Added snapshot package and tests

pkg/util/fs_util.go

@@ -24,6 +24,7 @@ import (
 	"github.com/sirupsen/logrus"
 	"io"
 	"os"
+	"path/filepath"
 	"strings"
 )
 
@@ -47,6 +48,17 @@ func ExtractFileSystemFromImage(img string) error {
 	return pkgutil.GetFileSystemFromReference(ref, imgSrc, constants.RootDir, whitelist)
 }
 
+// PathInWhitelist returns true if the path is whitelisted
+func PathInWhitelist(path, directory string) bool {
+	for _, d := range whitelist {
+		dirPath := filepath.Join(directory, d)
+		if pkgutil.HasFilepathPrefix(path, dirPath) {
+			return true
+		}
+	}
+	return false
+}
+
 // Get whitelist from roots of mounted files
 // Each line of /proc/self/mountinfo is in the form:
 // 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue

pkg/util/tar_util.go

@@ -0,0 +1,52 @@
+/*
+Copyright 2018 Google LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package util
+
+import (
+	"archive/tar"
+	"io"
+	"os"
+)
+
+// AddToTar adds the file i to tar w at path p
+func AddToTar(p string, i os.FileInfo, w *tar.Writer) error {
+	linkDst := ""
+	if i.Mode()&os.ModeSymlink != 0 {
+		var err error
+		linkDst, err = os.Readlink(p)
+		if err != nil {
+			return err
+		}
+	}
+	hdr, err := tar.FileInfoHeader(i, linkDst)
+	if err != nil {
+		return err
+	}
+	hdr.Name = p
+	w.WriteHeader(hdr)
+	if !i.Mode().IsRegular() {
+		return nil
+	}
+	r, err := os.Open(p)
+	if err != nil {
+		return err
+	}
+	if _, err := io.Copy(w, r); err != nil {
+		return err
+	}
+	return nil
+}

pkg/util/util.go

@@ -17,8 +17,12 @@ limitations under the License.
 package util
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
+	"io"
+	"os"
 )
 
 // SetLogLevel sets the logrus logging level
@@ -30,3 +34,30 @@ func SetLogLevel(logLevel string) error {
 	logrus.SetLevel(lvl)
 	return nil
 }
+
+// Hasher returns a hash function, used in snapshotting to determine if a file has changed
+func Hasher() func(string) string {
+	hasher := func(p string) string {
+		h := md5.New()
+		fi, err := os.Lstat(p)
+		if err != nil {
+			panic(err)
+		}
+		h.Write([]byte(fi.Mode().String()))
+		h.Write([]byte(fi.ModTime().String()))
+
+		if fi.Mode().IsRegular() {
+			f, err := os.Open(p)
+			if err != nil {
+				panic(err)
+			}
+			defer f.Close()
+			if _, err := io.Copy(h, f); err != nil {
+				panic(err)
+			}
+		}
+
+		return hex.EncodeToString(h.Sum(nil))
+	}
+	return hasher
+}