class HTTP2::Header::Compressor

Responsible for encoding header key-value pairs using HPACK algorithm.

Public Class Methods

new(**options) click to toggle source

@param options [Hash] encoding options

# File lib/http/2/compressor.rb, line 325
def initialize(**options)
  @cc = EncodingContext.new(options)
end

Public Instance Methods

encode(headers) click to toggle source

Encodes provided list of HTTP headers.

@param headers [Array] +[[name, value], …]+ @return [Buffer]

# File lib/http/2/compressor.rb, line 442
def encode(headers)
  buffer = Buffer.new

  # Literal header names MUST be translated to lowercase before
  # encoding and transmission.
  headers.map! { |hk, hv| [hk.downcase, hv] }

  commands = @cc.encode(headers)
  commands.each do |cmd|
    buffer << header(cmd)
  end

  buffer
end
header(h, buffer = Buffer.new) click to toggle source

Encodes header command with appropriate header representation.

@param h [Hash] header command @param buffer [String] @return [Buffer]

# File lib/http/2/compressor.rb, line 412
def header(h, buffer = Buffer.new)
  rep = HEADREP[h[:type]]

  case h[:type]
  when :indexed
    buffer << integer(h[:name] + 1, rep[:prefix])
  when :changetablesize
    buffer << integer(h[:value], rep[:prefix])
  else
    if h[:name].is_a? Integer
      buffer << integer(h[:name] + 1, rep[:prefix])
    else
      buffer << integer(0, rep[:prefix])
      buffer << string(h[:name])
    end

    buffer << string(h[:value])
  end

  # set header representation pattern on first byte
  fb = buffer.ord | rep[:pattern]
  buffer.setbyte(0, fb)

  buffer
end
integer(i, n) click to toggle source

Encodes provided value via integer representation.

If I < 2^N - 1, encode I on N bits
Else
    encode 2^N - 1 on N bits
    I = I - (2^N - 1)
    While I >= 128
         Encode (I % 128 + 128) on 8 bits
         I = I / 128
    encode (I) on 8 bits

@param i [Integer] value to encode @param n [Integer] number of available bits @return [String] binary string

# File lib/http/2/compressor.rb, line 350
def integer(i, n)
  limit = 2**n - 1
  return [i].pack('C') if i < limit

  bytes = []
  bytes.push limit unless n.zero?

  i -= limit
  while (i >= 128)
    bytes.push((i % 128) + 128)
    i /= 128
  end

  bytes.push i
  bytes.pack('C*')
end
string(str) click to toggle source

Encodes provided value via string literal representation.

  • tools.ietf.org/html/draft-ietf-httpbis-header-compression-10#section-5.2

  • The string length, defined as the number of bytes needed to store its UTF-8 representation, is represented as an integer with a seven bits prefix. If the string length is strictly less than 127, it is represented as one byte.

  • If the bit 7 of the first byte is 1, the string value is represented as a list of Huffman encoded octets (padded with bit 1's until next octet boundary).

  • If the bit 7 of the first byte is 0, the string value is represented as a list of UTF-8 encoded octets.

+@options [:huffman]+ controls whether to use Huffman encoding:

:never   Do not use Huffman encoding
:always  Always use Huffman encoding
:shorter Use Huffman when the result is strictly shorter

@param str [String] @return [String] binary string

# File lib/http/2/compressor.rb, line 387
def string(str)
  plain, huffman = nil, nil
  unless @cc.options[:huffman] == :always
    plain = integer(str.bytesize, 7) << str.dup.force_encoding(Encoding::BINARY)
  end
  unless @cc.options[:huffman] == :never
    huffman = Huffman.new.encode(str)
    huffman = integer(huffman.bytesize, 7) << huffman
    huffman.setbyte(0, huffman.ord | 0x80)
  end
  case @cc.options[:huffman]
  when :always
    huffman
  when :never
    plain
  else
    huffman.bytesize < plain.bytesize ? huffman : plain
  end
end
table_size=(size) click to toggle source

Set dynamic table size in EncodingContext @param size [Integer] new dynamic table size

# File lib/http/2/compressor.rb, line 331
def table_size=(size)
  @cc.table_size = size
end