Finalize TarSum Version 1 w/ refactor

The current Dev version of TarSum includes hashing of extended
file attributes and omits inclusion of modified time headers.

I refactored the logic around the version differences to make it
more clear that the difference between versions is in how tar
headers are selected and ordered.

TarSum Version 1 is now declared with the new Dev version continuing
to track it.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

pkg/tarsum/tarsum.go

@@ -7,8 +7,6 @@ import (
 	"encoding/hex"
 	"hash"
 	"io"
-	"sort"
-	"strconv"
 	"strings"
 
 	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
@@ -29,18 +27,20 @@ const (
 // including the byte payload of the image's json metadata as well, and for
 // calculating the checksums for buildcache.
 func NewTarSum(r io.Reader, dc bool, v Version) (TarSum, error) {
-	if _, ok := tarSumVersions[v]; !ok {
-		return nil, ErrVersionNotImplemented
+	headerSelector, err := getTarHeaderSelector(v)
+	if err != nil {
+		return nil, err
 	}
-	return &tarSum{Reader: r, DisableCompression: dc, tarSumVersion: v}, nil
+	return &tarSum{Reader: r, DisableCompression: dc, tarSumVersion: v, headerSelector: headerSelector}, nil
 }
 
 // Create a new TarSum, providing a THash to use rather than the DefaultTHash
 func NewTarSumHash(r io.Reader, dc bool, v Version, tHash THash) (TarSum, error) {
-	if _, ok := tarSumVersions[v]; !ok {
-		return nil, ErrVersionNotImplemented
+	headerSelector, err := getTarHeaderSelector(v)
+	if err != nil {
+		return nil, err
 	}
-	return &tarSum{Reader: r, DisableCompression: dc, tarSumVersion: v, tHash: tHash}, nil
+	return &tarSum{Reader: r, DisableCompression: dc, tarSumVersion: v, headerSelector: headerSelector, tHash: tHash}, nil
 }
 
 // TarSum is the generic interface for calculating fixed time
@@ -69,8 +69,9 @@ type tarSum struct {
 	currentFile        string
 	finished           bool
 	first              bool
-	DisableCompression bool    // false by default. When false, the output gzip compressed.
-	tarSumVersion      Version // this field is not exported so it can not be mutated during use
+	DisableCompression bool              // false by default. When false, the output gzip compressed.
+	tarSumVersion      Version           // this field is not exported so it can not be mutated during use
+	headerSelector     tarHeaderSelector // handles selecting and ordering headers for files in the archive
 }
 
 func (ts tarSum) Hash() THash {
@@ -103,49 +104,12 @@ type simpleTHash struct {
 func (sth simpleTHash) Name() string    { return sth.n }
 func (sth simpleTHash) Hash() hash.Hash { return sth.h() }
 
-func (ts tarSum) selectHeaders(h *tar.Header, v Version) (set [][2]string) {
-	for _, elem := range [][2]string{
-		{"name", h.Name},
-		{"mode", strconv.Itoa(int(h.Mode))},
-		{"uid", strconv.Itoa(h.Uid)},
-		{"gid", strconv.Itoa(h.Gid)},
-		{"size", strconv.Itoa(int(h.Size))},
-		{"mtime", strconv.Itoa(int(h.ModTime.UTC().Unix()))},
-		{"typeflag", string([]byte{h.Typeflag})},
-		{"linkname", h.Linkname},
-		{"uname", h.Uname},
-		{"gname", h.Gname},
-		{"devmajor", strconv.Itoa(int(h.Devmajor))},
-		{"devminor", strconv.Itoa(int(h.Devminor))},
-	} {
-		if v >= VersionDev && elem[0] == "mtime" {
-			continue
-		}
-		set = append(set, elem)
-	}
-	return
-}
-
 func (ts *tarSum) encodeHeader(h *tar.Header) error {
-	for _, elem := range ts.selectHeaders(h, ts.Version()) {
+	for _, elem := range ts.headerSelector.selectHeaders(h) {
 		if _, err := ts.h.Write([]byte(elem[0] + elem[1])); err != nil {
 			return err
 		}
 	}
-
-	// include the additional pax headers, from an ordered list
-	if ts.Version() >= VersionDev {
-		var keys []string
-		for k := range h.Xattrs {
-			keys = append(keys, k)
-		}
-		sort.Strings(keys)
-		for _, k := range keys {
-			if _, err := ts.h.Write([]byte(k + h.Xattrs[k])); err != nil {
-				return err
-			}
-		}
-	}
 	return nil
 }
 

pkg/tarsum/versioning.go

@@ -2,7 +2,11 @@ package tarsum
 
 import (
 	"errors"
+	"sort"
+	"strconv"
 	"strings"
+
+	"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
 )
 
