1Storable(3) User Contributed Perl Documentation Storable(3)
2
6 Storable - persistence for Perl data structures
7
9 use Storable;
10 store \%table, 'file';
11 $hashref = retrieve('file');
12 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
14 # Network order
16 nstore \%table, 'file';
17 $hashref = retrieve('file'); # There is NO nretrieve()
18 # Storing to and retrieving from an already opened file
20 store_fd \@array, \*STDOUT;
21 nstore_fd \%table, \*STDOUT;
22 $aryref = fd_retrieve(\*SOCKET);
23 $hashref = fd_retrieve(\*SOCKET);
24 # Serializing to memory
26 $serialized = freeze \%table;
27 %table_clone = %{ thaw($serialized) };
28 # Deep (recursive) cloning
30 $cloneref = dclone($ref);
31 # Advisory locking
33 use Storable qw(lock_store lock_nstore lock_retrieve)
34 lock_store \%table, 'file';
35 lock_nstore \%table, 'file';
36 $hashref = lock_retrieve('file');
37
39 The Storable package brings persistence to your Perl data structures
40 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can
41 be conveniently stored to disk and retrieved at a later time.
42 It can be used in the regular procedural way by calling "store" with a
44 reference to the object to be stored, along with the file name where
45 the image should be written.
46 The routine returns "undef" for I/O problems or other internal error, a
48 true value otherwise. Serious errors are propagated as a "die"
49 exception.
50 To retrieve data stored to disk, use "retrieve" with a file name. The
52 objects stored into that file are recreated into memory for you, and a
53 reference to the root object is returned. In case an I/O error occurs
54 while reading, "undef" is returned instead. Other serious errors are
55 propagated via "die".
56 Since storage is performed recursively, you might want to stuff
58 references to objects that share a lot of common data into a single
59 array or hash table, and then store that object. That way, when you
60 retrieve back the whole thing, the objects will continue to share what
61 they originally shared.
62 At the cost of a slight header overhead, you may store to an already
64 opened file descriptor using the "store_fd" routine, and retrieve from
65 a file via "fd_retrieve". Those names aren't imported by default, so
66 you will have to do that explicitly if you need those routines. The
67 file descriptor you supply must be already opened, for read if you're
68 going to retrieve and for write if you wish to store.
69 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
71 $hashref = fd_retrieve(*STDIN);
72 You can also store data in network order to allow easy sharing across
74 multiple platforms, or when storing on a socket known to be remotely
75 connected. The routines to call have an initial "n" prefix for network,
76 as in "nstore" and "nstore_fd". At retrieval time, your data will be
77 correctly restored so you don't have to know whether you're restoring
78 from native or network ordered data. Double values are stored
79 stringified to ensure portability as well, at the slight risk of
80 loosing some precision in the last decimals.
81 When using "fd_retrieve", objects are retrieved in sequence, one object
83 (i.e. one recursive tree) per associated "store_fd".
84 If you're more from the object-oriented camp, you can inherit from
86 Storable and directly store your objects by invoking "store" as a
87 method. The fact that the root of the to-be-stored tree is a blessed
88 reference (i.e. an object) is special-cased so that the retrieve does
89 not provide a reference to that object but rather the blessed object
90 reference itself. (Otherwise, you'd get a reference to that blessed
91 object).
92
94 The Storable engine can also store data into a Perl scalar instead, to
95 later retrieve them. This is mainly used to freeze a complex structure
96 in some safe compact memory place (where it can possibly be sent to
97 another process via some IPC, since freezing the structure also
98 serializes it in effect). Later on, and maybe somewhere else, you can
99 thaw the Perl scalar out and recreate the original complex structure in
100 memory.
101 Surprisingly, the routines to be called are named "freeze" and "thaw".
103 If you wish to send out the frozen scalar to another machine, use
104 "nfreeze" instead to get a portable image.
105 Note that freezing an object structure and immediately thawing it
107 actually achieves a deep cloning of that structure:
108 dclone(.) = thaw(freeze(.))
110 Storable provides you with a "dclone" interface which does not create
112 that intermediary scalar but instead freezes the structure in some
113 internal memory space and then immediately thaws it out.
