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1#
2# Copyright (c) 1995-2000, Raphael Manfredi
3#
4# You may redistribute only under the same terms as Perl 5, as specified
5# in the README file that comes with the distribution.
6#
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7
8require DynaLoader;
9require Exporter;
10package Storable; @ISA = qw(Exporter DynaLoader);
11
12@EXPORT = qw(store retrieve);
13@EXPORT_OK = qw(
9e21b3d0 14 nstore store_fd nstore_fd fd_retrieve
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15 freeze nfreeze thaw
16 dclone
9e21b3d0 17 retrieve_fd
dd19458b 18 lock_store lock_nstore lock_retrieve
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19);
20
21use AutoLoader;
01d7b99e 22use vars qw($canonical $forgive_me $VERSION);
7a6a85bf 23
17374ab3 24$VERSION = '2.04';
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25*AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
26
27#
28# Use of Log::Agent is optional
29#
30
31eval "use Log::Agent";
32
530b72ba 33require Carp;
7a6a85bf 34
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35#
36# They might miss :flock in Fcntl
37#
38
39BEGIN {
596596d5 40 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
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41 Fcntl->import(':flock');
42 } else {
43 eval q{
44 sub LOCK_SH () {1}
45 sub LOCK_EX () {2}
46 };
47 }
48}
49
b8778c7c 50# Can't Autoload cleanly as this clashes 8.3 with &retrieve
9e21b3d0 51sub retrieve_fd { &fd_retrieve } # Backward compatibility
cb3d9de5 52
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53# By default restricted hashes are downgraded on earlier perls.
54
55$Storable::downgrade_restricted = 1;
e8189732 56$Storable::accept_future_minor = 1;
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57bootstrap Storable;
581;
59__END__
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60#
61# Use of Log::Agent is optional. If it hasn't imported these subs then
62# Autoloader will kindly supply our fallback implementation.
63#
64
65sub logcroak {
66 Carp::croak(@_);
67}
68
69sub logcarp {
70 Carp::carp(@_);
71}
b8778c7c 72
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73#
74# Determine whether locking is possible, but only when needed.
75#
76
530b72ba 77sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
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78 return $CAN_FLOCK if defined $CAN_FLOCK;
79 require Config; import Config;
80 return $CAN_FLOCK =
81 $Config{'d_flock'} ||
82 $Config{'d_fcntl_can_lock'} ||
83 $Config{'d_lockf'};
84}
85
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86sub show_file_magic {
87 print <<EOM;
88#
89# To recognize the data files of the Perl module Storable,
90# the following lines need to be added to the local magic(5) file,
91# usually either /usr/share/misc/magic or /etc/magic.
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92#
930 string perl-store perl Storable(v0.6) data
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94>4 byte >0 (net-order %d)
95>>4 byte &01 (network-ordered)
96>>4 byte =3 (major 1)
97>>4 byte =2 (major 1)
98
0a0da639 990 string pst0 perl Storable(v0.7) data
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100>4 byte >0
101>>4 byte &01 (network-ordered)
102>>4 byte =5 (major 2)
103>>4 byte =4 (major 2)
104>>5 byte >0 (minor %d)
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105EOM
106}
107
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108sub read_magic {
109 my $header = shift;
110 return unless defined $header and length $header > 11;
111 my $result;
112 if ($header =~ s/^perl-store//) {
113 die "Can't deal with version 0 headers";
114 } elsif ($header =~ s/^pst0//) {
115 $result->{file} = 1;
116 }
117 # Assume it's a string.
118 my ($major, $minor, $bytelen) = unpack "C3", $header;
119
120 my $net_order = $major & 1;
121 $major >>= 1;
122 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
123
124 return $result if $net_order;
125
126 # I assume that it is rare to find v1 files, so this is an intentionally
127 # inefficient way of doing it, to make the rest of the code constant.
128 if ($major < 2) {
129 delete $result->{minor};
130 $header = '.' . $header;
131 $bytelen = $minor;
132 }
133
134 @$result{qw(byteorder intsize longsize ptrsize)} =
135 unpack "x3 A$bytelen C3", $header;
136
137 if ($major >= 2 and $minor >= 2) {
138 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
139 }
140 $result;
141}
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142
143#
144# store
145#
146# Store target object hierarchy, identified by a reference to its root.
