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596596d5 1;# $Id: Storable.pm,v 1.0.1.13 2001/12/01 13:34:49 ram Exp $
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2;#
3;# Copyright (c) 1995-2000, Raphael Manfredi
4;#
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5;# You may redistribute only under the same terms as Perl 5, as specified
6;# in the README file that comes with the distribution.
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7;#
8;# $Log: Storable.pm,v $
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9;# Revision 1.0.1.13 2001/12/01 13:34:49 ram
10;# patch14: avoid requiring Fcntl upfront, useful to embedded runtimes
11;# patch14: store_fd() will now correctly autoflush file if needed
12;#
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13;# Revision 1.0.1.12 2001/08/28 21:51:51 ram
14;# patch13: fixed truncation race with lock_retrieve() in lock_store()
15;#
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16;# Revision 1.0.1.11 2001/07/01 11:22:14 ram
17;# patch12: systematically use "=over 4" for POD linters
18;# patch12: updated version number
19;#
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20;# Revision 1.0.1.10 2001/03/15 00:20:25 ram
21;# patch11: updated version number
22;#
23;# Revision 1.0.1.9 2001/02/17 12:37:32 ram
24;# patch10: forgot to increase version number at previous patch
25;#
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26;# Revision 1.0.1.8 2001/02/17 12:24:37 ram
27;# patch8: fixed incorrect error message
28;#
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29;# Revision 1.0.1.7 2001/01/03 09:39:02 ram
30;# patch7: added CAN_FLOCK to determine whether we can flock() or not
31;#
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32;# Revision 1.0.1.6 2000/11/05 17:20:25 ram
33;# patch6: increased version number
34;#
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35;# Revision 1.0.1.5 2000/10/26 17:10:18 ram
36;# patch5: documented that store() and retrieve() can return undef
37;# patch5: added paragraph explaining the auto require for thaw hooks
38;#
39;# Revision 1.0.1.4 2000/10/23 18:02:57 ram
40;# patch4: protected calls to flock() for dos platform
41;# patch4: added logcarp emulation if they don't have Log::Agent
42;#
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43;# Revision 1.0.1.3 2000/09/29 19:49:01 ram
44;# patch3: updated version number
45;#
46;# Revision 1.0.1.2 2000/09/28 21:42:51 ram
47;# patch2: added lock_store lock_nstore lock_retrieve
48;#
49;# Revision 1.0.1.1 2000/09/17 16:46:21 ram
50;# patch1: documented that doubles are stringified by nstore()
51;# patch1: added Salvador Ortiz Garcia in CREDITS section
52;#
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53;# Revision 1.0 2000/09/01 19:40:41 ram
54;# Baseline for first official release.
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55;#
56
57require DynaLoader;
58require Exporter;
59package Storable; @ISA = qw(Exporter DynaLoader);
60
61@EXPORT = qw(store retrieve);
62@EXPORT_OK = qw(
9e21b3d0 63 nstore store_fd nstore_fd fd_retrieve
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64 freeze nfreeze thaw
65 dclone
9e21b3d0 66 retrieve_fd
dd19458b 67 lock_store lock_nstore lock_retrieve
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68);
69
70use AutoLoader;
71use vars qw($forgive_me $VERSION);
72
0a0da639 73$VERSION = '1.015';
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74*AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
75
76#
77# Use of Log::Agent is optional
78#
79
80eval "use Log::Agent";
81
530b72ba 82require Carp;
7a6a85bf 83
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84#
85# They might miss :flock in Fcntl
86#
87
88BEGIN {
596596d5 89 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
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90 Fcntl->import(':flock');
91 } else {
92 eval q{
93 sub LOCK_SH () {1}
94 sub LOCK_EX () {2}
95 };
96 }
97}
98
b8778c7c 99# Can't Autoload cleanly as this clashes 8.3 with &retrieve
9e21b3d0 100sub retrieve_fd { &fd_retrieve } # Backward compatibility
cb3d9de5 101
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102# By default restricted hashes are downgraded on earlier perls.
