Type Normalization

Overview

The purl specification defines type-specific normalization rules for certain package ecosystems. purl.cr automatically applies these rules when creating or parsing Package URLs.

Type is Always Lowercased

Regardless of the input, the type component is always converted to lowercase:

purl = Purl::PackageURL.new("NPM", nil, "express")
purl.type  # => "npm"

Normalization Rules by Type

npm

• Name and namespace are lowercased

purl = Purl::PackageURL.new("npm", "@Angular", "Core")
purl.namespace  # => "@angular"
purl.name       # => "core"

pypi

• Name is lowercased and underscores are replaced with hyphens

purl = Purl::PackageURL.new("pypi", nil, "Django_Rest_Framework")
purl.name  # => "django-rest-framework"

golang

• Name and namespace are lowercased

purl = Purl::PackageURL.new("golang", "GitHub.com/User", "Repo")
purl.namespace  # => "github.com/user"
purl.name       # => "repo"

deb

• Name and namespace are lowercased

purl = Purl::PackageURL.new("deb", "Debian", "Curl")
purl.namespace  # => "debian"
purl.name       # => "curl"

rpm

• Namespace is lowercased

purl = Purl::PackageURL.new("rpm", "Fedora", "curl")
purl.namespace  # => "fedora"

github / bitbucket

• Name and namespace are lowercased

purl = Purl::PackageURL.new("github", "HahWul", "Purl.CR")
purl.namespace  # => "hahwul"
purl.name       # => "purl.cr"

Other Types

Types not listed above (e.g., maven, gem, nuget, cargo) preserve the original case for name and namespace:

purl = Purl::PackageURL.new("maven", "org.Apache", "Commons")
purl.namespace  # => "org.Apache"
purl.name       # => "Commons"

Qualifier Normalization

Qualifier keys are always lowercased and validated:

• Must start with a lowercase letter
• May contain lowercase letters, digits, ., _, or -
• Empty values are discarded

purl = Purl::PackageURL.new(
  "deb", "debian", "curl", "7.50.3",
  qualifiers: {"Arch" => "amd64", "empty" => "  "}
)
purl.qualifiers  # => {"arch" => "amd64"} (key lowercased, empty removed)

Subpath Normalization

Subpath segments are cleaned:

• Empty segments are removed
• . and .. segments are stripped
• Leading/trailing slashes are removed

purl = Purl::PackageURL.new(
  "github", "user", "repo", nil,
  subpath: "./src/../src/lib/"
)
purl.subpath  # => "src/lib"