add StripComponents and PathInArchive options to compressor

StripComponents(--strip-components) strips segments of the path before
extracting. PathInArchive allows you to selectively chose what to
extract from the archive.

These are use in the bosh-agent to extract job bundles, since they have
more than one job per tarball.

[#161569370](https://www.pivotaltracker.com/story/show/161569370)

Co-authored-by: Christopher Brown <cbrown@pivotal.io>

fileutil/compressor_interface.go

@@ -1,7 +1,9 @@
 package fileutil
 
 type CompressorOptions struct {
-	SameOwner bool
+	SameOwner       bool
+	PathInArchive   string
+	StripComponents int
 }
 
 type Compressor interface {

fileutil/tarball_compressor.go

@@ -1,6 +1,8 @@
 package fileutil
 
 import (
+	"fmt"
+
 	bosherr "github.com/cloudfoundry/bosh-utils/errors"
 	boshsys "github.com/cloudfoundry/bosh-utils/system"
 )
@@ -51,7 +53,15 @@ func (c tarballCompressor) DecompressFileToDir(tarballPath string, dir string, o
 		sameOwnerOption = "--same-owner"
 	}
 
-	_, _, _, err := c.cmdRunner.RunCommand("tar", sameOwnerOption, "-xzf", tarballPath, "-C", dir)
+	args := []string{sameOwnerOption, "-xzf", tarballPath, "-C", dir}
+	if options.StripComponents != 0 {
+		args = append(args, fmt.Sprintf("--strip-components=%d", options.StripComponents))
+	}
+
+	if options.PathInArchive != "" {
+		args = append(args, options.PathInArchive)
+	}
+	_, _, _, err := c.cmdRunner.RunCommand("tar", args...)
 	if err != nil {
 		return bosherr.WrapError(err, "Shelling out to tar")
 	}

fileutil/tarball_compressor_test.go

@@ -263,6 +263,44 @@ var _ = Describe("tarballCompressor", func() {
 				},
 			))
 		})
+
+		It("uses PathInArchive to select files from archive", func() {
+			cmdRunner := fakesys.NewFakeCmdRunner()
+			compressor := NewTarballCompressor(cmdRunner, fs)
+
+			tarballPath := fixtureSrcTgz()
+			err := compressor.DecompressFileToDir(tarballPath, dstDir, CompressorOptions{PathInArchive: "some/path/in/archive"})
+			Expect(err).ToNot(HaveOccurred())
+
+			Expect(1).To(Equal(len(cmdRunner.RunCommands)))
+			Expect(cmdRunner.RunCommands[0]).To(Equal(
+				[]string{
+					"tar", "--no-same-owner",
+					"-xzf", tarballPath,
+					"-C", dstDir,
+					"some/path/in/archive",
+				},
+			))
+		})
+
+		It("uses StripComponents option", func() {
+			cmdRunner := fakesys.NewFakeCmdRunner()
+			compressor := NewTarballCompressor(cmdRunner, fs)
+
+			tarballPath := fixtureSrcTgz()
+			err := compressor.DecompressFileToDir(tarballPath, dstDir, CompressorOptions{StripComponents: 3})
+			Expect(err).ToNot(HaveOccurred())
+
+			Expect(1).To(Equal(len(cmdRunner.RunCommands)))
+			Expect(cmdRunner.RunCommands[0]).To(Equal(
+				[]string{
+					"tar", "--no-same-owner",
+					"-xzf", tarballPath,
+					"-C", dstDir,
+					"--strip-components=3",
+				},
+			))
+		})
 	})
 
 	Describe("CleanUp", func() {