NAME¶
Text::PDF::File - Holds the trailers and cross-reference tables for a PDF file
SYNOPSIS¶
$p = Text::PDF::File->open("filename.pdf", 1);
$p->new_obj($obj_ref);
$p->free_obj($obj_ref);
$p->append_file;
$p->close_file;
$p->release; # IMPORTANT!
DESCRIPTION¶
This class keeps track of the directory aspects of a PDF file. There are two
parts to the directory: the main directory object which is the parent to all
other objects and a chain of cross-reference tables and corresponding trailer
dictionaries starting with the main directory object.
INSTANCE VARIABLES¶
Within this class hierarchy, rather than making everything visible via methods,
which would be a lot of work, there are various instance variables which are
accessible via associative array referencing. To distinguish instance
variables from content variables (which may come from the PDF content itself),
each such variable will start with a space.
Variables which do not start with a space directly reflect elements in a PDF
dictionary. In the case of a Text::PDF::File, the elements reflect those in
the trailer dictionary.
Since some variables are not designed for class users to access, variables are
marked in the documentation with (R) to indicate that such an entry should
only be used as read-only information. (P) indicates that the information is
private and not designed for user use at all, but is included in the
documentation for completeness and to ensure that nobody else tries to use it.
- newroot
- This variable allows the user to create a new root entry to occur in the
trailer dictionary which is output when the file is written or appended.
If you wish to over-ride the root element in the dictionary you have, use
this entry to indicate that without losing the current Root entry. Notice
that newroot should point to a PDF level object and not just to a
dictionary which does not have object status.
- INFILE (R)
- Contains the filehandle used to read this information into this PDF
directory. Is an IO object.
- fname (R)
- This is the filename which is reflected by INFILE, or the original IO
object passed in.
- update (R)
- This indicates that the read file has been opened for update and that at
some point, $p-> appendfile() can be called to update the file
with the changes that have been made to the memory representation.
- maxobj (R)
- Contains the first useable object number above any that have already
appeared in the file so far.
- outlist (P)
- This is a list of Objind which are to be output when the next appendfile
or outfile occurs.
- firstfree (P)
- Contains the first free object in the free object list. Free objects are
removed from the front of the list and added to the end.
- lastfree (P)
- Contains the last free object in the free list. It may be the same as the
firstfree if there is only one free object.
- objcache (P)
- All objects are held in the cache to ensure that a system only has one
occurrence of each object. In effect, the objind class acts as a container
type class to hold the PDF object structure and it would be unfortunate if
there were two identical place-holders floating around a system.
- epos (P)
- The end location of the read-file.
Each trailer dictionary contains a number of private instance variables which
hold the chain together.
- loc (P)
- Contains the location of the start of the cross-reference table preceding
the trailer.
- xref (P)
- Contains an anonymous array of each cross-reference table entry.
- prev (P)
- A reference to the previous table. Note this differs from the Prev entry
which is in PDF which contains the location of the previous
cross-reference table.
METHODS¶
Text::PDF::File->new¶
Creates a new, empty file object which can act as the host to other PDF objects.
Since there is no file associated with this object, it is assumed that the
object is created in readiness for creating a new PDF file.
$p = Text::PDF::File->open($filename, $update)¶
Opens the file and reads all the trailers and cross reference tables to build a
complete directory of objects.
$update specifies whether this file is being opened for updating and editing, or
simply to be read.
$filename may be an IO object
$p->release()¶
Releases ALL of the memory used by the PDF document and all of its component
objects. After calling this method, do
NOT expect to have anything left
in the "Text::PDF::File" object (so if you need to save, be sure to
do it before calling this method).
NOTE, that it is important that you call this method on any
"Text::PDF::File" object when you wish to destruct it and free up
its memory. Internally, PDF files have an enormous number of cross-references
and this causes circular references within the internal data structures.
Calling '"release()"' forces a brute-force cleanup of the data
structures, freeing up all of the memory. Once you've called this method,
though, don't expect to be able to do anything else with the
"Text::PDF::File" object; it'll have
no internal state
whatsoever.
