sax2parser.rb

require 'rexml/parsers/baseparser'
require 'rexml/parseexception'
require 'rexml/namespace'
require 'rexml/text'

module REXML
  module Parsers
    # SAX2Parser
    class SAX2Parser
      def initialize source
        @parser = BaseParser.new(source)
        @listeners = []
        @procs = []
        @namespace_stack = []
        @has_listeners = false
        @tag_stack = []
        @entities = {}
      end

      def source
        @parser.source
      end

      def add_listener( listener )
        @parser.add_listener( listener )
      end

      # Listen arguments:
      #
      # Symbol, Array, Block
      #         Listen to Symbol events on Array elements
      # Symbol, Block
      #   Listen to Symbol events
      # Array, Listener
      #         Listen to all events on Array elements
      # Array, Block
      #         Listen to :start_element events on Array elements
      # Listener
      #         Listen to All events
      #
      # Symbol can be one of: :start_element, :end_element,
      # :start_prefix_mapping, :end_prefix_mapping, :characters,
      # :processing_instruction, :doctype, :attlistdecl, :elementdecl,
      # :entitydecl, :notationdecl, :cdata, :xmldecl, :comment
      #
      # There is an additional symbol that can be listened for: :progress.
      # This will be called for every event generated, passing in the current
      # stream position.
      #
      # Array contains regular expressions or strings which will be matched
      # against fully qualified element names.
      #
      # Listener must implement the methods in SAX2Listener
      #
      # Block will be passed the same arguments as a SAX2Listener method would
      # be, where the method name is the same as the matched Symbol.
      # See the SAX2Listener for more information.
      def listen( *args, &blok )
        if args[0].kind_of? Symbol
          if args.size == 2
            args[1].each { |match| @procs << [args[0], match, blok] }
          else
            add( [args[0], nil, blok] )
          end
        elsif args[0].kind_of? Array
          if args.size == 2
            args[0].each { |match| add( [nil, match, args[1]] ) }
          else
            args[0].each { |match| add( [ :start_element, match, blok ] ) }
          end
        else
          add([nil, nil, args[0]])
        end
      end

      def deafen( listener=nil, &blok )
        if listener
          @listeners.delete_if {|item| item[-1] == listener }
          @has_listeners = false if @listeners.size == 0
        else
          @procs.delete_if {|item| item[-1] == blok }
        end
      end

      def parse
        @procs.each { |sym,match,block| block.call if sym == :start_document }
        @listeners.each { |sym,match,block|
          block.start_document if sym == :start_document or sym.nil?
        }
        context = []
        while true
          event = @parser.pull
          case event[0]
          when :end_document
            handle( :end_document )
            break
          when :start_doctype
            handle( :doctype, *event[1..-1])
          when :end_doctype
            context = context[1]
          when :start_element
            @tag_stack.push(event[1])
            # find the observers for namespaces
            procs = get_procs( :start_prefix_mapping, event[1] )
            listeners = get_listeners( :start_prefix_mapping, event[1] )
            if procs or listeners
              # break out the namespace declarations
              # The attributes live in event[2]
              event[2].each {|n, v| event[2][n] = @parser.normalize(v)}
              nsdecl = event[2].find_all { |n, value| n =~ /^xmlns(:|$)/ }
              nsdecl.collect! { |n, value| [ n[6..-1], value ] }
              @namespace_stack.push({})
              nsdecl.each do |n,v|
                @namespace_stack[-1][n] = v
                # notify observers of namespaces
                procs.each { |ob| ob.call( n, v ) } if procs
                listeners.each { |ob| ob.start_prefix_mapping(n, v) } if listeners
              end
            end
            event[1] =~ Namespace::NAMESPLIT
            prefix = $1
            local = $2
            uri = get_namespace(prefix)
            # find the observers for start_element
            procs = get_procs( :start_element, event[1] )
            listeners = get_listeners( :start_element, event[1] )
            # notify observers
            procs.each { |ob| ob.call( uri, local, event[1], event[2] ) } if procs
            listeners.each { |ob|
              ob.start_element( uri, local, event[1], event[2] )
            } if listeners
          when :end_element
            @tag_stack.pop
            event[1] =~ Namespace::NAMESPLIT
            prefix = $1
            local = $2
            uri = get_namespace(prefix)
            # find the observers for start_element
            procs = get_procs( :end_element, event[1] )
            listeners = get_listeners( :end_element, event[1] )
            # notify observers
            procs.each { |ob| ob.call( uri, local, event[1] ) } if procs
            listeners.each { |ob|
              ob.end_element( uri, local, event[1] )
            } if listeners

