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tarsum.go
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tarsum.go
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package tarsum
import (
"bytes"
"compress/gzip"
"crypto/sha256"
"encoding/hex"
"hash"
"io"
"sort"
"strconv"
"strings"
"github.com/docker/docker/vendor/src/code.google.com/p/go/src/pkg/archive/tar"
"github.com/docker/docker/pkg/log"
)
const (
buf8K = 8 * 1024
buf16K = 16 * 1024
buf32K = 32 * 1024
)
// NewTarSum creates a new interface for calculating a fixed time checksum of a
// tar archive.
//
// This is used for calculating checksums of layers of an image, in some cases
// 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
}
return &tarSum{Reader: r, DisableCompression: dc, tarSumVersion: v}, nil
}
// TarSum is the generic interface for calculating fixed time
// checksums of a tar archive
type TarSum interface {
io.Reader
GetSums() map[string]string
Sum([]byte) string
Version() Version
}
// tarSum struct is the structure for a Version0 checksum calculation
type tarSum struct {
io.Reader
tarR *tar.Reader
tarW *tar.Writer
gz writeCloseFlusher
bufTar *bytes.Buffer
bufGz *bytes.Buffer
bufData []byte
h hash.Hash
sums map[string]string
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
}
func (ts tarSum) Version() Version {
return ts.tarSumVersion
}
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()) {
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
}
func (ts *tarSum) Read(buf []byte) (int, error) {
if ts.gz == nil {
ts.bufTar = bytes.NewBuffer([]byte{})
ts.bufGz = bytes.NewBuffer([]byte{})
ts.tarR = tar.NewReader(ts.Reader)
ts.tarW = tar.NewWriter(ts.bufTar)
if !ts.DisableCompression {
ts.gz = gzip.NewWriter(ts.bufGz)
} else {
ts.gz = &nopCloseFlusher{Writer: ts.bufGz}
}
ts.h = sha256.New()
ts.h.Reset()
ts.first = true
ts.sums = make(map[string]string)
}
if ts.finished {
return ts.bufGz.Read(buf)
}
if ts.bufData == nil {
switch {
case len(buf) <= buf8K:
ts.bufData = make([]byte, buf8K)
case len(buf) <= buf16K:
ts.bufData = make([]byte, buf16K)
case len(buf) <= buf32K:
ts.bufData = make([]byte, buf32K)
default:
ts.bufData = make([]byte, len(buf))
}
}
buf2 := ts.bufData[:len(buf)-1]
n, err := ts.tarR.Read(buf2)
if err != nil {
if err == io.EOF {
if _, err := ts.h.Write(buf2[:n]); err != nil {
return 0, err
}
if !ts.first {
ts.sums[ts.currentFile] = hex.EncodeToString(ts.h.Sum(nil))
ts.h.Reset()
} else {
ts.first = false
}
currentHeader, err := ts.tarR.Next()
if err != nil {
if err == io.EOF {
if err := ts.gz.Close(); err != nil {
return 0, err
}
ts.finished = true
return n, nil
}
return n, err
}
ts.currentFile = strings.TrimSuffix(strings.TrimPrefix(currentHeader.Name, "./"), "/")
if err := ts.encodeHeader(currentHeader); err != nil {
return 0, err
}
if err := ts.tarW.WriteHeader(currentHeader); err != nil {
return 0, err
}
if _, err := ts.tarW.Write(buf2[:n]); err != nil {
return 0, err
}
ts.tarW.Flush()
if _, err := io.Copy(ts.gz, ts.bufTar); err != nil {
return 0, err
}
ts.gz.Flush()
return ts.bufGz.Read(buf)
}
return n, err
}
// Filling the hash buffer
if _, err = ts.h.Write(buf2[:n]); err != nil {
return 0, err
}
// Filling the tar writter
if _, err = ts.tarW.Write(buf2[:n]); err != nil {
return 0, err
}
ts.tarW.Flush()
// Filling the gz writter
if _, err = io.Copy(ts.gz, ts.bufTar); err != nil {
return 0, err
}
ts.gz.Flush()
return ts.bufGz.Read(buf)
}
func (ts *tarSum) Sum(extra []byte) string {
var sums []string
for _, sum := range ts.sums {
sums = append(sums, sum)
}
sort.Strings(sums)
h := sha256.New()
if extra != nil {
h.Write(extra)
}
for _, sum := range sums {
log.Debugf("-->%s<--", sum)
h.Write([]byte(sum))
}
checksum := ts.Version().String() + "+sha256:" + hex.EncodeToString(h.Sum(nil))
log.Debugf("checksum processed: %s", checksum)
return checksum
}
func (ts *tarSum) GetSums() map[string]string {
return ts.sums
}