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digest.go
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/
digest.go
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package digest
import (
"fmt"
"math/big"
"strings"
"github.com/pkg/errors"
)
// Algorithm describes the digest algorithm
type Algorithm int
const (
_ Algorithm = iota
// SHA256 is the sha256 algorithm
SHA256
// SHA384 is the sha384 algorithm
SHA384
)
// String returns the textual representation
func (t Algorithm) String() string {
switch t {
case SHA256:
return "sha256"
case SHA384:
return "sha384"
default:
return "undefined"
}
}
// Digest contains a checksum
type Digest struct {
Sum big.Int
Algorithm Algorithm
}
// String returns '<Algorithm>:<checksum>'
func (d *Digest) String() string {
return fmt.Sprintf("%s:%s", d.Algorithm, d.Sum.Text(16))
}
// FromString converts a "sha256:<hash> string to Digest
func FromString(in string) (*Digest, error) {
var algorithm Algorithm
spl := strings.Split(strings.TrimSpace(in), ":")
if len(spl) != 2 {
return nil, errors.New("invalid format, must contain exactly 1 ':'")
}
switch a := strings.ToLower(spl[0]); a {
case "sha256":
if len(spl[1]) != 64 {
return nil, fmt.Errorf("hash length is %d, expected length 64", len(spl[1]))
}
algorithm = SHA256
case "sha384":
if len(spl[1]) != 96 {
return nil, fmt.Errorf("hash length is %d, expected length 96", len(spl[1]))
}
algorithm = SHA384
default:
return nil, errors.New("unsupported format %q")
}
sum := big.Int{}
_, err := fmt.Sscan("0x"+spl[1], &sum)
if err != nil {
return nil, errors.Wrap(err, "converting digest to big int failed")
}
return &Digest{
Sum: sum,
Algorithm: algorithm,
}, nil
}