distribution/reference/reference.go

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// Package reference provides a general type to represent any way of referencing images within the registry.
// Its main purpose is to abstract tags and digests (content-addressable hash).
//
// Grammar
//
// reference := repository [ ":" tag ] [ "@" digest ]
//
// // repository.go
// repository := hostname ['/' component]+
// hostname := hostcomponent [':' port-number]
// component := subcomponent [separator subcomponent]*
// subcomponent := alpha-numeric ['-'* alpha-numeric]*
// hostcomponent := [hostpart '.']* hostpart
// alpha-numeric := /[a-z0-9]+/
// separator := /([_.]|__)/
// port-number := /[0-9]+/
// hostpart := /([a-z0-9]|[a-z0-9][a-z0-9-]*[a-z0-9])/
//
// // tag.go
// tag := /[\w][\w.-]{0,127}/
//
// // from the digest package
// digest := digest-algorithm ":" digest-hex
// digest-algorithm := digest-algorithm-component [ digest-algorithm-separator digest-algorithm-component ]
// digest-algorithm-separator := /[+.-_]/
// digest-algorithm-component := /[A-Za-z][A-Za-z0-9]*/
// digest-hex := /[0-9a-fA-F]{32,}/ ; Atleast 128 bit digest value
package reference
import (
"errors"
"fmt"
"github.com/docker/distribution/digest"
)
const (
// NameTotalLengthMax is the maximum total number of characters in a repository name.
NameTotalLengthMax = 255
)
var (
// ErrReferenceInvalidFormat represents an error while trying to parse a string as a reference.
ErrReferenceInvalidFormat = errors.New("invalid reference format")
// ErrNameEmpty is returned for empty, invalid repository names.
ErrNameEmpty = errors.New("repository name must have at least one component")
// ErrNameTooLong is returned when a repository name is longer than
// RepositoryNameTotalLengthMax
ErrNameTooLong = fmt.Errorf("repository name must not be more than %v characters", NameTotalLengthMax)
)
// Reference is an opaque object reference identifier that may include
// modifiers such as a hostname, name, tag, and digest.
type Reference interface {
// String returns the full reference
String() string
}
// Field provides a wrapper type for resolving correct reference types when
// working with encoding.
type Field struct {
reference Reference
}
// AsField wraps a reference in a Field for encoding.
func AsField(reference Reference) Field {
return Field{reference}
}
// Reference unwraps the reference type from the field to
// return the Reference object. This object should be
// of the appropriate type to further check for different
// reference types.
func (f Field) Reference() Reference {
return f.reference
}
// MarshalText serializes the field to byte text which
// is the string of the reference.
func (f Field) MarshalText() (p []byte, err error) {
return []byte(f.reference.String()), nil
}
// UnmarshalText parses text bytes by invoking the
// reference parser to ensure the appropriately
// typed reference object is wrapped by field.
func (f *Field) UnmarshalText(p []byte) error {
r, err := Parse(string(p))
if err != nil {
return err
}
f.reference = r
return nil
}
// Named is an object with a full name
type Named interface {
Reference
Name() string
}
// Tagged is an object which has a tag
type Tagged interface {
Reference
Tag() string
}
// Digested is an object which has a digest
// in which it can be referenced by
type Digested interface {
Reference
Digest() digest.Digest
}
// Canonical reference is an object with a fully unique
// name including a name with hostname and digest
type Canonical interface {
Named
Digest() digest.Digest
}
// SplitHostname splits a named reference into a
// hostname and name string. If no valid hostname is
// found, the hostname is empty and the full value
// is returned as name
func SplitHostname(named Named) (string, string) {
name := named.Name()
match := anchoredNameRegexp.FindStringSubmatch(name)
if match == nil || len(match) != 3 {
return "", name
}
return match[1], match[2]
}
// Parse parses s and returns a syntactically valid Reference.
// If an error was encountered it is returned, along with a nil Reference.
// NOTE: Parse will not handle short digests.
func Parse(s string) (Reference, error) {
matches := ReferenceRegexp.FindStringSubmatch(s)
if matches == nil {
if s == "" {
return nil, ErrNameEmpty
}
// TODO(dmcgowan): Provide more specific and helpful error
return nil, ErrReferenceInvalidFormat
}
if len(matches[1]) > NameTotalLengthMax {
return nil, ErrNameTooLong
}
ref := reference{
name: matches[1],
tag: matches[2],
}
if matches[3] != "" {
var err error
ref.digest, err = digest.ParseDigest(matches[3])
if err != nil {
return nil, err
}
}
r := getBestReferenceType(ref)
if r == nil {
return nil, ErrNameEmpty
}
return r, nil
}
// ParseNamed parses the input string and returns a named
// object representing the given string. If the input is
// invalid ErrReferenceInvalidFormat will be returned.
func ParseNamed(name string) (Named, error) {
if !anchoredNameRegexp.MatchString(name) {
return nil, ErrReferenceInvalidFormat
}
return repository(name), nil
}
func getBestReferenceType(ref reference) Reference {
if ref.name == "" {
// Allow digest only references
if ref.digest != "" {
return digestReference(ref.digest)
}
return nil
}
if ref.tag == "" {
if ref.digest != "" {
return canonicalReference{
name: ref.name,
digest: ref.digest,
}
}
return repository(ref.name)
}
if ref.digest == "" {
return taggedReference{
name: ref.name,
tag: ref.tag,
}
}
return ref
}
type reference struct {
name string
tag string
digest digest.Digest
}
func (r reference) String() string {
return r.name + ":" + r.tag + "@" + r.digest.String()
}
func (r reference) Name() string {
return r.name
}
func (r reference) Tag() string {
return r.tag
}
func (r reference) Digest() digest.Digest {
return r.digest
}
type repository string
func (r repository) String() string {
return string(r)
}
func (r repository) Name() string {
return string(r)
}
type digestReference digest.Digest
func (d digestReference) String() string {
return d.String()
}
func (d digestReference) Digest() digest.Digest {
return digest.Digest(d)
}
type taggedReference struct {
name string
tag string
}
func (t taggedReference) String() string {
return t.name + ":" + t.tag
}
func (t taggedReference) Name() string {
return t.name
}
func (t taggedReference) Tag() string {
return t.tag
}
type canonicalReference struct {
name string
digest digest.Digest
}
func (c canonicalReference) String() string {
return c.name + "@" + c.digest.String()
}
func (c canonicalReference) Name() string {
return c.name
}
func (c canonicalReference) Digest() digest.Digest {
return c.digest
}