114
116 The "lock_store" and "lock_nstore" routine are equivalent to "store"
117 and "nstore", except that they get an exclusive lock on the file before
118 writing. Likewise, "lock_retrieve" does the same as "retrieve", but
119 also gets a shared lock on the file before reading.
120 As with any advisory locking scheme, the protection only works if you
122 systematically use "lock_store" and "lock_retrieve". If one side of
123 your application uses "store" whilst the other uses "lock_retrieve",
124 you will get no protection at all.
125 The internal advisory locking is implemented using Perl's flock()
127 routine. If your system does not support any form of flock(), or if
128 you share your files across NFS, you might wish to use other forms of
129 locking by using modules such as LockFile::Simple which lock a file
130 using a filesystem entry, instead of locking the file descriptor.
131
133 The heart of Storable is written in C for decent speed. Extra low-level
134 optimizations have been made when manipulating perl internals, to
135 sacrifice encapsulation for the benefit of greater speed.
136
138 Normally, Storable stores elements of hashes in the order they are
139 stored internally by Perl, i.e. pseudo-randomly. If you set
140 $Storable::canonical to some "TRUE" value, Storable will store hashes
141 with the elements sorted by their key. This allows you to compare data
142 structures by comparing their frozen representations (or even the
143 compressed frozen representations), which can be useful for creating
144 lookup tables for complicated queries.
145 Canonical order does not imply network order; those are two orthogonal
147 settings.
148
150 Since Storable version 2.05, CODE references may be serialized with the
151 help of B::Deparse. To enable this feature, set $Storable::Deparse to a
152 true value. To enable deserialization, $Storable::Eval should be set to
153 a true value. Be aware that deserialization is done through "eval",
154 which is dangerous if the Storable file contains malicious data. You
155 can set $Storable::Eval to a subroutine reference which would be used
156 instead of "eval". See below for an example using a Safe compartment
157 for deserialization of CODE references.
158 If $Storable::Deparse and/or $Storable::Eval are set to false values,
160 then the value of $Storable::forgive_me (see below) is respected while
161 serializing and deserializing.
162
164 This release of Storable can be used on a newer version of Perl to
165 serialize data which is not supported by earlier Perls. By default,
166 Storable will attempt to do the right thing, by "croak()"ing if it
167 encounters data that it cannot deserialize. However, the defaults can
168 be changed as follows:
169 utf8 data
171 Perl 5.6 added support for Unicode characters with code points >
172 255, and Perl 5.8 has full support for Unicode characters in hash
173 keys. Perl internally encodes strings with these characters using
174 utf8, and Storable serializes them as utf8. By default, if an
175 older version of Perl encounters a utf8 value it cannot represent,
176 it will "croak()". To change this behaviour so that Storable
177 deserializes utf8 encoded values as the string of bytes
178 (effectively dropping the is_utf8 flag) set $Storable::drop_utf8 to
179 some "TRUE" value. This is a form of data loss, because with
180 $drop_utf8 true, it becomes impossible to tell whether the original
181 data was the Unicode string, or a series of bytes that happen to be
182 valid utf8.
183 restricted hashes
185 Perl 5.8 adds support for restricted hashes, which have keys
186 restricted to a given set, and can have values locked to be read
187 only. By default, when Storable encounters a restricted hash on a
188 perl that doesn't support them, it will deserialize it as a normal
189 hash, silently discarding any placeholder keys and leaving the keys
190 and all values unlocked. To make Storable "croak()" instead, set
191 $Storable::downgrade_restricted to a "FALSE" value. To restore the
192 default set it back to some "TRUE" value.
193 The cperl PERL_PERTURB_KEYS_TOP hash strategy has a known problem
195 with restricted hashes.
196 huge objects
198 On 64bit systems some data structures may exceed the 2G (i.e.
199 I32_MAX) limit. On 32bit systems also strings between I32 and U32
200 (2G-4G). Since Storable 3.00 (not in perl5 core) we are able to
201 store and retrieve these objects, even if perl5 itself is not able
202 to handle them. These are strings longer then 4G, arrays with more
203 then 2G elements and hashes with more then 2G elements. cperl
204 forbids hashes with more than 2G elements, but this fail in cperl
205 then. perl5 itself at least until 5.26 allows it, but cannot
206 iterate over them. Note that creating those objects might cause
207 out of memory exceptions by the operating system before perl has a
208 chance to abort.