            namespace_mapping = @namespace_stack.pop
            # find the observers for namespaces
            procs = get_procs( :end_prefix_mapping, event[1] )
            listeners = get_listeners( :end_prefix_mapping, event[1] )
            if procs or listeners
              namespace_mapping.each do |ns_prefix, ns_uri|
                # notify observers of namespaces
                procs.each { |ob| ob.call( ns_prefix ) } if procs
                listeners.each { |ob| ob.end_prefix_mapping(ns_prefix) } if listeners
              end
            end
          when :text
            #normalized = @parser.normalize( event[1] )
            #handle( :characters, normalized )
            copy = event[1].clone

            esub = proc { |match|
              if @entities.has_key?($1)
                @entities[$1].gsub(Text::REFERENCE, &esub)
              else
                match
              end
            }

            copy.gsub!( Text::REFERENCE, &esub )
            copy.gsub!( Text::NUMERICENTITY ) {|m|
              m=$1
              m = "0#{m}" if m[0] == ?x
              [Integer(m)].pack('U*')
            }
            handle( :characters, copy )
          when :entitydecl
            @entities[ event[1] ] = event[2] if event.size == 3
            handle( *event )
          when :processing_instruction, :comment, :attlistdecl,
            :elementdecl, :cdata, :notationdecl, :xmldecl
            handle( *event )
          end
          handle( :progress, @parser.position )
        end
      end

      private
      def handle( symbol, *arguments )
        tag = @tag_stack[-1]
        procs = get_procs( symbol, tag )
        listeners = get_listeners( symbol, tag )
        # notify observers
        procs.each { |ob| ob.call( *arguments ) } if procs
        listeners.each { |l|
          l.send( symbol.to_s, *arguments )
        } if listeners
      end

      # The following methods are duplicates, but it is faster than using
      # a helper
      def get_procs( symbol, name )
        return nil if @procs.size == 0
        @procs.find_all do |sym, match, block|
          #puts sym.inspect+"=="+symbol.inspect+ "\t"+match.inspect+"=="+name.inspect+ "\t"+( (sym.nil? or symbol == sym) and ((name.nil? and match.nil?) or match.nil? or ( (name == match) or (match.kind_of? Regexp and name =~ match)))).to_s
          (
            (sym.nil? or symbol == sym) and
            ((name.nil? and match.nil?) or match.nil? or (
              (name == match) or
              (match.kind_of? Regexp and name =~ match)
              )
            )
          )
        end.collect{|x| x[-1]}
      end
      def get_listeners( symbol, name )
        return nil if @listeners.size == 0
        @listeners.find_all do |sym, match, block|
          (
            (sym.nil? or symbol == sym) and
            ((name.nil? and match.nil?) or match.nil? or (
              (name == match) or
              (match.kind_of? Regexp and name =~ match)
              )
            )
          )
        end.collect{|x| x[-1]}
      end

      def add( pair )
        if pair[-1].respond_to? :call
          @procs << pair unless @procs.include? pair
        else
          @listeners << pair unless @listeners.include? pair
          @has_listeners = true
        end
      end

      def get_namespace( prefix )
        uris = (@namespace_stack.find_all { |ns| not ns[prefix].nil? }) ||
          (@namespace_stack.find { |ns| not ns[nil].nil? })
        uris[-1][prefix] unless uris.nil? or 0 == uris.size
      end
    end
  end
end