147# The stored object tree may later be retrieved to memory via retrieve.
148# Returns undef if an I/O error occurred, in which case the file is
149# removed.
150#
151sub store {
dd19458b 152 return _store(\&pstore, @_, 0);
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153}
154
155#
156# nstore
157#
158# Same as store, but in network order.
159#
160sub nstore {
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161 return _store(\&net_pstore, @_, 0);
162}
163
164#
165# lock_store
166#
167# Same as store, but flock the file first (advisory locking).
168#
169sub lock_store {
170 return _store(\&pstore, @_, 1);
171}
172
173#
174# lock_nstore
175#
176# Same as nstore, but flock the file first (advisory locking).
177#
178sub lock_nstore {
179 return _store(\&net_pstore, @_, 1);
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180}
181
182# Internal store to file routine
183sub _store {
184 my $xsptr = shift;
185 my $self = shift;
dd19458b 186 my ($file, $use_locking) = @_;
7a6a85bf 187 logcroak "not a reference" unless ref($self);
b12202d0 188 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
7a6a85bf 189 local *FILE;
dd19458b 190 if ($use_locking) {
6e0ac6f5 191 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
862382c7 192 unless (&CAN_FLOCK) {
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193 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
194 return undef;
f567092b 195 }
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196 flock(FILE, LOCK_EX) ||
197 logcroak "can't get exclusive lock on $file: $!";
198 truncate FILE, 0;
199 # Unlocking will happen when FILE is closed
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200 } else {
201 open(FILE, ">$file") || logcroak "can't create $file: $!";
dd19458b 202 }
6e0ac6f5 203 binmode FILE; # Archaic systems...
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204 my $da = $@; # Don't mess if called from exception handler
205 my $ret;
206 # Call C routine nstore or pstore, depending on network order
207 eval { $ret = &$xsptr(*FILE, $self) };
208 close(FILE) or $ret = undef;
209 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
210 logcroak $@ if $@ =~ s/\.?\n$/,/;
211 $@ = $da;
212 return $ret ? $ret : undef;
213}
214
215#
216# store_fd
217#
218# Same as store, but perform on an already opened file descriptor instead.
219# Returns undef if an I/O error occurred.
220#
221sub store_fd {
222 return _store_fd(\&pstore, @_);
223}
224
225#
226# nstore_fd
227#
228# Same as store_fd, but in network order.
229#
230sub nstore_fd {
231 my ($self, $file) = @_;
232 return _store_fd(\&net_pstore, @_);
233}
234
235# Internal store routine on opened file descriptor
236sub _store_fd {
237 my $xsptr = shift;
238 my $self = shift;
239 my ($file) = @_;
240 logcroak "not a reference" unless ref($self);
241 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
242 my $fd = fileno($file);
243 logcroak "not a valid file descriptor" unless defined $fd;
244 my $da = $@; # Don't mess if called from exception handler
245 my $ret;
246 # Call C routine nstore or pstore, depending on network order
247 eval { $ret = &$xsptr($file, $self) };
248 logcroak $@ if $@ =~ s/\.?\n$/,/;
596596d5 249 local $\; print $file ''; # Autoflush the file if wanted
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250 $@ = $da;
251 return $ret ? $ret : undef;
252}
253
254#
255# freeze
256#
257# Store oject and its hierarchy in memory and return a scalar
258# containing the result.
259#
260sub freeze {
261 _freeze(\&mstore, @_);
262}
263
264#
265# nfreeze
266#
267# Same as freeze but in network order.
268#
269sub nfreeze {
270 _freeze(\&net_mstore, @_);
271}
272
273# Internal freeze routine
274sub _freeze {
275 my $xsptr = shift;
276 my $self = shift;
277 logcroak "not a reference" unless ref($self);
278 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
279 my $da = $@; # Don't mess if called from exception handler
280 my $ret;
281 # Call C routine mstore or net_mstore, depending on network order
282 eval { $ret = &$xsptr($self) };
283 logcroak $@ if $@ =~ s/\.?\n$/,/;
284 $@ = $da;
285 return $ret ? $ret : undef;
286}
287
288#
289# retrieve
290#
291# Retrieve object hierarchy from disk, returning a reference to the root
292# object of that tree.
