Add support for PDF/A-1b

lib/pdf/core.rb

@@ -17,6 +17,7 @@
 require_relative 'core/outline_item'
 require_relative 'core/renderer'
 require_relative 'core/text'
+require_relative 'core/xmp_metadata'
 
 module PDF
   module Core

lib/pdf/core/document_state.rb

@@ -4,15 +4,10 @@ class DocumentState #:nodoc:
       def initialize(options)
         normalize_metadata(options)
 
-        @store =
-          if options[:print_scaling]
-            PDF::Core::ObjectStore.new(
-              info: options[:info],
-              print_scaling: options[:print_scaling]
-            )
-          else
-            PDF::Core::ObjectStore.new(info: options[:info])
-          end
+        store_params = options.select do |key|
+          %i[info print_scaling enable_pdfa_1b].include?(key)
+        end
+        @store = PDF::Core::ObjectStore.new(store_params)
 
         @version                 = 1.3
         @pages                   = []

lib/pdf/core/object_store.rb

@@ -19,6 +19,20 @@ def initialize(opts = {})
 
         @info  ||= ref(opts[:info] || {}).identifier
         @root  ||= ref(Type: :Catalog).identifier
+
+        if opts[:enable_pdfa_1b]
+          # PDF/A-1b requirement: XMP metadata
+          @xmp_metadata ||= ref(Type: :Metadata, Subtype: :XML).identifier
+          root.data[:Metadata] = xmp_metadata
+          xmp_metadata_content = XmpMetadata.new(opts[:info] || {})
+          xmp_metadata_content.enable_pdfa_1b = true
+          xmp_metadata.stream = Stream.new
+          xmp_metadata.stream << xmp_metadata_content.render
+
+          # PDF/A-1b requirement: OutputIntent with ICC profile stream
+          initialize_output_intent
+        end
+
         if opts[:print_scaling] == :none
           root.data[:ViewerPreferences] = { PrintScaling: :None }
         end
@@ -39,6 +53,10 @@ def root
         @objects[@root]
       end
 
+      def xmp_metadata
+        @objects[@xmp_metadata]
+      end
+
       def pages
         root.data[:Pages]
       end
@@ -96,6 +114,24 @@ def object_id_for_page(k)
         flat_page_ids = get_page_objects(pages).flatten
         flat_page_ids[k]
       end
+
+      private
+
+      def initialize_output_intent
+        icc_profile_name = 'sRGB2014.icc'.freeze
+
+        icc_profile_stream = ref(N: 3)
+        icc_profile_stream.stream = Stream.new
+        icc_profile_stream << File.binread(File.join(File.dirname(__FILE__), '..', '..', '..', 'data', icc_profile_name))
+
+        root.data[:OutputIntents] = [{
+          Type: :OutputIntent,
+          S: :GTS_PDFA1,
+          OutputConditionIdentifier: LiteralString.new('Custom'),
+          Info: LiteralString.new(File.basename(icc_profile_name, '.*')),
+          DestOutputProfile: icc_profile_stream
+        }]
+      end
     end
   end
 end

lib/pdf/core/renderer.rb

@@ -1,4 +1,5 @@
 require 'stringio'
+require 'digest'
 
 module PDF
   module Core
@@ -162,9 +163,20 @@ def render(output = StringIO.new)
         finalize_all_page_contents
 
         render_header(output)
-        render_body(output)
+
+        # We render the body into a temporary buffer to avoid
+        # two render passes for output and hashing.
+        # We must have the same offset as in output, otherwise
+        # the refs won't match.
+        body_output = StringIO.new(' ' * output.tell)
+        body_output.set_encoding(::Encoding::ASCII_8BIT)
+        body_output.seek(output.tell)
+        render_body(body_output)
+        body_output = body_output.string[output.tell..-1]
+        output.write(body_output)
+
         render_xref(output)
-        render_trailer(output)
+        render_trailer(output, hash_body(body_output))
         if output.instance_of?(StringIO)
           str = output.string
           str.force_encoding(::Encoding::ASCII_8BIT)
@@ -200,6 +212,12 @@ def render_body(output)
         state.render_body(output)
       end
 
+      # Create a hash from the body data. Needed for creating the trailer ID.
+      #
+      def hash_body(body_data)
+        Digest::MD5.digest(body_data)
+      end
+
       # Write out the PDF Cross Reference Table, as per spec 3.4.3
       #
       def render_xref(output)
@@ -215,11 +233,13 @@ def render_xref(output)
 
