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# frozen_string_literal: true
# Copyright, 2018, by Samuel G. D. Williams. <http://www.codeotaku.com>
# Copyrigh, 2013, by Ilya Grigorik.
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
require_relative 'context'
require_relative 'huffman'
module Protocol
module HPACK
# 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.
class Decompressor
def initialize(buffer, context = Context.new, table_size_limit: nil)
@buffer = buffer
@context = context
@offset = 0
@table_size_limit = table_size_limit
end
attr :buffer
attr :context
attr :offset
attr :table_size_limit
def end?
@offset >= @buffer.bytesize
end
def read_byte
if byte = @buffer.getbyte(@offset)
@offset += 1
end
return byte
end
def peek_byte
@buffer.getbyte(@offset)
end
def read_bytes(length)
slice = @buffer.byteslice(@offset, length)
@offset += length
return slice
end
# Decodes integer value from provided buffer.
#
# @param bits [Integer] number of available bits
# @return [Integer]
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
# Decodes string value from provided buffer.
#
# @return [String] UTF-8 encoded string
# @raise [CompressionError] when input is malformed
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
# Decodes header command from provided buffer.
#
# @param buffer [Buffer]
# @return [Hash] command
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
# Decodes and processes header commands within provided buffer.
#
# @param buffer [Buffer]
# @return [Array] +[[name, value], ...]+
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
end
end
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