(cfg); err != nil {
		return nil, fmt.Errorf("could not parse environment variables: %w", err)
	}

	return cfg, nil
}

func getVersion() string {
	if info, ok := debug.ReadBuildInfo(); ok && info.Main.Version != "(devel)" {
		return info.Main.Version
	}
	return Version
}