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package reference
import "regexp"
var (
// alphaNumericRegexp defines the alpha numeric atom, typically a
// component of names. This only allows lower case characters and digits.
alphaNumericRegexp = match(`[a-z0-9]+`)
// separatorRegexp defines the separators allowed to be embedded in name
// components. This allow one period, one or two underscore and multiple
// dashes.
separatorRegexp = match(`(?:[._]|__|[-]*)`)
// nameComponentRegexp restricts registry path component names to start
// with at least one letter or number, with following parts able to be
// separated by one period, one or two underscore and multiple dashes.
nameComponentRegexp = expression(
optional(repeated(separatorRegexp, alphaNumericRegexp)))
// domainComponentRegexp restricts the registry domain component of a
// repository name to start with a component as defined by DomainRegexp
// and followed by an optional port.
domainComponentRegexp = match(`(?:[a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])`)
// DomainRegexp 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.
DomainRegexp = expression(
optional(repeated(literal(`.`), domainComponentRegexp)),
optional(literal(`:`), match(`[0-9]+`)))
// TagRegexp matches valid tag names. From docker/docker:graph/tags.go.
TagRegexp = match(`[\w][\w.-]{0,127}`)
// anchoredTagRegexp matches valid tag names, anchored at the start and
// end of the matched string.
anchoredTagRegexp = anchored(TagRegexp)
// DigestRegexp matches valid digests.
DigestRegexp = match(`[A-Za-z][A-Za-z0-9]*(?:[-_+.][A-Za-z][A-Za-z0-9]*)*[:][[:xdigit:]]{32,}`)
// anchoredDigestRegexp matches valid digests, anchored at the start and
// end of the matched string.
anchoredDigestRegexp = anchored(DigestRegexp)
// NameRegexp is the format for the name component of references. The
// regexp has capturing groups for the domain and name part omitting
// the separating forward slash from either.
NameRegexp = expression(
optional(DomainRegexp, literal(`/`)),
optional(repeated(literal(`/`), nameComponentRegexp)))
// anchoredNameRegexp is used to parse a name value, capturing the
// domain and trailing components.
anchoredNameRegexp = anchored(
optional(capture(DomainRegexp), literal(`/`)),
optional(repeated(literal(`/`), nameComponentRegexp))))
// ReferenceRegexp is the full supported format of a reference. The regexp
// is anchored and has capturing groups for name, tag, and digest
// components.
ReferenceRegexp = anchored(capture(NameRegexp),
optional(literal(":"), capture(TagRegexp)),
optional(literal("@"), capture(DigestRegexp)))
// 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.
IdentifierRegexp = match(`([a-f0-9]{64})`)
// ShortIdentifierRegexp is the format used to represent a prefix
// of an identifier. A prefix may be used to match a sha256 identifier
// within a list of trusted identifiers.
ShortIdentifierRegexp = match(`([a-f0-9]{6,64})`)
// anchoredIdentifierRegexp is used to check or match an
// identifier value, anchored at start and end of string.
anchoredIdentifierRegexp = anchored(IdentifierRegexp)
// anchoredShortIdentifierRegexp is used to check if a value
// is a possible identifier prefix, anchored at start and end
// of string.
anchoredShortIdentifierRegexp = anchored(ShortIdentifierRegexp)
// match compiles the string to a regular expression.
var match = regexp.MustCompile
// literal compiles s into a literal regular expression, escaping any regexp
// reserved characters.
func literal(s string) *regexp.Regexp {
re := match(regexp.QuoteMeta(s))
if _, complete := re.LiteralPrefix(); !complete {
panic("must be a literal")
return re
// expression defines a full expression, where each regular expression must
// follow the previous.
func expression(res ...*regexp.Regexp) *regexp.Regexp {
var s string
for _, re := range res {
s += re.String()
return match(s)
// optional wraps the expression in a non-capturing group and makes the
// production optional.
func optional(res ...*regexp.Regexp) *regexp.Regexp {
return match(group(expression(res...)).String() + `?`)
// repeated wraps the regexp in a non-capturing group to get one or more
// matches.
func repeated(res ...*regexp.Regexp) *regexp.Regexp {
return match(group(expression(res...)).String() + `+`)
// group wraps the regexp in a non-capturing group.
func group(res ...*regexp.Regexp) *regexp.Regexp {
return match(`(?:` + expression(res...).String() + `)`)
// capture wraps the expression in a capturing group.
func capture(res ...*regexp.Regexp) *regexp.Regexp {
return match(`(` + expression(res...).String() + `)`)
// anchored anchors the regular expression by adding start and end delimiters.
func anchored(res ...*regexp.Regexp) *regexp.Regexp {
return match(`^` + expression(res...).String() + `$`)
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