Class: HTTP2::Header::Compressor

Inherits:
Object
  • Object
show all
Includes:
BufferUtils, PackingExtensions
Defined in:
lib/http/2/header/compressor.rb

Overview

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

Instance Method Summary collapse

Methods included from BufferUtils

#append_str, #read_str, #read_uint32, #shift_byte

Methods included from PackingExtensions

#pack

Constructor Details

#initialize(options = {}) ⇒ Compressor 



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# File 'lib/http/2/header/compressor.rb', line 11

def initialize(options = {})
  @cc = EncodingContext.new(options)
end

Instance Method Details

#encode(headers) ⇒ Buffer

Encodes provided list of HTTP headers.



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# File 'lib/http/2/header/compressor.rb', line 132

def encode(headers)
  buffer = "".b
  headers.partition { |f, _| f.start_with? ":" }.each do |hs|
    @cc.encode(hs) do |cmd|
      header(cmd, buffer)
    end
  end

  buffer
end

#header(h, buffer = "".b) ⇒ Buffer

Encodes header command with appropriate header representation.



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# File 'lib/http/2/header/compressor.rb', line 99

def header(h, buffer = "".b)
  type = h[:type]
  rep = HEADREP[type]
  offset = buffer.size

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

    string(h[:value], buffer)
  end

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

  buffer
end

#integer(i, n, buffer:, offset: buffer.size) ⇒ String

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



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# File 'lib/http/2/header/compressor.rb', line 38

def integer(i, n, buffer:, offset: buffer.size)
  limit = (1 << n) - 1
  return pack([i], "C", buffer: buffer, offset: offset) 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
  pack(bytes, "C*", buffer: buffer, offset: offset)
end

#string(str, buffer = "".b) ⇒ String

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



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# File 'lib/http/2/header/compressor.rb', line 76

def string(str, buffer = "".b)
  case @cc.options[:huffman]
  when :always
    huffman_string(str, buffer)
  when :never
    plain_string(str, buffer)
  else
    huffman = Huffman.encode(str)
    if huffman.bytesize < str.bytesize
      huffman_offset = buffer.bytesize
      append_str(buffer, huffman)
      set_huffman_size(buffer, huffman_offset)
    else
      plain_string(str, buffer)
    end
  end
end

#table_size=(size) ⇒ Object

Set dynamic table size in EncodingContext



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# File 'lib/http/2/header/compressor.rb', line 17

def table_size=(size)
  @cc.table_size = size
end