103
104$Storable::downgrade_restricted = 1;
e8189732 105$Storable::accept_future_minor = 1;
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106bootstrap Storable;
1071;
108__END__
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109#
110# Use of Log::Agent is optional. If it hasn't imported these subs then
111# Autoloader will kindly supply our fallback implementation.
112#
113
114sub logcroak {
115 Carp::croak(@_);
116}
117
118sub logcarp {
119 Carp::carp(@_);
120}
b8778c7c 121
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122#
123# Determine whether locking is possible, but only when needed.
124#
125
530b72ba 126sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
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127 return $CAN_FLOCK if defined $CAN_FLOCK;
128 require Config; import Config;
129 return $CAN_FLOCK =
130 $Config{'d_flock'} ||
131 $Config{'d_fcntl_can_lock'} ||
132 $Config{'d_lockf'};
133}
134
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135sub show_file_magic {
136 print <<EOM;
137#
138# To recognize the data files of the Perl module Storable,
139# the following lines need to be added to the local magic(5) file,
140# usually either /usr/share/misc/magic or /etc/magic.
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141#
1420 string perl-store perl Storable(v0.6) data
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143>4 byte >0 (net-order %d)
144>>4 byte &01 (network-ordered)
145>>4 byte =3 (major 1)
146>>4 byte =2 (major 1)
147
0a0da639 1480 string pst0 perl Storable(v0.7) data
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149>4 byte >0
150>>4 byte &01 (network-ordered)
151>>4 byte =5 (major 2)
152>>4 byte =4 (major 2)
153>>5 byte >0 (minor %d)
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154EOM
155}
156
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157sub read_magic {
158 my $header = shift;
159 return unless defined $header and length $header > 11;
160 my $result;
161 if ($header =~ s/^perl-store//) {
162 die "Can't deal with version 0 headers";
163 } elsif ($header =~ s/^pst0//) {
164 $result->{file} = 1;
165 }
166 # Assume it's a string.
167 my ($major, $minor, $bytelen) = unpack "C3", $header;
168
169 my $net_order = $major & 1;
170 $major >>= 1;
171 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
172
173 return $result if $net_order;
174
175 # I assume that it is rare to find v1 files, so this is an intentionally
176 # inefficient way of doing it, to make the rest of the code constant.
177 if ($major < 2) {
178 delete $result->{minor};
179 $header = '.' . $header;
180 $bytelen = $minor;
181 }
182
183 @$result{qw(byteorder intsize longsize ptrsize)} =
184 unpack "x3 A$bytelen C3", $header;
185
186 if ($major >= 2 and $minor >= 2) {
187 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
188 }
189 $result;
190}
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191
192#
193# store
194#
195# Store target object hierarchy, identified by a reference to its root.
196# The stored object tree may later be retrieved to memory via retrieve.
197# Returns undef if an I/O error occurred, in which case the file is
198# removed.
199#
200sub store {
dd19458b 201 return _store(\&pstore, @_, 0);
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202}
203
204#
205# nstore
206#
207# Same as store, but in network order.
208#
209sub nstore {
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210 return _store(\&net_pstore, @_, 0);
211}
212
213#
214# lock_store
215#
216# Same as store, but flock the file first (advisory locking).
217#
218sub lock_store {
219 return _store(\&pstore, @_, 1);
220}
221
222#
223# lock_nstore
224#
225# Same as nstore, but flock the file first (advisory locking).
226#
227sub lock_nstore {
228 return _store(\&net_pstore, @_, 1);
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229}
230
231# Internal store to file routine
232sub _store {
233 my $xsptr = shift;
234 my $self = shift;
dd19458b 235 my ($file, $use_locking) = @_;
7a6a85bf 236 logcroak "not a reference" unless ref($self);
b12202d0 237 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
7a6a85bf 238 local *FILE;
dd19458b 239 if ($use_locking) {
6e0ac6f5 240 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
862382c7 241 unless (&CAN_FLOCK) {
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242 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
243 return undef;
f567092b 244 }
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245 flock(FILE, LOCK_EX) ||
246 logcroak "can't get exclusive lock on $file: $!";
247 truncate FILE, 0;
248 # Unlocking will happen when FILE is closed
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249 } else {
250 open(FILE, ">$file") || logcroak "can't create $file: $!";
dd19458b 251 }
6e0ac6f5 252 binmode FILE; # Archaic systems...