293#
294sub retrieve {
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295 _retrieve($_[0], 0);
296}
297
298#
299# lock_retrieve
300#
301# Same as retrieve, but with advisory locking.
302#
303sub lock_retrieve {
304 _retrieve($_[0], 1);
305}
306
307# Internal retrieve routine
308sub _retrieve {
309 my ($file, $use_locking) = @_;
7a6a85bf 310 local *FILE;
dd19458b 311 open(FILE, $file) || logcroak "can't open $file: $!";
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312 binmode FILE; # Archaic systems...
313 my $self;
314 my $da = $@; # Could be from exception handler
dd19458b 315 if ($use_locking) {
862382c7 316 unless (&CAN_FLOCK) {
8be2b38b 317 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
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318 return undef;
319 }
8be2b38b 320 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
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321 # Unlocking will happen when FILE is closed
322 }
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323 eval { $self = pretrieve(*FILE) }; # Call C routine
324 close(FILE);
325 logcroak $@ if $@ =~ s/\.?\n$/,/;
326 $@ = $da;
327 return $self;
328}
329
330#
9e21b3d0 331# fd_retrieve
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332#
333# Same as retrieve, but perform from an already opened file descriptor instead.
334#
9e21b3d0 335sub fd_retrieve {
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336 my ($file) = @_;
337 my $fd = fileno($file);
338 logcroak "not a valid file descriptor" unless defined $fd;
339 my $self;
340 my $da = $@; # Could be from exception handler
341 eval { $self = pretrieve($file) }; # Call C routine
342 logcroak $@ if $@ =~ s/\.?\n$/,/;
343 $@ = $da;
344 return $self;
345}
346
347#
348# thaw
349#
350# Recreate objects in memory from an existing frozen image created
351# by freeze. If the frozen image passed is undef, return undef.
352#
353sub thaw {
354 my ($frozen) = @_;
355 return undef unless defined $frozen;
356 my $self;
357 my $da = $@; # Could be from exception handler
358 eval { $self = mretrieve($frozen) }; # Call C routine
359 logcroak $@ if $@ =~ s/\.?\n$/,/;
360 $@ = $da;
361 return $self;
362}
363
364=head1 NAME
365
f062ea6c 366Storable - persistence for Perl data structures
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367
368=head1 SYNOPSIS
369
370 use Storable;
371 store \%table, 'file';
372 $hashref = retrieve('file');
373
374 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
375
376 # Network order
377 nstore \%table, 'file';
378 $hashref = retrieve('file'); # There is NO nretrieve()
379
380 # Storing to and retrieving from an already opened file
381 store_fd \@array, \*STDOUT;
382 nstore_fd \%table, \*STDOUT;
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383 $aryref = fd_retrieve(\*SOCKET);
384 $hashref = fd_retrieve(\*SOCKET);
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385
386 # Serializing to memory
387 $serialized = freeze \%table;
388 %table_clone = %{ thaw($serialized) };
389
390 # Deep (recursive) cloning
391 $cloneref = dclone($ref);
392
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393 # Advisory locking
394 use Storable qw(lock_store lock_nstore lock_retrieve)
395 lock_store \%table, 'file';
396 lock_nstore \%table, 'file';
397 $hashref = lock_retrieve('file');
398
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399=head1 DESCRIPTION
400
f062ea6c 401The Storable package brings persistence to your Perl data structures
7a6a85bf 402containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
c261f00e 403conveniently stored to disk and retrieved at a later time.
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404
405It can be used in the regular procedural way by calling C<store> with
406a reference to the object to be stored, along with the file name where
407the image should be written.
775ecd75 408
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409The routine returns C<undef> for I/O problems or other internal error,
410a true value otherwise. Serious errors are propagated as a C<die> exception.
411
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412To retrieve data stored to disk, use C<retrieve> with a file name.
