DEV: Support passing relative URLs CSP builder (#19176)

Raw paths like `/test/path` are not supported natively in the CSP. This commit prepends the site's base URL to these paths. This allows plugins to add 'local' assets to the CSP without needing to hardcode the site's hostname.

lib/content_security_policy/builder.rb

@@ -27,12 +27,13 @@ class ContentSecurityPolicy
 
     def initialize(base_url:)
       @directives = Default.new(base_url: base_url).directives
+      @base_url = base_url
     end
 
     def <<(extension)
       return unless valid_extension?(extension)
 
-      extension.each { |directive, sources| extend_directive(normalize(directive), sources) }
+      extension.each { |directive, sources| extend_directive(normalize_directive(directive), sources) }
     end
 
     def build
@@ -51,20 +52,27 @@ class ContentSecurityPolicy
 
     private
 
-    def normalize(directive)
+    def normalize_directive(directive)
       directive.to_s.gsub('-', '_').to_sym
     end
 
+    def normalize_source(source)
+      if source.starts_with?("/")
+        "#{@base_url}#{source}"
+      else
+        source
+      end
+    rescue URI::ParseError
+      source
+    end
+
     def extend_directive(directive, sources)
       return unless extendable?(directive)
 
       @directives[directive] ||= []
 
-      if sources.is_a?(Array)
-        @directives[directive].concat(sources)
-      else
-        @directives[directive] << sources
-      end
+      sources = Array(sources).map { |s| normalize_source(s) }
+      @directives[directive].concat(sources)
 
       @directives[directive].delete(:none) if @directives[directive].count > 1
     end

spec/fixtures/plugins/csp_extension/plugin.rb

@@ -6,7 +6,7 @@
 # authors: xrav3nz
 
 extend_content_security_policy(
-  script_src: ['https://from-plugin.com'],
+  script_src: ['https://from-plugin.com', '/local/path'],
   object_src: ['https://test-stripping.com'],
   frame_ancestors: ['https://frame-ancestors-plugin.ext'],
   manifest_src: ['https://manifest-src.com']

spec/lib/content_security_policy_spec.rb

@@ -222,6 +222,7 @@ RSpec.describe ContentSecurityPolicy do
 
       plugin.enabled = true
       expect(parse(policy)['script-src']).to include('https://from-plugin.com')
+      expect(parse(policy)['script-src']).to include('http://test.localhost/local/path')
       expect(parse(policy)['object-src']).to include('https://test-stripping.com')
       expect(parse(policy)['object-src']).to_not include("'none'")
       expect(parse(policy)['manifest-src']).to include("'self'")