209 files from future versions of Storable
211 Earlier versions of Storable would immediately croak if they
212 encountered a file with a higher internal version number than the
213 reading Storable knew about. Internal version numbers are
214 increased each time new data types (such as restricted hashes) are
215 added to the vocabulary of the file format. This meant that a
216 newer Storable module had no way of writing a file readable by an
217 older Storable, even if the writer didn't store newer data types.
218 This version of Storable will defer croaking until it encounters a
220 data type in the file that it does not recognize. This means that
221 it will continue to read files generated by newer Storable modules
222 which are careful in what they write out, making it easier to
223 upgrade Storable modules in a mixed environment.
224 The old behaviour of immediate croaking can be re-instated by
226 setting $Storable::accept_future_minor to some "FALSE" value.
227 All these variables have no effect on a newer Perl which supports the
229 relevant feature.
230
232 Storable uses the "exception" paradigm, in that it does not try to
233 workaround failures: if something bad happens, an exception is
234 generated from the caller's perspective (see Carp and "croak()"). Use
235 eval {} to trap those exceptions.
236 When Storable croaks, it tries to report the error via the "logcroak()"
238 routine from the "Log::Agent" package, if it is available.
239 Normal errors are reported by having store() or retrieve() return
241 "undef". Such errors are usually I/O errors (or truncated stream
242 errors at retrieval).
243 When Storable throws the "Max. recursion depth with nested structures
245 exceeded" error we are already out of stack space. Unfortunately on
246 some earlier perl versions cleaning up a recursive data structure
247 recurses into the free calls, which will lead to stack overflows in the
248 cleanup. This data structure is not properly cleaned up then, it will
249 only be destroyed during global destruction.
250
252 Hooks
253 Any class may define hooks that will be called during the serialization
254 and deserialization process on objects that are instances of that
255 class. Those hooks can redefine the way serialization is performed
256 (and therefore, how the symmetrical deserialization should be
257 conducted).
258 Since we said earlier:
260 dclone(.) = thaw(freeze(.))
262 everything we say about hooks should also hold for deep cloning.
264 However, hooks get to know whether the operation is a mere
265 serialization, or a cloning.
266 Therefore, when serializing hooks are involved,
268 dclone(.) <> thaw(freeze(.))
270 Well, you could keep them in sync, but there's no guarantee it will
272 always hold on classes somebody else wrote. Besides, there is little
273 to gain in doing so: a serializing hook could keep only one attribute
274 of an object, which is probably not what should happen during a deep
275 cloning of that same object.
276 Here is the hooking interface:
278 "STORABLE_freeze" obj, cloning
280 The serializing hook, called on the object during serialization.
281 It can be inherited, or defined in the class itself, like any other
282 method.
283 Arguments: obj is the object to serialize, cloning is a flag
285 indicating whether we're in a dclone() or a regular serialization
286 via store() or freeze().
287 Returned value: A LIST "($serialized, $ref1, $ref2, ...)" where
289 $serialized is the serialized form to be used, and the optional
290 $ref1, $ref2, etc... are extra references that you wish to let the
291 Storable engine serialize.
292 At deserialization time, you will be given back the same LIST, but
294 all the extra references will be pointing into the deserialized
295 structure.
296 The first time the hook is hit in a serialization flow, you may
298 have it return an empty list. That will signal the Storable engine
299 to further discard that hook for this class and to therefore revert
300 to the default serialization of the underlying Perl data. The hook
301 will again be normally processed in the next serialization.
302 Unless you know better, serializing hook should always say:
304 sub STORABLE_freeze {
306 my ($self, $cloning) = @_;
307 return if $cloning; # Regular default serialization
308 ....
309 }
310 in order to keep reasonable dclone() semantics.
312 "STORABLE_thaw" obj, cloning, serialized, ...
314 The deserializing hook called on the object during deserialization.
315 But wait: if we're deserializing, there's no object yet... right?
316 Wrong: the Storable engine creates an empty one for you. If you
318 know Eiffel, you can view "STORABLE_thaw" as an alternate creation
319 routine.
