Refactor handling of runtime configuration to prepare for reloading

cmd/backup/command.go

@@ -0,0 +1,155 @@
+// Copyright 2024 - Offen Authors <[email protected]>
+// SPDX-License-Identifier: MPL-2.0
+
+package main
+
+import (
+	"fmt"
+	"log/slog"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/robfig/cron/v3"
+)
+
+type command struct {
+	logger    *slog.Logger
+	schedules []cron.EntryID
+	cr        *cron.Cron
+	reload    chan struct{}
+}
+
+func newCommand() *command {
+	return &command{
+		logger: slog.New(slog.NewTextHandler(os.Stdout, nil)),
+	}
+}
+
+// runAsCommand executes a backup run for each configuration that is available
+// and then returns
+func (c *command) runAsCommand() error {
+	configurations, err := sourceConfiguration(configStrategyEnv)
+	if err != nil {
+		return fmt.Errorf("runAsCommand: error loading env vars: %w", err)
+	}
+
+	for _, config := range configurations {
+		if err := runScript(config); err != nil {
+			return fmt.Errorf("runAsCommand: error running script: %w", err)
+		}
+	}
+
+	return nil
+}
+
+type foregroundOpts struct {
+	profileCronExpression string
+}
+
+// runInForeground starts the program as a long running process, scheduling
+// a job for each configuration that is available.
+func (c *command) runInForeground(opts foregroundOpts) error {
+	c.cr = cron.New(
+		cron.WithParser(
+			cron.NewParser(
+				cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor,
+			),
+		),
+	)
+
+	if err := c.schedule(configStrategyConfd); err != nil {
+		return fmt.Errorf("runInForeground: error scheduling: %w", err)
+	}
+
+	if opts.profileCronExpression != "" {
+		if _, err := c.cr.AddFunc(opts.profileCronExpression, c.profile); err != nil {
+			return fmt.Errorf("runInForeground: error adding profiling job: %w", err)
+		}
+	}
+
+	var quit = make(chan os.Signal, 1)
+	c.reload = make(chan struct{}, 1)
+	signal.Notify(quit, syscall.SIGTERM, syscall.SIGINT)
+	c.cr.Start()
+
+	for {
+		select {
+		case <-quit:
+			ctx := c.cr.Stop()
+			<-ctx.Done()
+			return nil
+		case <-c.reload:
+			if err := c.schedule(configStrategyConfd); err != nil {
+				return fmt.Errorf("runInForeground: error reloading configuration: %w", err)
+			}
+		}
+	}
+}
+
+// schedule wipes all existing schedules and enqueues all schedules available
+// using the given configuration strategy
+func (c *command) schedule(strategy configStrategy) error {
+	for _, id := range c.schedules {
+		c.cr.Remove(id)
+	}
+
+	configurations, err := sourceConfiguration(strategy)
+	if err != nil {
+		return fmt.Errorf("schedule: error sourcing configuration: %w", err)
+	}
+
+	for _, cfg := range configurations {
+		config := cfg
+		id, err := c.cr.AddFunc(config.BackupCronExpression, func() {
+			c.logger.Info(
+				fmt.Sprintf(
+					"Now running script on schedule %s",
+					config.BackupCronExpression,
+				),
+			)
+
+			if err := runScript(config); err != nil {
+				c.logger.Error(
+					fmt.Sprintf(
+						"Unexpected error running schedule %s: %v",
+						config.BackupCronExpression,
+						err,
+					),
+					"error",
+					err,
+				)
+			}
+		})
+
+		if err != nil {
+			return fmt.Errorf("addJob: error adding schedule %s: %w", config.BackupCronExpression, err)
+		}
+		c.logger.Info(fmt.Sprintf("Successfully scheduled backup %s with expression %s", config.source, config.BackupCronExpression))
+		if ok := checkCronSchedule(config.BackupCronExpression); !ok {
+			c.logger.Warn(
+				fmt.Sprintf("Scheduled cron expression %s will never run, is this intentional?", config.BackupCronExpression),
+			)
+
+			if err != nil {
+				return fmt.Errorf("schedule: error scheduling: %w", err)
+			}
+			c.schedules = append(c.schedules, id)
+		}
+	}
+
+	return nil
+}
+
+// must exits the program when passed an error. It should be the only
+// place where the application exits forcefully.
+func (c *command) must(err error) {
+	if err != nil {
+		c.logger.Error(
+			fmt.Sprintf("Fatal error running command: %v", err),
+			"error",
+			err,
+		)
+		os.Exit(1)
+	}
+}

