packageurl.go

/*
Copyright (c) the purl authors

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

// Package packageurl implements the package-url spec
package packageurl

import (
	"errors"
	"fmt"
	"net/url"
	"path"
	"regexp"
	"strings"
)

var (
	// QualifierKeyPattern describes a valid qualifier key:
	//
	// - The key must be composed only of ASCII letters and numbers, '.',
	//   '-' and '_' (period, dash and underscore).
	// - A key cannot start with a number.
	QualifierKeyPattern = regexp.MustCompile(`^[A-Za-z\.\-_][0-9A-Za-z\.\-_]*$`)
)

// These are the known purl types as defined in the spec. Some of these require
// special treatment during parsing.
// https://github.com/package-url/purl-spec#known-purl-types
var (
	// TypeAlpm is a pkg:alpm purl.
	TypeAlpm = "alpm"
	// TypeApk is a pkg:apk purl.
	TypeApk = "apk"
	// TypeBitbucket is a pkg:bitbucket purl.
	TypeBitbucket = "bitbucket"
	// TypeCocoapods is a pkg:cocoapods purl.
	TypeCocoapods = "cocoapods"
	// TypeCargo is a pkg:cargo purl.
	TypeCargo = "cargo"
	// TypeComposer is a pkg:composer purl.
	TypeComposer = "composer"
	// TypeConan is a pkg:conan purl.
	TypeConan = "conan"
	// TypeConda is a pkg:conda purl.
	TypeConda = "conda"
	// TypeCran is a pkg:cran purl.
	TypeCran = "cran"
	// TypeDebian is a pkg:deb purl.
	TypeDebian = "deb"
	// TypeDocker is a pkg:docker purl.
	TypeDocker = "docker"
	// TypeGem is a pkg:gem purl.
	TypeGem = "gem"
	// TypeGeneric is a pkg:generic purl.
	TypeGeneric = "generic"
	// TypeGithub is a pkg:github purl.
	TypeGithub = "github"
	// TypeGolang is a pkg:golang purl.
	TypeGolang = "golang"
	// TypeHackage is a pkg:hackage purl.
	TypeHackage = "hackage"
	// TypeHex is a pkg:hex purl.
	TypeHex = "hex"
	// TypeMaven is a pkg:maven purl.
	TypeMaven = "maven"
	// TypeNPM is a pkg:npm purl.
	TypeNPM = "npm"
	// TypeNuget is a pkg:nuget purl.
	TypeNuget = "nuget"
	// TypeQPKG is a pkg:qpkg purl.
	TypeQpkg = "qpkg"
	// TypeOCI is a pkg:oci purl
	TypeOCI = "oci"
	// TypePyPi is a pkg:pypi purl.
	TypePyPi = "pypi"
	// TypeRPM is a pkg:rpm purl.
	TypeRPM = "rpm"
	// TypeSWID is pkg:swid purl
	TypeSWID = "swid"
	// TypeSwift is pkg:swift purl
	TypeSwift = "swift"
	// TypeHuggingface is pkg:huggingface purl.
	TypeHuggingface = "huggingface"
	// TypeMLflow is pkg:mlflow purl.
	TypeMLFlow = "mlflow"
	// TypeJulia is a pkg:julia purl
	TypeJulia = "julia"
)

type Qualifiers = url.Values

// PackageURL is the struct representation of the parts that make a package url
type PackageURL struct {
	Type       string
	Namespace  string
	Name       string
	Version    string
	Qualifiers Qualifiers
	Subpath    string
}

// NewPackageURL creates a new PackageURL struct instance based on input
func NewPackageURL(purlType, namespace, name, version string,
	qualifiers Qualifiers, subpath string) *PackageURL {

	return &PackageURL{
		Type:       purlType,
		Namespace:  namespace,
		Name:       name,
		Version:    version,
		Qualifiers: qualifiers,
		Subpath:    subpath,
	}
}

