143 lines
3.9 KiB
Go
143 lines
3.9 KiB
Go
package digest
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import (
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"fmt"
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"hash"
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"io"
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"regexp"
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"strings"
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)
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const (
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// DigestSha256EmptyTar is the canonical sha256 digest of empty data
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DigestSha256EmptyTar = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
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)
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// Digest allows simple protection of hex formatted digest strings, prefixed
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// by their algorithm. Strings of type Digest have some guarantee of being in
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// the correct format and it provides quick access to the components of a
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// digest string.
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//
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// The following is an example of the contents of Digest types:
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//
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// sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc
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//
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// This allows to abstract the digest behind this type and work only in those
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// terms.
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type Digest string
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// NewDigest returns a Digest from alg and a hash.Hash object.
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func NewDigest(alg Algorithm, h hash.Hash) Digest {
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return Digest(fmt.Sprintf("%s:%x", alg, h.Sum(nil)))
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}
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// NewDigestFromHex returns a Digest from alg and a the hex encoded digest.
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func NewDigestFromHex(alg, hex string) Digest {
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return Digest(fmt.Sprintf("%s:%s", alg, hex))
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}
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// DigestRegexp matches valid digest types.
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var DigestRegexp = regexp.MustCompile(`[a-zA-Z0-9-_+.]+:[a-fA-F0-9]+`)
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// DigestRegexpAnchored matches valid digest types, anchored to the start and end of the match.
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var DigestRegexpAnchored = regexp.MustCompile(`^` + DigestRegexp.String() + `$`)
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var (
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// ErrDigestInvalidFormat returned when digest format invalid.
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ErrDigestInvalidFormat = fmt.Errorf("invalid checksum digest format")
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// ErrDigestInvalidLength returned when digest has invalid length.
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ErrDigestInvalidLength = fmt.Errorf("invalid checksum digest length")
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// ErrDigestUnsupported returned when the digest algorithm is unsupported.
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ErrDigestUnsupported = fmt.Errorf("unsupported digest algorithm")
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)
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// ParseDigest parses s and returns the validated digest object. An error will
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// be returned if the format is invalid.
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func ParseDigest(s string) (Digest, error) {
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d := Digest(s)
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return d, d.Validate()
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}
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// FromReader returns the most valid digest for the underlying content using
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// the canonical digest algorithm.
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func FromReader(rd io.Reader) (Digest, error) {
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return Canonical.FromReader(rd)
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}
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// FromBytes digests the input and returns a Digest.
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func FromBytes(p []byte) Digest {
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digester := Canonical.New()
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if _, err := digester.Hash().Write(p); err != nil {
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// Writes to a Hash should never fail. None of the existing
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// hash implementations in the stdlib or hashes vendored
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// here can return errors from Write. Having a panic in this
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// condition instead of having FromBytes return an error value
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// avoids unnecessary error handling paths in all callers.
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panic("write to hash function returned error: " + err.Error())
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}
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return digester.Digest()
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}
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// Validate checks that the contents of d is a valid digest, returning an
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// error if not.
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func (d Digest) Validate() error {
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s := string(d)
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if !DigestRegexpAnchored.MatchString(s) {
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return ErrDigestInvalidFormat
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}
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i := strings.Index(s, ":")
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if i < 0 {
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return ErrDigestInvalidFormat
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}
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// case: "sha256:" with no hex.
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if i+1 == len(s) {
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return ErrDigestInvalidFormat
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}
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switch algorithm := Algorithm(s[:i]); algorithm {
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case SHA256, SHA384, SHA512:
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if algorithm.Size()*2 != len(s[i+1:]) {
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return ErrDigestInvalidLength
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}
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break
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default:
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return ErrDigestUnsupported
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}
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return nil
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}
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// Algorithm returns the algorithm portion of the digest. This will panic if
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// the underlying digest is not in a valid format.
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func (d Digest) Algorithm() Algorithm {
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return Algorithm(d[:d.sepIndex()])
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}
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// Hex returns the hex digest portion of the digest. This will panic if the
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// underlying digest is not in a valid format.
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func (d Digest) Hex() string {
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return string(d[d.sepIndex()+1:])
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}
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func (d Digest) String() string {
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return string(d)
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}
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func (d Digest) sepIndex() int {
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i := strings.Index(string(d), ":")
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if i < 0 {
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panic("could not find ':' in digest: " + d)
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}
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return i
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}
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