Move fallback to config sourcing

cmd/backup/config.go

@@ -181,19 +181,22 @@ type envVarLookup struct {
 	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.Setenv(lookup.key, lookup.value); err != nil {
-					return fmt.Errorf("(*Config).injectEnv: error setting back env var %s: %w", lookup.key, err)
-				}
-			} else {
+			if !lookup.ok {
 				if err := os.Unsetenv(lookup.key); err != nil {
-					return fmt.Errorf("(*Config).injectEnv: error unsetting env var %s: %w", lookup.key, err)
+					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
@@ -203,7 +206,7 @@ func (c *Config) applyEnv() (func() error, error) {
 		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).injectEnv: error setting env var: %w", err)
+			return unset, fmt.Errorf("(*Config).applyEnv: error setting env var: %w", err)
 		}
 	}
 	return unset, nil

cmd/backup/config_provider.go

@@ -19,21 +19,32 @@ const (
 	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:
-		return loadConfigsFromEnvFiles("/etc/dockervolumebackup/conf.d")
+		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("newConfig: received unknown config strategy: %v", strategy)
+		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)

cmd/backup/main.go

@@ -37,6 +37,8 @@ func newCommand() *command {
 	}
 }
 
+// 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(
@@ -48,6 +50,10 @@ func (c *command) must(err error) {
 	}
 }
 
+// runScript instantiates a new script object and orchestrates a backup run.
+// To ensure it runs mutually exclusive a global file lock is acquired before
+// it starts running. Any panic within the script will be recovered and returned
+// as an error.
 func runScript(c *Config) (err error) {
 	defer func() {
 		if derr := recover(); derr != nil {
@@ -139,6 +145,8 @@ func runScript(c *Config) (err error) {
 	}()
 }
 
+// runInForeground starts the program as a long running process, scheduling
+// a job for each configuration that is available.
 func (c *command) runInForeground(profileCronExpression string) error {
 	cr := cron.New(
 		cron.WithParser(
@@ -184,15 +192,7 @@ func (c *command) runInForeground(profileCronExpression string) error {
 
 	cs, err := sourceConfiguration(configStrategyConfd)
 	if err != nil {
-		if !os.IsNotExist(err) {
-			return fmt.Errorf("runInForeground: could not load config from environment files: %w", err)
-		}
-		cs, err = sourceConfiguration(configStrategyEnv)
-		if err != nil {
-			return fmt.Errorf("runInForeground: could not load configuration: %w", err)
-		}
-	} else {
-		c.logger.Info("/etc/dockervolumebackup/conf.d was found, using configuration files from this directory.")
+		return fmt.Errorf("runInForeground: error sourcing configuration: %w", err)
 	}
 
 	for _, config := range cs {
@@ -218,6 +218,8 @@ func (c *command) runInForeground(profileCronExpression string) error {
 	return 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 {