Class: HTTP::HPACK::Decompressor

Inherits:
Object
  • Object
show all
Defined in:
lib/http/hpack/decompressor.rb

Overview

Responsible for decoding received headers and maintaining compression context of the opposing peer. Decompressor must be initialized with appropriate starting context based on local role: client or server.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(buffer, context = Context.new) ⇒ Decompressor

Returns a new instance of Decompressor.



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# File 'lib/http/hpack/decompressor.rb', line 31

def initialize(buffer, context = Context.new)
  @buffer = buffer
  @context = context
  @offset = 0
end

Instance Attribute Details

#buffer ⇒ Object (readonly)

Returns the value of attribute buffer.



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# File 'lib/http/hpack/decompressor.rb', line 37

def buffer
  @buffer
end

#context ⇒ Object (readonly)

Returns the value of attribute context.



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# File 'lib/http/hpack/decompressor.rb', line 38

def context
  @context
end

#offset ⇒ Object (readonly)

Returns the value of attribute offset.



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# File 'lib/http/hpack/decompressor.rb', line 39

def offset
  @offset
end

Instance Method Details

#decode(list = []) ⇒ Array

Decodes and processes header commands within provided buffer.

Parameters:

  • buffer (Buffer)

Returns:

  • (Array) —

    [[name, value], …]



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# File 'lib/http/hpack/decompressor.rb', line 143

def decode(list = [])
  while !end?
    if pair = @context.decode(read_header)
      list << pair
    end
  end
  
  return list
end

#end? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/http/hpack/decompressor.rb', line 41

def end?
  @offset >= @buffer.bytesize
end

#peek_byte ⇒ Object 



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# File 'lib/http/hpack/decompressor.rb', line 54

def peek_byte
  @buffer.getbyte(@offset)
end

#read_byte ⇒ Object 



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# File 'lib/http/hpack/decompressor.rb', line 45

def read_byte
  if byte = @buffer.getbyte(@offset)
    @offset += 1
  end
  
  return byte
end

#read_bytes(length) ⇒ Object 



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# File 'lib/http/hpack/decompressor.rb', line 58

def read_bytes(length)
  slice = @buffer.byteslice(@offset, length)
  
  @offset += length
  
  return slice
end

#read_header ⇒ Hash

Decodes header command from provided buffer.

Parameters:

  • buffer (Buffer)

Returns:

  • (Hash) —

    command

Raises:



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# File 'lib/http/hpack/decompressor.rb', line 107

def read_header
  pattern = peek_byte

  header = {}
  header[:type], type = HEADER_REPRESENTATION.find do |_t, desc|
    mask = (pattern >> desc[:prefix]) << desc[:prefix]
    mask == desc[:pattern]
  end

  raise CompressionError unless header[:type]

  header[:name] = read_integer(type[:prefix])

  case header[:type]
  when :indexed
    raise CompressionError if header[:name].zero?
    header[:name] -= 1
  when :changetablesize
    header[:value] = header[:name]
  else
    if (header[:name]).zero?
      header[:name] = read_string
    else
      header[:name] -= 1
    end
    
    header[:value] = read_string
  end

  return header
end

#read_integer(bits) ⇒ Integer

Decodes integer value from provided buffer.

Parameters:

  • bits (Integer) —

    number of available bits

Returns:

  • (Integer) 


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# File 'lib/http/hpack/decompressor.rb', line 70

def read_integer(bits)
  limit = 2**bits - 1
  value = !bits.zero? ? (read_byte & limit) : 0
  
  shift = 0
  
  while byte = read_byte
    value += ((byte & 127) << shift)
    shift += 7
    
    break if (byte & 128).zero?
  end if (value == limit)

  return value
end

#read_string ⇒ String

Decodes string value from provided buffer.

Returns:

  • (String) —

    UTF-8 encoded string

Raises:



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# File 'lib/http/hpack/decompressor.rb', line 90

def read_string
  huffman = (peek_byte & 0x80) == 0x80
  
  length = read_integer(7)
  string = read_bytes(length)
  
  raise CompressionError, "Invalid string length, got #{string.bytesize}, expecting #{length}!" unless string.bytesize == length
  
  string = Huffman.new.decode(string) if huffman
  
  return string.force_encoding(Encoding::UTF_8)
end