// ToString returns the human-readable instance of the PackageURL structure.
// This is the literal purl as defined by the spec.
func (p *PackageURL) ToString() string {
	u := &url.URL{
		Scheme:   "pkg",
		RawQuery: p.Qualifiers.Encode(),
		Fragment: p.Subpath,
	}

	paths := []string{p.Type}
	// we need to escape each segment by itself, so that we don't escape "/" in the namespace.
	for _, segment := range strings.Split(p.Namespace, "/") {
		if segment == "" {
			continue
		}
		paths = append(paths, escape(segment))
	}

	nameWithVersion := escape(p.Name)
	if p.Version != "" {
		nameWithVersion += "@" + escape(p.Version)
	}

	paths = append(paths, nameWithVersion)

	u.Opaque = strings.Join(paths, "/")
	return u.String()
}

func (p PackageURL) String() string {
	return p.ToString()
}

// FromString parses a valid package url string into a PackageURL structure
func FromString(purl string) (PackageURL, error) {
	u, err := url.Parse(purl)
	if err != nil {
		return PackageURL{}, fmt.Errorf("failed to parse as URL: %w", err)
	}

	if u.Scheme != "pkg" {
		return PackageURL{}, fmt.Errorf("purl scheme is not \"pkg\": %q", u.Scheme)
	}

	p := u.Opaque
	// if a purl starts with pkg:/ or even pkg://, we need to fall back to host + path.
	if p == "" {
		p = strings.TrimPrefix(path.Join(u.Host, u.Path), "/")
	}

	typ, p, ok := strings.Cut(p, "/")
	if !ok {
		return PackageURL{}, fmt.Errorf("purl is missing type or name")
	}
	typ = strings.ToLower(typ)

	qualifiers, err := getQualifiers(u.RawQuery)
	if err != nil {
		return PackageURL{}, fmt.Errorf("invalid qualifiers: %w", err)
	}

	namespace, name, version, err := separateNamespaceNameVersion(p)
	if err != nil {
		return PackageURL{}, err
	}

	pURL := PackageURL{
		Qualifiers: qualifiers,
		Type:       typ,
		Namespace:  typeAdjustNamespace(typ, namespace),
		Name:       typeAdjustName(typ, name, qualifiers),
		Version:    typeAdjustVersion(typ, version),
		Subpath:    strings.Trim(u.Fragment, "/"),
	}

	return pURL, validCustomRules(pURL)
}

func getQualifiers(rawQuery string) (url.Values, error) {
	qualifiers, err := url.ParseQuery(rawQuery)
	if err != nil {
		return nil, fmt.Errorf("could not parse qualifiers: %w", err)
	}

	for k := range qualifiers {
		if !validQualifierKey(k) {
			return nil, fmt.Errorf("invalid qualifier key: %q", k)
		}

		v := qualifiers.Get(k)
		// only the first character needs to be lowercased. Note that pURL is alwyas UTF8, so we
		// don't need to care about unicode here.
		normalisedValue := strings.ToLower(v[:1]) + v[1:]

		if normalisedKey := strings.ToLower(k); normalisedKey != k {
			qualifiers.Del(k)
			qualifiers.Set(normalisedKey, normalisedValue)
		} else if normalisedValue != v {
			qualifiers.Set(k, normalisedValue)
		}
	}

	return qualifiers, nil
}

// escape the given string in a purl-compatible way.
func escape(s string) string {
	// for compatibility with other implementations and the purl-spec, we want to escape all
	// characters, which is what "QueryEscape" does. The issue with QueryEscape is that it encodes
	// " " (space) as "+", which is valid in a query, but invalid in a path (see
	// https://stackoverflow.com/questions/2678551/when-should-space-be-encoded-to-plus-or-20) for
	// context).
	// To work around that, we replace the "+" signs with the path-compatible "%20".
	return strings.ReplaceAll(url.QueryEscape(s), "+", "%20")
}

func separateNamespaceNameVersion(path string) (ns, name, version string, err error) {
	name = path

	if namespaceSep := strings.LastIndex(name, "/"); namespaceSep != -1 {
		ns, name = name[:namespaceSep], name[namespaceSep+1:]

