distribution/common/tarsum.go

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package common
import (
"fmt"
"regexp"
)
// TarSumRegexp defines a reguler expression to match tarsum identifiers.
var TarsumRegexp = regexp.MustCompile("tarsum(?:.[a-z0-9]+)?\\+[a-zA-Z0-9]+:[A-Fa-f0-9]+")
// TarsumRegexpCapturing defines a reguler expression to match tarsum identifiers with
// capture groups corresponding to each component.
var TarsumRegexpCapturing = regexp.MustCompile("(tarsum)(.([a-z0-9]+))?\\+([a-zA-Z0-9]+):([A-Fa-f0-9]+)")
// TarSumInfo contains information about a parsed tarsum.
type TarSumInfo struct {
// Version contains the version of the tarsum.
Version string
// Algorithm contains the algorithm for the final digest
Algorithm string
// Digest contains the hex-encoded digest.
Digest string
}
// InvalidTarSumError provides informations about a TarSum that cannot be parsed
// by ParseTarSum.
type InvalidTarSumError struct {
TarSum string
}
func (e InvalidTarSumError) Error() string {
return fmt.Sprintf("invalid tarsum: %q", e.TarSum)
}
// ParseTarSum parses a tarsum string into its components of interest. For
// example, this method may receive the tarsum in the following format:
//
// tarsum.v1+sha256:220a60ecd4a3c32c282622a625a54db9ba0ff55b5ba9c29c7064a2bc358b6a3e
//
// The function will return the following:
//
// TarSumInfo{
// Version: "v1",
// Algorithm: "sha256",
// Digest: "220a60ecd4a3c32c282622a625a54db9ba0ff55b5ba9c29c7064a2bc358b6a3e",
// }
//
func ParseTarSum(tarSum string) (tsi TarSumInfo, err error) {
components := TarsumRegexpCapturing.FindStringSubmatch(tarSum)
if len(components) != 1+TarsumRegexpCapturing.NumSubexp() {
return TarSumInfo{}, InvalidTarSumError{TarSum: tarSum}
}
return TarSumInfo{
Version: components[3],
Algorithm: components[4],
Digest: components[5],
}, nil
}
// String returns the valid, string representation of the tarsum info.
func (tsi TarSumInfo) String() string {
if tsi.Version == "" {
return fmt.Sprintf("tarsum+%s:%s", tsi.Algorithm, tsi.Digest)
}
return fmt.Sprintf("tarsum.%s+%s:%s", tsi.Version, tsi.Algorithm, tsi.Digest)
}