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

default[RW]

pdf_version[R]

sec_handler[R]

trailer[R]

Public Class Methods

new(input, opts = {}) click to toggle source

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 43
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

[](key) click to toggle source

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 74
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

deref(key)

Alias for: object

deref!(key) click to toggle source

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 106
def deref!(key)
  deref_internal!(key, {})
end

each() { |ref, self| ... } click to toggle source

iterate over each key, value. Just like a ruby hash.

# File lib/pdf/reader/object_hash.rb, line 135
def each(&block)
  @xref.each do |ref|
    yield ref, self[ref]
  end
end

Also aliased as: each_pair

each_key() { |id| ... } click to toggle source

iterate over each key. Just like a ruby hash.

# File lib/pdf/reader/object_hash.rb, line 144
def each_key(&block)
  each do |id, obj|
    yield id
  end
end

each_pair(&block)

Alias for: each

each_value() { |obj| ... } click to toggle source

iterate over each value. Just like a ruby hash.

# File lib/pdf/reader/object_hash.rb, line 152
def each_value(&block)
  each do |id, obj|
    yield obj
  end
end

empty?() click to toggle source

return true if there are no objects in this file

# File lib/pdf/reader/object_hash.rb, line 167
def empty?
  size == 0 ? true : false
end

encrypted?() click to toggle source

# File lib/pdf/reader/object_hash.rb, line 247
def encrypted?
  trailer.has_key?(:Encrypt)
end

fetch(key, local_default = nil) click to toggle source

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 122
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

has_key?(check_key) click to toggle source

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 174
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

Also aliased as: include?, key?, member?, value?

has_value?(value) click to toggle source

return true if the specifiedvalue exists in the file

# File lib/pdf/reader/object_hash.rb, line 191
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

include?(check_key)

Alias for: has_key?

key?(check_key)

Alias for: has_key?

keys() click to toggle source

return an array of all keys in the file

# File lib/pdf/reader/object_hash.rb, line 206
def keys
  ret = []
  each_key { |k| ret << k }
  ret
end

length()

Alias for: size

member?(check_key)

Alias for: has_key?

obj_type(ref) click to toggle source

returns the type of object a ref points to

# File lib/pdf/reader/object_hash.rb, line 54
def obj_type(ref)
  self[ref].class.to_s.to_sym
rescue
  nil
end

object(key) click to toggle source

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 98
def object(key)
  key.is_a?(PDF::Reader::Reference) ? self[key] : key
end

Also aliased as: deref

page_references() click to toggle source

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 242
def page_references
  root  = fetch(trailer[:Root])
  @page_references ||= get_page_objects(root[:Pages]).flatten
end

sec_handler?() click to toggle source

# File lib/pdf/reader/object_hash.rb, line 251
def sec_handler?
  !!sec_handler
end

size() click to toggle source

return the number of objects in the file. An object with multiple generations is counted once.

# File lib/pdf/reader/object_hash.rb, line 160
def size
  xref.size
end

Also aliased as: length

stream?(ref) click to toggle source

returns true if the supplied references points to an object with a stream

# File lib/pdf/reader/object_hash.rb, line 61
def stream?(ref)
  self.has_key?(ref) && self[ref].is_a?(PDF::Reader::Stream)
end

to_a() click to toggle source

return an array of arrays. Each sub array contains a key/value pair.

# File lib/pdf/reader/object_hash.rb, line 228
def to_a
  ret = []
  each do |id, obj|
    ret << [id, obj]
  end
  ret
end

to_s() click to toggle source

# File lib/pdf/reader/object_hash.rb, line 200
def to_s
  "<PDF::Reader::ObjectHash size: #{self.size}>"
end

value?(check_key)

Alias for: has_key?

values() click to toggle source

return an array of all values in the file

# File lib/pdf/reader/object_hash.rb, line 214
def values
  ret = []
  each_value { |v| ret << v }
  ret
end

values_at(*ids) click to toggle source

return an array of all values from the specified keys

# File lib/pdf/reader/object_hash.rb, line 222
def values_at(*ids)
  ids.map { |id| self[id] }
end

Private Instance Methods

build_security_handler(opts = {}) click to toggle source

# File lib/pdf/reader/object_hash.rb, line 290
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

decrypt(ref, obj) click to toggle source

# File lib/pdf/reader/object_hash.rb, line 320
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

deref_internal!(key, seen) click to toggle source

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 261
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

extract_io_from(input) click to toggle source

# File lib/pdf/reader/object_hash.rb, line 372
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

get_page_objects(ref) click to toggle source

returns a nested array of object references for all pages in this object store.

# File lib/pdf/reader/object_hash.rb, line 351
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

new_buffer(offset = 0) click to toggle source

# File lib/pdf/reader/object_hash.rb, line 337
def new_buffer(offset = 0)
  PDF::Reader::Buffer.new(@io, :seek => offset)
end

object_streams() click to toggle source

# File lib/pdf/reader/object_hash.rb, line 345
def object_streams
  @object_stream ||= {}
end

read_as_binary(input) click to toggle source

# File lib/pdf/reader/object_hash.rb, line 382
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

read_version() click to toggle source

# File lib/pdf/reader/object_hash.rb, line 365
def read_version
  @io.seek(0)
  _m, version = *@io.read(10).match(/PDF-(\d.\d)/)
  @io.seek(0)
  version.to_f
end

xref() click to toggle source

# File lib/pdf/reader/object_hash.rb, line 341
def xref
  @xref
end