/
object_hash.rb
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/
object_hash.rb
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# coding: utf-8
class PDF::Reader
# Provides low level access to the objects in a PDF file via a hash-like
# object.
#
# A PDF file can be viewed as a large hash map. It is a series of objects
# stored at precise byte offsets, and a table that maps object IDs to byte
# offsets. Given an object ID, looking up an object is an O(1) operation.
#
# Each PDF object can be mapped to a ruby object, so by passing an object
# ID to the [] method, a ruby representation of that object will be
# retrieved.
#
# 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.
#
# == Basic Usage
#
# h = PDF::Reader::ObjectHash.new("somefile.pdf")
# h[1]
# => 3469
#
# h[PDF::Reader::Reference.new(1,0)]
# => 3469
#
class ObjectHash
include Enumerable
attr_accessor :default
attr_reader :trailer, :pdf_version
attr_reader :sec_handler
# Creates a new ObjectHash object. Input can be a string with a valid filename
# or an IO-like object.
#
# Valid options:
#
# :password - the user password to decrypt the source PDF
#
def initialize(input, opts = {})
@io = extract_io_from(input)
@xref = PDF::Reader::XRef.new(@io)
@pdf_version = read_version
@trailer = @xref.trailer
@cache = opts[:cache] || PDF::Reader::ObjectCache.new
@sec_handler = NullSecurityHandler.new
@sec_handler = build_security_handler(opts)
end
# returns the type of object a ref points to
def obj_type(ref)
self[ref].class.to_s.to_sym
rescue
nil
end
# returns true if the supplied references points to an object with a stream
def stream?(ref)
self.has_key?(ref) && self[ref].is_a?(PDF::Reader::Stream)
end
# Access an object from the PDF. key can be an int or a PDF::Reader::Reference
# object.
#
# If an int is used, the object with that ID and a generation number of 0 will
# be returned.
#
# If a PDF::Reader::Reference object is used the exact ID and generation number
# can be specified.
#
def [](key)
return default if key.to_i <= 0
unless key.is_a?(PDF::Reader::Reference)
key = PDF::Reader::Reference.new(key.to_i, 0)
end
if @cache.has_key?(key)
@cache[key]
elsif xref[key].is_a?(Integer)
buf = new_buffer(xref[key])
@cache[key] = decrypt(key, Parser.new(buf, self).object(key.id, key.gen))
elsif xref[key].is_a?(PDF::Reader::Reference)
container_key = xref[key]
object_streams[container_key] ||= PDF::Reader::ObjectStream.new(object(container_key))
@cache[key] = object_streams[container_key][key.id]
end
rescue InvalidObjectError
return default
end
# If key is a PDF::Reader::Reference object, lookup the corresponding
# object in the PDF and return it. Otherwise return key untouched.
#
def object(key)
key.is_a?(PDF::Reader::Reference) ? self[key] : key
end
alias :deref :object
# Recursively dereferences the object refered to be +key+. If +key+ is not
# a PDF::Reader::Reference, the key is returned unchanged.
#
def deref!(key)
deref_internal!(key, {})
end
# Access an object from the PDF. key can be an int or a PDF::Reader::Reference
# object.
#
# If an int is used, the object with that ID and a generation number of 0 will
# be returned.
#
# If a PDF::Reader::Reference object is used the exact ID and generation number
# can be specified.
#
# local_default is the object that will be returned if the requested key doesn't
# exist.
#
def fetch(key, local_default = nil)
obj = self[key]
if obj
return obj
elsif local_default
return local_default
else
raise IndexError, "#{key} is invalid" if key.to_i <= 0
end
end
# iterate over each key, value. Just like a ruby hash.
#
def each(&block)
@xref.each do |ref|
yield ref, self[ref]
end
end
alias :each_pair :each
# iterate over each key. Just like a ruby hash.
#
def each_key(&block)
each do |id, obj|
yield id
end
end
# iterate over each value. Just like a ruby hash.
#
def each_value(&block)
each do |id, obj|
yield obj
end
end
# return the number of objects in the file. An object with multiple generations
# is counted once.
def size
xref.size
end
alias :length :size
# return true if there are no objects in this file
#
def empty?
size == 0 ? true : false
end
# return true if the specified key exists in the file. key
# can be an int or a PDF::Reader::Reference
#
def has_key?(check_key)
# TODO update from O(n) to O(1)
each_key do |key|
if check_key.kind_of?(PDF::Reader::Reference)
return true if check_key == key
else
return true if check_key.to_i == key.id
end
end
return false
end
alias :include? :has_key?
alias :key? :has_key?
alias :member? :has_key?
