1PDF::API2::Basic::PDF::UFsielre(C3o)ntributed Perl DocumPeDnFt:a:tAiPoIn2::Basic::PDF::File(3)
2
6 PDF::API2::Basic::PDF::File - Holds the trailers and cross-reference
7 tables for a PDF file
8
10 $p = PDF::API2::Basic::PDF::File->open("filename.pdf", 1);
11 $p->new_obj($obj_ref);
12 $p->free_obj($obj_ref);
13 $p->append_file;
14 $p->close_file;
15 $p->release; # IMPORTANT!
16
18 This class keeps track of the directory aspects of a PDF file. There
19 are two parts to the directory: the main directory object which is the
20 parent to all other objects and a chain of cross-reference tables and
21 corresponding trailer dictionaries starting with the main directory
22 object.
23
25 Within this class hierarchy, rather than making everything visible via
26 methods, which would be a lot of work, there are various instance
27 variables which are accessible via associative array referencing. To
28 distinguish instance variables from content variables (which may come
29 from the PDF content itself), each such variable will start with a
30 space.
31 Variables which do not start with a space directly reflect elements in
33 a PDF dictionary. In the case of a PDF::API2::Basic::PDF::File, the
34 elements reflect those in the trailer dictionary.
35 Since some variables are not designed for class users to access,
37 variables are marked in the documentation with (R) to indicate that
38 such an entry should only be used as read-only information. (P)
39 indicates that the information is private and not designed for user use
40 at all, but is included in the documentation for completeness and to
41 ensure that nobody else tries to use it.
42 newroot
44 This variable allows the user to create a new root entry to occur
45 in the trailer dictionary which is output when the file is written
46 or appended. If you wish to over-ride the root element in the
47 dictionary you have, use this entry to indicate that without losing
48 the current Root entry. Notice that newroot should point to a PDF
49 level object and not just to a dictionary which does not have
50 object status.
51 INFILE (R)
53 Contains the filehandle used to read this information into this PDF
54 directory. Is an IO object.
55 fname (R)
57 This is the filename which is reflected by INFILE, or the original
58 IO object passed in.
59 update (R)
61 This indicates that the read file has been opened for update and
62 that at some point, $p->appendfile() can be called to update the
63 file with the changes that have been made to the memory
64 representation.
65 maxobj (R)
67 Contains the first usable object number above any that have already
68 appeared in the file so far.
69 outlist (P)
71 This is a list of Objind which are to be output when the next
72 appendfile or outfile occurs.
73 firstfree (P)
75 Contains the first free object in the free object list. Free
76 objects are removed from the front of the list and added to the
77 end.
78 lastfree (P)
80 Contains the last free object in the free list. It may be the same
81 as the firstfree if there is only one free object.
82 objcache (P)
84 All objects are held in the cache to ensure that a system only has
85 one occurrence of each object. In effect, the objind class acts as
86 a container type class to hold the PDF object structure and it
87 would be unfortunate if there were two identical place-holders
88 floating around a system.
89 epos (P)
91 The end location of the read-file.
92 Each trailer dictionary contains a number of private instance variables
94 which hold the chain together.
95 loc (P)
97 Contains the location of the start of the cross-reference table
98 preceding the trailer.
99 xref (P)
101 Contains an anonymous array of each cross-reference table entry.
102 prev (P)
104 A reference to the previous table. Note this differs from the Prev
105 entry which is in PDF which contains the location of the previous
106 cross-reference table.
107
109 PDF::API2::Basic::PDF::File->new
110 Creates a new, empty file object which can act as the host to other PDF
111 objects. Since there is no file associated with this object, it is
112 assumed that the object is created in readiness for creating a new PDF
113 file.
114 $p = PDF::API2::Basic::PDF::File->open($filename, $update)
116 Opens the file and reads all the trailers and cross reference tables to
117 build a complete directory of objects.
118 $update specifies whether this file is being opened for updating and
120 editing, or simply to be read.
121 $filename may be an IO object
123 $p->release()
125 Releases ALL of the memory used by the PDF document and all of its
126 component objects. After calling this method, do NOT expect to have
127 anything left in the "PDF::API2::Basic::PDF::File" object (so if you
128 need to save, be sure to do it before calling this method).
