Add generations command

cmd/litestream/main.go

@@ -4,9 +4,15 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"log"
 	"os"
+	"os/user"
+	"path/filepath"
 	"strings"
+
+	"github.com/benbjohnson/litestream"
+	"gopkg.in/yaml.v2"
 )
 
 // Build information.
@@ -14,6 +20,9 @@ var (
 	Version = "(development build)"
 )
 
+// DefaultConfigPath is the default configuration path.
+const DefaultConfigPath = "/etc/litestream.yml"
+
 func main() {
 	log.SetFlags(0)
 
@@ -39,6 +48,8 @@ func (m *Main) Run(ctx context.Context, args []string) (err error) {
 	}
 
 	switch cmd {
+	case "generations":
+		return (&GenerationsCommand{}).Run(ctx, args)
 	case "replicate":
 		return (&ReplicateCommand{}).Run(ctx, args)
 	case "version":
@@ -66,3 +77,89 @@ The commands are:
 	version     prints the version
 `[1:])
 }
+
+// Config represents a configuration file for the litestream daemon.
+type Config struct {
+	DBs []*DBConfig `yaml:"databases"`
+}
+
+// DefaultConfig returns a new instance of Config with defaults set.
+func DefaultConfig() Config {
+	return Config{}
+}
+
+// ReadConfigFile unmarshals config from filename. Expands path if needed.
+func ReadConfigFile(filename string) (Config, error) {
+	config := DefaultConfig()
+
+	// Expand filename, if necessary.
+	if prefix := "~" + string(os.PathSeparator); strings.HasPrefix(filename, prefix) {
+		u, err := user.Current()
+		if err != nil {
+			return config, err
+		} else if u.HomeDir == "" {
+			return config, fmt.Errorf("home directory unset")
+		}
+		filename = filepath.Join(u.HomeDir, strings.TrimPrefix(filename, prefix))
+	}
+
+	// Read & deserialize configuration.
+	if buf, err := ioutil.ReadFile(filename); os.IsNotExist(err) {
+		return config, fmt.Errorf("config file not found: %s", filename)
+	} else if err != nil {
+		return config, err
+	} else if err := yaml.Unmarshal(buf, &config); err != nil {
+		return config, err
+	}
+	return config, nil
+}
+
+type DBConfig struct {
+	Path     string           `yaml:"path"`
+	Replicas []*ReplicaConfig `yaml:"replicas"`
+}
+
+type ReplicaConfig struct {
+	Type string `yaml:"type"` // "file", "s3"
+	Name string `yaml:"name"` // name of replicator, optional.
+	Path string `yaml:"path"` // used for file replicators
+}
+
+func registerConfigFlag(fs *flag.FlagSet, p *string) {
+	fs.StringVar(p, "config", DefaultConfigPath, "config path")
+}
+
+// newDBFromConfig instantiates a DB based on a configuration.
+func newDBFromConfig(config *DBConfig) (*litestream.DB, error) {
+	// Initialize database with given path.
+	db := litestream.NewDB(config.Path)
+
+	// Instantiate and attach replicators.
+	for _, rconfig := range config.Replicas {
+		r, err := newReplicatorFromConfig(db, rconfig)
+		if err != nil {
+			return nil, err
+		}
+		db.Replicators = append(db.Replicators, r)
+	}
+
+	return db, nil
+}
+
+// newReplicatorFromConfig instantiates a replicator for a DB based on a config.
+func newReplicatorFromConfig(db *litestream.DB, config *ReplicaConfig) (litestream.Replicator, error) {
+	switch config.Type {
+	case "", "file":
+		return newFileReplicatorFromConfig(db, config)
+	default:
+		return nil, fmt.Errorf("unknown replicator type in config: %q", config.Type)
+	}
+}
+
+// newFileReplicatorFromConfig returns a new instance of FileReplicator build from config.
+func newFileReplicatorFromConfig(db *litestream.DB, config *ReplicaConfig) (*litestream.FileReplicator, error) {
+	if config.Path == "" {
+		return nil, fmt.Errorf("file replicator path require for db %q", db.Path())
+	}
+	return litestream.NewFileReplicator(db, config.Name, config.Path), nil
+}