320 This means the hook can be inherited like any other method, and
322 that obj is your blessed reference for this particular instance.
323 The other arguments should look familiar if you know
325 "STORABLE_freeze": cloning is true when we're part of a deep clone
326 operation, serialized is the serialized string you returned to the
327 engine in "STORABLE_freeze", and there may be an optional list of
328 references, in the same order you gave them at serialization time,
329 pointing to the deserialized objects (which have been processed
330 courtesy of the Storable engine).
331 When the Storable engine does not find any "STORABLE_thaw" hook
333 routine, it tries to load the class by requiring the package
334 dynamically (using the blessed package name), and then re-attempts
335 the lookup. If at that time the hook cannot be located, the engine
336 croaks. Note that this mechanism will fail if you define several
337 classes in the same file, but perlmod warned you.
338 It is up to you to use this information to populate obj the way you
340 want.
341 Returned value: none.
343 "STORABLE_attach" class, cloning, serialized
345 While "STORABLE_freeze" and "STORABLE_thaw" are useful for classes
346 where each instance is independent, this mechanism has difficulty
347 (or is incompatible) with objects that exist as common process-
348 level or system-level resources, such as singleton objects,
349 database pools, caches or memoized objects.
350 The alternative "STORABLE_attach" method provides a solution for
352 these shared objects. Instead of "STORABLE_freeze" -->
353 "STORABLE_thaw", you implement "STORABLE_freeze" -->
354 "STORABLE_attach" instead.
355 Arguments: class is the class we are attaching to, cloning is a
357 flag indicating whether we're in a dclone() or a regular de-
358 serialization via thaw(), and serialized is the stored string for
359 the resource object.
360 Because these resource objects are considered to be owned by the
362 entire process/system, and not the "property" of whatever is being
363 serialized, no references underneath the object should be included
364 in the serialized string. Thus, in any class that implements
365 "STORABLE_attach", the "STORABLE_freeze" method cannot return any
366 references, and "Storable" will throw an error if "STORABLE_freeze"
367 tries to return references.
368 All information required to "attach" back to the shared resource
370 object must be contained only in the "STORABLE_freeze" return
371 string. Otherwise, "STORABLE_freeze" behaves as normal for
372 "STORABLE_attach" classes.
373 Because "STORABLE_attach" is passed the class (rather than an
375 object), it also returns the object directly, rather than modifying
376 the passed object.
377 Returned value: object of type "class"
379 Predicates
381 Predicates are not exportable. They must be called by explicitly
382 prefixing them with the Storable package name.
383 "Storable::last_op_in_netorder"
385 The "Storable::last_op_in_netorder()" predicate will tell you
386 whether network order was used in the last store or retrieve
387 operation. If you don't know how to use this, just forget about
388 it.
389 "Storable::is_storing"
391 Returns true if within a store operation (via STORABLE_freeze
392 hook).
393 "Storable::is_retrieving"
395 Returns true if within a retrieve operation (via STORABLE_thaw
396 hook).
397 Recursion
399 With hooks comes the ability to recurse back to the Storable engine.
400 Indeed, hooks are regular Perl code, and Storable is convenient when it
401 comes to serializing and deserializing things, so why not use it to
402 handle the serialization string?
403 There are a few things you need to know, however:
405 • From Storable 3.05 to 3.13 we probed for the stack recursion limit
407 for references, arrays and hashes to a maximal depth of
408 ~1200-35000, otherwise we might fall into a stack-overflow. On
409 JSON::XS this limit is 512 btw. With references not immediately
410 referencing each other there's no such limit yet, so you might fall
411 into such a stack-overflow segfault.
412 This probing and the checks we performed have some limitations:
414 • the stack size at build time might be different at run time,
416 eg. the stack size may have been modified with ulimit(1). If
417 it's larger at run time Storable may fail the freeze() or
418 thaw() unnecessarily. If it's larger at build time Storable
419 may segmentation fault when processing a deep structure at run
420 time.
421 • the stack size might be different in a thread.