       # Write out the PDF Trailer, as per spec 3.4.4
       #
-      def render_trailer(output)
+      def render_trailer(output, body_hash)
+        trailer_id = PDF::Core::ByteString.new(body_hash)
         trailer_hash = {
           Size: state.store.size + 1,
           Root: state.store.root,
-          Info: state.store.info
+          Info: state.store.info,
+          ID: [trailer_id, trailer_id] # PDF/A-1b requirement
         }
         trailer_hash.merge!(state.trailer) if state.trailer
 

lib/pdf/core/xmp_metadata.rb

@@ -0,0 +1,95 @@
+module PDF
+  module Core
+    class XmpMetadata
+      attr_accessor :enable_pdfa_1b
+
+      # These attributes must all be synchronized with their counterparts in the
+      # document information dictionary to be PDF/A-1b compliant.
+      attr_accessor :dc_title, :dc_creator, :dc_description,
+        :pdf_keywords, :xmp_creator_tool, :pdf_producer,
+        :xmp_create_date, :xmp_modify_date
+
+      def initialize(options = {})
+        # Convert options for the document information dictionary to their
+        # counterparts in XMP.
+        @dc_title = options[:Title] if options[:Title]
+        @dc_creator = options[:Author] if options[:Author]
+        @dc_description = options[:Subject] if options[:Subject]
+        @pdf_keywords = options[:Keywords] if options[:Keywords]
+        @xmp_creator_tool = options[:Creator] if options[:Creator]
+        @pdf_producer = options[:Producer] if options[:Producer]
+        @xmp_create_date = options[:CreationDate] if options[:CreationDate]
+        @xmp_modify_date = options[:ModDate] if options[:ModDate]
+      end
+
+      def render
+        result = "<?xpacket begin=\"\" id=\"W5M0MpCehiHzreSzNTczkc9d\"?>\n"
+        result << "<rdf:RDF xmlns:rdf=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\">\n"
+        result << render_pdfaid if @enable_pdfa_1b
+        result << render_xmp if @xmp_creator_tool || @xmp_create_date || @xmp_modify_date
+        result << render_pdf if @pdf_keywords || @pdf_producer
+        result << render_dc if @dc_title || @dc_creator || @dc_description
+        result << "</rdf:RDF>\n"
+        result << '<?xpacket end="r"?>'
+      end
+
+      private
+
+      def render_pdfaid
+        "  <rdf:Description xmlns:pdfaid=\"http://www.aiim.org/pdfa/ns/id/\" rdf:about=\"\">\n" \
+        "    <pdfaid:part>1</pdfaid:part>\n" \
+        "    <pdfaid:conformance>B</pdfaid:conformance>\n" \
+        "  </rdf:Description>\n"
+      end
+
+      def render_xmp
+        result = "  <rdf:Description xmlns:xmp=\"http://ns.adobe.com/xap/1.0/\" rdf:about=\"\">\n"
+        result << "    <xmp:CreatorTool>#{xml_char_data(@xmp_creator_tool)}</xmp:CreatorTool>\n" if @xmp_creator_tool
+        result << "    <xmp:CreateDate>#{xml_char_data(to_xmp_timestamp(@xmp_create_date))}</xmp:CreateDate>\n" if @xmp_create_date
+        result << "    <xmp:ModifyDate>#{xml_char_data(to_xmp_timestamp(@xmp_modify_date))}</xmp:ModifyDate>\n" if @xmp_modify_date
+        result << "  </rdf:Description>\n"
+      end
+
+      def render_pdf
+        result = "  <rdf:Description xmlns:pdf=\"http://ns.adobe.com/pdf/1.3/\" rdf:about=\"\">\n"
+        result << "    <pdf:Keywords>#{xml_char_data(@pdf_keywords)}</pdf:Keywords>\n" if @pdf_keywords
+        result << "    <pdf:Producer>#{xml_char_data(@pdf_producer)}</pdf:Producer>\n" if @pdf_producer
+        result << "  </rdf:Description>\n"
+      end
+
+      def render_dc
+        result = "  <rdf:Description xmlns:dc=\"http://purl.org/dc/elements/1.1/\" rdf:about=\"\">\n"
+        if @dc_title
+          result << "    <dc:title>\n"
+          result << "      <rdf:Alt>\n"
+          result << "        <rdf:li xml:lang=\"x-default\">#{xml_char_data(@dc_title)}</rdf:li>\n"
+          result << "      </rdf:Alt>\n"
+          result << "    </dc:title>\n"
+        end
+        if @dc_creator
+          result << "    <dc:creator>\n"
+          result << "      <rdf:Seq>\n"
+          result << "        <rdf:li>#{xml_char_data(@dc_creator)}</rdf:li>\n"
+          result << "      </rdf:Seq>\n"
+          result << "    </dc:creator>\n"
+        end
+        if @dc_description
+          result << "    <dc:description>\n"
+          result << "      <rdf:Alt>\n"
+          result << "        <rdf:li xml:lang=\"x-default\">#{xml_char_data(@dc_description)}</rdf:li>\n"
+          result << "      </rdf:Alt>\n"
+          result << "    </dc:description>\n"
+        end
+        result << "  </rdf:Description>\n" \
+      end
+
+      def to_xmp_timestamp(time)
+        time.strftime('%Y-%m-%dT%H:%M:%S%:z')
+      end
+
+      def xml_char_data(string)
+        string.gsub('&', '&amp;').gsub('<', '&lt;')
+      end
+    end
+  end
+end

pdf-core.gemspec

@@ -6,6 +6,7 @@ Gem::Specification.new do |spec|
   spec.files =  Dir.glob('lib/**/**/*') +
                 %w[COPYING GPLv2 GPLv3 LICENSE] +
                 %w[Gemfile Rakefile] +
+                ['data/sRGB2014.icc'] +
                 ['pdf-core.gemspec']
   spec.require_path = 'lib'
   spec.required_ruby_version = '>= 1.9.3'