Move cron scheduling inside application (#338)

* Move cron scheduling inside application

* Make envvar a fallback and check for errors

* Panic significantly less

* propagate error out of runBackup

* Add structured logging

* FIx error propagation to exit

* Enable the new scheduler by default

* Review fixes

* Added docs and better error propagation

cmd/backup/config.go

@@ -34,6 +34,7 @@ type Config struct {
 	BackupFilenameExpand          bool            `split_words:"true"`
 	BackupLatestSymlink           string          `split_words:"true"`
 	BackupArchive                 string          `split_words:"true" default:"/archive"`
+	BackupCronExpression          string          `split_words:"true" default:"@daily"`
 	BackupRetentionDays           int32           `split_words:"true" default:"-1"`
 	BackupPruningLeeway           time.Duration   `split_words:"true" default:"1m"`
 	BackupPruningPrefix           string          `split_words:"true"`

cmd/backup/config_provider.go

@@ -0,0 +1,81 @@
+// 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("failed to process configuration values, error: %w", err)
+	}
+
+	return c, nil
+}
+
+func loadEnvVars() (*Config, error) {
+	return loadConfig(os.LookupEnv)
+}
+
+func loadEnvFiles(directory string) ([]*Config, error) {
+	items, err := os.ReadDir(directory)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, err
+		}
+		return nil, fmt.Errorf("failed to read files from env directory, error: %w", err)
+	}
+
+	var cs = make([]*Config, 0)
+	for _, item := range items {
+		if !item.IsDir() {
+			p := filepath.Join(directory, item.Name())
+			envFile, err := godotenv.Read(p)
+			if err != nil {
+				return nil, fmt.Errorf("error reading config file %s, error: %w", p, err)
+			}
+			lookup := func(key string) (string, bool) {
+				val, ok := envFile[key]
+				return val, ok
+			}
+			c, err := loadConfig(lookup)
+			if err != nil {
+				return nil, fmt.Errorf("error loading config from file %s, error: %w", p, err)
+			}
+			cs = append(cs, c)
+		}
+	}
+
+	return cs, nil
+}

cmd/backup/main.go

@@ -4,21 +4,33 @@
 package main
 
 import (
+	"flag"
 	"fmt"
+	"log/slog"
 	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/robfig/cron/v3"
 )
 
-func main() {
-	s, err := newScript()
+func runScript(c *Config) (ret error) {
+	s, err := newScript(c)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
 	unlock, err := s.lock("/var/lock/dockervolumebackup.lock")
+	if err != nil {
+		return err
+	}
+
 	defer func() {
-		s.must(unlock())
+		err = unlock()
+		if err != nil {
+			ret = err
+		}
 	}()
-	s.must(err)
 
 	defer func() {
 		if pArg := recover(); pArg != nil {
@@ -31,9 +43,14 @@ func main() {
 						fmt.Sprintf("An error occurred calling the registered hooks: %s", hookErr),
 					)
 				}
-				os.Exit(1)
+				ret = err
+			} else {
+				s.logger.Error(
+					fmt.Sprintf("Executing the script encountered an unrecoverable panic: %v", err),
+				)
+
+				panic(pArg)
 			}
-			panic(pArg)
 		}
 