423 • array and hash recursion limits are checked separately against
425 the same recursion depth, a frozen structure with a large
426 sequence of nested arrays within many nested hashes may exhaust
427 the processor stack without triggering Storable's recursion
428 protection.
429 So these now have simple defaults rather than probing at build-
431 time.
432 You can control the maximum array and hash recursion depths by
434 modifying $Storable::recursion_limit and
435 $Storable::recursion_limit_hash respectively. Either can be set to
436 "-1" to prevent any depth checks, though this isn't recommended.
437 If you want to test what the limits are, the stacksize tool is
439 included in the "Storable" distribution.
440 • You can create endless loops if the things you serialize via
442 freeze() (for instance) point back to the object we're trying to
443 serialize in the hook.
444 • Shared references among objects will not stay shared: if we're
446 serializing the list of object [A, C] where both object A and C
447 refer to the SAME object B, and if there is a serializing hook in A
448 that says freeze(B), then when deserializing, we'll get [A', C']
449 where A' refers to B', but C' refers to D, a deep clone of B'. The
450 topology was not preserved.
451 • The maximal stack recursion limit for your system is returned by
453 "stack_depth()" and "stack_depth_hash()". The hash limit is usually
454 half the size of the array and ref limit, as the Perl hash API is
455 not optimal.
456 That's why "STORABLE_freeze" lets you provide a list of references to
458 serialize. The engine guarantees that those will be serialized in the
459 same context as the other objects, and therefore that shared objects
460 will stay shared.
461 In the above [A, C] example, the "STORABLE_freeze" hook could return:
463 ("something", $self->{B})
465 and the B part would be serialized by the engine. In "STORABLE_thaw",
467 you would get back the reference to the B' object, deserialized for
468 you.
469 Therefore, recursion should normally be avoided, but is nonetheless
471 supported.
472 Deep Cloning
474 There is a Clone module available on CPAN which implements deep cloning
475 natively, i.e. without freezing to memory and thawing the result. It
476 is aimed to replace Storable's dclone() some day. However, it does not
477 currently support Storable hooks to redefine the way deep cloning is
478 performed.
479
481 Yes, there's a lot of that :-) But more precisely, in UNIX systems
482 there's a utility called "file", which recognizes data files based on
483 their contents (usually their first few bytes). For this to work, a
484 certain file called magic needs to taught about the signature of the
485 data. Where that configuration file lives depends on the UNIX flavour;
486 often it's something like /usr/share/misc/magic or /etc/magic. Your
487 system administrator needs to do the updating of the magic file. The
488 necessary signature information is output to STDOUT by invoking
489 Storable::show_file_magic(). Note that the GNU implementation of the
490 "file" utility, version 3.38 or later, is expected to contain support
491 for recognising Storable files out-of-the-box, in addition to other
492 kinds of Perl files.
493 You can also use the following functions to extract the file header
495 information from Storable images:
496 $info = Storable::file_magic( $filename )
498 If the given file is a Storable image return a hash describing it.
499 If the file is readable, but not a Storable image return "undef".
500 If the file does not exist or is unreadable then croak.
501 The hash returned has the following elements:
503 "version"
505 This returns the file format version. It is a string like
506 "2.7".
507 Note that this version number is not the same as the version
509 number of the Storable module itself. For instance Storable
510 v0.7 create files in format v2.0 and Storable v2.15 create
511 files in format v2.7. The file format version number only
512 increment when additional features that would confuse older
513 versions of the module are added.
514 Files older than v2.0 will have the one of the version numbers
516 "-1", "0" or "1". No minor number was used at that time.
517 "version_nv"
519 This returns the file format version as number. It is a string
520 like "2.007". This value is suitable for numeric comparisons.
521 The constant function "Storable::BIN_VERSION_NV" returns a
523 comparable number that represents the highest file version
524 number that this version of Storable fully supports (but see
525 discussion of $Storable::accept_future_minor above). The
526 constant "Storable::BIN_WRITE_VERSION_NV" function returns what
527 file version is written and might be less than
528 "Storable::BIN_VERSION_NV" in some configurations.
529 "major", "minor"
531 This also returns the file format version. If the version is
532 "2.7" then major would be 2 and minor would be 7. The minor
533 element is missing for when major is less than 2.
