Class: Protocol::HPACK::Huffman::Generator::Node

Inherits:
Object
  • Object
show all
Defined in:
lib/protocol/hpack/huffman/generator.rb

Defined Under Namespace

Classes: Transition

Constant Summary collapse

MACHINE_PATH = 
File.expand_path("machine.rb", __dir__)
@@id = 
0

Class Attribute Summary collapse

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(depth) ⇒ Node 



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# File 'lib/protocol/hpack/huffman/generator.rb', line 27

def initialize(depth)
  @next = [nil, nil]
  @id = @@id
  @@id += 1
  @final = false
  @depth = depth
end

Class Attribute Details

.root ⇒ Object (readonly)

Returns the value of attribute root.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 163

def root
  @root
end

Instance Attribute Details

#depth ⇒ Object

Returns the value of attribute depth.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 21

def depth
  @depth
end

#emit ⇒ Object

Returns the value of attribute emit.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 21

def emit
  @emit
end

#final ⇒ Object

Returns the value of attribute final.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 21

def final
  @final
end

#id ⇒ Object

Returns the value of attribute id.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 23

def id
  @id
end

#next ⇒ Object

Returns the value of attribute next.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 21

def next
  @next
end

#transitions ⇒ Object

Returns the value of attribute transitions.



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# File 'lib/protocol/hpack/huffman/generator.rb', line 22

def transitions
  @transitions
end

Class Method Details

.decode(input) ⇒ Object

Test decoder



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# File 'lib/protocol/hpack/huffman/generator.rb', line 167

def self.decode(input)
  emit = ""
  n = root
  nibbles = input.unpack("C*").flat_map {|b| [((b & 0xf0) >> 4), b & 0xf]}
  until nibbles.empty?
    nb = nibbles.shift
    t = n.transitions[nb]
    emit << t.emit
    n = t.node
  end
  unless n.final && nibbles.all? {|x| x == 0xf}
    puts "len = #{emit.size} n.final = #{n.final} nibbles = #{nibbles}"
  end
  emit
end

.generate_machine ⇒ Object 



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# File 'lib/protocol/hpack/huffman/generator.rb', line 64

def self.generate_machine
  generate_tree
  
  # Using un-ordered sets (potentially) produces non-deterministic results:
  togo = Set[@root]
  @states = Set[@root]
  
  until togo.empty?
    node = togo.first
    togo.delete(node)
    
    next if node.transitions
    node.transitions = Array[1 << BITS_AT_ONCE]
    
    (1 << BITS_AT_ONCE).times do |input|
      n = node
      emit = +""
      (BITS_AT_ONCE - 1).downto(0) do |i|
        bit = (input & (1 << i)).zero? ? 0 : 1
        n = n.next[bit]
        next unless n.emit
        if n.emit == EOS
          emit = EOS # cause error on decoding
        else
          emit << n.emit.chr(Encoding::BINARY) unless emit == EOS
        end
        n = @root
      end
      node.transitions[input] = Transition.new(emit, n)
      togo << n
      @states << n
    end
  end
  puts "#{@states.size} states"
  @root
end

.generate_state_table(output_path = MACHINE_PATH) ⇒ Object 



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# File 'lib/protocol/hpack/huffman/generator.rb', line 103

def self.generate_state_table(output_path = MACHINE_PATH)
  generate_machine
  state_id = {}
  id_state = {}
  state_id[@root] = 0
  id_state[0] = @root
  max_final = 0
  id = 1
  (@states - [@root]).sort_by {|s| s.final ? 0 : 1}.each do |s|
    state_id[s] = id
    id_state[id] = s
    max_final = id if s.final
    id += 1
  end

  File.open(output_path, "w") do |file|
    file.print "      # frozen_string_literal: true\n\n      # Released under the MIT License.\n      # Copyright, 2018-2024, by Samuel Williams.\n\n      # Machine generated Huffman decoder state machine.\n      # DO NOT EDIT THIS FILE.\n\n      module Protocol\n        module HPACK\n          class Huffman\n            # :nodoc:\n            MAX_FINAL_STATE = \#{max_final}\n            MACHINE = [\n    HEADER\n    \n    id.times do |i|\n      n = id_state[i]\n      file.print \"\\t\\t\\t\\t[\"\n      string = (1 << BITS_AT_ONCE).times.map do |t|\n        transition = n.transitions.fetch(t)\n        emit = transition.emit\n        unless emit == EOS\n          bytes = emit.bytes\n          fail ArgumentError if bytes.size > 1\n          emit = bytes.first\n        end\n        \"[\#{emit.inspect}, \#{state_id.fetch(transition.node)}]\"\n      end.join(\", \")\n      file.print(string)\n      file.print \"],\\n\"\n    end\n    \n    file.print <<~FOOTER\n            ].each {|arr| arr.each {|subarr| subarr.each(&:freeze)}.freeze}.freeze\n          end\n        end\n      end\n    FOOTER\n  end\nend\n"

.generate_tree ⇒ Object 



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# File 'lib/protocol/hpack/huffman/generator.rb', line 54

def self.generate_tree
  @root = new(0)
  Protocol::HPACK::Huffman::CODES.each_with_index do |c, chr|
    code, len = c
    @root.add(code, len, chr)
  end
  puts "#{@@id} nodes"
  @root
end

Instance Method Details

#add(code, len, chr) ⇒ Object 



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# File 'lib/protocol/hpack/huffman/generator.rb', line 35

def add(code, len, chr)
  self.final = true if chr == EOS && @depth <= 7
  if len.zero?
    @emit = chr
  else
    bit = (code & (1 << (len - 1))).zero? ? 0 : 1
    node = @next[bit] ||= Node.new(@depth + 1)
    node.add(code, len - 1, chr)
  end
end