Add generations command

cmd/litestream/generations.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"text/tabwriter"
+	"time"
+)
+
+type GenerationsCommand struct {
+	ConfigPath string
+	Config     Config
+
+	DBPath string
+}
+
+func NewGenerationsCommand() *GenerationsCommand {
+	return &GenerationsCommand{}
+}
+
+func (c *GenerationsCommand) Run(ctx context.Context, args []string) (err error) {
+	fs := flag.NewFlagSet("litestream-generations", flag.ContinueOnError)
+	registerConfigFlag(fs, &c.ConfigPath)
+	fs.Usage = c.Usage
+	if err := fs.Parse(args); err != nil {
+		return err
+	} else if fs.NArg() > 1 {
+		return fmt.Errorf("too many arguments")
+	}
+
+	// Load configuration.
+	if c.ConfigPath == "" {
+		return errors.New("-config required")
+	}
+	config, err := ReadConfigFile(c.ConfigPath)
+	if err != nil {
+		return err
+	}
+
+	// Determine absolute path for database, if specified.
+	if c.DBPath = fs.Arg(0); c.DBPath != "" {
+		if c.DBPath, err = filepath.Abs(c.DBPath); err != nil {
+			return err
+		}
+	}
+
+	// List each generation.
+	w := tabwriter.NewWriter(os.Stdout, 0, 8, 1, '\t', 0)
+	fmt.Fprintln(w, "db\tname\tgeneration\tlag\tstart\tend")
+	for _, dbConfig := range config.DBs {
+		// Filter database, if specified in the arguments.
+		if c.DBPath != "" && dbConfig.Path != c.DBPath {
+			continue
+		}
+
+		// Instantiate DB from from configuration.
+		db, err := newDBFromConfig(dbConfig)
+		if err != nil {
+			return err
+		}
+
+		// Determine last time database or WAL was updated.
+		updatedAt, err := db.UpdatedAt()
+		if err != nil {
+			return err
+		}
+
+		// Iterate over each replicator in the database.
+		for _, r := range db.Replicators {
+			generations, err := r.Generations()
+			if err != nil {
+				log.Printf("%s: cannot list generations", r.Name(), err)
+				continue
+			}
+
+			// Iterate over each generation for the replicator.
+			for _, generation := range generations {
+				stats, err := r.GenerationStats(generation)
+				if err != nil {
+					log.Printf("%s: cannot find generation stats: %s", r.Name(), err)
+					continue
+				}
+
+				fmt.Fprintf(w, "%s\t%s\t%s\t%s\t%s\t%s\n",
+					db.Path(),
+					r.Name(),
+					generation,
+					truncateDuration(stats.UpdatedAt.Sub(updatedAt)).String(),
+					stats.CreatedAt.Format(time.RFC3339),
+					stats.UpdatedAt.Format(time.RFC3339),
+				)
+			}
+		}
+	}
+	w.Flush()
+
+	return nil
+}
+
+func (c *GenerationsCommand) Usage() {
+	fmt.Printf(`
+The generations command lists all generations across all replicas along with
+stats about their lag behind the primary database and the time range they cover.
+
+Usage:
+
+	litestream generations [arguments] DB
+
+Arguments:
+
+	-config PATH
+	    Specifies the configuration file. Defaults to %s
+
+`[1:],
+		DefaultConfigPath,
+	)
+}
+
+func truncateDuration(d time.Duration) time.Duration {
+	if d > time.Hour {
+		return d.Truncate(time.Hour)
+	} else if d > time.Minute {
+		return d.Truncate(time.Minute)
+	} else if d > time.Second {
+		return d.Truncate(time.Second)
+	} else if d > time.Millisecond {
+		return d.Truncate(time.Millisecond)
+	} else if d > time.Microsecond {
+		return d.Truncate(time.Microsecond)
+	}
+	return d
+}