registry/reference/reference.go

// 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
}