534 "hdrsize"
536 The is the number of bytes that the Storable header occupies.
537 "netorder"
539 This is TRUE if the image store data in network order. This
540 means that it was created with nstore() or similar.
541 "byteorder"
543 This is only present when "netorder" is FALSE. It is the
544 $Config{byteorder} string of the perl that created this image.
545 It is a string like "1234" (32 bit little endian) or "87654321"
546 (64 bit big endian). This must match the current perl for the
547 image to be readable by Storable.
548 "intsize", "longsize", "ptrsize", "nvsize"
550 These are only present when "netorder" is FALSE. These are the
551 sizes of various C datatypes of the perl that created this
552 image. These must match the current perl for the image to be
553 readable by Storable.
554 The "nvsize" element is only present for file format v2.2 and
556 higher.
557 "file"
559 The name of the file.
560 $info = Storable::read_magic( $buffer )
562 $info = Storable::read_magic( $buffer, $must_be_file )
563 The $buffer should be a Storable image or the first few bytes of
564 it. If $buffer starts with a Storable header, then a hash
565 describing the image is returned, otherwise "undef" is returned.
566 The hash has the same structure as the one returned by
568 Storable::file_magic(). The "file" element is true if the image is
569 a file image.
570 If the $must_be_file argument is provided and is TRUE, then return
572 "undef" unless the image looks like it belongs to a file dump.
573 The maximum size of a Storable header is currently 21 bytes. If
575 the provided $buffer is only the first part of a Storable image it
576 should at least be this long to ensure that read_magic() will
577 recognize it as such.
578
580 Here are some code samples showing a possible usage of Storable:
581 use Storable qw(store retrieve freeze thaw dclone);
583 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
585 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
587 $colref = retrieve('mycolors');
589 die "Unable to retrieve from mycolors!\n" unless defined $colref;
590 printf "Blue is still %lf\n", $colref->{'Blue'};
591 $colref2 = dclone(\%color);
593 $str = freeze(\%color);
595 printf "Serialization of %%color is %d bytes long.\n", length($str);
596 $colref3 = thaw($str);
597 which prints (on my machine):
599 Blue is still 0.100000
601 Serialization of %color is 102 bytes long.
602 Serialization of CODE references and deserialization in a safe
604 compartment:
605 use Storable qw(freeze thaw);
607 use Safe;
608 use strict;
609 my $safe = new Safe;
610 # because of opcodes used in "use strict":
611 $safe->permit(qw(:default require));
612 local $Storable::Deparse = 1;
613 local $Storable::Eval = sub { $safe->reval($_[0]) };
614 my $serialized = freeze(sub { 42 });
615 my $code = thaw($serialized);
616 $code->() == 42;
617
619 Do not accept Storable documents from untrusted sources!
620 Some features of Storable can lead to security vulnerabilities if you
622 accept Storable documents from untrusted sources with the default
623 flags. Most obviously, the optional (off by default) CODE reference
624 serialization feature allows transfer of code to the deserializing
625 process. Furthermore, any serialized object will cause Storable to
626 helpfully load the module corresponding to the class of the object in
627 the deserializing module. For manipulated module names, this can load
628 almost arbitrary code. Finally, the deserialized object's destructors
629 will be invoked when the objects get destroyed in the deserializing
630 process. Maliciously crafted Storable documents may put such objects in
631 the value of a hash key that is overridden by another key/value pair in
632 the same hash, thus causing immediate destructor execution.
633 To disable blessing objects while thawing/retrieving remove the flag
635 "BLESS_OK" = 2 from $Storable::flags or set the 2nd argument for
636 thaw/retrieve to 0.
637 To disable tieing data while thawing/retrieving remove the flag
639 "TIE_OK" = 4 from $Storable::flags or set the 2nd argument for
640 thaw/retrieve to 0.
641 With the default setting of $Storable::flags = 6, creating or
643 destroying random objects, even renamed objects can be controlled by an
644 attacker. See CVE-2015-1592 and its metasploit module.
645 If your application requires accepting data from untrusted sources, you
647 are best off with a less powerful and more-likely safe serialization
648 format and implementation. If your data is sufficiently simple,
649 Cpanel::JSON::XS, Data::MessagePack or Sereal are the best choices and
650 offer maximum interoperability, but note that Sereal is unsafe by
651 default.