		ns, err = url.PathUnescape(ns)
		if err != nil {
			return "", "", "", fmt.Errorf("error unescaping namespace: %w", err)
		}
	}

	if versionSep := strings.LastIndex(name, "@"); versionSep != -1 {
		name, version = name[:versionSep], name[versionSep+1:]

		version, err = url.PathUnescape(version)
		if err != nil {
			return "", "", "", fmt.Errorf("error unescaping version: %w", err)
		}
	}

	name, err = url.PathUnescape(name)
	if err != nil {
		return "", "", "", fmt.Errorf("error unescaping name: %w", err)
	}

	if name == "" {
		return "", "", "", fmt.Errorf("purl is missing name")
	}

	return ns, name, version, nil
}

// Make any purl type-specific adjustments to the parsed namespace.
// See https://github.com/package-url/purl-spec#known-purl-types
func typeAdjustNamespace(purlType, ns string) string {
	switch purlType {
	case TypeAlpm,
		TypeApk,
		TypeBitbucket,
		TypeComposer,
		TypeDebian,
		TypeGithub,
		TypeGolang,
		TypeNPM,
		TypeRPM,
		TypeQpkg:
		return strings.ToLower(ns)
	}
	return ns
}

// Make any purl type-specific adjustments to the parsed name.
// See https://github.com/package-url/purl-spec#known-purl-types
func typeAdjustName(purlType, name string, qualifiers Qualifiers) string {
	switch purlType {
	case TypeAlpm,
		TypeApk,
		TypeBitbucket,
		TypeComposer,
		TypeDebian,
		TypeGithub,
		TypeGolang,
		TypeNPM:
		return strings.ToLower(name)
	case TypePyPi:
		return strings.ToLower(strings.ReplaceAll(name, "_", "-"))
	case TypeMLFlow:
		return adjustMlflowName(name, qualifiers)
	}
	return name
}

// Make any purl type-specific adjustments to the parsed version.
// See https://github.com/package-url/purl-spec#known-purl-types
func typeAdjustVersion(purlType, version string) string {
	switch purlType {
	case TypeHuggingface:
		return strings.ToLower(version)
	}
	return version
}

// https://github.com/package-url/purl-spec/blob/master/PURL-TYPES.rst#mlflow
func adjustMlflowName(name string, qualifiers Qualifiers) string {
	switch v := qualifiers.Get("repository_url"); {
	case v == "":
		// No repository qualifier given, keep as-is
		return name

	case strings.Contains(v, "azureml"):
		// Azure ML is case-sensitive and must be kept as-is
		return name

	case strings.Contains(v, "databricks"):
		// Databricks is case-insensitive and must be lowercased
		return strings.ToLower(name)

	default:
		// Unknown repository type, keep as-is
		return name
	}
}

// validQualifierKey validates a qualifierKey against our QualifierKeyPattern.
func validQualifierKey(key string) bool {
	return QualifierKeyPattern.MatchString(key)
}

// validCustomRules evaluates additional rules for each package url type, as specified in the package-url specification.
// On success, it returns nil. On failure, a descriptive error will be returned.
func validCustomRules(p PackageURL) error {
	q := p.Qualifiers
	switch p.Type {
	case TypeConan:
		switch channelSet, nsSet := q.Has("channel"), p.Namespace != ""; {
		case nsSet && channelSet:
			if q.Get("channel") == "" {
				return errors.New("the qualifier channel must be not empty if namespace is present")
			}

		case nsSet && !channelSet:
			return errors.New("channel qualifier does not exist")

		case !nsSet && channelSet:
			if q.Get("channel") != "" {
				return errors.New("namespace is required if channel is non empty")
			}
		}

	case TypeSwift:
		if p.Namespace == "" {
			return errors.New("namespace is required")
		}
		if p.Version == "" {
			return errors.New("version is required")
		}
	case TypeCran:
		if p.Version == "" {
			return errors.New("version is required")
		}
	}
	return nil
}