NAME

       PDF::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.

   $p->append_file()
       Appends the objects for output to the read file and then appends the appropriate table.

   $p->out_file($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.