cmd/backup/config.go

@@ -80,6 +80,8 @@ type Config struct {
 	DropboxAppSecret              string          `split_words:"true"`
 	DropboxRemotePath             string          `split_words:"true"`
 	DropboxConcurrencyLevel       NaturalNumber   `split_words:"true" default:"6"`
+	source                        string
+	additionalEnvVars             map[string]string
 }
 
 type CompressionType string
@@ -172,3 +174,40 @@ func (n *WholeNumber) Decode(v string) error {
 func (n *WholeNumber) Int() int {
 	return int(*n)
 }
+
+type envVarLookup struct {
+	ok    bool
+	key   string
+	value string
+}
+
+// applyEnv sets the values in `additionalEnvVars` as environment variables.
+// It returns a function that reverts all values that have been set to its
+// previous state.
+func (c *Config) applyEnv() (func() error, error) {
+	lookups := []envVarLookup{}
+
+	unset := func() error {
+		for _, lookup := range lookups {
+			if !lookup.ok {
+				if err := os.Unsetenv(lookup.key); err != nil {
+					return fmt.Errorf("(*Config).applyEnv: error unsetting env var %s: %w", lookup.key, err)
+				}
+				continue
+			}
+			if err := os.Setenv(lookup.key, lookup.value); err != nil {
+				return fmt.Errorf("(*Config).applyEnv: error setting back env var %s: %w", lookup.key, err)
+			}
+		}
+		return nil
+	}
+
+	for key, value := range c.additionalEnvVars {
+		current, ok := os.LookupEnv(key)
+		lookups = append(lookups, envVarLookup{ok: ok, key: key, value: current})
+		if err := os.Setenv(key, value); err != nil {
+			return unset, fmt.Errorf("(*Config).applyEnv: error setting env var: %w", err)
+		}
+	}
+	return unset, nil
+}

cmd/backup/config_provider.go

@@ -12,9 +12,39 @@ import (
 	"github.com/offen/envconfig"
 )
 
+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, fmt.Errorf("sourceConfiguration: error loading config files: %w", err)
+		}
+		return cs, nil
+	default:
+		return nil, fmt.Errorf("sourceConfiguration: 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)
@@ -44,17 +74,16 @@ func loadConfig(lookup envProxy) (*Config, error) {
 	return c, nil
 }
 
-func loadEnvVars() (*Config, error) {
-	return loadConfig(os.LookupEnv)
-}
-
-type configFile struct {
-	name              string
-	config            *Config
-	additionalEnvVars map[string]string
+func loadConfigFromEnvVars() (*Config, error) {
+	c, err := loadConfig(os.LookupEnv)
+	if err != nil {
+		return nil, fmt.Errorf("loadEnvVars: error loading config from environment: %w", err)
+	}
+	c.source = "from environment"
+	return c, nil
 }
 
-func loadEnvFiles(directory string) ([]configFile, error) {
+func loadConfigsFromEnvFiles(directory string) ([]*Config, error) {
 	items, err := os.ReadDir(directory)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -63,7 +92,7 @@ func loadEnvFiles(directory string) ([]configFile, error) {
 		return nil, fmt.Errorf("loadEnvFiles: failed to read files from env directory: %w", err)
 	}
 
-	cs := []configFile{}
+	configs := []*Config{}
 	for _, item := range items {
 		if item.IsDir() {
 			continue
@@ -88,8 +117,10 @@ func loadEnvFiles(directory string) ([]configFile, error) {
 		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})
+		c.source = item.Name()
+		c.additionalEnvVars = envFile
+		configs = append(configs, c)
 	}
 
-	return cs, nil
+	return configs, nil
 }

cmd/backup/copy_archive.go

@@ -0,0 +1,41 @@
+// Copyright 2024 - Offen Authors <[email protected]>
+// SPDX-License-Identifier: MPL-2.0
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"path"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// copyArchive makes sure the backup file is copied to both local and remote locations
+// as per the given configuration.
+func (s *script) copyArchive() error {
+	_, name := path.Split(s.file)
+	if stat, err := os.Stat(s.file); err != nil {
+		return fmt.Errorf("copyArchive: unable to stat backup file: %w", err)
+	} else {
+		size := stat.Size()
+		s.stats.BackupFile = BackupFileStats{
+			Size:     uint64(size),
+			Name:     name,
+			FullPath: s.file,
+		}
+	}
+
+	eg := errgroup.Group{}
+	for _, backend := range s.storages {
+		b := backend
+		eg.Go(func() error {
+			return b.Copy(s.file)
+		})
+	}
+	if err := eg.Wait(); err != nil {
+		return fmt.Errorf("copyArchive: error copying archive: %w", err)
+	}
+
+	return nil
+}