Add v1util.EstargzReadCloser utility.

This adds the first utility function we will need to start producing estargz layers.

pkg/v1/v1util/zip.go

@@ -18,6 +18,10 @@ import (
 	"bytes"
 	"compress/gzip"
 	"io"
+	"io/ioutil"
+
+	"github.com/containerd/stargz-snapshotter/estargz"
+	v1 "github.com/google/go-containerregistry/pkg/v1"
 )
 
 var gzipMagicHeader = []byte{'\x1f', '\x8b'}
@@ -80,6 +84,27 @@ func GunzipReadCloser(r io.ReadCloser) (io.ReadCloser, error) {
 	}, nil
 }
 
+// EstargzReadCloser reads uncompressed input data from the io.ReadCloser and
+// returns an io.ReadCloser from which compressed data may be read.
+// Refer to estargz for the options:
+// https://pkg.go.dev/github.com/containerd/[email protected]/estargz#Option
+func EstargzReadCloser(r io.ReadCloser, opts ...estargz.Option) (io.ReadCloser, v1.Hash, error) {
+	defer r.Close()
+
+	bs, err := ioutil.ReadAll(r)
+	if err != nil {
+		return nil, v1.Hash{}, err
+	}
+	br := bytes.NewReader(bs)
+
+	rc, d, err := estargz.Build(io.NewSectionReader(br, 0, int64(len(bs))), nil, opts...)
+	if err != nil {
+		return nil, v1.Hash{}, err
+	}
+	h, err := v1.NewHash(d.String())
+	return rc, h, err
+}
+
 // IsGzipped detects whether the input stream is compressed.
 func IsGzipped(r io.Reader) (bool, error) {
 	magicHeader := make([]byte, 2)

pkg/v1/v1util/zip_test.go

@@ -15,8 +15,10 @@
 package v1util
 
 import (
+	"archive/tar"
 	"bytes"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"strings"
 	"testing"
@@ -43,6 +45,65 @@ func TestReader(t *testing.T) {
 	}
 }
 
+func TestEstargzReader(t *testing.T) {
+	want := "This is the input string."
+	buf := bytes.NewBuffer(nil)
+	tw := tar.NewWriter(buf)
+
+	if err := tw.WriteHeader(&tar.Header{
+		Name: "foo",
+		Size: int64(len(want)),
+	}); err != nil {
+		t.Fatal("WriteHeader() =", err)
+	}
+	if _, err := tw.Write([]byte(want)); err != nil {
+		t.Fatal("tw.Write() =", err)
+	}
+	tw.Close()
+
+	zipped, _, err := EstargzReadCloser(ioutil.NopCloser(buf))
+	if err != nil {
+		t.Fatal("EstargzReadCloser() =", err)
+	}
+	unzipped, err := GunzipReadCloser(zipped)
+	if err != nil {
+		t.Error("GunzipReadCloser() =", err)
+	}
+	defer unzipped.Close()
+
+	found := false
+
+	r := tar.NewReader(unzipped)
+	for {
+		hdr, err := r.Next()
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			t.Fatal("tar.Next() =", err)
+		}
+
+		if hdr.Name != "foo" {
+			continue
+		}
+		found = true
+
+		b, err := ioutil.ReadAll(r)
+		if err != nil {
+			t.Error("ReadAll() =", err)
+		}
+		if got := string(b); got != want {
+			t.Errorf("ReadAll(); got %q, want %q", got, want)
+		}
+		if err := unzipped.Close(); err != nil {
+			t.Error("Close() =", err)
+		}
+	}
+
+	if !found {
+		t.Error(`Did not find the expected file "foo"`)
+	}
+}
+
 func TestIsGzipped(t *testing.T) {
 	tests := []struct {
 		in  []byte