Class: PDF::Reader::XRef
- Inherits:
-
Object
- Object
- PDF::Reader::XRef
- Includes:
- Enumerable
- Defined in:
- lib/pdf/reader/xref.rb
Overview
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.
Instance Attribute Summary collapse
-
#trailer ⇒ Object
readonly
Returns the value of attribute trailer.
Instance Method Summary collapse
-
#[](ref) ⇒ Object
returns the byte offset for the specified PDF object.
-
#each(&block) ⇒ Object
iterate over each object in the xref table.
-
#initialize(io) ⇒ XRef
constructor
create a new Xref table based on the contents of the supplied io object.
-
#size ⇒ Object
return the number of objects in this file.
Constructor Details
#initialize(io) ⇒ XRef
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
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# File 'lib/pdf/reader/xref.rb', line 54 def initialize (io) @io = io @xref = {} @trailer = load_offsets end |
Instance Attribute Details
#trailer ⇒ Object (readonly)
Returns the value of attribute trailer.
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# File 'lib/pdf/reader/xref.rb', line 47 def trailer @trailer end |
Instance Method Details
#[](ref) ⇒ Object
returns the byte offset for the specified PDF object.
ref - a PDF::Reader::Reference object containing an object ID and revision number
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# File 'lib/pdf/reader/xref.rb', line 69 def [](ref) @xref[ref.id][ref.gen] rescue raise InvalidObjectError, "Object #{ref.id}, Generation #{ref.gen} is invalid" end |
#each(&block) ⇒ Object
iterate over each object in the xref table
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# File 'lib/pdf/reader/xref.rb', line 76 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 |
#size ⇒ Object
return the number of objects in this file. Objects with multiple generations are only counter once.
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# File 'lib/pdf/reader/xref.rb', line 62 def size @xref.size end |