Class: Protocol::HPACK::Decompressor

Inherits:
Object
  • Object
show all
Defined in:
lib/protocol/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, table_size_limit: nil) ⇒ Decompressor

Returns a new instance of Decompressor.



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

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

Instance Attribute Details

#buffer ⇒ Object (readonly)

Returns the value of attribute buffer.



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

def buffer
  @buffer
end

#context ⇒ Object (readonly)

Returns the value of attribute context.



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# File 'lib/protocol/hpack/decompressor.rb', line 40

def context
  @context
end

#offset ⇒ Object (readonly)

Returns the value of attribute offset.



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

def offset
  @offset
end

#table_size_limit ⇒ Object (readonly)

Returns the value of attribute table_size_limit.



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# File 'lib/protocol/hpack/decompressor.rb', line 43

def table_size_limit
  @table_size_limit
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/protocol/hpack/decompressor.rb', line 153

def decode(list = [])
  while !end?
    command = read_header
    
    if pair = @context.decode(command)
      list << pair
    end
  end
  
  if command and command[:type] == :change_table_size
    raise CompressionError, "Trailing table size update!"
  end
  
  return list
end

#end? ⇒ Boolean

Returns:

  • (Boolean) 


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

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

#peek_byte ⇒ Object 



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# File 'lib/protocol/hpack/decompressor.rb', line 57

def peek_byte
  @buffer.getbyte(@offset)
end

#read_byte ⇒ Object 



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# File 'lib/protocol/hpack/decompressor.rb', line 49

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

#read_bytes(length) ⇒ Object 



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# File 'lib/protocol/hpack/decompressor.rb', line 61

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/protocol/hpack/decompressor.rb', line 113

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 :change_table_size
    header[:value] = header[:name]
    
    if @table_size_limit and header[:value] > @table_size_limit
      raise CompressionError, "Table size #{header[:value]} exceeds limit #{@table_size_limit}!"
    end
  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/protocol/hpack/decompressor.rb', line 73

def read_integer(bits)
  limit = 2**bits - 1
  value = bits.zero? ? 0 : (read_byte & limit)
  
  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/protocol/hpack/decompressor.rb', line 93

def read_string
  huffman = (peek_byte & 0x80) == 0x80
  
  length = read_integer(7)
  
  raise CompressionError, "Invalid string length!" unless length
  
  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