652
654 If you're using references as keys within your hash tables, you're
655 bound to be disappointed when retrieving your data. Indeed, Perl
656 stringifies references used as hash table keys. If you later wish to
657 access the items via another reference stringification (i.e. using the
658 same reference that was used for the key originally to record the value
659 into the hash table), it will work because both references stringify to
660 the same string.
661 It won't work across a sequence of "store" and "retrieve" operations,
663 however, because the addresses in the retrieved objects, which are part
664 of the stringified references, will probably differ from the original
665 addresses. The topology of your structure is preserved, but not hidden
666 semantics like those.
667 On platforms where it matters, be sure to call "binmode()" on the
669 descriptors that you pass to Storable functions.
670 Storing data canonically that contains large hashes can be
672 significantly slower than storing the same data normally, as temporary
673 arrays to hold the keys for each hash have to be allocated, populated,
674 sorted and freed. Some tests have shown a halving of the speed of
675 storing -- the exact penalty will depend on the complexity of your
676 data. There is no slowdown on retrieval.
677
679 Storable now has experimental support for storing regular expressions,
680 but there are significant limitations:
681 • perl 5.8 or later is required.
683 • regular expressions with code blocks, ie "/(?{ ... })/" or "/(??{
685 ... })/" will throw an exception when thawed.
686 • regular expression syntax and flags have changed over the history
688 of perl, so a regular expression that you freeze in one version of
689 perl may fail to thaw or behave differently in another version of
690 perl.
691 • depending on the version of perl, regular expressions can change in
693 behaviour depending on the context, but later perls will bake that
694 behaviour into the regexp.
695 Storable will throw an exception if a frozen regular expression cannot
697 be thawed.
698
700 You can't store GLOB, FORMLINE, etc.... If you can define semantics for
701 those operations, feel free to enhance Storable so that it can deal
702 with them.
703 The store functions will "croak" if they run into such references
705 unless you set $Storable::forgive_me to some "TRUE" value. In that
706 case, the fatal message is converted to a warning and some meaningless
707 string is stored instead.
708 Setting $Storable::canonical may not yield frozen strings that compare
710 equal due to possible stringification of numbers. When the string
711 version of a scalar exists, it is the form stored; therefore, if you
712 happen to use your numbers as strings between two freezing operations
713 on the same data structures, you will get different results.
714 When storing doubles in network order, their value is stored as text.
716 However, you should also not expect non-numeric floating-point values
717 such as infinity and "not a number" to pass successfully through a
718 nstore()/retrieve() pair.
719 As Storable neither knows nor cares about character sets (although it
721 does know that characters may be more than eight bits wide), any
722 difference in the interpretation of character codes between a host and
723 a target system is your problem. In particular, if host and target use
724 different code points to represent the characters used in the text
725 representation of floating-point numbers, you will not be able be able
726 to exchange floating-point data, even with nstore().
727 "Storable::drop_utf8" is a blunt tool. There is no facility either to
729 return all strings as utf8 sequences, or to attempt to convert utf8
730 data back to 8 bit and "croak()" if the conversion fails.
731 Prior to Storable 2.01, no distinction was made between signed and
733 unsigned integers on storing. By default Storable prefers to store a
734 scalars string representation (if it has one) so this would only cause
735 problems when storing large unsigned integers that had never been
736 converted to string or floating point. In other words values that had
737 been generated by integer operations such as logic ops and then not
738 used in any string or arithmetic context before storing.
739 64 bit data in perl 5.6.0 and 5.6.1
741 This section only applies to you if you have existing data written out
742 by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux
743 which has been configured with 64 bit integer support (not the default)
744 If you got a precompiled perl, rather than running Configure to build
745 your own perl from source, then it almost certainly does not affect
746 you, and you can stop reading now (unless you're curious). If you're
747 using perl on Windows it does not affect you.
