1PDF::Builder::Basic::PDUFs:e:rFiCloen(t3r)ibuted Perl DoPcDuFm:e:nBtuaitlidoenr::Basic::PDF::File(3)
2
6 PDF::Builder::Basic::PDF::File - Holds the trailers and cross-reference
7 tables for a PDF file
8
10 $p = PDF::Builder::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::Builder::Basic::PDF::File",
34 the 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
40 use at all, but is included in the documentation for completeness and
41 to 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 override 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. It 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::Builder::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 $p = PDF::Builder::Basic::PDF::File->open($filename, $update, %options)
116 Opens the file and reads all the trailers and cross reference tables to
117 build a complete directory of objects.
118 $filename may be a string or an IO object.
120 $update specifies whether this file is being opened for updating and
122 editing (TRUE value), or simply to be read (FALSE or undefined value).
123 %options may include
125 -diags => 1
127 If "-diags" is set to 1, various warning messages will be given if
128 a suspicious PDF structure is found, and some fixup may be
129 attempted. There is no guarantee that any fixup will change the PDF
130 to legitimate, or that there won't be other problems found further
131 down the line. If this flag is not given, and a structural problem
132 is found, it is fairly likely that errors (and even a program
133 crash) may happen further along. If you experience crashes when
134 reading in a PDF file, try running with "-diags" and see what is
135 reported.
136 There are many PDF files out "in the wild" which, while failing to
138 conform to Adobe's standards, appear to be tolerated by PDF
139 Readers. Thus, Builder will no longer fail on them, but merely
140 comment on their existence.
141 $p->release()
143 Releases ALL of the memory used by the PDF document and all of its
144 component objects. After calling this method, do NOT expect to have
145 anything left in the "PDF::Builder::Basic::PDF::File" object (so if you
146 need to save, be sure to do it before calling this method).
147 NOTE, that it is important that you call this method on any
149 "PDF::Builder::Basic::PDF::File" object when you wish to destroy it and
150 free up its memory. Internally, PDF files have an enormous number of
151 cross-references, and this causes circular references within the
152 internal data structures. Calling "release()" causes a brute-force
153 cleanup of the data structures, freeing up all of the memory. Once
154 you've called this method, though, don't expect to be able to do
155 anything else with the "PDF::Builder::Basic::PDF::File" object; it'll
156 have no internal state whatsoever.
157 $p->append_file()
159 Appends the objects for output to the read file and then appends the
160 appropriate table.
161 $p->out_file($fname)
163 Writes a PDF file to a file of the given filename, based on the current
164 list of objects to be output. It creates the trailer dictionary based
165 on information in $self.
166 $fname may be a string or an IO object.
168 $p->create_file($fname)
170 Creates a new output file (no check is made of an existing open file)
171 of the given filename or IO object. Note: make sure that "$p->{'
172 version'}" is set correctly before calling this function.
173 $p->close_file()
175 Closes up the open file for output, by outputting the trailer, etc.
176 ($value, $str) = $p->readval($str, %opts)
178 Reads a PDF value from the current position in the file. If $str is too
179 short, read some more from the current location in the file until the
180 whole object is read. This is a recursive call which may slurp in a
181 whole big stream (unprocessed).
182 Returns the recursive data structure read and also the current $str
184 that has been read from the file.
185 $ref = $p->read_obj($objind, %opts)
187 Given an indirect object reference, locate it and read the object
188 returning the read in object.
189 $ref = $p->read_objnum($num, $gen, %opts)
191 Returns a fully read object of given number and generation in this file
192 $objind = $p->new_obj($obj)
194 Creates a new, free object reference based on free space in the cross
195 reference chain. If nothing is free, then think up a new number. If
196 $obj, then turns that object into this new object rather than returning
197 a new object.
198 $p->out_obj($obj)
200 Indicates that the given object reference should appear in the output
201 xref table whether with data or freed.
202 $p->free_obj($obj)
204 Marks an object reference for output as being freed.
205 $p->remove_obj($objind)
207 Removes the object from all places where we might remember it.
208 $p->ship_out(@objects)
210 $p->ship_out()
211 Ships the given objects (or all objects for output if @objects is
212 empty) to the currently open output file (assuming there is one). Freed
213 objects are not shipped, and once an object is shipped it is switched
214 such that this file becomes its source and it will not be shipped again
215 unless out_obj is called again. Notice that a shipped out object can be
216 re-output or even freed, but that it will not cause the data already
217 output to be changed.
218 $p->copy($outpdf, \&filter)
220 Iterates over every object in the file reading the object, calling
221 "filter" with the object, and outputting the result. If "filter" is not
222 defined, just copies input to output.
223
225 The following methods and functions are considered private to this
226 class. This does not mean you cannot use them if you have a need, just
227 that they aren't really designed for users of this class.
228 $offset = $p->locate_obj($num, $gen)
230 Returns a file offset to the object asked for by following the chain of
231 cross reference tables until it finds the one you want.
232 update($fh, $str, $instream)
234 Keeps reading $fh for more data to ensure that $str has at least a line
235 full for "readval" to work on. At this point we also take the
236 opportunity to ignore comments.
237 $objind = $p->test_obj($num, $gen)
239 Tests the cache to see whether an object reference (which may or may
240 not have been getobj()ed) has been cached. Returns it if it has.
241 $p->add_obj($objind)
243 Adds the given object to the internal object cache.
244 $tdict = $p->readxrtr($xpos, %options)
246 Recursive function which reads each of the cross-reference and trailer
247 tables in turn until there are no more.
248 Returns a dictionary corresponding to the trailer chain. Each trailer
250 also includes the corresponding cross-reference table.
251 The structure of the xref private element in a trailer dictionary is of
253 an anonymous hash of cross reference elements by object number. Each
254 element consists of an array of 3 elements corresponding to the three
255 elements read in [location, generation number, free or used]. See the
256 PDF specification for details.
257 See "open" for options allowed.
259 $p->out_trailer($tdict, $update)
261 $p->out_trailer($tdict)
262 Outputs the body and trailer for a PDF file by outputting all the
263 objects in the ' outlist' and then outputting a xref table for those
264 objects and any freed ones. It then outputs the trailing dictionary and
265 the trailer code.
266 PDF::Builder::Basic::PDF::File->_new()
268 Creates a very empty PDF file object (used by new() and open())
269
271 Martin Hosken Martin_Hosken@sil.org
272 Copyright Martin Hosken 1999 and onwards
274 No warranty or expression of effectiveness, least of all regarding
276 anyone's safety, is implied in this software or documentation.
277perl v5.34.0 2021-07-22 PDF::Builder::Basic::PDF::File(3)