129 NOTE, that it is important that you call this method on any
131 "PDF::API2::Basic::PDF::File" object when you wish to destruct it and
132 free up its memory. Internally, PDF files have an enormous number of
133 cross-references and this causes circular references within the
134 internal data structures. Calling '"release()"' forces a brute-force
135 cleanup of the data structures, freeing up all of the memory. Once
136 you've called this method, though, don't expect to be able to do
137 anything else with the "PDF::API2::Basic::PDF::File" object; it'll have
138 no internal state whatsoever.
139 $p->append_file()
141 Appends the objects for output to the read file and then appends the
142 appropriate table.
143 $p->out_file($fname)
145 Writes a PDF file to a file of the given filename based on the current
146 list of objects to be output. It creates the trailer dictionary based
147 on information in $self.
148 $fname may be an IO object;
150 $p->create_file($fname)
152 Creates a new output file (no check is made of an existing open file)
153 of the given filename or IO object. Note, make sure that $p->{'
154 version'} is set correctly before calling this function.
155 $p->close_file
157 Closes up the open file for output by outputting the trailer etc.
158 ($value, $str) = $p->readval($str, %opts)
160 Reads a PDF value from the current position in the file. If $str is too
161 short then read some more from the current location in the file until
162 the whole object is read. This is a recursive call which may slurp in a
163 whole big stream (unprocessed).
164 Returns the recursive data structure read and also the current $str
166 that has been read from the file.
167 $ref = $p->read_obj($objind, %opts)
169 Given an indirect object reference, locate it and read the object
170 returning the read in object.
171 $ref = $p->read_objnum($num, $gen, %opts)
173 Returns a fully read object of given number and generation in this file
174 $objind = $p->new_obj($obj)
176 Creates a new, free object reference based on free space in the cross
177 reference chain. If nothing free then thinks up a new number. If $obj
178 then turns that object into this new object rather than returning a new
179 object.
180 $p->out_obj($objind)
182 Indicates that the given object reference should appear in the output
183 xref table whether with data or freed.
184 $p->free_obj($objind)
186 Marks an object reference for output as being freed.
187 $p->remove_obj($objind)
189 Removes the object from all places where we might remember it
190 $p->ship_out(@objects)
192 Ships the given objects (or all objects for output if @objects is
193 empty) to the currently open output file (assuming there is one). Freed
194 objects are not shipped, and once an object is shipped it is switched
195 such that this file becomes its source and it will not be shipped again
196 unless out_obj is called again. Notice that a shipped out object can be
197 re-output or even freed, but that it will not cause the data already
198 output to be changed.
199 $p->copy($outpdf, \&filter)
201 Iterates over every object in the file reading the object, calling
202 filter with the object and outputting the result. if filter is not
203 defined, then just copies input to output.
204
206 The following methods and functions are considered private to this
207 class. This does not mean you cannot use them if you have a need, just
208 that they aren't really designed for users of this class.
209 $offset = $p->locate_obj($num, $gen)
211 Returns a file offset to the object asked for by following the chain of
212 cross reference tables until it finds the one you want.
213 update($fh, $str, $instream)
215 Keeps reading $fh for more data to ensure that $str has at least a line
216 full for "readval" to work on. At this point we also take the
217 opportunity to ignore comments.
218 $objind = $p->test_obj($num, $gen)
220 Tests the cache to see whether an object reference (which may or may
221 not have been getobj()ed) has been cached. Returns it if it has.
222 $p->add_obj($objind)
224 Adds the given object to the internal object cache.
225 $tdict = $p->readxrtr($xpos)
227 Recursive function which reads each of the cross-reference and trailer
228 tables in turn until there are no more.
229 Returns a dictionary corresponding to the trailer chain. Each trailer
231 also includes the corresponding cross-reference table.
232 The structure of the xref private element in a trailer dictionary is of
234 an anonymous hash of cross reference elements by object number. Each
235 element consists of an array of 3 elements corresponding to the three
236 elements read in [location, generation number, free or used]. See the
237 PDF specification for details.
238 $p->out_trailer($tdict)
240 Outputs the body and trailer for a PDF file by outputting all the
241 objects in the ' outlist' and then outputting a xref table for those
242 objects and any freed ones. It then outputs the trailing dictionary and
243 the trailer code.
244 PDF::API2::Basic::PDF::File->_new
246 Creates a very empty PDF file object (used by new and open)
247
249 Martin Hosken Martin_Hosken@sil.org
250 Copyright Martin Hosken 1999 and onwards
252 No warranty or expression of effectiveness, least of all regarding
254 anyone's safety, is implied in this software or documentation.
255perl v5.32.0 2020-07-28 PDF::API2::Basic::PDF::File(3)