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253 my $da = $@; # Don't mess if called from exception handler
254 my $ret;
255 # Call C routine nstore or pstore, depending on network order
256 eval { $ret = &$xsptr(*FILE, $self) };
257 close(FILE) or $ret = undef;
258 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
259 logcroak $@ if $@ =~ s/\.?\n$/,/;
260 $@ = $da;
261 return $ret ? $ret : undef;
262}
263
264#
265# store_fd
266#
267# Same as store, but perform on an already opened file descriptor instead.
268# Returns undef if an I/O error occurred.
269#
270sub store_fd {
271 return _store_fd(\&pstore, @_);
272}
273
274#
275# nstore_fd
276#
277# Same as store_fd, but in network order.
278#
279sub nstore_fd {
280 my ($self, $file) = @_;
281 return _store_fd(\&net_pstore, @_);
282}
283
284# Internal store routine on opened file descriptor
285sub _store_fd {
286 my $xsptr = shift;
287 my $self = shift;
288 my ($file) = @_;
289 logcroak "not a reference" unless ref($self);
290 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
291 my $fd = fileno($file);
292 logcroak "not a valid file descriptor" unless defined $fd;
293 my $da = $@; # Don't mess if called from exception handler
294 my $ret;
295 # Call C routine nstore or pstore, depending on network order
296 eval { $ret = &$xsptr($file, $self) };
297 logcroak $@ if $@ =~ s/\.?\n$/,/;
596596d5 298 local $\; print $file ''; # Autoflush the file if wanted
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299 $@ = $da;
300 return $ret ? $ret : undef;
301}
302
303#
304# freeze
305#
306# Store oject and its hierarchy in memory and return a scalar
307# containing the result.
308#
309sub freeze {
310 _freeze(\&mstore, @_);
311}
312
313#
314# nfreeze
315#
316# Same as freeze but in network order.
317#
318sub nfreeze {
319 _freeze(\&net_mstore, @_);
320}
321
322# Internal freeze routine
323sub _freeze {
324 my $xsptr = shift;
325 my $self = shift;
326 logcroak "not a reference" unless ref($self);
327 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
328 my $da = $@; # Don't mess if called from exception handler
329 my $ret;
330 # Call C routine mstore or net_mstore, depending on network order
331 eval { $ret = &$xsptr($self) };
332 logcroak $@ if $@ =~ s/\.?\n$/,/;
333 $@ = $da;
334 return $ret ? $ret : undef;
335}
336
337#
338# retrieve
339#
340# Retrieve object hierarchy from disk, returning a reference to the root
341# object of that tree.
342#
343sub retrieve {
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344 _retrieve($_[0], 0);
345}
346
347#
348# lock_retrieve
349#
350# Same as retrieve, but with advisory locking.
351#
352sub lock_retrieve {
353 _retrieve($_[0], 1);
354}
355
356# Internal retrieve routine
357sub _retrieve {
358 my ($file, $use_locking) = @_;
7a6a85bf 359 local *FILE;
dd19458b 360 open(FILE, $file) || logcroak "can't open $file: $!";
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361 binmode FILE; # Archaic systems...
362 my $self;
363 my $da = $@; # Could be from exception handler
dd19458b 364 if ($use_locking) {
862382c7 365 unless (&CAN_FLOCK) {
8be2b38b 366 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
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367 return undef;
368 }
8be2b38b 369 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
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370 # Unlocking will happen when FILE is closed
371 }
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372 eval { $self = pretrieve(*FILE) }; # Call C routine
373 close(FILE);
374 logcroak $@ if $@ =~ s/\.?\n$/,/;
375 $@ = $da;
376 return $self;
377}
378
379#
9e21b3d0 380# fd_retrieve
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381#
382# Same as retrieve, but perform from an already opened file descriptor instead.