413The objects stored into that file are recreated into memory for you,
414and a I<reference> to the root object is returned. In case an I/O error
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415occurs while reading, C<undef> is returned instead. Other serious
416errors are propagated via C<die>.
417
418Since storage is performed recursively, you might want to stuff references
419to objects that share a lot of common data into a single array or hash
420table, and then store that object. That way, when you retrieve back the
421whole thing, the objects will continue to share what they originally shared.
422
423At the cost of a slight header overhead, you may store to an already
424opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 425from a file via C<fd_retrieve>. Those names aren't imported by default,
c261f00e 426so you will have to do that explicitly if you need those routines.
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427The file descriptor you supply must be already opened, for read
428if you're going to retrieve and for write if you wish to store.
429
430 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 431 $hashref = fd_retrieve(*STDIN);
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432
433You can also store data in network order to allow easy sharing across
434multiple platforms, or when storing on a socket known to be remotely
435connected. The routines to call have an initial C<n> prefix for I<network>,
436as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
437correctly restored so you don't have to know whether you're restoring
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438from native or network ordered data. Double values are stored stringified
439to ensure portability as well, at the slight risk of loosing some precision
440in the last decimals.
7a6a85bf 441
9e21b3d0 442When using C<fd_retrieve>, objects are retrieved in sequence, one
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443object (i.e. one recursive tree) per associated C<store_fd>.
444
445If you're more from the object-oriented camp, you can inherit from
446Storable and directly store your objects by invoking C<store> as
447a method. The fact that the root of the to-be-stored tree is a
448blessed reference (i.e. an object) is special-cased so that the
449retrieve does not provide a reference to that object but rather the
450blessed object reference itself. (Otherwise, you'd get a reference
451to that blessed object).
452
453=head1 MEMORY STORE
454
455The Storable engine can also store data into a Perl scalar instead, to
456later retrieve them. This is mainly used to freeze a complex structure in
457some safe compact memory place (where it can possibly be sent to another
458process via some IPC, since freezing the structure also serializes it in
459effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
460out and recreate the original complex structure in memory.
461
462Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
463If you wish to send out the frozen scalar to another machine, use
464C<nfreeze> instead to get a portable image.
465
466Note that freezing an object structure and immediately thawing it
467actually achieves a deep cloning of that structure:
468
469 dclone(.) = thaw(freeze(.))
470
471Storable provides you with a C<dclone> interface which does not create
472that intermediary scalar but instead freezes the structure in some
c261f00e 473internal memory space and then immediately thaws it out.
7a6a85bf 474
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475=head1 ADVISORY LOCKING
476
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477The C<lock_store> and C<lock_nstore> routine are equivalent to
478C<store> and C<nstore>, except that they get an exclusive lock on
479the file before writing. Likewise, C<lock_retrieve> does the same
480as C<retrieve>, but also gets a shared lock on the file before reading.
dd19458b 481
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482As with any advisory locking scheme, the protection only works if you
483systematically use C<lock_store> and C<lock_retrieve>. If one side of
484your application uses C<store> whilst the other uses C<lock_retrieve>,
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485you will get no protection at all.
486
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487The internal advisory locking is implemented using Perl's flock()
488routine. If your system does not support any form of flock(), or if
489you share your files across NFS, you might wish to use other forms
490of locking by using modules such as LockFile::Simple which lock a
491file using a filesystem entry, instead of locking the file descriptor.
dd19458b 492
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493=head1 SPEED
494
495The heart of Storable is written in C for decent speed. Extra low-level
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496optimizations have been made when manipulating perl internals, to
497sacrifice encapsulation for the benefit of greater speed.
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498
499=head1 CANONICAL REPRESENTATION
500
f062ea6c 501Normally, Storable stores elements of hashes in the order they are
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502stored internally by Perl, i.e. pseudo-randomly. If you set
503C<$Storable::canonical> to some C<TRUE> value, Storable will store
504hashes with the elements sorted by their key. This allows you to
505compare data structures by comparing their frozen representations (or
506even the compressed frozen representations), which can be useful for
507creating lookup tables for complicated queries.
508
f062ea6c 509Canonical order does not imply network order; those are two orthogonal
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510settings.
