fix(config): reject snapshot retention shorter than interval

cmd/litestream/main.go

@@ -50,17 +50,18 @@ var errStop = errors.New("stop")
 
 // Sentinel errors for configuration validation
 var (
-	ErrInvalidSnapshotInterval         = errors.New("snapshot interval must be greater than 0")
-	ErrInvalidSnapshotRetention        = errors.New("snapshot retention must be greater than 0")
-	ErrInvalidCompactionInterval       = errors.New("compaction interval must be greater than 0")
-	ErrInvalidSyncInterval             = errors.New("sync interval must be greater than 0")
-	ErrInvalidL0Retention              = errors.New("l0 retention must not be negative")
-	ErrInvalidL0RetentionCheckInterval = errors.New("l0 retention check interval must be greater than 0")
-	ErrInvalidShutdownSyncTimeout      = errors.New("shutdown-sync-timeout must be >= 0")
-	ErrInvalidShutdownSyncInterval     = errors.New("shutdown sync interval must be greater than 0")
-	ErrInvalidHeartbeatURL             = errors.New("heartbeat URL must be a valid HTTP or HTTPS URL")
-	ErrInvalidHeartbeatInterval        = errors.New("heartbeat interval must be at least 1 minute")
-	ErrConfigFileNotFound              = errors.New("config file not found")
+	ErrInvalidSnapshotInterval          = errors.New("snapshot interval must be greater than 0")
+	ErrInvalidSnapshotRetention         = errors.New("snapshot retention must be greater than 0")
+	ErrInvalidSnapshotRetentionInterval = errors.New("snapshot retention must not be shorter than snapshot interval")
+	ErrInvalidCompactionInterval        = errors.New("compaction interval must be greater than 0")
+	ErrInvalidSyncInterval              = errors.New("sync interval must be greater than 0")
+	ErrInvalidL0Retention               = errors.New("l0 retention must not be negative")
+	ErrInvalidL0RetentionCheckInterval  = errors.New("l0 retention check interval must be greater than 0")
+	ErrInvalidShutdownSyncTimeout       = errors.New("shutdown-sync-timeout must be >= 0")
+	ErrInvalidShutdownSyncInterval      = errors.New("shutdown sync interval must be greater than 0")
+	ErrInvalidHeartbeatURL              = errors.New("heartbeat URL must be a valid HTTP or HTTPS URL")
+	ErrInvalidHeartbeatInterval         = errors.New("heartbeat interval must be at least 1 minute")
+	ErrConfigFileNotFound               = errors.New("config file not found")
 )
 
 // ConfigValidationError wraps a validation error with additional context
@@ -432,6 +433,13 @@ func (c *Config) Validate() error {
 			Value: *c.Snapshot.Retention,
 		}
 	}
+	if c.Snapshot.Interval != nil && c.Snapshot.Retention != nil && *c.Snapshot.Retention < *c.Snapshot.Interval {
+		return &ConfigValidationError{
+			Err:   ErrInvalidSnapshotRetentionInterval,
+			Field: "snapshot.retention",
+			Value: *c.Snapshot.Retention,
+		}
+	}
 	if c.L0Retention != nil && *c.L0Retention < 0 {
 		return &ConfigValidationError{
 			Err:   ErrInvalidL0Retention,
@@ -532,6 +540,13 @@ func (c *Config) Validate() error {
 				Value: *db.Snapshot.Retention,
 			}
 		}
+		if db.Snapshot.Interval != nil && db.Snapshot.Retention != nil && *db.Snapshot.Retention < *db.Snapshot.Interval {
+			return &ConfigValidationError{
+				Err:   ErrInvalidSnapshotRetentionInterval,
+				Field: fmt.Sprintf("dbs[%s].snapshot.retention", dbIdentifier),
+				Value: *db.Snapshot.Retention,
+			}
+		}
 
 		// Validate sync intervals for replicas
 		if db.Replica != nil && db.Replica.SyncInterval != nil && *db.Replica.SyncInterval <= 0 {

cmd/litestream/main_test.go

@@ -711,6 +711,38 @@ snapshot:
 		}
 	})
 
+	t.Run("RetentionShorterThanInterval", func(t *testing.T) {
+		yaml := `
+snapshot:
+  interval: 1h
+  retention: 30m
+`
+		_, err := main.ParseConfig(strings.NewReader(yaml), false)
+		if err == nil {
+			t.Fatal("expected error for retention shorter than snapshot interval")
+		}
+		if !errors.Is(err, main.ErrInvalidSnapshotRetentionInterval) {
+			t.Errorf("expected ErrInvalidSnapshotRetentionInterval, got %v", err)
+		}
+	})
+
+	t.Run("DBRetentionShorterThanInterval", func(t *testing.T) {
+		yaml := `
+ dbs:
+  - path: /tmp/test.db
+    snapshot:
+      interval: 1h
+      retention: 30m
+`
+		_, err := main.ParseConfig(strings.NewReader(yaml), false)
+		if err == nil {
+			t.Fatal("expected error for database retention shorter than snapshot interval")
+		}
+		if !errors.Is(err, main.ErrInvalidSnapshotRetentionInterval) {
+			t.Errorf("expected ErrInvalidSnapshotRetentionInterval, got %v", err)
+		}
+	})
+
 	t.Run("NegativeInterval", func(t *testing.T) {
 		yaml := `
 snapshot: