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

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// Copyright 2024 - offen.software <hioffen@posteo.de>
// SPDX-License-Identifier: MPL-2.0
package main
import (
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"bufio"
"fmt"
"os"
"path/filepath"
"strings"
"github.com/joho/godotenv"
"github.com/offen/docker-volume-backup/internal/errwrap"
"github.com/offen/envconfig"
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shell "mvdan.cc/sh/v3/shell"
)
type configStrategy string
const (
configStrategyEnv configStrategy = "env"
configStrategyConfd configStrategy = "confd"
)
// sourceConfiguration returns a list of config objects using the given
// strategy. It should be the single entrypoint for retrieving configuration
// for all consumers.
func sourceConfiguration(strategy configStrategy) ([]*Config, error) {
switch strategy {
case configStrategyEnv:
c, err := loadConfigFromEnvVars()
return []*Config{c}, err
case configStrategyConfd:
cs, err := loadConfigsFromEnvFiles("/etc/dockervolumebackup/conf.d")
if err != nil {
if os.IsNotExist(err) {
return sourceConfiguration(configStrategyEnv)
}
return nil, errwrap.Wrap(err, "error loading config files")
}
return cs, nil
default:
return nil, errwrap.Wrap(nil, fmt.Sprintf("received unknown config strategy: %v", strategy))
}
}
// envProxy is a function that mimics os.LookupEnv but can read values from any other source
type envProxy func(string) (string, bool)
// loadConfig creates a config object using the given lookup function
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, errwrap.Wrap(err, "failed to process configuration values")
}
return c, nil
}
func loadConfigFromEnvVars() (*Config, error) {
c, err := loadConfig(os.LookupEnv)
if err != nil {
return nil, errwrap.Wrap(err, "error loading config from environment")
}
c.source = "from environment"
return c, nil
}
func loadConfigsFromEnvFiles(directory string) ([]*Config, error) {
items, err := os.ReadDir(directory)
if err != nil {
if os.IsNotExist(err) {
return nil, err
}
return nil, errwrap.Wrap(err, "failed to read files from env directory")
}
configs := []*Config{}
for _, item := range items {
if item.IsDir() {
continue
}
p := filepath.Join(directory, item.Name())
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envFile, err := source(p)
if err != nil {
return nil, errwrap.Wrap(err, fmt.Sprintf("error reading config file %s", p))
}
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, errwrap.Wrap(err, fmt.Sprintf("error loading config from file %s", p))
}
c.source = item.Name()
c.additionalEnvVars = envFile
configs = append(configs, c)
}
return configs, nil
}
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// source tries to mimic the pre v2.37.0 behavior of calling
// `set +a; source $path; set -a` and returns the env vars as a map
func source(path string) (map[string]string, error) {
f, err := os.Open(path)
if err != nil {
return nil, errwrap.Wrap(err, fmt.Sprintf("error opening %s", path))
}
result := map[string]string{}
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := scanner.Text()
line = strings.TrimSpace(line)
if strings.HasPrefix(line, "#") {
continue
}
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withExpansion, err := shell.Expand(line, nil)
if err != nil {
return nil, errwrap.Wrap(err, "error expanding env")
}
m, err := godotenv.Unmarshal(withExpansion)
if err != nil {
return nil, errwrap.Wrap(err, fmt.Sprintf("error sourcing %s", path))
}
for key, value := range m {
currentValue, currentOk := os.LookupEnv(key)
defer func() {
if currentOk {
os.Setenv(key, currentValue)
return
}
os.Unsetenv(key)
}()
result[key] = value
os.Setenv(key, value)
}
}
return result, nil
}