383#
9e21b3d0 384sub fd_retrieve {
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385 my ($file) = @_;
386 my $fd = fileno($file);
387 logcroak "not a valid file descriptor" unless defined $fd;
388 my $self;
389 my $da = $@; # Could be from exception handler
390 eval { $self = pretrieve($file) }; # Call C routine
391 logcroak $@ if $@ =~ s/\.?\n$/,/;
392 $@ = $da;
393 return $self;
394}
395
396#
397# thaw
398#
399# Recreate objects in memory from an existing frozen image created
400# by freeze. If the frozen image passed is undef, return undef.
401#
402sub thaw {
403 my ($frozen) = @_;
404 return undef unless defined $frozen;
405 my $self;
406 my $da = $@; # Could be from exception handler
407 eval { $self = mretrieve($frozen) }; # Call C routine
408 logcroak $@ if $@ =~ s/\.?\n$/,/;
409 $@ = $da;
410 return $self;
411}
412
413=head1 NAME
414
415Storable - persistency for perl data structures
416
417=head1 SYNOPSIS
418
419 use Storable;
420 store \%table, 'file';
421 $hashref = retrieve('file');
422
423 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
424
425 # Network order
426 nstore \%table, 'file';
427 $hashref = retrieve('file'); # There is NO nretrieve()
428
429 # Storing to and retrieving from an already opened file
430 store_fd \@array, \*STDOUT;
431 nstore_fd \%table, \*STDOUT;
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432 $aryref = fd_retrieve(\*SOCKET);
433 $hashref = fd_retrieve(\*SOCKET);
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434
435 # Serializing to memory
436 $serialized = freeze \%table;
437 %table_clone = %{ thaw($serialized) };
438
439 # Deep (recursive) cloning
440 $cloneref = dclone($ref);
441
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442 # Advisory locking
443 use Storable qw(lock_store lock_nstore lock_retrieve)
444 lock_store \%table, 'file';
445 lock_nstore \%table, 'file';
446 $hashref = lock_retrieve('file');
447
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448=head1 DESCRIPTION
449
c261f00e 450The Storable package brings persistence to your perl data structures
7a6a85bf 451containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
c261f00e 452conveniently stored to disk and retrieved at a later time.
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453
454It can be used in the regular procedural way by calling C<store> with
455a reference to the object to be stored, along with the file name where
456the image should be written.
457The routine returns C<undef> for I/O problems or other internal error,
458a true value otherwise. Serious errors are propagated as a C<die> exception.
459
460To retrieve data stored to disk, use C<retrieve> with a file name,
461and the objects stored into that file are recreated into memory for you,
462a I<reference> to the root object being returned. In case an I/O error
463occurs while reading, C<undef> is returned instead. Other serious
464errors are propagated via C<die>.
465
466Since storage is performed recursively, you might want to stuff references
467to objects that share a lot of common data into a single array or hash
468table, and then store that object. That way, when you retrieve back the
469whole thing, the objects will continue to share what they originally shared.
470
471At the cost of a slight header overhead, you may store to an already
472opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 473from a file via C<fd_retrieve>. Those names aren't imported by default,
c261f00e 474so you will have to do that explicitly if you need those routines.
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475The file descriptor you supply must be already opened, for read
476if you're going to retrieve and for write if you wish to store.
477
478 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 479 $hashref = fd_retrieve(*STDIN);
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480
481You can also store data in network order to allow easy sharing across
482multiple platforms, or when storing on a socket known to be remotely
483connected. The routines to call have an initial C<n> prefix for I<network>,
484as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
485correctly restored so you don't have to know whether you're restoring
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486from native or network ordered data. Double values are stored stringified
487to ensure portability as well, at the slight risk of loosing some precision
488in the last decimals.
7a6a85bf 489
9e21b3d0 490When using C<fd_retrieve>, objects are retrieved in sequence, one
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491object (i.e. one recursive tree) per associated C<store_fd>.
