distribution/reference/regexp.go
Sebastiaan van Stijn 02e88c0f15
reference: move exported regexes to separate block
This makes them easier to find between the non-exported ones, and puts
them as separate sections in the generated docs. While updating, also
extended documentation for some to be more descriptive.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
2022-11-23 00:01:57 +01:00

163 lines
7 KiB
Go

package reference
import (
"regexp"
"strings"
)
// DigestRegexp matches well-formed digests, including algorithm (e.g. "sha256:<encoded>").
var DigestRegexp = regexp.MustCompile(digestPat)
// 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).
//
// [RFC 6874]: https://www.rfc-editor.org/rfc/rfc6874.
var DomainRegexp = regexp.MustCompile(domainAndPort)
// 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 IdentifierRegexp = regexp.MustCompile(identifier)
// NameRegexp is the format for the name component of references, including
// an optional domain and port, but without tag or digest suffix.
var NameRegexp = regexp.MustCompile(namePat)
// ReferenceRegexp is the full supported format of a reference. The regexp
// is anchored and has capturing groups for name, tag, and digest
// components.
var ReferenceRegexp = regexp.MustCompile(referencePat)
// TagRegexp matches valid tag names. From [docker/docker:graph/tags.go].
//
// [docker/docker:graph/tags.go]: https://github.com/moby/moby/blob/v1.6.0/graph/tags.go#L26-L28
var TagRegexp = regexp.MustCompile(tag)
const (
// alphanumeric defines the alphanumeric atom, typically a
// component of names. This only allows lower case characters and digits.
alphanumeric = `[a-z0-9]+`
// separator defines the separators allowed to be embedded in name
// components. This allows one period, one or two underscore and multiple
// dashes. Repeated dashes and underscores are intentionally treated
// differently. In order to support valid hostnames as name components,
// supporting repeated dash was added. Additionally double underscore is
// now allowed as a separator to loosen the restriction for previously
// supported names.
separator = `(?:[._]|__|[-]*)`
// localhost is treated as a special value for domain-name. Any other
// domain-name without a "." or a ":port" are considered a path component.
localhost = `localhost`
// domainNameComponent restricts the registry domain component of a
// repository name to start with a component as defined by DomainRegexp.
domainNameComponent = `(?:[a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]*[a-zA-Z0-9])`
// optionalPort matches an optional port-number including the port separator
// (e.g. ":80").
optionalPort = `(?::[0-9]+)?`
// tag matches valid tag names. From docker/docker:graph/tags.go.
tag = `[\w][\w.-]{0,127}`
// digestPat matches well-formed digests, including algorithm (e.g. "sha256:<encoded>").
//
// TODO(thaJeztah): this should follow the same rules as https://pkg.go.dev/github.com/opencontainers/go-digest@v1.0.0#DigestRegexp
// so that go-digest defines the canonical format. Note that the go-digest is
// more relaxed:
// - it allows multiple algorithms (e.g. "sha256+b64:<encoded>") to allow
// future expansion of supported algorithms.
// - it allows the "<encoded>" value to use urlsafe base64 encoding as defined
// in [rfc4648, section 5].
//
// [rfc4648, section 5]: https://www.rfc-editor.org/rfc/rfc4648#section-5.
digestPat = `[A-Za-z][A-Za-z0-9]*(?:[-_+.][A-Za-z][A-Za-z0-9]*)*[:][[:xdigit:]]{32,}`
// identifier is the format for a content addressable identifier using sha256.
// These identifiers are like digests without the algorithm, since sha256 is used.
identifier = `([a-f0-9]{64})`
// ipv6address are enclosed between square brackets and may be represented
// in many ways, see rfc5952. Only IPv6 in compressed or uncompressed format
// are allowed, IPv6 zone identifiers (rfc6874) or Special addresses such as
// IPv4-Mapped are deliberately excluded.
ipv6address = `\[(?:[a-fA-F0-9:]+)\]`
)
var (
// domainName 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. This includes IPv4 addresses on decimal format.
domainName = domainNameComponent + anyTimes(`\.`+domainNameComponent)
// host defines the structure of potential domains based on the URI
// Host subcomponent on rfc3986. It may be a subset of DNS domain name,
// or an IPv4 address in decimal format, or an IPv6 address between square
// brackets (excluding zone identifiers as defined by rfc6874 or special
// addresses such as IPv4-Mapped).
host = `(?:` + domainName + `|` + ipv6address + `)`
// allowed by the URI Host subcomponent on rfc3986 to ensure backwards
// compatibility with Docker image names.
domainAndPort = host + optionalPort
// anchoredTagRegexp matches valid tag names, anchored at the start and
// end of the matched string.
anchoredTagRegexp = regexp.MustCompile(anchored(tag))
// anchoredDigestRegexp matches valid digests, anchored at the start and
// end of the matched string.
anchoredDigestRegexp = regexp.MustCompile(anchored(digestPat))
// pathComponent restricts path-components to start with an alphanumeric
// character, with following parts able to be separated by a separator
// (one period, one or two underscore and multiple dashes).
pathComponent = alphanumeric + anyTimes(separator+alphanumeric)
// remoteName matches the remote-name of a repository. It consists of one
// or more forward slash (/) delimited path-components:
//
// pathComponent[[/pathComponent] ...] // e.g., "library/ubuntu"
remoteName = pathComponent + anyTimes(`/`+pathComponent)
namePat = optional(domainAndPort+`/`) + remoteName
// anchoredNameRegexp is used to parse a name value, capturing the
// domain and trailing components.
anchoredNameRegexp = regexp.MustCompile(anchored(optional(capture(domainAndPort), `/`), capture(remoteName)))
referencePat = anchored(capture(namePat), optional(`:`, capture(tag)), optional(`@`, capture(digestPat)))
// anchoredIdentifierRegexp is used to check or match an
// identifier value, anchored at start and end of string.
anchoredIdentifierRegexp = regexp.MustCompile(anchored(identifier))
)
// optional wraps the expression in a non-capturing group and makes the
// production optional.
func optional(res ...string) string {
return `(?:` + strings.Join(res, "") + `)?`
}
// anyTimes wraps the expression in a non-capturing group that can occur
// any number of times.
func anyTimes(res ...string) string {
return `(?:` + strings.Join(res, "") + `)*`
}
// capture wraps the expression in a capturing group.
func capture(res ...string) string {
return `(` + strings.Join(res, "") + `)`
}
// anchored anchors the regular expression by adding start and end delimiters.
func anchored(res ...string) string {
return `^` + strings.Join(res, "") + `$`
}