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# frozen_string_literal: true
desc "Generate Huffman precompiled table in huffman_statemachine.rb"
task :generate_huffman_table do
HuffmanTable::Node.generate_state_table
end
require_relative "../lib/http/2/header/huffman"
module HuffmanTable
BITS_AT_ONCE = HTTP2::Header::Huffman::BITS_AT_ONCE
EOS = 256
class Node
attr_accessor :next, :emit, :final, :depth, :transitions, :id
@@id = 0 # rubocop:disable Style/ClassVars
def initialize(depth)
@next = [nil, nil]
@id = @@id
@@id += 1 # rubocop:disable Style/ClassVars
@final = false
@depth = depth
end
def add(code, len, chr)
self.final = true if chr == EOS && @depth <= 7
if len.zero?
@emit = chr
else
bit = code.nobits?((1 << (len - 1))) ? 0 : 1
node = @next[bit] ||= Node.new(@depth + 1)
node.add(code, len - 1, chr)
end
end
class Transition
attr_accessor :emit, :node
def initialize(emit, node)
@emit = emit
@node = node
end
end
def self.generate_tree
@root = new(0)
HTTP2::Header::Huffman::CODES.each_with_index do |c, chr|
code, len = c
@root.add(code, len, chr)
end
puts "#{@@id} nodes"
@root
end
def self.generate_machine
generate_tree
togo = Set[@root]
@states = Set[@root]
until togo.empty?
node = togo.first
togo.delete(node)
next if node.transitions
node.transitions = [1 << BITS_AT_ONCE]
(1 << BITS_AT_ONCE).times do |input|
n = node
emit = "".b
(BITS_AT_ONCE - 1).downto(0) do |i|
bit = input.nobits?((1 << i)) ? 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
def self.generate_state_table
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(File.expand_path("../lib/http/2/header/huffman_statemachine.rb", File.dirname(__FILE__)), "w") do |f|
f.print <<~HEADER
# Machine generated Huffman decoder state machine.
# DO NOT EDIT THIS FILE.
# The following task generates this file.
# rake generate_huffman_table
module HTTP2
module Header
class Huffman
# :nodoc:
MAX_FINAL_STATE = #{max_final}
MACHINE = [
HEADER
id.times do |i|
n = id_state[i]
f.print " ["
string = Array.new((1 << 4)) do |t|
transition = n.transitions.fetch(t)
emit = transition.emit
unless emit == EOS
bytes = emit.bytes
raise ArgumentError if bytes.size > 1
emit = bytes.first
end
"[#{emit.inspect}, #{state_id.fetch(transition.node)}]"
end.join(", ")
f.print(string)
f.print "],\n"
end
f.print <<~TAILER
].each { |arr| arr.each { |subarr| subarr.freeze }.freeze }.freeze
end
end
end
TAILER
end
end
class << self
attr_reader :root
end
# Test decoder
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
puts "len = #{emit.size} n.final = #{n.final} nibbles = #{nibbles}" unless n.final && nibbles.all?(0xf)
emit
end
end
end
|
