distribution/reference/reference.go
Stephen J Day 3150937b9f reference: refactor grammar and regular expressions
To resolve some inconsistencies between the grammar and the regular
expressions, the grammar has been slightly refactored to match the intent. The
regular expressions have been redefined with the same structure to make it
easier to verify the grammar is correct.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
2015-12-04 17:54:23 -08:00

336 lines
8.4 KiB
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 ]
// name := [hostname '/'] component ['/' component]*
// hostname := hostcomponent ['.' hostcomponent]* [':' port-number]
// hostcomponent := /([a-z0-9]|[a-z0-9][a-z0-9-]*[a-z0-9])/
// port-number := /[0-9]+/
// component := alpha-numeric [separator alpha-numeric]*
// alpha-numeric := /[a-z0-9]+/
// separator := /[_.]|__|[-]*/
//
// tag := /[\w][\w.-]{0,127}/
//
// 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,}/ ; At least 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")
// ErrTagInvalidFormat represents an error while trying to parse a string as a tag.
ErrTagInvalidFormat = errors.New("invalid tag format")
// ErrDigestInvalidFormat represents an error while trying to parse a string as a tag.
ErrDigestInvalidFormat = errors.New("invalid digest 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
}
// NamedTagged is an object including a name and tag.
type NamedTagged interface {
Named
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 s and returns a syntactically valid reference implementing
// the Named interface. The reference must have a name, otherwise an error is
// returned.
// If an error was encountered it is returned, along with a nil Reference.
// NOTE: ParseNamed will not handle short digests.
func ParseNamed(s string) (Named, error) {
ref, err := Parse(s)
if err != nil {
return nil, err
}
named, isNamed := ref.(Named)
if !isNamed {
return nil, fmt.Errorf("reference %s has no name", ref.String())
}
return named, nil
}
// WithName returns a named object representing the given string. If the input
// is invalid ErrReferenceInvalidFormat will be returned.
func WithName(name string) (Named, error) {
if len(name) > NameTotalLengthMax {
return nil, ErrNameTooLong
}
if !anchoredNameRegexp.MatchString(name) {
return nil, ErrReferenceInvalidFormat
}
return repository(name), nil
}
// WithTag combines the name from "name" and the tag from "tag" to form a
// reference incorporating both the name and the tag.
func WithTag(name Named, tag string) (NamedTagged, error) {
if !anchoredTagRegexp.MatchString(tag) {
return nil, ErrTagInvalidFormat
}
return taggedReference{
name: name.Name(),
tag: tag,
}, nil
}
// WithDigest combines the name from "name" and the digest from "digest" to form
// a reference incorporating both the name and the digest.
func WithDigest(name Named, digest digest.Digest) (Canonical, error) {
if !anchoredDigestRegexp.MatchString(digest.String()) {
return nil, ErrDigestInvalidFormat
}
return canonicalReference{
name: name.Name(),
digest: digest,
}, 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
}