PDF::API2::Basic::PDF:UsereContributed Perl DocuPDF::API2::Basic::PDF::File(3)NAMEPDF::API2::Basic::PDF::File - Holds the trailers and cross-reference
tables for a PDF file
SYNOPSIS
$p = PDF::API2::Basic::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 PDF::API2::Basic::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
PDF::API2::Basic::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.
$p = PDF::API2::Basic::PDF::File->open($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 "PDF::API2::Basic::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
"PDF::API2::Basic::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 "PDF::API2::Basic::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 "PDF::API2::Basic::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, $instream)
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.
PDF::API2::Basic::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.
perl v5.14.1 2011-01-24 PDF::API2::Basic::PDF::File(3)
