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|
package digest
import (
"fmt"
"hash"
"io"
"regexp"
"strings"
)
const (
// DigestSha256EmptyTar is the canonical sha256 digest of empty data
DigestSha256EmptyTar = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
)
// 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
//
// 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 Algorithm, h hash.Hash) Digest {
return NewDigestFromBytes(alg, h.Sum(nil))
}
// NewDigestFromBytes returns a new digest from the byte contents of p.
// Typically, this can come from hash.Hash.Sum(...) or xxx.SumXXX(...)
// functions. This is also useful for rebuilding digests from binary
// serializations.
func NewDigestFromBytes(alg Algorithm, p []byte) Digest {
return Digest(fmt.Sprintf("%s:%x", alg, p))
}
// NewDigestFromHex returns a Digest from alg and a the hex encoded digest.
func NewDigestFromHex(alg, hex string) Digest {
return Digest(fmt.Sprintf("%s:%s", alg, hex))
}
// DigestRegexp matches valid digest types.
var DigestRegexp = regexp.MustCompile(`[a-zA-Z0-9-_+.]+:[a-fA-F0-9]+`)
// DigestRegexpAnchored matches valid digest types, anchored to the start and end of the match.
var DigestRegexpAnchored = regexp.MustCompile(`^` + DigestRegexp.String() + `$`)
var (
// ErrDigestInvalidFormat returned when digest format invalid.
ErrDigestInvalidFormat = fmt.Errorf("invalid checksum digest format")
// ErrDigestInvalidLength returned when digest has invalid length.
ErrDigestInvalidLength = fmt.Errorf("invalid checksum digest length")
// ErrDigestUnsupported returned when the digest algorithm is unsupported.
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 using
// the canonical digest algorithm.
func FromReader(rd io.Reader) (Digest, error) {
return Canonical.FromReader(rd)
}
// FromBytes digests the input and returns a Digest.
func FromBytes(p []byte) Digest {
return Canonical.FromBytes(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)
if !DigestRegexpAnchored.MatchString(s) {
return ErrDigestInvalidFormat
}
i := strings.Index(s, ":")
if i < 0 {
return ErrDigestInvalidFormat
}
// case: "sha256:" with no hex.
if i+1 == len(s) {
return ErrDigestInvalidFormat
}
switch algorithm := Algorithm(s[:i]); algorithm {
case SHA256, SHA384, SHA512:
if algorithm.Size()*2 != len(s[i+1:]) {
return ErrDigestInvalidLength
}
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() Algorithm {
return Algorithm(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("could not find ':' in digest: " + d)
}
return i
}
|