748 Storable writes a file header which contains the sizes of various C
750 language types for the C compiler that built Storable (when not writing
751 in network order), and will refuse to load files written by a Storable
752 not on the same (or compatible) architecture. This check and a check
753 on machine byteorder is needed because the size of various fields in
754 the file are given by the sizes of the C language types, and so files
755 written on different architectures are incompatible. This is done for
756 increased speed. (When writing in network order, all fields are
757 written out as standard lengths, which allows full interworking, but
758 takes longer to read and write)
759 Perl 5.6.x introduced the ability to optional configure the perl
761 interpreter to use C's "long long" type to allow scalars to store 64
762 bit integers on 32 bit systems. However, due to the way the Perl
763 configuration system generated the C configuration files on non-Windows
764 platforms, and the way Storable generates its header, nothing in the
765 Storable file header reflected whether the perl writing was using 32 or
766 64 bit integers, despite the fact that Storable was storing some data
767 differently in the file. Hence Storable running on perl with 64 bit
768 integers will read the header from a file written by a 32 bit perl, not
769 realise that the data is actually in a subtly incompatible format, and
770 then go horribly wrong (possibly crashing) if it encountered a stored
771 integer. This is a design failure.
772 Storable has now been changed to write out and read in a file header
774 with information about the size of integers. It's impossible to detect
775 whether an old file being read in was written with 32 or 64 bit
776 integers (they have the same header) so it's impossible to
777 automatically switch to a correct backwards compatibility mode. Hence
778 this Storable defaults to the new, correct behaviour.
779 What this means is that if you have data written by Storable 1.x
781 running on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix
782 or Linux then by default this Storable will refuse to read it, giving
783 the error Byte order is not compatible. If you have such data then you
784 should set $Storable::interwork_56_64bit to a true value to make this
785 Storable read and write files with the old header. You should also
786 migrate your data, or any older perl you are communicating with, to
787 this current version of Storable.
788 If you don't have data written with specific configuration of perl
790 described above, then you do not and should not do anything. Don't set
791 the flag - not only will Storable on an identically configured perl
792 refuse to load them, but Storable a differently configured perl will
793 load them believing them to be correct for it, and then may well fail
794 or crash part way through reading them.
795
797 Thank you to (in chronological order):
798 Jarkko Hietaniemi <jhi@iki.fi>
800 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
801 Benjamin A. Holzman <bholzman@earthlink.net>
802 Andrew Ford <A.Ford@ford-mason.co.uk>
803 Gisle Aas <gisle@aas.no>
804 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
805 Murray Nesbitt <murray@activestate.com>
806 Marc Lehmann <pcg@opengroup.org>
807 Justin Banks <justinb@wamnet.com>
808 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
809 Salvador Ortiz Garcia <sog@msg.com.mx>
810 Dominic Dunlop <domo@computer.org>
811 Erik Haugan <erik@solbors.no>
812 Benjamin A. Holzman <ben.holzman@grantstreet.com>
813 Reini Urban <rurban@cpan.org>
814 Todd Rinaldo <toddr@cpanel.net>
815 Aaron Crane <arc@cpan.org>
816 for their bug reports, suggestions and contributions.
818 Benjamin Holzman contributed the tied variable support, Andrew Ford
820 contributed the canonical order for hashes, and Gisle Aas fixed a few
821 misunderstandings of mine regarding the perl internals, and optimized
822 the emission of "tags" in the output streams by simply counting the
823 objects instead of tagging them (leading to a binary incompatibility
824 for the Storable image starting at version 0.6--older images are, of
825 course, still properly understood). Murray Nesbitt made Storable
826 thread-safe. Marc Lehmann added overloading and references to tied
827 items support. Benjamin Holzman added a performance improvement for
828 overloaded classes; thanks to Grant Street Group for footing the bill.
829 Reini Urban took over maintenance from p5p, and added security fixes
830 and huge object support.
831
833 Storable was written by Raphael Manfredi <Raphael_Manfredi@pobox.com>
834 Maintenance is now done by cperl <http://perl11.org/cperl>
835 Please e-mail us with problems, bug fixes, comments and complaints,
837 although if you have compliments you should send them to Raphael.
838 Please don't e-mail Raphael with problems, as he no longer works on
839 Storable, and your message will be delayed while he forwards it to us.
840
842 Clone.
843perl v5.34.0 2021-08-30 Storable(3)