492
493If you're more from the object-oriented camp, you can inherit from
494Storable and directly store your objects by invoking C<store> as
495a method. The fact that the root of the to-be-stored tree is a
496blessed reference (i.e. an object) is special-cased so that the
497retrieve does not provide a reference to that object but rather the
498blessed object reference itself. (Otherwise, you'd get a reference
499to that blessed object).
500
501=head1 MEMORY STORE
502
503The Storable engine can also store data into a Perl scalar instead, to
504later retrieve them. This is mainly used to freeze a complex structure in
505some safe compact memory place (where it can possibly be sent to another
506process via some IPC, since freezing the structure also serializes it in
507effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
508out and recreate the original complex structure in memory.
509
510Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
511If you wish to send out the frozen scalar to another machine, use
512C<nfreeze> instead to get a portable image.
513
514Note that freezing an object structure and immediately thawing it
515actually achieves a deep cloning of that structure:
516
517 dclone(.) = thaw(freeze(.))
518
519Storable provides you with a C<dclone> interface which does not create
520that intermediary scalar but instead freezes the structure in some
c261f00e 521internal memory space and then immediately thaws it out.
7a6a85bf 522
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523=head1 ADVISORY LOCKING
524
525The C<lock_store> and C<lock_nstore> routine are equivalent to C<store>
526and C<nstore>, only they get an exclusive lock on the file before
527writing. Likewise, C<lock_retrieve> performs as C<retrieve>, but also
528gets a shared lock on the file before reading.
529
530Like with any advisory locking scheme, the protection only works if
531you systematically use C<lock_store> and C<lock_retrieve>. If one
532side of your application uses C<store> whilst the other uses C<lock_retrieve>,
533you will get no protection at all.
534
535The internal advisory locking is implemented using Perl's flock() routine.
536If your system does not support any form of flock(), or if you share
537your files across NFS, you might wish to use other forms of locking by
538using modules like LockFile::Simple which lock a file using a filesystem
539entry, instead of locking the file descriptor.
540
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541=head1 SPEED
542
543The heart of Storable is written in C for decent speed. Extra low-level
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544optimizations have been made when manipulating perl internals, to
545sacrifice encapsulation for the benefit of greater speed.
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546
547=head1 CANONICAL REPRESENTATION
548
549Normally Storable stores elements of hashes in the order they are
550stored internally by Perl, i.e. pseudo-randomly. If you set
551C<$Storable::canonical> to some C<TRUE> value, Storable will store
552hashes with the elements sorted by their key. This allows you to
553compare data structures by comparing their frozen representations (or
554even the compressed frozen representations), which can be useful for
555creating lookup tables for complicated queries.
556
557Canonical order does not imply network order, those are two orthogonal
558settings.
559
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560=head1 FORWARD COMPATIBILITY
561
562This release of Storable can be used on a newer version of Perl to
563serialize data which is not supported by earlier Perls. By default
564Storable will attempt to do the right thing, by C<croak()>ing if it
565encounters data that it cannot deserialize. However, the defaults can be
566changed as follows
567
568=over 4
569
570=item utf8 data
571
572Perl 5.6 added support for Unicode characters with code points > 255,
573and Perl 5.8 has full support for Unicode characters in hash keys.
574Perl internally encodes strings with these characters using utf8, and
575Storable serializes them as utf8. By default, if an older version of
576Perl encounters a utf8 value it cannot represent, it will C<croak()>.
577To change this behaviour so that Storable deserializes utf8 encoded
578values as the string of bytes (effectively dropping the I<is_utf8> flag)
579set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
580data loss, because with C<$drop_utf8> true, it becomes impossible to tell
581whether the original data was the Unicode string, or a series of bytes
582that happen to be valid utf8.
583
584=item restricted hashes
585
586Perl 5.8 adds support for restricted hashes, which have keys restricted to
587a given set, and can have values locked to be read only. By default
588when Storable encounters a restricted hash on a perl that doesn't support
589them, it will deserialize it as a normal hash, silently discarding any
590placeholder keys and leaving the keys and all values unlocked. To make
591Storable C<croak()> instead, set C<$Storable::downgrade_restricted> to
592a false value. To restore the default set it back to some C<TRUE> value.
