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.

Instance Method Summary collapse

Constructor Details

#initialize(**options) ⇒ Compressor


329
330
331
# File 'lib/http/2/compressor.rb', line 329

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

Instance Method Details

#encode(headers) ⇒ Buffer

Encodes provided list of HTTP headers.


446
447
448
449
450
451
452
453
454
455
# File 'lib/http/2/compressor.rb', line 446

def encode(headers)
  buffer = Buffer.new

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

  buffer
end

#header(h, buffer = Buffer.new) ⇒ Buffer

Encodes header command with appropriate header representation.


416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
# File 'lib/http/2/compressor.rb', line 416

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) ⇒ 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

354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
# File 'lib/http/2/compressor.rb', line 354

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) ⇒ 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

391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
# File 'lib/http/2/compressor.rb', line 391

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) ⇒ Object

Set dynamic table size in EncodingContext


335
336
337
# File 'lib/http/2/compressor.rb', line 335

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