distribution/digest/digest.go

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package digest
import (
"bytes"
"crypto/sha256"
"fmt"
"hash"
"io"
"io/ioutil"
"strings"
"github.com/docker/docker-registry/common"
"github.com/docker/docker/pkg/tarsum"
)
// Digest allows simple protection of hex formatted digest strings, prefixed
// by their algorithm. Strings of type Digest have some guarantee of being in
// the correct format and it provides quick access to the components of a
// digest string.
//
// The following is an example of the contents of Digest types:
//
// sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc
//
// More important for this code base, this type is compatible with tarsum
// digests. For example, the following would be a valid Digest:
//
// tarsum+sha256:e58fcf7418d4390dec8e8fb69d88c06ec07039d651fedd3aa72af9972e7d046b
//
// This allows to abstract the digest behind this type and work only in those
// terms.
type Digest string
// NewDigest returns a Digest from alg and a hash.Hash object.
func NewDigest(alg string, h hash.Hash) Digest {
return Digest(fmt.Sprintf("%s:%x", alg, h.Sum(nil)))
}
var (
// ErrDigestInvalidFormat returned when digest format invalid.
ErrDigestInvalidFormat = fmt.Errorf("invalid checksum digest format")
// ErrDigestUnsupported returned when the digest algorithm is unsupported by registry.
ErrDigestUnsupported = fmt.Errorf("unsupported digest algorithm")
)
// ParseDigest parses s and returns the validated digest object. An error will
// be returned if the format is invalid.
func ParseDigest(s string) (Digest, error) {
d := Digest(s)
return d, d.Validate()
}
// FromReader returns the most valid digest for the underlying content.
func FromReader(rd io.Reader) (Digest, error) {
// TODO(stevvooe): This is pretty inefficient to always be calculating a
// sha256 hash to provide fallback, but it provides some nice semantics in
// that we never worry about getting the right digest for a given reader.
// For the most part, we can detect tar vs non-tar with only a few bytes,
// so a scheme that saves those bytes would probably be better here.
h := sha256.New()
tr := io.TeeReader(rd, h)
ts, err := tarsum.NewTarSum(tr, true, tarsum.Version1)
if err != nil {
return "", err
}
// Try to copy from the tarsum, if we fail, copy the remaining bytes into
// hash directly.
if _, err := io.Copy(ioutil.Discard, ts); err != nil {
if err.Error() != "archive/tar: invalid tar header" {
return "", err
}
if _, err := io.Copy(h, rd); err != nil {
return "", err
}
return NewDigest("sha256", h), nil
}
d, err := ParseDigest(ts.Sum(nil))
if err != nil {
return "", err
}
return d, nil
}
// FromBytes digests the input and returns a Digest.
func FromBytes(p []byte) (Digest, error) {
return FromReader(bytes.NewReader(p))
}
// Validate checks that the contents of d is a valid digest, returning an
// error if not.
func (d Digest) Validate() error {
s := string(d)
// Common case will be tarsum
_, err := common.ParseTarSum(s)
if err == nil {
return nil
}
// Continue on for general parser
i := strings.Index(s, ":")
if i < 0 {
return ErrDigestInvalidFormat
}
// case: "sha256:" with no hex.
if i+1 == len(s) {
return ErrDigestInvalidFormat
}
switch s[:i] {
case "md5", "sha1", "sha256":
break
default:
return ErrDigestUnsupported
}
return nil
}
// Algorithm returns the algorithm portion of the digest. This will panic if
// the underlying digest is not in a valid format.
func (d Digest) Algorithm() string {
return string(d[:d.sepIndex()])
}
// Hex returns the hex digest portion of the digest. This will panic if the
// underlying digest is not in a valid format.
func (d Digest) Hex() string {
return string(d[d.sepIndex()+1:])
}
func (d Digest) String() string {
return string(d)
}
func (d Digest) sepIndex() int {
i := strings.Index(string(d), ":")
if i < 0 {
panic("invalid digest: " + d)
}
return i
}