511
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512=head1 FORWARD COMPATIBILITY
513
514This release of Storable can be used on a newer version of Perl to
f062ea6c 515serialize data which is not supported by earlier Perls. By default,
c261f00e 516Storable will attempt to do the right thing, by C<croak()>ing if it
775ecd75 517encounters data that it cannot deserialize. However, the defaults
f062ea6c 518can be changed as follows:
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519
520=over 4
521
522=item utf8 data
523
524Perl 5.6 added support for Unicode characters with code points > 255,
525and Perl 5.8 has full support for Unicode characters in hash keys.
526Perl internally encodes strings with these characters using utf8, and
527Storable serializes them as utf8. By default, if an older version of
528Perl encounters a utf8 value it cannot represent, it will C<croak()>.
529To change this behaviour so that Storable deserializes utf8 encoded
530values as the string of bytes (effectively dropping the I<is_utf8> flag)
531set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
532data loss, because with C<$drop_utf8> true, it becomes impossible to tell
533whether the original data was the Unicode string, or a series of bytes
534that happen to be valid utf8.
535
536=item restricted hashes
537
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538Perl 5.8 adds support for restricted hashes, which have keys
539restricted to a given set, and can have values locked to be read only.
540By default, when Storable encounters a restricted hash on a perl
541that doesn't support them, it will deserialize it as a normal hash,
542silently discarding any placeholder keys and leaving the keys and
543all values unlocked. To make Storable C<croak()> instead, set
544C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
545the default set it back to some C<TRUE> value.
c261f00e 546
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547=item files from future versions of Storable
548
549Earlier versions of Storable would immediately croak if they encountered
550a file with a higher internal version number than the reading Storable
551knew about. Internal version numbers are increased each time new data
552types (such as restricted hashes) are added to the vocabulary of the file
553format. This meant that a newer Storable module had no way of writing a
f062ea6c 554file readable by an older Storable, even if the writer didn't store newer
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555data types.
556
557This version of Storable will defer croaking until it encounters a data
558type in the file that it does not recognize. This means that it will
559continue to read files generated by newer Storable modules which are careful
560in what they write out, making it easier to upgrade Storable modules in a
561mixed environment.
562
563The old behaviour of immediate croaking can be re-instated by setting
f062ea6c 564C<$Storable::accept_future_minor> to some C<FALSE> value.
e8189732 565
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566=back
567
f062ea6c 568All these variables have no effect on a newer Perl which supports the
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569relevant feature.
570
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571=head1 ERROR REPORTING
572
573Storable uses the "exception" paradigm, in that it does not try to workaround
574failures: if something bad happens, an exception is generated from the
575caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
576those exceptions.
577
578When Storable croaks, it tries to report the error via the C<logcroak()>
579routine from the C<Log::Agent> package, if it is available.
580
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581Normal errors are reported by having store() or retrieve() return C<undef>.
582Such errors are usually I/O errors (or truncated stream errors at retrieval).
583
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584=head1 WIZARDS ONLY
585
586=head2 Hooks
587
588Any class may define hooks that will be called during the serialization
589and deserialization process on objects that are instances of that class.
590Those hooks can redefine the way serialization is performed (and therefore,
c261f00e 591how the symmetrical deserialization should be conducted).
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592
593Since we said earlier:
594
595 dclone(.) = thaw(freeze(.))
596
597everything we say about hooks should also hold for deep cloning. However,
598hooks get to know whether the operation is a mere serialization, or a cloning.
599
600Therefore, when serializing hooks are involved,
601
602 dclone(.) <> thaw(freeze(.))
603
604Well, you could keep them in sync, but there's no guarantee it will always
605hold on classes somebody else wrote. Besides, there is little to gain in
f062ea6c 606doing so: a serializing hook could keep only one attribute of an object,
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607which is probably not what should happen during a deep cloning of that
608same object.
609
610Here is the hooking interface:
611
bbc7dcd2 612=over 4
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613
614=item C<STORABLE_freeze> I<obj>, I<cloning>
615
616The serializing hook, called on the object during serialization. It can be
617inherited, or defined in the class itself, like any other method.
618
619Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
620whether we're in a dclone() or a regular serialization via store() or freeze().
