/usr/lib/ruby/vendor_ruby/pdf/reader/xref.rb is in ruby-pdf-reader 1.3.3-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 | # coding: utf-8
################################################################################
#
# Copyright (C) 2006 Peter J Jones (pjones@pmade.com)
#
# 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.
#
################################################################################
class PDF::Reader
################################################################################
# An internal PDF::Reader class that represents the XRef table in a PDF file as a
# hash-like object.
#
# An Xref table is a map of object identifiers and byte offsets. Any time a particular
# object needs to be found, the Xref table is used to find where it is stored in the
# file.
#
# Hash keys are object ids, values are either:
#
# * a byte offset where the object starts (regular PDF objects)
# * a PDF::Reader::Reference instance that points to a stream that contains the
# desired object (PDF objects embedded in an object stream)
#
# The class behaves much like a standard Ruby hash, including the use of
# the Enumerable mixin. The key difference is no []= method - the hash
# is read only.
#
class XRef
include Enumerable
attr_reader :trailer
################################################################################
# create a new Xref table based on the contents of the supplied io object
#
# io - must be an IO object, generally either a file or a StringIO
#
def initialize (io)
@io = io
@junk_offset = calc_junk_offset(io) || 0
@xref = {}
@trailer = load_offsets
end
################################################################################
# return the number of objects in this file. Objects with multiple generations are
# only counter once.
def size
@xref.size
end
################################################################################
# returns the byte offset for the specified PDF object.
#
# ref - a PDF::Reader::Reference object containing an object ID and revision number
def [](ref)
@xref[ref.id][ref.gen]
rescue
raise InvalidObjectError, "Object #{ref.id}, Generation #{ref.gen} is invalid"
end
################################################################################
# iterate over each object in the xref table
def each(&block)
ids = @xref.keys.sort
ids.each do |id|
gen = @xref[id].keys.sort[-1]
yield PDF::Reader::Reference.new(id, gen)
end
end
################################################################################
private
################################################################################
# Read a xref table from the underlying buffer.
#
# If offset is specified the table will be loaded from there, otherwise the
# default offset will be located and used.
#
# After seeking to the offset, processing is handed of to either load_xref_table()
# or load_xref_stream() based on what we find there.
#
def load_offsets(offset = nil)
offset ||= new_buffer.find_first_xref_offset
offset += @junk_offset
buf = new_buffer(offset)
tok_one = buf.token
return load_xref_table(buf) if tok_one == "xref" || tok_one == "ref"
tok_two = buf.token
tok_three = buf.token
if tok_one.to_i >= 0 && tok_two.to_i >= 0 && tok_three == "obj"
buf = new_buffer(offset)
stream = PDF::Reader::Parser.new(buf).object(tok_one.to_i, tok_two.to_i)
return load_xref_stream(stream)
end
raise PDF::Reader::MalformedPDFError,
"xref table not found at offset #{offset} (#{tok_one} != xref)"
end
################################################################################
# Assumes the underlying buffer is positioned at the start of a traditional
# Xref table and processes it into memory.
def load_xref_table(buf)
params = []
while !params.include?("trailer") && !params.include?(nil)
if params.size == 2
objid, count = params[0].to_i, params[1].to_i
count.times do
offset = buf.token.to_i
generation = buf.token.to_i
state = buf.token
store(objid, generation, offset + @junk_offset) if state == "n" && offset > 0
objid += 1
params.clear
end
end
params << buf.token
end
trailer = Parser.new(buf, self).parse_token
unless trailer.kind_of?(Hash)
raise MalformedPDFError, "PDF malformed, trailer should be a dictionary"
end
load_offsets(trailer[:XRefStm]) if trailer.has_key?(:XRefStm)
load_offsets(trailer[:Prev].to_i) if trailer.has_key?(:Prev)
trailer
end
################################################################################
# Read an XRef stream from the underlying buffer instead of a traditional xref table.
#
def load_xref_stream(stream)
unless stream.is_a?(PDF::Reader::Stream) && stream.hash[:Type] == :XRef
raise PDF::Reader::MalformedPDFError, "xref stream not found when expected"
end
trailer = Hash[stream.hash.select { |key, value|
[:Size, :Prev, :Root, :Encrypt, :Info, :ID].include?(key)
}]
widths = stream.hash[:W]
entry_length = widths.inject(0) { |s, w| s + w }
raw_data = StringIO.new(stream.unfiltered_data)
if stream.hash[:Index]
index = stream.hash[:Index]
else
index = [0, stream.hash[:Size]]
end
index.each_slice(2) do |start_id, size|
obj_ids = (start_id..(start_id+(size-1)))
obj_ids.each do |objid|
entry = raw_data.read(entry_length) || ""
f1 = unpack_bytes(entry[0,widths[0]])
f2 = unpack_bytes(entry[widths[0],widths[1]])
f3 = unpack_bytes(entry[widths[0]+widths[1],widths[2]])
if f1 == 1 && f2 > 0
store(objid, f3, f2 + @junk_offset)
elsif f1 == 2 && f2 > 0
store(objid, 0, PDF::Reader::Reference.new(f2, 0))
end
end
end
load_offsets(trailer[:Prev].to_i) if trailer.has_key?(:Prev)
trailer
end
################################################################################
# XRef streams pack info into integers 1-N bytes wide. Depending on the number of
# bytes they need to be converted to an int in different ways.
#
def unpack_bytes(bytes)
if bytes.to_s.size == 0
0
elsif bytes.size == 1
bytes.unpack("C")[0]
elsif bytes.size == 2
bytes.unpack("n")[0]
elsif bytes.size == 3
("\x00" + bytes).unpack("N")[0]
elsif bytes.size == 4
bytes.unpack("N")[0]
else
raise UnsupportedFeatureError, "Unable to unpack xref stream entries with more than 4 bytes"
end
end
################################################################################
# Wrap the io stream we're working with in a buffer that can tokenise it for us.
#
# We create multiple buffers so we can be tokenising multiple sections of the file
# at the same time without worrying about clearing the buffers contents.
#
def new_buffer(offset = 0)
PDF::Reader::Buffer.new(@io, :seek => offset)
end
################################################################################
# Stores an offset value for a particular PDF object ID and revision number
#
def store (id, gen, offset)
(@xref[id] ||= {})[gen] ||= offset
end
################################################################################
# Returns the offset of the PDF document in the +stream+. In theory this
# should always be 0, but all sort of crazy junk is prefixed to PDF files
# in the real world.
#
# Checks up to 50 chars into the file, returns nil if no PDF data detected.
#
def calc_junk_offset(io)
io.rewind
offset = io.pos
until (c = io.readchar) == '%' || c == 37 || offset > 50
offset += 1
end
io.rewind
offset < 50 ? offset : nil
rescue EOFError
return nil
end
end
################################################################################
end
################################################################################
|