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 150

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 110

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? ? (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/protocol/hpack/decompressor.rb', line 93

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