reference

README

Distribution reference

Go library to handle references to container images.

This repository contains a library for handling references to container images held in container registries. Please see godoc for details.

Contribution

Please see CONTRIBUTING.md for details on how to contribute issues, fixes, and patches to this project.

Communication

For async communication and long running discussions please use issues and pull requests on the github repo. This will be the best place to discuss design and implementation.

For sync communication we have a #distribution channel in the CNCF Slack that everyone is welcome to join and chat about development.

Licenses

The distribution codebase is released under the Apache 2.0 license.

Documentation

Overview

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                       := name [ ":" tag ] [ "@" digest ]
name                            := [domain '/'] remote-name
domain                          := host [':' port-number]
host                            := domain-name | IPv4address | \[ IPv6address \]	; rfc3986 appendix-A
domain-name                     := domain-component ['.' domain-component]*
domain-component                := /([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])/
port-number                     := /[0-9]+/
path-component                  := alpha-numeric [separator alpha-numeric]*
path (or "remote-name")         := path-component ['/' path-component]*
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

identifier                      := /[a-f0-9]{64}/

Index

• Constants
• Variables
• func Domain(named Named) string
• func FamiliarMatch(pattern string, ref Reference) (bool, error)
• func FamiliarName(ref Named) string
• func FamiliarString(ref Reference) string
• func IsNameOnly(ref Named) bool
• func Path(named Named) (name string)
• func Sort(references []string) []string
• type Canonical
  • func WithDigest(name Named, digest digest.Digest) (Canonical, error)
• type Digested
• type Field
  • func AsField(reference Reference) Field
  • func (f Field) MarshalText() (p []byte, err error)
  • func (f Field) Reference() Reference
  • func (f *Field) UnmarshalText(p []byte) error
• type Named
  • func ParseDockerRef(ref string) (Named, error)
  • func ParseNamed(s string) (Named, error)
  • func ParseNormalizedNamed(s string) (Named, error)
  • func TagNameOnly(ref Named) Named
  • func TrimNamed(ref Named) Named
  • func WithName(name string) (Named, error)
• type NamedTagged
  • func WithTag(name Named, tag string) (NamedTagged, error)
• type Reference
  • func Parse(s string) (Reference, error)
  • func ParseAnyReference(ref string) (Reference, error)
• type Tagged

Constants

const (
	// RepositoryNameTotalLengthMax is the maximum total number of characters in a repository name.
	RepositoryNameTotalLengthMax = 255

	// NameTotalLengthMax is the maximum total number of characters in a repository name.
	//
	// Deprecated: use [RepositoryNameTotalLengthMax] instead.
	NameTotalLengthMax = RepositoryNameTotalLengthMax
)

Variables

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")

	// ErrNameContainsUppercase is returned for invalid repository names that contain uppercase characters.
	ErrNameContainsUppercase = errors.New("repository name must be lowercase")

	// 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", RepositoryNameTotalLengthMax)

	// ErrNameNotCanonical is returned when a name is not canonical.
	ErrNameNotCanonical = errors.New("repository name must be canonical")
)

var DigestRegexp = regexp.MustCompile(digestPat)

DigestRegexp matches well-formed digests, including algorithm (e.g. "sha256:<encoded>").

var DomainRegexp = regexp.MustCompile(domainAndPort)

DomainRegexp matches hostname or IP-addresses, optionally including a port number. It defines the structure of potential domain components that may be part of image names. This is purposely a subset of what is allowed by DNS to ensure backwards compatibility with Docker image names. It may be a subset of DNS domain name, an IPv4 address in decimal format, or an IPv6 address between square brackets (excluding zone identifiers as defined by RFC 6874 or special addresses such as IPv4-Mapped).

var IdentifierRegexp = regexp.MustCompile(identifier)

IdentifierRegexp is the format for string identifier used as a content addressable identifier using sha256. These identifiers are like digests without the algorithm, since sha256 is used.

var NameRegexp = regexp.MustCompile(namePat)

NameRegexp is the format for the name component of references, including an optional domain and port, but without tag or digest suffix.

var ReferenceRegexp = regexp.MustCompile(referencePat)

ReferenceRegexp is the full supported format of a reference. The regexp is anchored and has capturing groups for name, tag, and digest components.

var TagRegexp = regexp.MustCompile(tag)

TagRegexp matches valid tag names. From docker/docker:graph/tags.go.

Functions

func Domain

func Domain(named Named) string

Domain returns the domain part of the Named reference.

func FamiliarMatch

func FamiliarMatch(pattern string, ref Reference) (bool, error)

FamiliarMatch reports whether ref matches the specified pattern. See path.Match for supported patterns.

func FamiliarName

func FamiliarName(ref Named) string

FamiliarName returns the familiar name string for the given named, familiarizing if needed.

func FamiliarString

func FamiliarString(ref Reference) string

FamiliarString returns the familiar string representation for the given reference, familiarizing if needed.

func IsNameOnly

func IsNameOnly(ref Named) bool

IsNameOnly returns true if reference only contains a repo name.

func Path

func Path(named Named) (name string)

Path returns the name without the domain part of the Named reference.

func Sort

func Sort(references []string) []string

Sort sorts string references preferring higher information references.

