docker-volume-backup/cmd/backup/config_provider.go

// Copyright 2021-2022 - Offen Authors <hioffen@posteo.de>
// SPDX-License-Identifier: MPL-2.0

package main

import (
	"fmt"
	"os"
	"path/filepath"

	"github.com/joho/godotenv"
	"github.com/offen/envconfig"
)

// envProxy is a function that mimics os.LookupEnv but can read values from any other source
type envProxy func(string) (string, bool)

func loadConfig(lookup envProxy) (*Config, error) {
	envconfig.Lookup = func(key string) (string, bool) {
		value, okValue := lookup(key)
		location, okFile := lookup(key + "_FILE")

		switch {
		case okValue && !okFile: // only value
			return value, true
		case !okValue && okFile: // only file
			contents, err := os.ReadFile(location)
			if err != nil {
				return "", false
			}
			return string(contents), true
		case okValue && okFile: // both
			return "", false
		default: // neither, ignore
			return "", false
		}
	}

	var c = &Config{}
	if err := envconfig.Process("", c); err != nil {
		return nil, fmt.Errorf("loadConfig: failed to process configuration values: %w", err)
	}

	return c, nil
}

func loadEnvVars() (*Config, error) {
	return loadConfig(os.LookupEnv)
}

type configFile struct {
	name              string
	config            *Config
	additionalEnvVars map[string]string
}

func loadEnvFiles(directory string) ([]configFile, error) {
	items, err := os.ReadDir(directory)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, err
		}
		return nil, fmt.Errorf("loadEnvFiles: failed to read files from env directory: %w", err)
	}

	cs := []configFile{}
	for _, item := range items {
		if item.IsDir() {
			continue
		}
		p := filepath.Join(directory, item.Name())
		f, err := os.ReadFile(p)
		if err != nil {
			return nil, fmt.Errorf("loadEnvFiles: error reading %s: %w", item.Name(), err)
		}
		envFile, err := godotenv.Unmarshal(os.ExpandEnv(string(f)))
		if err != nil {
			return nil, fmt.Errorf("loadEnvFiles: error reading config file %s: %w", p, err)
		}
		lookup := func(key string) (string, bool) {
			val, ok := envFile[key]
			if ok {
				return val, ok
			}
			return os.LookupEnv(key)
		}
		c, err := loadConfig(lookup)
		if err != nil {
			return nil, fmt.Errorf("loadEnvFiles: error loading config from file %s: %w", p, err)
		}
		cs = append(cs, configFile{config: c, name: item.Name(), additionalEnvVars: envFile})
	}

	return cs, nil
}