Class: HTTP2::Header::Compressor

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

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

Returns a new instance of Compressor.

Parameters:

  • options (Hash) (defaults to: {}) —

    encoding options



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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.

Parameters:

  • headers (Array) —

    [[name, value], ...]

  • (Enumerable[header_pair])

Returns:

  • (Buffer) 


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# File 'lib/http/2/header/compressor.rb', line 134

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.

Parameters:

  • h (Hash) —

    header command

  • buffer (String) (defaults to: "".b)
  • (header_command)
  • (String)

Returns:

  • (Buffer) 


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# File 'lib/http/2/header/compressor.rb', line 101

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.getbyte(offset) | rep[:pattern]
  buffer.setbyte(offset, fb)

  buffer
end

#huffman_string(str, buffer = "".b) ⇒ String

Returns binary string.

Parameters:

  • str (String)
  • buffer (String) (defaults to: "".b)

Returns:

  • (String) —

    binary string



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# File 'lib/http/2/header/compressor.rb', line 150

def huffman_string(str, buffer = "".b)
  huffman_offset = buffer.bytesize
  buffer << "\x00".b
  Huffman.encode(str, buffer)
  size = buffer.bytesize - huffman_offset - 1

  if size < 127
    buffer.setbyte(huffman_offset, 0x80 | size)
  else
    buffer.slice!(huffman_offset, 1)
    set_huffman_size(buffer, huffman_offset)
  end
  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

Parameters:

  • i (Integer) —

    value to encode

  • n (Integer) —

    number of available bits

  • buffer (String) —

    buffer to pack bytes into

  • offset (Integer) (defaults to: buffer.size) —

    offset to insert packed bytes in buffer

  • (Integer)
  • (Integer)
  • buffer: (String)
  • offset: (Integer) (defaults to: buffer.size)

Returns:

  • (String) —

    binary string



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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

#plain_string(str, plain = "".b) ⇒ String

Returns binary string.

Parameters:

  • str (String)
  • buffer (String)

Returns:

  • (String) —

    binary string



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# File 'lib/http/2/header/compressor.rb', line 168

def plain_string(str, plain = "".b)
  integer(str.bytesize, 7, buffer: plain)
  append_str(plain, str)
  plain
end

#set_huffman_size(buffer, huffman_offset) ⇒ String

Returns binary string.

Parameters:

  • buffer (String)
  • huffman_offset (Integer) —

    buffer offset where huffman string was introduced

  • str (String)

Returns:

  • (String) —

    binary string



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# File 'lib/http/2/header/compressor.rb', line 177

def set_huffman_size(buffer, huffman_offset)
  integer(buffer.bytesize - huffman_offset, 7, buffer: buffer, offset: huffman_offset)
  buffer.setbyte(huffman_offset, buffer.getbyte(huffman_offset) | 0x80)
  buffer
end

#string(str, buffer = "".b) ⇒ String

Encodes provided value via string literal representation.

  • 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

Parameters:

  • str (String)
  • buffer (String) (defaults to: "".b)
  • (String)

Returns:

  • (String) —

    binary string



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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
      integer(huffman.bytesize, 7, buffer: buffer)
      buffer.setbyte(huffman_offset, buffer.getbyte(huffman_offset) | 0x80)
      append_str(buffer, huffman)
      buffer
    else
      plain_string(str, buffer)
    end
  end
end

#table_size=(size) ⇒ void

This method returns an undefined value.

Set dynamic table size in EncodingContext

Parameters:

  • size (Integer) —

    new dynamic table size

  • (Integer) 


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

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