621
622Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
623is the serialized form to be used, and the optional $ref1, $ref2, etc... are
624extra references that you wish to let the Storable engine serialize.
625
626At deserialization time, you will be given back the same LIST, but all the
627extra references will be pointing into the deserialized structure.
628
629The B<first time> the hook is hit in a serialization flow, you may have it
630return an empty list. That will signal the Storable engine to further
631discard that hook for this class and to therefore revert to the default
632serialization of the underlying Perl data. The hook will again be normally
633processed in the next serialization.
634
635Unless you know better, serializing hook should always say:
636
637 sub STORABLE_freeze {
638 my ($self, $cloning) = @_;
639 return if $cloning; # Regular default serialization
640 ....
641 }
642
643in order to keep reasonable dclone() semantics.
644
645=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
646
647The deserializing hook called on the object during deserialization.
f062ea6c 648But wait: if we're deserializing, there's no object yet... right?
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649
650Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
651you can view C<STORABLE_thaw> as an alternate creation routine.
652
653This means the hook can be inherited like any other method, and that
654I<obj> is your blessed reference for this particular instance.
655
656The other arguments should look familiar if you know C<STORABLE_freeze>:
657I<cloning> is true when we're part of a deep clone operation, I<serialized>
658is the serialized string you returned to the engine in C<STORABLE_freeze>,
659and there may be an optional list of references, in the same order you gave
660them at serialization time, pointing to the deserialized objects (which
661have been processed courtesy of the Storable engine).
662
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663When the Storable engine does not find any C<STORABLE_thaw> hook routine,
664it tries to load the class by requiring the package dynamically (using
665the blessed package name), and then re-attempts the lookup. If at that
666time the hook cannot be located, the engine croaks. Note that this mechanism
c261f00e 667will fail if you define several classes in the same file, but L<perlmod>
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668warned you.
669
f062ea6c 670It is up to you to use this information to populate I<obj> the way you want.
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671
672Returned value: none.
673
674=back
675
676=head2 Predicates
677
c261f00e 678Predicates are not exportable. They must be called by explicitly prefixing
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679them with the Storable package name.
680
bbc7dcd2 681=over 4
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682
683=item C<Storable::last_op_in_netorder>
684
685The C<Storable::last_op_in_netorder()> predicate will tell you whether
686network order was used in the last store or retrieve operation. If you
687don't know how to use this, just forget about it.
688
689=item C<Storable::is_storing>
690
691Returns true if within a store operation (via STORABLE_freeze hook).
692
693=item C<Storable::is_retrieving>
694
f062ea6c 695Returns true if within a retrieve operation (via STORABLE_thaw hook).
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696
697=back
698
699=head2 Recursion
700
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701With hooks comes the ability to recurse back to the Storable engine.
702Indeed, hooks are regular Perl code, and Storable is convenient when
703it comes to serializing and deserializing things, so why not use it
704to handle the serialization string?
7a6a85bf 705
f062ea6c 706There are a few things you need to know, however:
7a6a85bf 707
bbc7dcd2 708=over 4
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709
710=item *
711
712You can create endless loops if the things you serialize via freeze()
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713(for instance) point back to the object we're trying to serialize in
714the hook.
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715
716=item *
717
718Shared references among objects will not stay shared: if we're serializing
719the list of object [A, C] where both object A and C refer to the SAME object
720B, and if there is a serializing hook in A that says freeze(B), then when
721deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
722a deep clone of B'. The topology was not preserved.
723
724=back
725
726That's why C<STORABLE_freeze> lets you provide a list of references
727to serialize. The engine guarantees that those will be serialized in the
728same context as the other objects, and therefore that shared objects will
729stay shared.
730
731In the above [A, C] example, the C<STORABLE_freeze> hook could return:
732
733 ("something", $self->{B})
734
735and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
736would get back the reference to the B' object, deserialized for you.
737
738Therefore, recursion should normally be avoided, but is nonetheless supported.
739
740=head2 Deep Cloning
741
f062ea6c 742There is a Clone module available on CPAN which implements deep cloning
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743natively, i.e. without freezing to memory and thawing the result. It is
744aimed to replace Storable's dclone() some day. However, it does not currently
745support Storable hooks to redefine the way deep cloning is performed.