# return true if the specifiedvalue exists in the file
#
def has_value?(value)
# TODO update from O(n) to O(1)
each_value do |obj|
return true if obj == value
end
return false
end
alias :value? :has_key?
def to_s
"<PDF::Reader::ObjectHash size: #{self.size}>"
end
# return an array of all keys in the file
#
def keys
ret = []
each_key { |k| ret << k }
ret
end
# return an array of all values in the file
#
def values
ret = []
each_value { |v| ret << v }
ret
end
# return an array of all values from the specified keys
#
def values_at(*ids)
ids.map { |id| self[id] }
end
# return an array of arrays. Each sub array contains a key/value pair.
#
def to_a
ret = []
each do |id, obj|
ret << [id, obj]
end
ret
end
# returns an array of PDF::Reader::References. Each reference in the
# array points a Page object, one for each page in the PDF. The first
# reference is page 1, second reference is page 2, etc.
#
# Useful for apps that want to extract data from specific pages.
#
def page_references
root = fetch(trailer[:Root])
@page_references ||= get_page_objects(root[:Pages]).flatten
end
def encrypted?
trailer.has_key?(:Encrypt)
end
def sec_handler?
!!sec_handler
end
private
# Private implementation of deref!, which exists to ensure the `seen` argument
# isn't publicly available. It's used to avoid endless loops in the recursion, and
# doesn't need to be part of the public API.
#
def deref_internal!(key, seen)
seen_key = key.is_a?(PDF::Reader::Reference) ? key : key.object_id
return seen[seen_key] if seen.key?(seen_key)
case object = deref(key)
when Hash
seen[seen_key] ||= {}
object.each do |k, value|
seen[seen_key][k] = deref_internal!(value, seen)
end
seen[seen_key]
when PDF::Reader::Stream
seen[seen_key] ||= PDF::Reader::Stream.new({}, object.data)
object.hash.each do |k,value|
seen[seen_key].hash[k] = deref_internal!(value, seen)
end
seen[seen_key]
when Array
seen[seen_key] ||= []
object.each do |value|
seen[seen_key] << deref_internal!(value, seen)
end
seen[seen_key]
else
object
end
end
def build_security_handler(opts = {})
return NullSecurityHandler.new if trailer[:Encrypt].nil?
enc = deref(trailer[:Encrypt])
filter = enc.fetch(:Filter, :Standard)
version = enc.fetch(:V, 0)
if filter == :Standard && version >= 5
UnimplementedSecurityHandler.new
elsif filter == :Standard && version >= 4 && enc.fetch(:CF, {}).fetch(enc[:StmF], {}).fetch(:CFM, nil) == :AESV2
UnimplementedSecurityHandler.new
elsif filter == :Standard
encmeta = enc.has_key?(:EncryptMetadata)? enc[:EncryptMetadata].to_s == "true" : true
StandardSecurityHandler.new(
key_length: (enc[:Length] || 40).to_i,
revision: enc[:R],
owner_key: enc[:O],
user_key: enc[:U],
permissions: enc[:P].to_i,
encrypted_metadata: encmeta,
file_id: (deref(trailer[:ID]) || []).first,
password: opts[:password]
)
else
UnimplementedSecurityHandler.new
end
end
def decrypt(ref, obj)
case obj
when PDF::Reader::Stream then
obj.data = sec_handler.decrypt(obj.data, ref)
obj
when Hash then
arr = obj.map { |key,val| [key, decrypt(ref, val)] }.flatten(1)
Hash[*arr]
when Array then
obj.collect { |item| decrypt(ref, item) }
when String
sec_handler.decrypt(obj, ref)
else
obj
end
end
def new_buffer(offset = 0)
PDF::Reader::Buffer.new(@io, :seek => offset)
end
def xref
@xref
end
def object_streams
@object_stream ||= {}
end
# returns a nested array of object references for all pages in this object store.
#
def get_page_objects(ref)
obj = fetch(ref)
if obj[:Type] == :Page
ref
elsif obj[:Kids]
deref(obj[:Kids]).map { |kid| get_page_objects(kid) }
end
end
def read_version
@io.seek(0)
_m, version = *@io.read(10).match(/PDF-(\d.\d)/)
@io.seek(0)
version.to_f
end
def extract_io_from(input)
if input.respond_to?(:seek) && input.respond_to?(:read)
input
elsif File.file?(input.to_s)
StringIO.new read_as_binary(input)
else
raise ArgumentError, "input must be an IO-like object or a filename"
end
end
def read_as_binary(input)
if File.respond_to?(:binread)
File.binread(input.to_s)
else
File.open(input.to_s,"rb") { |f| f.read }
end
end
end
end