Add crane-based methods for extraction

- create a new api package to encapsulate image manipulation
- use new api method to calculate delta

Fixes #258
Fixes #204
Fixes #90

pkg/api/core/image/delta.go

@@ -0,0 +1,111 @@
+// Copyright © 2021 Ettore Di Giacinto <mudler@mocaccino.org>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, see <http://www.gnu.org/licenses/>.
+
+package image
+
+import (
+	"archive/tar"
+	"io"
+	"regexp"
+
+	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/mutate"
+)
+
+func compileRegexes(regexes []string) []*regexp.Regexp {
+	var result []*regexp.Regexp
+	for _, i := range regexes {
+		r, e := regexp.Compile(i)
+		if e != nil {
+			continue
+		}
+		result = append(result, r)
+	}
+	return result
+}
+
+type ImageDiffNode struct {
+	Name string `json:"Name"`
+	Size int    `json:"Size"`
+}
+type ImageDiff struct {
+	Additions []ImageDiffNode `json:"Adds"`
+	Deletions []ImageDiffNode `json:"Dels"`
+	Changes   []ImageDiffNode `json:"Mods"`
+}
+
+func Delta(srcimg, dstimg v1.Image) (res ImageDiff, err error) {
+	srcReader := mutate.Extract(srcimg)
+	defer srcReader.Close()
+
+	dstReader := mutate.Extract(dstimg)
+	defer dstReader.Close()
+
+	filesSrc, filesDst := map[string]int64{}, map[string]int64{}
+
+	srcTar := tar.NewReader(srcReader)
+	dstTar := tar.NewReader(dstReader)
+
+	for {
+		var hdr *tar.Header
+		hdr, err = srcTar.Next()
+		if err == io.EOF {
+			// end of tar archive
+			break
+		}
+		if err != nil {
+			return
+		}
+		filesSrc[hdr.Name] = hdr.Size
+	}
+
+	for {
+		var hdr *tar.Header
+		hdr, err = dstTar.Next()
+		if err == io.EOF {
+			// end of tar archive
+			break
+		}
+		if err != nil {
+			return
+		}
+		filesDst[hdr.Name] = hdr.Size
+	}
+	err = nil
+
+	for f, size := range filesDst {
+		if size2, exist := filesSrc[f]; exist && size2 != size {
+			res.Changes = append(res.Changes, ImageDiffNode{
+				Name: f,
+				Size: int(size),
+			})
+		} else if !exist {
+			res.Additions = append(res.Additions, ImageDiffNode{
+				Name: f,
+				Size: int(size),
+			})
+		}
+	}
+	for f, size := range filesSrc {
+		if _, exist := filesDst[f]; !exist {
+			res.Deletions = append(res.Deletions, ImageDiffNode{
+				Name: f,
+				Size: int(size),
+			})
+		}
+	}
+
+	return
+}