Class: HTTP2::Header::Compressor

Inherits:
Object
  • Object
show all
Defined in:
lib/http/2/compressor.rb

Overview

Responsible for encoding header key-value pairs using HPACK algorithm. Compressor must be initialized with appropriate starting context based on local role: client or server.

Examples:

client_role = Compressor.new(:request)
server_role = Compressor.new(:response)

Instance Method Summary collapse

Constructor Details

#initialize(type) ⇒ Compressor

Returns a new instance of Compressor.



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# File 'lib/http/2/compressor.rb', line 291

def initialize(type)
  @cc = CompressionContext.new(type)
end

Instance Method Details

#encode(headers) ⇒ String

Encodes provided list of HTTP headers.

Parameters:

  • headers (Hash)

Returns:

  • (String) —

    binary string



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# File 'lib/http/2/compressor.rb', line 387

def encode(headers)
  commands = []
  @cc.update_sets

  # Remove missing headers from the working set
  @cc.workset.each do |idx, (wk,wv)|
    if headers.find {|(hk,hv)| hk == wk && hv == wv }.nil?
      commands.push @cc.removecmd idx
    end
  end

  # Add missing headers to the working set
  headers.each do |(hk,hv)|
    if @cc.workset.find {|i,(wk,wv)| hk == wk && hv == wv}.nil?
      commands.push @cc.addcmd [hk, hv]
    end
  end

  commands.map do |cmd|
    @cc.process cmd.dup
    header cmd
  end.join
end

#header(h, buffer = "") ⇒ Object

Encodes header command with appropriate header representation.

Parameters:

  • h (Hash) —

    header command

  • buffer (String) (defaults to: "") 


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# File 'lib/http/2/compressor.rb', line 351

def header(h, buffer = "")
  rep = HEADREP[h[:type]]

  if h[:type] == :indexed
    buffer << integer(h[:name], 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

    if h[:type] == :substitution
      buffer << integer(h[:index], 0)
    end

    if h[:value].is_a? Integer
      buffer << integer(h[:value], 0)
    else
      buffer << string(h[:value])
    end
  end

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

  buffer
end

#integer(i, n) ⇒ String

Encodes provided value via integer representation.

  • tools.ietf.org/html/draft-ietf-httpbis-header-compression-01#section-4.2.1

    If I < 2^N - 1, encode I on N bits Else, encode 2^N - 1 on N bits and do the following steps:

    Set I to (I - (2^N - 1)) and Q to 1
While Q > 0
  Compute Q and R, quotient and remainder of I divided by 2^7
  If Q is strictly greater than 0, write one 1 bit; otherwise, write one 0 bit
  Encode R on the next 7 bits
  I = Q

Parameters:

  • i (Integer) —

    value to encode

  • n (Integer) —

    number of available bits

Returns:

  • (String) —

    binary string



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# File 'lib/http/2/compressor.rb', line 310

def integer(i, n)
  limit = 2**n - 1
  return [i].pack('C') if (i < limit)

  bytes = []
  bytes.push limit if !n.zero?

  i -= limit
  q = 1

  while (q > 0) do
    q, r = i.divmod(128)
    r += 128 if (q > 0)
    i = q

    bytes.push(r)
  end

  bytes.pack('C*')
end

#string(str) ⇒ String

Encodes provided value via string literal representation.

Parameters:

  • str (String)

Returns:

  • (String) —

    binary string



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# File 'lib/http/2/compressor.rb', line 342

def string(str)
  integer(str.bytesize, 0) + str.dup.force_encoding('binary')
end