Class: JhoveTechnicalMetadata

Inherits:
Nokogiri::XML::SAX::Document
  • Object
show all
Defined in:
lib/jhove_technical_metadata.rb

Overview

A SAX handler for filtering JHOVE output to create a technicalMetadata datastream The previous mechanism (uising XSLT tranformation) was causing out of memory errors, due to XSLT’s behavior of loading both the input and output objects into memory.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ JhoveTechnicalMetadata

Returns a new instance of JhoveTechnicalMetadata.



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# File 'lib/jhove_technical_metadata.rb', line 17

def initialize()
  @indent = 0
  @ios = STDOUT #File.open(STDOUT, 'w')
end

Instance Attribute Details

#digital_object_id ⇒ String

Returns The druid of the object, which gets inserted in the root element of the output.

Returns:

  • (String) —

    The druid of the object, which gets inserted in the root element of the output



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# File 'lib/jhove_technical_metadata.rb', line 15

def digital_object_id
  @digital_object_id
end

#ios ⇒ IO

Returns the output stream for the result.

Returns:

  • (IO) —

    the output stream for the result



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# File 'lib/jhove_technical_metadata.rb', line 12

def ios
  @ios
end

Instance Method Details

#characters(string) ⇒ void

This method returns an undefined value.

Returns this method is called by the sax parser when a text node is encountered.

Parameters:

  • tag (String) —

    the value of a text node found in the parsed XML



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# File 'lib/jhove_technical_metadata.rb', line 64

def characters(string)
  @text = string
end

#end_element(tag) ⇒ void

This method returns an undefined value.

Returns this method is called by the sax parser at the end of an element.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input



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# File 'lib/jhove_technical_metadata.rb', line 70

def end_element(tag)
  case tag
    when 'jhove'
      root_close
    when 'repInfo'
      file_wrapper_close
    when 'properties'
      properties_close
    else
      if tag[0..2] == 'mix'
        mix_close(tag)
      elsif @in_jhove
        jhove_close(tag)
      elsif @in_properties
        linebreak_close(tag)
      end
  end
end

#file_wrapper_close ⇒ void

This method returns an undefined value.

but first inset a textMD stanza if the file has a text format



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# File 'lib/jhove_technical_metadata.rb', line 123

def file_wrapper_close
  case @format
    when 'ASCII', 'HTML','TEXT','UTF-8'
      output_textmd(@linebreak)
  end
  @indent -= 1
  output "  </jhove:properties>" if @in_properties

  output "</file>"
  @in_jhove = false
  @in_properties=false
end

#file_wrapper_open(attrs) ⇒ void

This method returns an undefined value.

Returns Append a <file> element to the output, setting the id attribute to the file path.

Parameters:

  • attrs (Hash) —

    the attributes of the <jhove> element in the XML input



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# File 'lib/jhove_technical_metadata.rb', line 113

def file_wrapper_open(attrs)
  filepath=nil
  attrs.each { |attr| filepath=attr[1] if attr[0]=='uri'}
  output "<file id='#{filepath}'>"
  @indent += 1
  @in_jhove = true
end

#jhove_close(tag) ⇒ void

This method returns an undefined value.

Returns Output a closing tag, preceded by cached data, if such exists.



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# File 'lib/jhove_technical_metadata.rb', line 157

def jhove_close(tag)
  if @text && tag == @jhove_tag
    output "<jhove:#{@jhove_tag}#{@jhove_attrs}>#{@text}</jhove:#{tag}>"
  elsif tag == @jhove_tag
    output "<jhove:#{@jhove_tag}#{@jhove_attrs}/>"
  else
    @indent -=1
    output "</jhove:#{tag}>"
  end
  @format = @text if tag == 'format'
  @text = nil
  @jhove_tag = nil
  @jhove_attrs=""
end

#jhove_open(tag, attrs) ⇒ void

This method returns an undefined value.

Returns Copy this jhove element tag and its attributes verbatum.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input

  • attrs (Hash) —

    the attributes of the <jhove> element in the XML input



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# File 'lib/jhove_technical_metadata.rb', line 139

def jhove_open(tag, attrs)
  if @jhove_tag # saved previously
    # we encountered a new element so output what was previously cached
    output "<jhove:#{@jhove_tag}#{@jhove_attrs}>"
    @indent += 1
  end
  # cache the element name and its attributes
  @jhove_tag = tag
  @jhove_attrs = ""
  attrs.each do |attr|
    @jhove_attrs += " #{attr[0]}='#{attr[1]}'"
  end
  @text = nil
  @linebreak='LF'
end

#linebreak_close(tag) ⇒ void

This method returns an undefined value.

Returns Look for the LineEndings name/value pair, which is spread across multiple elements.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input



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# File 'lib/jhove_technical_metadata.rb', line 222

def linebreak_close(tag)
  case tag
    when 'name'
      @in_line_endings = false
      @in_line_endings = true if @text == 'LineEndings'
    when 'value'
      @linebreak = @text if @in_line_endings
      @in_line_endings = false
  end
end

#linebreak_open(tag) ⇒ void

This method returns an undefined value.

Returns Keep clearing the text cache any time a new element is encountered.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input



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# File 'lib/jhove_technical_metadata.rb', line 216

def linebreak_open(tag)
  @text = nil if @text
end

#mix_close(tag) ⇒ void

This method returns an undefined value.