593
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594=item files from future versions of Storable
595
596Earlier versions of Storable would immediately croak if they encountered
597a file with a higher internal version number than the reading Storable
598knew about. Internal version numbers are increased each time new data
599types (such as restricted hashes) are added to the vocabulary of the file
600format. This meant that a newer Storable module had no way of writing a
601file readable by an older Storable, even if writer didn't store newer
602data types.
603
604This version of Storable will defer croaking until it encounters a data
605type in the file that it does not recognize. This means that it will
606continue to read files generated by newer Storable modules which are careful
607in what they write out, making it easier to upgrade Storable modules in a
608mixed environment.
609
610The old behaviour of immediate croaking can be re-instated by setting
611C<$Storable::accept_future_minor> to false.
612
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613=back
614
615Both these variables have no effect on a newer Perl which supports the
616relevant feature.
617
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618=head1 ERROR REPORTING
619
620Storable uses the "exception" paradigm, in that it does not try to workaround
621failures: if something bad happens, an exception is generated from the
622caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
623those exceptions.
624
625When Storable croaks, it tries to report the error via the C<logcroak()>
626routine from the C<Log::Agent> package, if it is available.
627
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628Normal errors are reported by having store() or retrieve() return C<undef>.
629Such errors are usually I/O errors (or truncated stream errors at retrieval).
630
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631=head1 WIZARDS ONLY
632
633=head2 Hooks
634
635Any class may define hooks that will be called during the serialization
636and deserialization process on objects that are instances of that class.
637Those hooks can redefine the way serialization is performed (and therefore,
c261f00e 638how the symmetrical deserialization should be conducted).
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639
640Since we said earlier:
641
642 dclone(.) = thaw(freeze(.))
643
644everything we say about hooks should also hold for deep cloning. However,
645hooks get to know whether the operation is a mere serialization, or a cloning.
646
647Therefore, when serializing hooks are involved,
648
649 dclone(.) <> thaw(freeze(.))
650
651Well, you could keep them in sync, but there's no guarantee it will always
652hold on classes somebody else wrote. Besides, there is little to gain in
653doing so: a serializing hook could only keep one attribute of an object,
654which is probably not what should happen during a deep cloning of that
655same object.
656
657Here is the hooking interface:
658
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660
661=item C<STORABLE_freeze> I<obj>, I<cloning>
662
663The serializing hook, called on the object during serialization. It can be
664inherited, or defined in the class itself, like any other method.
665
666Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
667whether we're in a dclone() or a regular serialization via store() or freeze().
668
669Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
670is the serialized form to be used, and the optional $ref1, $ref2, etc... are
671extra references that you wish to let the Storable engine serialize.
672
673At deserialization time, you will be given back the same LIST, but all the
674extra references will be pointing into the deserialized structure.
675
676The B<first time> the hook is hit in a serialization flow, you may have it
677return an empty list. That will signal the Storable engine to further
678discard that hook for this class and to therefore revert to the default
679serialization of the underlying Perl data. The hook will again be normally
680processed in the next serialization.
681
682Unless you know better, serializing hook should always say:
683
684 sub STORABLE_freeze {
685 my ($self, $cloning) = @_;
686 return if $cloning; # Regular default serialization
687 ....
688 }
689
690in order to keep reasonable dclone() semantics.
691
692=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
693
694The deserializing hook called on the object during deserialization.
695But wait. If we're deserializing, there's no object yet... right?
696
697Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
698you can view C<STORABLE_thaw> as an alternate creation routine.
699
700This means the hook can be inherited like any other method, and that
701I<obj> is your blessed reference for this particular instance.
702
703The other arguments should look familiar if you know C<STORABLE_freeze>:
704I<cloning> is true when we're part of a deep clone operation, I<serialized>
705is the serialized string you returned to the engine in C<STORABLE_freeze>,
706and there may be an optional list of references, in the same order you gave
707them at serialization time, pointing to the deserialized objects (which
708have been processed courtesy of the Storable engine).
