class PDF::Reader::ObjectHash
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
Attributes
Public Class Methods
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
# File lib/pdf/reader/object_hash.rb, line 42 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
Public Instance Methods
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.
# File lib/pdf/reader/object_hash.rb, line 73 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
Recursively dereferences the object refered to be key
. If key
is not a PDF::Reader::Reference
, the key is returned unchanged.
# File lib/pdf/reader/object_hash.rb, line 105 def deref!(key) deref_internal!(key, {}) end
iterate over each key, value. Just like a ruby hash.
# File lib/pdf/reader/object_hash.rb, line 134 def each(&block) @xref.each do |ref| yield ref, self[ref] end end
iterate over each key. Just like a ruby hash.
# File lib/pdf/reader/object_hash.rb, line 143 def each_key(&block) each do |id, obj| yield id end end
iterate over each value. Just like a ruby hash.
# File lib/pdf/reader/object_hash.rb, line 151 def each_value(&block) each do |id, obj| yield obj end end
return true if there are no objects in this file
# File lib/pdf/reader/object_hash.rb, line 166 def empty? size == 0 ? true : false end
# File lib/pdf/reader/object_hash.rb, line 246 def encrypted? trailer.has_key?(:Encrypt) 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.
# File lib/pdf/reader/object_hash.rb, line 121 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
return true if the specified key exists in the file. key can be an int or a PDF::Reader::Reference
# File lib/pdf/reader/object_hash.rb, line 173 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
return true if the specifiedvalue exists in the file
# File lib/pdf/reader/object_hash.rb, line 190 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
return an array of all keys in the file
# File lib/pdf/reader/object_hash.rb, line 205 def keys ret = [] each_key { |k| ret << k } ret end
returns the type of object a ref points to
# File lib/pdf/reader/object_hash.rb, line 53 def obj_type(ref) self[ref].class.to_s.to_sym rescue nil end
If key is a PDF::Reader::Reference
object, lookup the corresponding object in the PDF and return it. Otherwise return key untouched.
# File lib/pdf/reader/object_hash.rb, line 97 def object(key) key.is_a?(PDF::Reader::Reference) ? self[key] : key 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.
# File lib/pdf/reader/object_hash.rb, line 241 def page_references root = fetch(trailer[:Root]) @page_references ||= get_page_objects(root[:Pages]).flatten end
# File lib/pdf/reader/object_hash.rb, line 250 def sec_handler? !!sec_handler end
return the number of objects in the file. An object with multiple generations is counted once.
# File lib/pdf/reader/object_hash.rb, line 159 def size xref.size end
returns true if the supplied references points to an object with a stream
# File lib/pdf/reader/object_hash.rb, line 60 def stream?(ref) self.has_key?(ref) && self[ref].is_a?(PDF::Reader::Stream) end
return an array of arrays. Each sub array contains a key/value pair.
# File lib/pdf/reader/object_hash.rb, line 227 def to_a ret = [] each do |id, obj| ret << [id, obj] end ret end
# File lib/pdf/reader/object_hash.rb, line 199 def to_s "<PDF::Reader::ObjectHash size: #{self.size}>" end
return an array of all values in the file
# File lib/pdf/reader/object_hash.rb, line 213 def values ret = [] each_value { |v| ret << v } ret end
return an array of all values from the specified keys
# File lib/pdf/reader/object_hash.rb, line 221 def values_at(*ids) ids.map { |id| self[id] } end
Private Instance Methods
# File lib/pdf/reader/object_hash.rb, line 289 def build_security_handler(opts = {}) encrypt = deref(trailer[:Encrypt]) if NullSecurityHandler.supports?(encrypt) NullSecurityHandler.new elsif StandardSecurityHandler.supports?(encrypt) encmeta = !encrypt.has_key?(:EncryptMetadata) || encrypt[:EncryptMetadata].to_s == "true" StandardSecurityHandler.new( key_length: (encrypt[:Length] || 40).to_i, revision: encrypt[:R], owner_key: encrypt[:O], user_key: encrypt[:U], permissions: encrypt[:P].to_i, encrypted_metadata: encmeta, file_id: (deref(trailer[:ID]) || []).first, password: opts[:password], cfm: encrypt.fetch(:CF, {}).fetch(encrypt[:StmF], {}).fetch(:CFM, nil) ) elsif StandardSecurityHandlerV5.supports?(encrypt) StandardSecurityHandlerV5.new( O: encrypt[:O], U: encrypt[:U], OE: encrypt[:OE], UE: encrypt[:UE], password: opts[:password] ) else UnimplementedSecurityHandler.new end end
# File lib/pdf/reader/object_hash.rb, line 319 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
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.
# File lib/pdf/reader/object_hash.rb, line 260 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
# File lib/pdf/reader/object_hash.rb, line 371 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
returns a nested array of object references for all pages in this object store.
# File lib/pdf/reader/object_hash.rb, line 350 def get_page_objects(ref) obj = deref(ref) unless obj.kind_of?(::Hash) raise MalformedPDFError, "Dereferenced page object must be a dict" end if obj[:Type] == :Page ref elsif obj[:Kids] deref(obj[:Kids]).map { |kid| get_page_objects(kid) } end end
# File lib/pdf/reader/object_hash.rb, line 336 def new_buffer(offset = 0) PDF::Reader::Buffer.new(@io, :seek => offset) end
# File lib/pdf/reader/object_hash.rb, line 344 def object_streams @object_stream ||= {} end
# File lib/pdf/reader/object_hash.rb, line 381 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
# File lib/pdf/reader/object_hash.rb, line 364 def read_version @io.seek(0) _m, version = *@io.read(10).match(/PDF-(\d.\d)/) @io.seek(0) version.to_f end
# File lib/pdf/reader/object_hash.rb, line 340 def xref @xref end