class HTTP2::Header::Huffman
Huffman
encoder/decoder
Constants
- BITS_AT_ONCE
- CODES
Huffman
table as specified in- ENCODE_TABLE
- EOS
Public Instance Methods
decode(buf)
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Decodes provided Huffman
coded string.
@param buf [Buffer] @return [String] binary string @raise [CompressionError] when Huffman
coded string is malformed
# File lib/http/2/huffman.rb, line 32 def decode(buf) emit = '' state = 0 # start state mask = (1 << BITS_AT_ONCE) - 1 buf.each_byte do |chr| (8 / BITS_AT_ONCE - 1).downto(0) do |shift| branch = (chr >> (shift * BITS_AT_ONCE)) & mask # MACHINE[state] = [final, [transitions]] # [final] unfinished bits so far are prefix of the EOS code. # Each transition is [emit, next] # [emit] character to be emitted on this transition, empty string, or EOS. # [next] next state number. trans = MACHINE[state][branch] fail CompressionError, 'Huffman decode error (EOS found)' if trans.first == EOS emit << trans.first.chr if trans.first state = trans.last end end # Check whether partial input is correctly filled unless state <= MAX_FINAL_STATE fail CompressionError, 'Huffman decode error (EOS invalid)' end emit.force_encoding(Encoding::BINARY) end
encode(str)
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Encodes provided value via huffman encoding. Length is not encoded in this method.
@param str [String] @return [String] binary string
# File lib/http/2/huffman.rb, line 21 def encode(str) bitstring = str.each_byte.map { |chr| ENCODE_TABLE[chr] }.join bitstring << '1' * ((8 - bitstring.size) % 8) [bitstring].pack('B*') end