Add local cache

cache.go

@@ -0,0 +1,92 @@
+package restic
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/restic/restic/backend"
+)
+
+type Cache struct {
+	base string
+}
+
+func NewCache() (*Cache, error) {
+	dir, err := GetCacheDir()
+	if err != nil {
+		return nil, err
+	}
+
+	return &Cache{base: dir}, nil
+}
+
+func (c *Cache) Has(t backend.Type, id backend.ID) (bool, error) {
+	// try to open file
+	filename, err := c.filename(t, id)
+	if err != nil {
+		return false, err
+	}
+
+	fd, err := os.Open(filename)
+	defer fd.Close()
+	if err != nil {
+		if os.IsNotExist(err) {
+			return false, nil
+		}
+
+		return false, err
+	}
+
+	return true, nil
+}
+
+func (c *Cache) Store(t backend.Type, id backend.ID, rd io.Reader) error {
+	filename, err := c.filename(t, id)
+	if err != nil {
+		return err
+	}
+
+	dirname := filepath.Dir(filename)
+	err = os.MkdirAll(dirname, 0700)
+	if err != nil {
+		return err
+	}
+
+	file, err := os.Create(filename)
+	defer file.Close()
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(file, rd)
+	return err
+}
+
+func (c *Cache) Load(t backend.Type, id backend.ID) (io.ReadCloser, error) {
+	// try to open file
+	filename, err := c.filename(t, id)
+	if err != nil {
+		return nil, err
+	}
+
+	return os.Open(filename)
+}
+
+// Construct file name for given Type.
+func (c *Cache) filename(t backend.Type, id backend.ID) (string, error) {
+	cachedir, err := GetCacheDir()
+	if err != nil {
+		return "", err
+	}
+
+	switch t {
+	case backend.Snapshot:
+		return filepath.Join(cachedir, "snapshots", id.String()), nil
+	case backend.Tree:
+		return filepath.Join(cachedir, "trees", id.String()), nil
+	}
+
+	return "", fmt.Errorf("cache not supported for type %v", t)
+}