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moby--moby/pkg/tarsum/versioning.go

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package tarsum // import "github.com/docker/docker/pkg/tarsum"
import (
"archive/tar"
"errors"
"io"
"sort"
"strconv"
"strings"
)
// Version is used for versioning of the TarSum algorithm
// based on the prefix of the hash used
// i.e. "tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b"
type Version int
// Prefix of "tarsum"
const (
Version0 Version = iota
Version1
// VersionDev this constant will be either the latest or an unsettled next-version of the TarSum calculation
VersionDev
)
// WriteV1Header writes a tar header to a writer in V1 tarsum format.
func WriteV1Header(h *tar.Header, w io.Writer) {
for _, elem := range v1TarHeaderSelect(h) {
w.Write([]byte(elem[0] + elem[1]))
}
}
// VersionLabelForChecksum returns the label for the given tarsum
// checksum, i.e., everything before the first `+` character in
// the string or an empty string if no label separator is found.
func VersionLabelForChecksum(checksum string) string {
// Checksums are in the form: {versionLabel}+{hashID}:{hex}
sepIndex := strings.Index(checksum, "+")
if sepIndex < 0 {
return ""
}
return checksum[:sepIndex]
}
// GetVersions gets a list of all known tarsum versions.
func GetVersions() []Version {
v := []Version{}
for k := range tarSumVersions {
v = append(v, k)
}
return v
}
var (
tarSumVersions = map[Version]string{
Version0: "tarsum",
Version1: "tarsum.v1",
VersionDev: "tarsum.dev",
}
tarSumVersionsByName = map[string]Version{
"tarsum": Version0,
"tarsum.v1": Version1,
"tarsum.dev": VersionDev,
}
)
func (tsv Version) String() string {
return tarSumVersions[tsv]
}
// GetVersionFromTarsum returns the Version from the provided string.
func GetVersionFromTarsum(tarsum string) (Version, error) {
tsv := tarsum
if strings.Contains(tarsum, "+") {
tsv = strings.SplitN(tarsum, "+", 2)[0]
}
for v, s := range tarSumVersions {
if s == tsv {
return v, nil
}
}
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.FormatInt(h.Mode, 10)},
{"uid", strconv.Itoa(h.Uid)},
{"gid", strconv.Itoa(h.Gid)},
{"size", strconv.FormatInt(h.Size, 10)},
{"mtime", strconv.FormatInt(h.ModTime.UTC().Unix(), 10)},
{"typeflag", string([]byte{h.Typeflag})},
{"linkname", h.Linkname},
{"uname", h.Uname},
{"gname", h.Gname},
{"devmajor", strconv.FormatInt(h.Devmajor, 10)},
{"devminor", strconv.FormatInt(h.Devminor, 10)},
}
}
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
}