Developer note: As part of the brute-force cleanup done here, this method
will throw a warning message whenever unexpected key values are found within
the "Text::PDF::File" object. This is done to help ensure that any
unexpected and unfreed values are brought to your attention so that you can
bug us to keep the module updated properly; otherwise the potential for memory
leaks due to dangling circular references will exist.
$p->append_file()¶
Appends the objects for output to the read file and then appends the appropriate
tale.
$p->out_file($fname)¶
Writes a PDF file to a file of the given filename based on the current list of
objects to be output. It creates the trailer dictionary based on information
in $self.
$fname may be an IO object;
$p->create_file($fname)¶
Creates a new output file (no check is made of an existing open file) of the
given filename or IO object. Note, make sure that $p->{' version'} is set
correctly before calling this function.
$p->close_file¶
Closes up the open file for output by outputting the trailer etc.
($value, $str) = $p->readval($str, %opts)¶
Reads a PDF value from the current position in the file. If $str is too short
then read some more from the current location in the file until the whole
object is read. This is a recursive call which may slurp in a whole big stream
(unprocessed).
Returns the recursive data structure read and also the current $str that has
been read from the file.
$ref = $p->read_obj($objind, %opts)¶
Given an indirect object reference, locate it and read the object returning the
read in object.
$ref = $p->read_objnum($num, $gen, %opts)¶
Returns a fully read object of given number and generation in this file
$objind = $p->new_obj($obj)¶
Creates a new, free object reference based on free space in the cross reference
chain. If nothing free then thinks up a new number. If $obj then turns that
object into this new object rather than returning a new object.
$p->out_obj($objind)¶
Indicates that the given object reference should appear in the output xref table
whether with data or freed.
$p->free_obj($objind)¶
Marks an object reference for output as being freed.
$p->remove_obj($objind)¶
Removes the object from all places where we might remember it
$p->ship_out(@objects)¶
Ships the given objects (or all objects for output if @objects is empty) to the
currently open output file (assuming there is one). Freed objects are not
shipped, and once an object is shipped it is switched such that this file
becomes its source and it will not be shipped again unless out_obj is called
again. Notice that a shipped out object can be re-output or even freed, but
that it will not cause the data already output to be changed.
$p->copy($outpdf, \&filter)¶
Iterates over every object in the file reading the object, calling filter with
the object and outputting the result. if filter is not defined, then just
copies input to output.
PRIVATE METHODS & FUNCTIONS¶
The following methods and functions are considered private to this class. This
does not mean you cannot use them if you have a need, just that they aren't
really designed for users of this class.
$offset = $p->locate_obj($num, $gen)¶
Returns a file offset to the object asked for by following the chain of cross
reference tables until it finds the one you want.
update($fh, $str)¶
Keeps reading $fh for more data to ensure that $str has at least a line full for
"readval" to work on. At this point we also take the opportunity to
ignore comments.
$objind = $p->test_obj($num, $gen)¶
Tests the cache to see whether an object reference (which may or may not have
been
getobj()ed) has been cached. Returns it if it has.
$p->add_obj($objind)¶
Adds the given object to the internal object cache.
$tdict = $p->readxrtr($xpos)¶
Recursive function which reads each of the cross-reference and trailer tables in
turn until there are no more.
Returns a dictionary corresponding to the trailer chain. Each trailer also
includes the corresponding cross-reference table.
The structure of the xref private element in a trailer dictionary is of an
anonymous hash of cross reference elements by object number. Each element
consists of an array of 3 elements corresponding to the three elements read in
[location, generation number, free or used]. See the PDF Specification for
details.
$p->out_trailer($tdict)¶
Outputs the body and trailer for a PDF file by outputting all the objects in the
' outlist' and then outputting a xref table for those objects and any freed
ones. It then outputs the trailing dictionary and the trailer code.
Text::PDF::File->_new¶
Creates a very empty PDF file object (used by new and open)
AUTHOR¶
Martin Hosken Martin_Hosken@sil.org
Copyright Martin Hosken 1999 and onwards
No warranty or expression of effectiveness, least of all regarding anyone's
safety, is implied in this software or documentation.
Licensing¶
This Perl Text::PDF module is licensed under the Perl Artistic License.