 		if err := s.runHooks(nil); err != nil {
@@ -43,7 +60,7 @@ func main() {
 					err,
 				),
 			)
-			os.Exit(1)
+			ret = err
 		}
 		s.logger.Info("Finished running backup tasks.")
 	}()
@@ -65,4 +82,90 @@ func main() {
 	s.must(s.withLabeledCommands(lifecyclePhaseProcess, s.encryptArchive)())
 	s.must(s.withLabeledCommands(lifecyclePhaseCopy, s.copyArchive)())
 	s.must(s.withLabeledCommands(lifecyclePhasePrune, s.pruneBackups)())
+
+	return nil
+}
+
+func runInForeground() error {
+	cr := cron.New(
+		cron.WithParser(
+			cron.NewParser(
+				cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
+			),
+		),
+	)
+
+	addJob := func(c *Config) error {
+		_, err := cr.AddFunc(c.BackupCronExpression, func() {
+			err := runScript(c)
+			if err != nil {
+				slog.Error("unexpected error during backup", "error", err)
+			}
+		})
+		return err
+	}
+
+	cs, err := loadEnvFiles("/etc/dockervolumebackup/conf.d")
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return fmt.Errorf("could not load config from environment files, error: %w", err)
+		}
+
+		c, err := loadEnvVars()
+		if err != nil {
+			return fmt.Errorf("could not load config from environment variables")
+		} else {
+			err = addJob(c)
+			if err != nil {
+				return fmt.Errorf("could not add cron job, error: %w", err)
+			}
+		}
+	} else {
+		for _, c := range cs {
+			err = addJob(c)
+			if err != nil {
+				return fmt.Errorf("could not add cron job, error: %w", err)
+			}
+		}
+	}
+
+	var quit = make(chan os.Signal, 1)
+	signal.Notify(quit, syscall.SIGTERM, syscall.SIGINT)
+	cr.Start()
+	<-quit
+	ctx := cr.Stop()
+	<-ctx.Done()
+
+	return nil
+}
+
+func runAsCommand() error {
+	c, err := loadEnvVars()
+	if err != nil {
+		return fmt.Errorf("could not load config from environment variables, error: %w", err)
+	}
+
+	err = runScript(c)
+	if err != nil {
+		return fmt.Errorf("unexpected error during backup, error: %w", err)
+	}
+
+	return nil
+}
+
+func main() {
+	serve := flag.Bool("foreground", false, "run the tool in the foreground")
+	flag.Parse()
+
+	var err error
+	if *serve {
+		err = runInForeground()
+	} else {
+		err = runAsCommand()
+	}
+
+	if err != nil {
+		slog.Error("ran into an issue during execution", "error", err)
+		os.Exit(1)
+	}
 }

cmd/backup/script.go

@@ -30,7 +30,6 @@ import (
 	"github.com/containrrr/shoutrrr/pkg/router"
 	"github.com/docker/docker/client"
 	"github.com/leekchan/timeutil"
-	"github.com/offen/envconfig"
 	"github.com/otiai10/copy"
 	"golang.org/x/sync/errgroup"
 )
@@ -58,10 +57,10 @@ type script struct {
 // remote resources like the Docker engine or remote storage locations. All
 // reading from env vars or other configuration sources is expected to happen
 // in this method.
-func newScript() (*script, error) {
+func newScript(c *Config) (*script, error) {
 	stdOut, logBuffer := buffer(os.Stdout)
 	s := &script{
-		c:      &Config{},
+		c:      c,
 		logger: slog.New(slog.NewTextHandler(stdOut, nil)),
 		stats: &Stats{
 			StartTime: time.Now(),
@@ -83,32 +82,6 @@ func newScript() (*script, error) {
 		return nil
 	})
 
-	envconfig.Lookup = func(key string) (string, bool) {
-		value, okValue := os.LookupEnv(key)
-		location, okFile := os.LookupEnv(key + "_FILE")
-
-		switch {
-		case okValue && !okFile: // only value
-			return value, true
-		case !okValue && okFile: // only file
-			contents, err := os.ReadFile(location)
-			if err != nil {
-				s.must(fmt.Errorf("newScript: failed to read %s! Error: %s", location, err))
-				return "", false
-			}
-			return string(contents), true
-		case okValue && okFile: // both
-			s.must(fmt.Errorf("newScript: both %s and %s are set!", key, key+"_FILE"))
-			return "", false
-		default: // neither, ignore
-			return "", false
-		}
-	}
-
-	if err := envconfig.Process("", s.c); err != nil {
-		return nil, fmt.Errorf("newScript: failed to process configuration values: %w", err)
-	}
-
 	s.file = path.Join("/tmp", s.c.BackupFilename)
 
 	tmplFileName, tErr := template.New("extension").Parse(s.file)