 // versioning of the TarSum algorithm
@@ -10,11 +14,11 @@ import (
 // i.e. "tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b"
 type Version int
 
+// Prefix of "tarsum"
 const (
-	// Prefix of "tarsum"
 	Version0 Version = iota
-	// Prefix of "tarsum.dev"
-	// NOTE: this variable will be of an unsettled next-version of the TarSum calculation
+	Version1
+	// NOTE: this variable will be either the latest or an unsettled next-version of the TarSum calculation
 	VersionDev
 )
 
@@ -28,8 +32,9 @@ func GetVersions() []Version {
 }
 
 var tarSumVersions = map[Version]string{
-	0: "tarsum",
-	1: "tarsum.dev",
+	Version0:   "tarsum",
+	Version1:   "tarsum.v1",
+	VersionDev: "tarsum.dev",
 }
 
 func (tsv Version) String() string {
@@ -50,7 +55,78 @@ func GetVersionFromTarsum(tarsum string) (Version, error) {
 	return -1, ErrNotVersion
 }
 
+// Errors that may be returned by functions in this package
 var (
 	ErrNotVersion            = errors.New("string does not include a TarSum Version")
 	ErrVersionNotImplemented = errors.New("TarSum Version is not yet implemented")
 )
+
+// tarHeaderSelector is the interface which different versions
+// of tarsum should use for selecting and ordering tar headers
+// for each item in the archive.
+type tarHeaderSelector interface {
+	selectHeaders(h *tar.Header) (orderedHeaders [][2]string)
+}
+
+type tarHeaderSelectFunc func(h *tar.Header) (orderedHeaders [][2]string)
+
+func (f tarHeaderSelectFunc) selectHeaders(h *tar.Header) (orderedHeaders [][2]string) {
+	return f(h)
+}
+
+func v0TarHeaderSelect(h *tar.Header) (orderedHeaders [][2]string) {
+	return [][2]string{
+		{"name", h.Name},
+		{"mode", strconv.Itoa(int(h.Mode))},
+		{"uid", strconv.Itoa(h.Uid)},
+		{"gid", strconv.Itoa(h.Gid)},
+		{"size", strconv.Itoa(int(h.Size))},
+		{"mtime", strconv.Itoa(int(h.ModTime.UTC().Unix()))},
+		{"typeflag", string([]byte{h.Typeflag})},
+		{"linkname", h.Linkname},
+		{"uname", h.Uname},
+		{"gname", h.Gname},
+		{"devmajor", strconv.Itoa(int(h.Devmajor))},
+		{"devminor", strconv.Itoa(int(h.Devminor))},
+	}
+}
+
+func v1TarHeaderSelect(h *tar.Header) (orderedHeaders [][2]string) {
+	// Get extended attributes.
+	xAttrKeys := make([]string, len(h.Xattrs))
+	for k := range h.Xattrs {
+		xAttrKeys = append(xAttrKeys, k)
+	}
+	sort.Strings(xAttrKeys)
+
+	// Make the slice with enough capacity to hold the 11 basic headers
+	// we want from the v0 selector plus however many xattrs we have.
+	orderedHeaders = make([][2]string, 0, 11+len(xAttrKeys))
+
+	// Copy all headers from v0 excluding the 'mtime' header (the 5th element).
+	v0headers := v0TarHeaderSelect(h)
+	orderedHeaders = append(orderedHeaders, v0headers[0:5]...)
+	orderedHeaders = append(orderedHeaders, v0headers[6:]...)
+
+	// Finally, append the sorted xattrs.
+	for _, k := range xAttrKeys {
+		orderedHeaders = append(orderedHeaders, [2]string{k, h.Xattrs[k]})
+	}
+
+	return
+}
+
+var registeredHeaderSelectors = map[Version]tarHeaderSelectFunc{
+	Version0:   v0TarHeaderSelect,
+	Version1:   v1TarHeaderSelect,
+	VersionDev: v1TarHeaderSelect,
+}
+
+func getTarHeaderSelector(v Version) (tarHeaderSelector, error) {
+	headerSelector, ok := registeredHeaderSelectors[v]
+	if !ok {
+		return nil, ErrVersionNotImplemented
+	}
+
+	return headerSelector, nil
+}

pkg/tarsum/versioning_test.go

@@ -11,11 +11,17 @@ func TestVersion(t *testing.T) {
 		t.Errorf("expected %q, got %q", expected, v.String())
 	}
 
-	expected = "tarsum.dev"
+	expected = "tarsum.v1"
 	v = 1
 	if v.String() != expected {
 		t.Errorf("expected %q, got %q", expected, v.String())
 	}
+
+	expected = "tarsum.dev"
+	v = 2
+	if v.String() != expected {
+		t.Errorf("expected %q, got %q", expected, v.String())
+	}
 }
 
 func TestGetVersion(t *testing.T) {