The precedence is as follows:

1. Named + Tagged + Digested (e.g., "docker.io/library/busybox:latest@sha256:<digest>")
2. Named + Tagged (e.g., "docker.io/library/busybox:latest")
3. Named + Digested (e.g., "docker.io/library/busybo@sha256:<digest>")
4. Named (e.g., "docker.io/library/busybox")
5. Digested (e.g., "docker.io@sha256:<digest>")
6. Parse error

Types

type Canonical

type Canonical interface {
	Named
	Digest() digest.Digest
}

Canonical reference is an object with a fully unique name including a name with domain and digest

func WithDigest

func WithDigest(name Named, digest digest.Digest) (Canonical, error)

WithDigest combines the name from "name" and the digest from "digest" to form a reference incorporating both the name and the digest.

type Digested

type Digested interface {
	Reference
	Digest() digest.Digest
}

Digested is an object which has a digest in which it can be referenced by

type Field

type Field struct {
	// contains filtered or unexported fields
}

Field provides a wrapper type for resolving correct reference types when working with encoding.

func AsField

func AsField(reference Reference) Field

AsField wraps a reference in a Field for encoding.

func (Field) MarshalText

func (f Field) MarshalText() (p []byte, err error)

MarshalText serializes the field to byte text which is the string of the reference.

func (Field) Reference

func (f Field) Reference() 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 (*Field) UnmarshalText

func (f *Field) UnmarshalText(p []byte) error

UnmarshalText parses text bytes by invoking the reference parser to ensure the appropriately typed reference object is wrapped by field.

type Named

type Named interface {
	Reference
	Name() string
}

Named is an object with a full name

func ParseDockerRef

func ParseDockerRef(ref string) (Named, error)

ParseDockerRef normalizes the image reference following the docker convention, which allows for references to contain both a tag and a digest. It returns a reference that is either tagged or digested. For references containing both a tag and a digest, it returns a digested reference. For example, the following reference:

docker.io/library/busybox:latest@sha256:7cc4b5aefd1d0cadf8d97d4350462ba51c694ebca145b08d7d41b41acc8db5aa

Is returned as a digested reference (with the ":latest" tag removed):

docker.io/library/busybox@sha256:7cc4b5aefd1d0cadf8d97d4350462ba51c694ebca145b08d7d41b41acc8db5aa

References that are already "tagged" or "digested" are returned unmodified:

// Already a digested reference
docker.io/library/busybox@sha256:7cc4b5aefd1d0cadf8d97d4350462ba51c694ebca145b08d7d41b41acc8db5aa

// Already a named reference
docker.io/library/busybox:latest

func ParseNamed

func ParseNamed(s string) (Named, error)

ParseNamed parses s and returns a syntactically valid reference implementing the Named interface. The reference must have a name and be in the canonical form, otherwise an error is returned. If an error was encountered it is returned, along with a nil Reference.

func ParseNormalizedNamed

func ParseNormalizedNamed(s string) (Named, error)

ParseNormalizedNamed parses a string into a named reference transforming a familiar name from Docker UI to a fully qualified reference. If the value may be an identifier use ParseAnyReference.

func TagNameOnly

func TagNameOnly(ref Named) Named

TagNameOnly adds the default tag "latest" to a reference if it only has a repo name.

func TrimNamed

func TrimNamed(ref Named) Named

TrimNamed removes any tag or digest from the named reference.

func WithName

func WithName(name string) (Named, error)

WithName returns a named object representing the given string. If the input is invalid ErrReferenceInvalidFormat will be returned.

type NamedTagged

type NamedTagged interface {
	Named
	Tag() string
}

NamedTagged is an object including a name and tag.

func WithTag

func WithTag(name Named, tag string) (NamedTagged, error)

WithTag combines the name from "name" and the tag from "tag" to form a reference incorporating both the name and the tag.

type Reference

type Reference interface {
	// String returns the full reference
	String() string
}

Reference is an opaque object reference identifier that may include modifiers such as a hostname, name, tag, and digest.

func Parse

func Parse(s string) (Reference, error)

Parse parses s and returns a syntactically valid Reference. If an error was encountered it is returned, along with a nil Reference.

func ParseAnyReference

func ParseAnyReference(ref string) (Reference, error)

ParseAnyReference parses a reference string as a possible identifier, full digest, or familiar name.

type Tagged

type Tagged interface {
	Reference
	Tag() string
}

Tagged is an object which has a tag