746
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747=head1 Storable magic
748
749Yes, there's a lot of that :-) But more precisely, in UNIX systems
750there's a utility called C<file>, which recognizes data files based on
751their contents (usually their first few bytes). For this to work,
8b793558 752a certain file called F<magic> needs to taught about the I<signature>
0a0da639 753of the data. Where that configuration file lives depends on the UNIX
f062ea6c 754flavour; often it's something like F</usr/share/misc/magic> or
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755F</etc/magic>. Your system administrator needs to do the updating of
756the F<magic> file. The necessary signature information is output to
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757STDOUT by invoking Storable::show_file_magic(). Note that the GNU
758implementation of the C<file> utility, version 3.38 or later,
759is expected to contain support for recognising Storable files
760out-of-the-box, in addition to other kinds of Perl files.
0a0da639 761
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762=head1 EXAMPLES
763
764Here are some code samples showing a possible usage of Storable:
765
766 use Storable qw(store retrieve freeze thaw dclone);
767
768 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
769
770 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
771
772 $colref = retrieve('/tmp/colors');
773 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
774 printf "Blue is still %lf\n", $colref->{'Blue'};
775
776 $colref2 = dclone(\%color);
777
778 $str = freeze(\%color);
779 printf "Serialization of %%color is %d bytes long.\n", length($str);
780 $colref3 = thaw($str);
781
782which prints (on my machine):
783
784 Blue is still 0.100000
785 Serialization of %color is 102 bytes long.
786
787=head1 WARNING
788
789If you're using references as keys within your hash tables, you're bound
f062ea6c 790to be disappointed when retrieving your data. Indeed, Perl stringifies
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791references used as hash table keys. If you later wish to access the
792items via another reference stringification (i.e. using the same
793reference that was used for the key originally to record the value into
794the hash table), it will work because both references stringify to the
795same string.
796
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797It won't work across a sequence of C<store> and C<retrieve> operations,
798however, because the addresses in the retrieved objects, which are
799part of the stringified references, will probably differ from the
800original addresses. The topology of your structure is preserved,
801but not hidden semantics like those.
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802
803On platforms where it matters, be sure to call C<binmode()> on the
804descriptors that you pass to Storable functions.
805
806Storing data canonically that contains large hashes can be
807significantly slower than storing the same data normally, as
c261f00e 808temporary arrays to hold the keys for each hash have to be allocated,
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809populated, sorted and freed. Some tests have shown a halving of the
810speed of storing -- the exact penalty will depend on the complexity of
811your data. There is no slowdown on retrieval.
812
813=head1 BUGS
814
f062ea6c 815You can't store GLOB, CODE, FORMLINE, etc.... If you can define
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816semantics for those operations, feel free to enhance Storable so that
817it can deal with them.
818
819The store functions will C<croak> if they run into such references
820unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
821case, the fatal message is turned in a warning and some
822meaningless string is stored instead.
823
824Setting C<$Storable::canonical> may not yield frozen strings that
825compare equal due to possible stringification of numbers. When the
f062ea6c 826string version of a scalar exists, it is the form stored; therefore,
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827if you happen to use your numbers as strings between two freezing
828operations on the same data structures, you will get different
829results.
830
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831When storing doubles in network order, their value is stored as text.
832However, you should also not expect non-numeric floating-point values
833such as infinity and "not a number" to pass successfully through a
834nstore()/retrieve() pair.
835
836As Storable neither knows nor cares about character sets (although it
837does know that characters may be more than eight bits wide), any difference
838in the interpretation of character codes between a host and a target
839system is your problem. In particular, if host and target use different
840code points to represent the characters used in the text representation
841of floating-point numbers, you will not be able be able to exchange
842floating-point data, even with nstore().
843
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844C<Storable::drop_utf8> is a blunt tool. There is no facility either to
845return B<all> strings as utf8 sequences, or to attempt to convert utf8
846data back to 8 bit and C<croak()> if the conversion fails.