709
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710When the Storable engine does not find any C<STORABLE_thaw> hook routine,
711it tries to load the class by requiring the package dynamically (using
712the blessed package name), and then re-attempts the lookup. If at that
713time the hook cannot be located, the engine croaks. Note that this mechanism
c261f00e 714will fail if you define several classes in the same file, but L<perlmod>
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715warned you.
716
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717It is up to you to use these information to populate I<obj> the way you want.
718
719Returned value: none.
720
721=back
722
723=head2 Predicates
724
c261f00e 725Predicates are not exportable. They must be called by explicitly prefixing
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726them with the Storable package name.
727
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729
730=item C<Storable::last_op_in_netorder>
731
732The C<Storable::last_op_in_netorder()> predicate will tell you whether
733network order was used in the last store or retrieve operation. If you
734don't know how to use this, just forget about it.
735
736=item C<Storable::is_storing>
737
738Returns true if within a store operation (via STORABLE_freeze hook).
739
740=item C<Storable::is_retrieving>
741
742Returns true if within a retrieve operation, (via STORABLE_thaw hook).
743
744=back
745
746=head2 Recursion
747
748With hooks comes the ability to recurse back to the Storable engine. Indeed,
749hooks are regular Perl code, and Storable is convenient when it comes to
750serialize and deserialize things, so why not use it to handle the
751serialization string?
752
753There are a few things you need to know however:
754
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756
757=item *
758
759You can create endless loops if the things you serialize via freeze()
760(for instance) point back to the object we're trying to serialize in the hook.
761
762=item *
763
764Shared references among objects will not stay shared: if we're serializing
765the list of object [A, C] where both object A and C refer to the SAME object
766B, and if there is a serializing hook in A that says freeze(B), then when
767deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
768a deep clone of B'. The topology was not preserved.
769
770=back
771
772That's why C<STORABLE_freeze> lets you provide a list of references
773to serialize. The engine guarantees that those will be serialized in the
774same context as the other objects, and therefore that shared objects will
775stay shared.
776
777In the above [A, C] example, the C<STORABLE_freeze> hook could return:
778
779 ("something", $self->{B})
780
781and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
782would get back the reference to the B' object, deserialized for you.
783
784Therefore, recursion should normally be avoided, but is nonetheless supported.
785
786=head2 Deep Cloning
787
788There is a new Clone module available on CPAN which implements deep cloning
789natively, i.e. without freezing to memory and thawing the result. It is
790aimed to replace Storable's dclone() some day. However, it does not currently
791support Storable hooks to redefine the way deep cloning is performed.
792
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793=head1 Storable magic
794
795Yes, there's a lot of that :-) But more precisely, in UNIX systems
796there's a utility called C<file>, which recognizes data files based on
797their contents (usually their first few bytes). For this to work,
8b793558 798a certain file called F<magic> needs to taught about the I<signature>
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799of the data. Where that configuration file lives depends on the UNIX
800flavour, often it's something like F</usr/share/misc/magic> or
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801F</etc/magic>. Your system administrator needs to do the updating of
802the F<magic> file. The necessary signature information is output to
c261f00e 803STDOUT by invoking Storable::show_file_magic(). Note that the open
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804source implementation of the C<file> utility 3.38 (or later)
805is expected to contain the support for recognising Storable files,
806in addition to other kinds of Perl files.
0a0da639 807
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808=head1 EXAMPLES
809
810Here are some code samples showing a possible usage of Storable:
811
812 use Storable qw(store retrieve freeze thaw dclone);
813
814 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
815
816 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
817
818 $colref = retrieve('/tmp/colors');
819 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
820 printf "Blue is still %lf\n", $colref->{'Blue'};
821
822 $colref2 = dclone(\%color);
823
824 $str = freeze(\%color);
825 printf "Serialization of %%color is %d bytes long.\n", length($str);
826 $colref3 = thaw($str);
827
828which prints (on my machine):
829
830 Blue is still 0.100000
831 Serialization of %color is 102 bytes long.
832
833=head1 WARNING
834
835If you're using references as keys within your hash tables, you're bound
c261f00e 836to disappointment when retrieving your data. Indeed, Perl stringifies
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837references used as hash table keys. If you later wish to access the
838items via another reference stringification (i.e. using the same
839reference that was used for the key originally to record the value into
840the hash table), it will work because both references stringify to the
841same string.
