Module: Cataract::ImportResolver

Defined in:
lib/cataract/import_resolver.rb

Overview

Resolves @import statements in CSS Handles fetching imported files and inlining them with proper security controls

Constant Summary collapse

SAFE_DEFAULTS =

Default options for safe import resolution

{
  max_depth: 5,                      # Prevent infinite recursion
  allowed_schemes: ['https'],        # Only HTTPS by default
  extensions: ['css'],               # Only .css files
  timeout: 10,                       # 10 second timeout for fetches
  follow_redirects: true,            # Follow redirects
  base_path: nil                     # Base path for resolving relative imports
}.freeze

Class Method Summary collapse

Class Method Details

.extract_imports(css) ⇒ Object

Extract @import statements from CSS Returns array of hashes: { url: “…”, media: “…”, full_match: “…” } Delegates to C implementation for performance



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# File 'lib/cataract/import_resolver.rb', line 101

def self.extract_imports(css)
  Cataract.extract_imports(css)
end

.fetch_http(uri, options) ⇒ Object

Fetch content via HTTP/HTTPS



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# File 'lib/cataract/import_resolver.rb', line 199

def self.fetch_http(uri, options)
  # Use open-uri with timeout
  open_uri_options = {
    read_timeout: options[:timeout],
    redirect: options[:follow_redirects]
  }

  # Use uri.open instead of URI.open to avoid shell command injection
  uri.open(open_uri_options, &:read)
end

.fetch_url(url, options) ⇒ Object

Fetch content from URL



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# File 'lib/cataract/import_resolver.rb', line 175

def self.fetch_url(url, options)
  uri = normalize_url(url, options[:base_path])

  case uri.scheme
  when 'file'
    # Read from local filesystem
    File.read(uri.path)
  when 'http', 'https'
    # Fetch from network
    fetch_http(uri, options)
  else
    raise ImportError, "Unsupported scheme: #{uri.scheme}"
  end
rescue Errno::ENOENT
  raise ImportError, "Import file not found: #{url}"
rescue OpenURI::HTTPError => e
  raise ImportError, "HTTP error fetching import: #{url} (#{e.message})"
rescue SocketError => e
  raise ImportError, "Network error fetching import: #{url} (#{e.message})"
rescue StandardError => e
  raise ImportError, "Error fetching import: #{url} (#{e.class}: #{e.message})"
end

.normalize_options(options) ⇒ Object

Normalize options with safe defaults



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# File 'lib/cataract/import_resolver.rb', line 86

def self.normalize_options(options)
  if options == true
    # imports: true -> use safe defaults
    SAFE_DEFAULTS.dup
  elsif options.is_a?(Hash)
    # imports: { ... } -> merge with safe defaults
    SAFE_DEFAULTS.merge(options)
  else
    raise ArgumentError, 'imports option must be true or a Hash'
  end
end

.normalize_url(url, base_path = nil) ⇒ Object

Normalize URL - handle relative paths and missing schemes Returns a URI object



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# File 'lib/cataract/import_resolver.rb', line 107

def self.normalize_url(url, base_path = nil)
  # Try to parse as-is first
  uri = URI.parse(url)

  # If no scheme, treat as relative file path
  if uri.scheme.nil?
    # Convert to file:// URL
    # Relative paths stay relative, absolute paths stay absolute
    if url.start_with?('/')
      uri = URI.parse("file://#{url}")
    else
      # Relative path - make it absolute relative to base_path or current directory
      absolute_path = if base_path
                        File.expand_path(url, base_path)
                      else
                        File.expand_path(url)
                      end
      uri = URI.parse("file://#{absolute_path}")
    end
  end

  uri
rescue URI::InvalidURIError => e
  raise ImportError, "Invalid import URL: #{url} (#{e.message})"
end

.resolve(css, options = {}, depth: 0, imported_urls: Set.new) ⇒ String

Resolve @import statements in CSS

Parameters:

  • css (String) —

    CSS content with @import statements

  • options (Hash) (defaults to: {}) —

    Import resolution options

  • depth (Integer) (defaults to: 0) —

    Current recursion depth (internal)

  • imported_urls (Set) (defaults to: Set.new) —

    Set of already imported URLs to prevent circular references

Returns:

  • (String) —

    CSS with imports inlined



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# File 'lib/cataract/import_resolver.rb', line 31

def self.resolve(css, options = {}, depth: 0, imported_urls: Set.new)
  # Normalize options
  opts = normalize_options(options)

  # Check recursion depth
  # depth starts at 0, max_depth is count of imports allowed
  # depth 0: parsing main file (counts as import 1)
  # depth 1: parsing first @import  (counts as import 2)
  # depth 2: parsing nested @import (counts as import 3)
  if depth > opts[:max_depth]
    raise ImportError, "Import nesting too deep: exceeded maximum depth of #{opts[:max_depth]}"
  end

  # Find all @import statements at the top of the file
  # Per CSS spec, @import must come before all rules except @charset
  imports = extract_imports(css)

  return css if imports.empty?

  # Process each import
  resolved_css = +'' # Mutable string
  remaining_css = css

  imports.each do |import_data|
    url = import_data[:url]
    media = import_data[:media]

    # Validate URL
    validate_url(url, opts)

    # Check for circular references
    raise ImportError, "Circular import detected: #{url}" if imported_urls.include?(url)

    # Fetch imported CSS
    imported_css = fetch_url(url, opts)

    # Recursively resolve imports in the imported CSS
    imported_urls_copy = imported_urls.dup
    imported_urls_copy.add(url)
    imported_css = resolve(imported_css, opts, depth: depth + 1, imported_urls: imported_urls_copy)

    # Wrap in @media if import had media query
    imported_css = "@media #{media} {\n#{imported_css}\n}" if media

    resolved_css << imported_css << "\n"

    # Remove this import from remaining CSS
    remaining_css = remaining_css.sub(import_data[:full_match], '')
  end

  # Return resolved imports + remaining CSS
  resolved_css + remaining_css
end

.validate_url(url, options) ⇒ Object

Validate URL against security options



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# File 'lib/cataract/import_resolver.rb', line 134

def self.validate_url(url, options)
  uri = normalize_url(url, options[:base_path])

  # Check scheme
  unless options[:allowed_schemes].include?(uri.scheme)
    raise ImportError,
          "Import scheme '#{uri.scheme}' not allowed. Allowed schemes: #{options[:allowed_schemes].join(', ')}"
  end

  # Check extension
  path = uri.path || ''
  ext = File.extname(path).delete_prefix('.')

  unless ext.empty? || options[:extensions].include?(ext)
    raise ImportError,
          "Import extension '.#{ext}' not allowed. Allowed extensions: #{options[:extensions].join(', ')}"
  end

  # Additional security checks for file:// scheme
  if uri.scheme == 'file'
    # Resolve to absolute path to prevent directory traversal
    file_path = uri.path

    # Check file exists and is readable
    unless File.exist?(file_path) && File.readable?(file_path)
      raise ImportError, "Import file not found or not readable: #{file_path}"
    end

    # Prevent reading sensitive files (basic check)
    dangerous_paths = ['/etc/', '/proc/', '/sys/', '/dev/']
    if dangerous_paths.any? { |prefix| file_path.start_with?(prefix) }
      raise ImportError, "Import of sensitive system files not allowed: #{file_path}"
    end
  end

  true
rescue URI::InvalidURIError => e
  raise ImportError, "Invalid import URL: #{url} (#{e.message})"
end