Returns Output a closing tag, preceded by cached data, if such exists.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input



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# File 'lib/jhove_technical_metadata.rb', line 201

def mix_close(tag)
  if @text && tag == @mix_tag
    output "<#{tag}>#{@text}</#{tag}>"
  elsif tag == @mix_tag
      output "<#{tag}/>"
  else
    @indent -=1
    output "</#{tag}>"
  end
  @text = nil
  @mix_tag = nil
end

#mix_open(tag) ⇒ void

This method returns an undefined value.

Returns Copy any Mix data verbatum,.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input



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# File 'lib/jhove_technical_metadata.rb', line 188

def mix_open(tag)
  if @mix_tag
    # we encountered a new element so output what was previously cached
    output "<#{@mix_tag}>"
    @indent += 1
  end
   # cache the element name
  @mix_tag = tag
  @text = nil
end

#output(string) ⇒ void

This method returns an undefined value.

Returns Append the specified string to the output stream.

Parameters:

  • string (String) —

    The character string to be appended to the output



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# File 'lib/jhove_technical_metadata.rb', line 30

def output(string)
  @ios.puts "  "*@indent + string
end

#output_file=(pathname) ⇒ void

This method returns an undefined value.

Returns Opens the output stream pointing to the specified file.

Parameters:

  • pathname (Pathname) —

    the location of the technicalMetadata.xml file to be created



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# File 'lib/jhove_technical_metadata.rb', line 24

def output_file=(pathname)
  @ios = pathname.open('w')
end

#output_textmd(linebreak) ⇒ void

This method returns an undefined value.

Returns Output a textMD section within the properties element.

Parameters:

  • linebreak (Object) —

    the CRLF or LF value found in the JHOVE output ()default is LF)



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# File 'lib/jhove_technical_metadata.rb', line 235

def output_textmd(linebreak)
  indent = @indent
  @indent = 0
  if @in_properties
    # properties element tags provided by other code
    output "    <textmd:textMD>\n      <textmd:character_info>\n        <textmd:byte_order>big</textmd:byte_order>\n        <textmd:byte_size>8</textmd:byte_size>\n        <textmd:character_size>1</textmd:character_size>\n        <textmd:linebreak>\#{linebreak}</textmd:linebreak>\n      </textmd:character_info>\n    </textmd:textMD>\n    EOF\n  else\n    # there were no properties elements in the input, so we must supply them ourselves\n    output <<-EOF\n    <jhove:properties>\n      <textmd:textMD>\n        <textmd:character_info>\n          <textmd:byte_order>big</textmd:byte_order>\n          <textmd:byte_size>8</textmd:byte_size>\n          <textmd:character_size>1</textmd:character_size>\n          <textmd:linebreak>\#{linebreak}</textmd:linebreak>\n        </textmd:character_info>\n      </textmd:textMD>\n    </jhove:properties>\n    EOF\n  end\n  @indent = indent\nend\n"

#properties_close ⇒ void

This method returns an undefined value.

Returns Appending of a closing tag is handled elsewhere.



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# File 'lib/jhove_technical_metadata.rb', line 182

def properties_close
  @indent -= 1
end

#properties_open ⇒ void

This method returns an undefined value.

Returns Output a <properties> element if one was encountered in the input, then ignore most input data from within the properties element, except mix and LineBreaks.



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# File 'lib/jhove_technical_metadata.rb', line 174

def properties_open
  output "<jhove:properties>"
  @indent += 1
  @in_jhove = false
  @in_properties=true
end

#root_close ⇒ void

This method returns an undefined value.

Returns add the closing element of the output document.



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# File 'lib/jhove_technical_metadata.rb', line 105

def root_close
  @indent -= 1
  output "</technicalMetadata>"
  @ios.close
end

#root_open(attrs) ⇒ void

This method returns an undefined value.

Returns create the <technicalMetadata> root element of the XML output and include namespace declararions.

Parameters:

  • attrs (Hash) —

    the attributes of the <jhove> element in the XML input



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# File 'lib/jhove_technical_metadata.rb', line 91

def root_open(attrs)
  if @digital_object_id
    output "<technicalMetadata objectId='#{@digital_object_id}' datetime='#{Time.now.utc.iso8601}'"
  else
    output "<technicalMetadata datetime='#{Time.now.utc.iso8601}'"
  end
  @indent += 2
  output "xmlns:jhove='http://hul.harvard.edu/ois/xml/ns/jhove'"
  output "xmlns:mix='http://www.loc.gov/mix/v10'"
  output "xmlns:textmd='info:lc/xmlns/textMD-v3' >"
  @indent -= 1
end

#start_element(tag, attrs = []) ⇒ void

This method returns an undefined value.

Returns this method is called by the sax parser at the beginning of an element.

Parameters:

  • tag (String) —

    the name of the XML element from the parsed input

  • attrs (Hash) (defaults to: []) —

    the XML attributes of the element



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# File 'lib/jhove_technical_metadata.rb', line 37

def start_element(tag, attrs = [])
  case tag
    when 'jhove'
      # <jhove> is the root element of the input
      root_open(attrs)
    when 'repInfo'
      # A <repInfo> element contains the data for each file
      file_wrapper_open(attrs)
    when 'properties'
      # A <properties> element contains the variable data for the file
      properties_open
    else
      if tag[0..2] == 'mix'
        # JHOVE output for image files contains tech md in MIX format that we copy verbatum to output
        mix_open(tag)
      elsif @in_jhove
        # we've encountered one of the JHOVE elements that we want to automatically copy
        jhove_open(tag, attrs)
      elsif @in_properties
        # we're looking for the LineEndings property in the JHOVE output
        linebreak_open(tag)
      end
  end
end