842
843It won't work across a C<store> and C<retrieve> operations however, because
844the addresses in the retrieved objects, which are part of the stringified
845references, will probably differ from the original addresses. The
846topology of your structure is preserved, but not hidden semantics
847like those.
848
849On platforms where it matters, be sure to call C<binmode()> on the
850descriptors that you pass to Storable functions.
851
852Storing data canonically that contains large hashes can be
853significantly slower than storing the same data normally, as
c261f00e 854temporary arrays to hold the keys for each hash have to be allocated,
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855populated, sorted and freed. Some tests have shown a halving of the
856speed of storing -- the exact penalty will depend on the complexity of
857your data. There is no slowdown on retrieval.
858
859=head1 BUGS
860
861You can't store GLOB, CODE, FORMLINE, etc... If you can define
862semantics for those operations, feel free to enhance Storable so that
863it can deal with them.
864
865The store functions will C<croak> if they run into such references
866unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
867case, the fatal message is turned in a warning and some
868meaningless string is stored instead.
869
870Setting C<$Storable::canonical> may not yield frozen strings that
871compare equal due to possible stringification of numbers. When the
872string version of a scalar exists, it is the form stored, therefore
873if you happen to use your numbers as strings between two freezing
874operations on the same data structures, you will get different
875results.
876
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877When storing doubles in network order, their value is stored as text.
878However, you should also not expect non-numeric floating-point values
879such as infinity and "not a number" to pass successfully through a
880nstore()/retrieve() pair.
881
882As Storable neither knows nor cares about character sets (although it
883does know that characters may be more than eight bits wide), any difference
884in the interpretation of character codes between a host and a target
885system is your problem. In particular, if host and target use different
886code points to represent the characters used in the text representation
887of floating-point numbers, you will not be able be able to exchange
888floating-point data, even with nstore().
889
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890C<Storable::drop_utf8> is a blunt tool. There is no facility either to
891return B<all> strings as utf8 sequences, or to attempt to convert utf8
892data back to 8 bit and C<croak()> if the conversion fails.
893
894Future compatibility does not yet extend to having the option of loading
895serialized data with higher than current minor version numbers. This
896ought to be fixed pronto.
897
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898=head1 CREDITS
899
900Thank you to (in chronological order):
901
902 Jarkko Hietaniemi <jhi@iki.fi>
903 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
904 Benjamin A. Holzman <bah@ecnvantage.com>
905 Andrew Ford <A.Ford@ford-mason.co.uk>
906 Gisle Aas <gisle@aas.no>
907 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
908 Murray Nesbitt <murray@activestate.com>
909 Marc Lehmann <pcg@opengroup.org>
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910 Justin Banks <justinb@wamnet.com>
911 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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912 Salvador Ortiz Garcia <sog@msg.com.mx>
913 Dominic Dunlop <domo@computer.org>
914 Erik Haugan <erik@solbors.no>
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915
916for their bug reports, suggestions and contributions.
917
918Benjamin Holzman contributed the tied variable support, Andrew Ford
919contributed the canonical order for hashes, and Gisle Aas fixed
920a few misunderstandings of mine regarding the Perl internals,
921and optimized the emission of "tags" in the output streams by
922simply counting the objects instead of tagging them (leading to
923a binary incompatibility for the Storable image starting at version
9240.6--older images are of course still properly understood).
925Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
926and reference to tied items support.
927
928=head1 TRANSLATIONS
929
930There is a Japanese translation of this man page available at
931http://member.nifty.ne.jp/hippo2000/perltips/storable.htm ,
932courtesy of Kawai, Takanori <kawai@nippon-rad.co.jp>.
933
934=head1 AUTHOR
935
936Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
937
938=head1 SEE ALSO
939
c261f00e 940L<Clone>.
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941
942=cut
943