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# frozen_string_literal: true
module HTTP2
module Header
# 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.
#
# @example
# server_role = Decompressor.new(:request)
# client_role = Decompressor.new(:response)
class Decompressor
include Error
include BufferUtils
FORBIDDEN_HEADERS = %w[connection te].freeze
# @param options [Hash] decoding options. Only :table_size is effective.
def initialize(options = {})
@cc = EncodingContext.new(options)
end
# Set dynamic table size in EncodingContext
# @param size [Integer] new dynamic table size
def table_size=(size)
@cc.table_size = size
end
# Decodes integer value from provided buffer.
#
# @param buf [String]
# @param n [Integer] number of available bits
# @return [Integer]
def integer(buf, n)
limit = (1 << n) - 1
i = n.zero? ? 0 : (shift_byte(buf) & limit)
m = 0
if i == limit
offset = 0
buf.each_byte.with_index do |byte, idx|
offset = idx
# while (byte = shift_byte(buf))
i += ((byte & 127) << m)
m += 7
break if byte.nobits?(128)
end
read_str(buf, offset + 1)
end
i
end
# Decodes string value from provided buffer.
#
# @param buf [String]
# @return [String] UTF-8 encoded string
# @raise [CompressionError] when input is malformed
def string(buf)
raise CompressionError, "invalid header block fragment" if buf.empty?
huffman = buf.getbyte(0).allbits?(0x80)
len = integer(buf, 7)
str = read_str(buf, len)
raise CompressionError, "string too short" unless str.bytesize == len
str = Huffman.decode(str) if huffman
str.force_encoding(Encoding::UTF_8)
end
# Decodes header command from provided buffer.
#
# @param buf [Buffer]
# @return [Hash] command
def header(buf)
peek = buf.getbyte(0)
header_type, type = HEADREP.find do |_, desc|
mask = (peek >> desc[:prefix]) << desc[:prefix]
mask == desc[:pattern]
end
raise CompressionError unless header_type && type
header_name = integer(buf, type[:prefix])
case header_type
when :indexed
raise CompressionError if header_name.zero?
header_name -= 1
{ type: header_type, name: header_name }
when :changetablesize
{ type: header_type, name: header_name, value: header_name }
else
if header_name.zero?
header_name = string(buf)
else
header_name -= 1
end
header_value = string(buf)
{ type: header_type, name: header_name, value: header_value }
end
end
# Decodes and processes header commands within provided buffer.
#
# @param buf [Buffer]
# @param frame [HTTP2::Frame, nil]
# @return [Array] +[[name, value], ...]
def decode(buf, frame = nil)
list = []
decoding_pseudo_headers = true
@cc.listen_on_table do
until buf.empty?
field, value = @cc.process(header(buf))
next if field.nil?
is_pseudo_header = field.start_with?(":")
if !decoding_pseudo_headers && is_pseudo_header
raise ProtocolError, "one or more pseudo headers encountered after regular headers"
end
decoding_pseudo_headers = is_pseudo_header
raise ProtocolError, "invalid header received: #{field}" if FORBIDDEN_HEADERS.include?(field)
if frame
case field
when ":status"
frame[:status] = Integer(value)
when ":method"
frame[:method] = value
when "content-length"
frame[:content_length] = Integer(value)
when "trailer"
(frame[:trailer] ||= []) << value
end
end
list << [field, value]
end
end
list
end
end
end
end
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