Start filling out the Store implementation

snapshot2/store.go

@@ -1,11 +1,13 @@
 package snapshot2
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
 	"log"
 	"os"
 	"path/filepath"
+	"sort"
 	"time"
 
 	"github.com/hashicorp/raft"
@@ -46,6 +48,7 @@ func NewStore(dir string) (*Store, error) {
 	return str, nil
 }
 
+// Create creates a new snapshot sink for the given parameters.
 func (s *Store) Create(version raft.SnapshotVersion, index, term uint64, configuration raft.Configuration,
 	configurationIndex uint64, trans raft.Transport) (raft.SnapshotSink, error) {
 	sink := NewSink(s.dir, &raft.SnapshotMeta{
@@ -63,10 +66,12 @@ func (s *Store) Create(version raft.SnapshotVersion, index, term uint64, configu
 	return sink, nil
 }
 
+// List returns the list of available snapshots.
 func (s *Store) List() ([]*raft.SnapshotMeta, error) {
-	return nil, nil
+	return getSnapshots(s.dir)
 }
 
+// Open opens the snapshot with the given ID for reading.
 func (s *Store) Open(id string) (*raft.SnapshotMeta, io.ReadCloser, error) {
 	return nil, nil, nil
 }
@@ -78,6 +83,73 @@ func (s *Store) check() error {
 	return nil
 }
 
+// getSnapshots returns the list of snapshots in the given directory,
+// sorted from newest to oldest.
+func getSnapshots(dir string) ([]*raft.SnapshotMeta, error) {
+	// Get the eligible snapshots
+	snapshots, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, err
+	}
+
+	// Populate the metadata
+	var snapMeta []*raft.SnapshotMeta
+	for _, snap := range snapshots {
+		// Snapshots are stored in directories, ignore any files.
+		if !snap.IsDir() {
+			continue
+		}
+
+		// Ignore any temporary snapshots
+		dirName := snap.Name()
+		if isTmpName(dirName) {
+			continue
+		}
+
+		// Try to read the meta data
+		meta, err := readMeta(filepath.Join(dir, dirName))
+		if err != nil {
+			return nil, fmt.Errorf("failed to read meta for snapshot %s: %s", dirName, err)
+		}
+
+		snapMeta = append(snapMeta, meta)
+	}
+
+	sort.Sort(snapMetaSlice(snapMeta))
+	return snapMeta, nil
+}
+
+type cmpSnapshotMeta raft.SnapshotMeta
+
+func (c *cmpSnapshotMeta) Less(other *cmpSnapshotMeta) bool {
+	if c.Term != other.Term {
+		return c.Term < other.Term
+	}
+	if c.Index != other.Index {
+		return c.Index < other.Index
+	}
+	return c.ID < other.ID
+}
+
+type snapMetaSlice []*raft.SnapshotMeta
+
+// Len implements the sort interface for snapMetaSlice.
+func (s snapMetaSlice) Len() int {
+	return len(s)
+}
+
+// Less implements the sort interface for snapMetaSlice.
+func (s snapMetaSlice) Less(i, j int) bool {
+	si := (*cmpSnapshotMeta)(s[i])
+	sj := (*cmpSnapshotMeta)(s[j])
+	return si.Less(sj)
+}
+
+// Swap implements the sort interface for snapMetaSlice.
+func (s snapMetaSlice) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
 // snapshotName generates a name for the snapshot.
 func snapshotName(term, index uint64) string {
 	now := time.Now()
@@ -89,3 +161,19 @@ func snapshotName(term, index uint64) string {
 func metaPath(dir string) string {
 	return filepath.Join(dir, metaFileName)
 }
+
+// readMeta is used to read the meta data in a given snapshot directory.
+func readMeta(dir string) (*raft.SnapshotMeta, error) {
+	fh, err := os.Open(metaPath(dir))
+	if err != nil {
+		return nil, err
+	}
+	defer fh.Close()
+
+	meta := &raft.SnapshotMeta{}
+	dec := json.NewDecoder(fh)
+	if err := dec.Decode(meta); err != nil {
+		return nil, err
+	}
+	return meta, nil
+}