testutil/pkgdata: Create deb programatically

Currently we only test with base-files deb which is embedded as base64
encoded binary in testutil/pkgdata.go. If we want to change the contents
of the data files, we have to un-ar it, un-tar it, change the data
files, tar it and ar it. Furthermore, these operations modify attributes
based on the workstation on which this process is run. So we end up with
arbitrary user/group ids/names names and dates.

Fix it by creating debs programatically. The new interface provides way
to create debs with arbitrary content of data tarball.

internal/testutil/pkgdata.go

@@ -1,7 +1,13 @@
 package testutil
 
 import (
+	"archive/tar"
+	"bytes"
 	"encoding/base64"
+	"time"
+
+	"github.com/blakesmith/ar"
+	"github.com/klauspost/compress/zstd"
 )
 
 var PackageData = map[string][]byte{}
@@ -150,3 +156,111 @@ BIsAGAJD+LGgIzDiD2ntudH6JU80wD0rklyRGBV2dEx8VJG5LVwpcXb8PI0lMdi+wwUPoBkQGEIN
 7UwLQKMDjg8YkdmAmRrEgCSRRhMWBgBBSuI7S4BVs7zODfj1ja0TF+KbjdQDGANIcRlZhwzQSlla
 abj2Z7KoYMBXz9dwNNP2Aw13FguKkogezW5cqy4lCg==
 `
+
+type TarEntry struct {
+	Header  tar.Header
+	NoFixup bool
+	Content []byte
+}
+
+var zeroTime time.Time
+var epochStartTime time.Time = time.Unix(0, 0)
+
+func fixupEntry(entry *TarEntry) {
+	hdr := &entry.Header
+	if hdr.Typeflag == 0 {
+		if hdr.Linkname != "" {
+			hdr.Typeflag = tar.TypeSymlink
+		} else if hdr.Name[len(hdr.Name)-1] == '/' {
+			hdr.Typeflag = tar.TypeDir
+		} else {
+			hdr.Typeflag = tar.TypeReg
+		}
+	}
+	if hdr.Mode == 0 {
+		switch hdr.Typeflag {
+		case tar.TypeDir:
+			hdr.Mode = 0755
+		case tar.TypeSymlink:
+			hdr.Mode = 0777
+		default:
+			hdr.Mode = 0644
+		}
+	}
+	if hdr.Size == 0 && entry.Content != nil {
+		hdr.Size = int64(len(entry.Content))
+	}
+	if hdr.Uid == 0 && hdr.Uname == "" {
+		hdr.Uname = "root"
+	}
+	if hdr.Gid == 0 && hdr.Gname == "" {
+		hdr.Gname = "root"
+	}
+	if hdr.ModTime == zeroTime {
+		hdr.ModTime = epochStartTime
+	}
+	if hdr.Format == 0 {
+		hdr.Format = tar.FormatGNU
+	}
+}
+
+func makeTar(entries []TarEntry) ([]byte, error) {
+	var buf bytes.Buffer
+	tw := tar.NewWriter(&buf)
+	for _, entry := range entries {
+		if !entry.NoFixup {
+			fixupEntry(&entry)
+		}
+		if err := tw.WriteHeader(&entry.Header); err != nil {
+			return nil, err
+		}
+		if entry.Content != nil {
+			if _, err := tw.Write(entry.Content); err != nil {
+				return nil, err
+			}
+		}
+	}
+	return buf.Bytes(), nil
+}
+
+func compressBytesZstd(input []byte) ([]byte, error) {
+	var buf bytes.Buffer
+	writer, err := zstd.NewWriter(&buf)
+	if _, err = writer.Write(input); err != nil {
+		return nil, err
+	}
+	if err = writer.Close(); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func MakeDeb(entries []TarEntry) ([]byte, error) {
+	var buf bytes.Buffer
+
+	tarData, err := makeTar(entries)
+	if err != nil {
+		return nil, err
+	}
+	compTarData, err := compressBytesZstd(tarData)
+	if err != nil {
+		return nil, err
+	}
+
+	writer := ar.NewWriter(&buf)
+	if err := writer.WriteGlobalHeader(); err != nil {
+		return nil, err
+	}
+	dataHeader := ar.Header{
+		Name: "data.tar.zst",
+		Mode: 0644,
+		Size: int64(len(compTarData)),
+	}
+	if err := writer.WriteHeader(&dataHeader); err != nil {
+		return nil, err
+	}
+	if _, err = writer.Write(compTarData); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}

internal/testutil/pkgdata_test.go

@@ -0,0 +1,62 @@
+package testutil_test
+
+import (
+	"archive/tar"
+
+	_ "embed"
+
+	"github.com/canonical/chisel/internal/testutil"
+	"gopkg.in/check.v1"
+)
+
+type pkgdataSuite struct{}
+
+var _ = check.Suite(&pkgdataSuite{})
+
+var pkgdataTestEntries = []testutil.TarEntry{{
+	Header: tar.Header{Name: "./"},
+}, {
+	Header: tar.Header{Name: "./admin/", Mode: 00700, Uname: "admin"},
+}, {
+	Header:  tar.Header{Name: "./admin/password", Mode: 00600, Uname: "admin"},
+	Content: []byte("swordf1sh"),
+}, {
+	Header:  tar.Header{Name: "./admin/setpassword", Mode: 04711, Uname: "admin"},
+	Content: []byte{0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01},
+}, {
+	Header: tar.Header{Name: "./data/"},
+}, {
+	Header:  tar.Header{Name: "./data/invoice.txt"},
+	Content: []byte("$ 10"),
+}, {
+	Header: tar.Header{Name: "./data/logs/"},
+}, {
+	Header:  tar.Header{Name: "./data/logs/task.log"},
+	Content: []byte("starting\nfinished\n"),
+}, {
+	Header: tar.Header{Name: "./data/shared/", Mode: 02777},
+}, {
+	Header: tar.Header{Name: "./home/"},
+}, {
+	Header: tar.Header{Name: "./home/alice/", Uid: 1000},
+}, {
+	Header:  tar.Header{Name: "./home/alice/notes", Uid: 1000},
+	Content: []byte("check the cat"),
+}, {
+	Header: tar.Header{Name: "./home/bob/", Uname: "bob", Uid: 1001},
+}, {
+	Header:  tar.Header{Name: "./home/bob/task.sh", Mode: 00700, Uname: "bob", Uid: 1001},
+	Content: []byte("#!/bin/sh\n"),
+}, {
+	Header: tar.Header{Name: "./logs/", Linkname: "data/logs"},
+}}
+
+//go:embed testdata/pkgdata.deb
+var pkgdataExpectedDeb []byte
+
+func (s *pkgdataSuite) TestMakeDeb(c *check.C) {
+	deb, err := testutil.MakeDeb(pkgdataTestEntries)
+	c.Assert(err, check.IsNil)
+	//os.WriteFile("/tmp/pkdata.deb", deb, 0644)
+	c.Assert(deb, check.DeepEquals, pkgdataExpectedDeb)
+}