847
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848Prior to Storable 2.01, no distinction was made between signed and
849unsigned integers on storing. By default Storable prefers to store a
850scalars string representation (if it has one) so this would only cause
851problems when storing large unsigned integers that had never been coverted
852to string or floating point. In other words values that had been generated
853by integer operations such as logic ops and then not used in any string or
854arithmetic context before storing.
855
856=head2 64 bit data in perl 5.6.0 and 5.6.1
857
858This section only applies to you if you have existing data written out
859by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
860has been configured with 64 bit integer support (not the default)
861If you got a precompiled perl, rather than running Configure to build
862your own perl from source, then it almost certainly does not affect you,
863and you can stop reading now (unless you're curious). If you're using perl
864on Windows it does not affect you.
865
866Storable writes a file header which contains the sizes of various C
867language types for the C compiler that built Storable (when not writing in
868network order), and will refuse to load files written by a Storable not
869on the same (or compatible) architecture. This check and a check on
870machine byteorder is needed because the size of various fields in the file
871are given by the sizes of the C language types, and so files written on
872different architectures are incompatible. This is done for increased speed.
873(When writing in network order, all fields are written out as standard
874lengths, which allows full interworking, but takes longer to read and write)
875
876Perl 5.6.x introduced the ability to optional configure the perl interpreter
877to use C's C<long long> type to allow scalars to store 64 bit integers on 32
878bit systems. However, due to the way the Perl configuration system
879generated the C configuration files on non-Windows platforms, and the way
880Storable generates its header, nothing in the Storable file header reflected
881whether the perl writing was using 32 or 64 bit integers, despite the fact
882that Storable was storing some data differently in the file. Hence Storable
883running on perl with 64 bit integers will read the header from a file
884written by a 32 bit perl, not realise that the data is actually in a subtly
885incompatible format, and then go horribly wrong (possibly crashing) if it
886encountered a stored integer. This is a design failure.
887
888Storable has now been changed to write out and read in a file header with
889information about the size of integers. It's impossible to detect whether
890an old file being read in was written with 32 or 64 bit integers (they have
891the same header) so it's impossible to automatically switch to a correct
892backwards compatibility mode. Hence this Storable defaults to the new,
893correct behaviour.
894
895What this means is that if you have data written by Storable 1.x running
896on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
897then by default this Storable will refuse to read it, giving the error
898I<Byte order is not compatible>. If you have such data then you you
899should set C<$Storable::interwork_56_64bit> to a true value to make this
900Storable read and write files with the old header. You should also
901migrate your data, or any older perl you are communicating with, to this
902current version of Storable.
903
904If you don't have data written with specific configuration of perl described
905above, then you do not and should not do anything. Don't set the flag -
906not only will Storable on an identically configured perl refuse to load them,
907but Storable a differently configured perl will load them believing them
908to be correct for it, and then may well fail or crash part way through
909reading them.
910
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911=head1 CREDITS
912
913Thank you to (in chronological order):
914
915 Jarkko Hietaniemi <jhi@iki.fi>
916 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
917 Benjamin A. Holzman <bah@ecnvantage.com>
918 Andrew Ford <A.Ford@ford-mason.co.uk>
919 Gisle Aas <gisle@aas.no>
920 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
921 Murray Nesbitt <murray@activestate.com>
922 Marc Lehmann <pcg@opengroup.org>
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923 Justin Banks <justinb@wamnet.com>
924 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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925 Salvador Ortiz Garcia <sog@msg.com.mx>
926 Dominic Dunlop <domo@computer.org>
927 Erik Haugan <erik@solbors.no>
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928
929for their bug reports, suggestions and contributions.
930
931Benjamin Holzman contributed the tied variable support, Andrew Ford
932contributed the canonical order for hashes, and Gisle Aas fixed
f062ea6c 933a few misunderstandings of mine regarding the perl internals,
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934and optimized the emission of "tags" in the output streams by
935simply counting the objects instead of tagging them (leading to
936a binary incompatibility for the Storable image starting at version
f062ea6c 9370.6--older images are, of course, still properly understood).
7a6a85bf 938Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
f062ea6c 939and references to tied items support.
7a6a85bf 940
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941=head1 AUTHOR
942
0ba8809e 943Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
775ecd75 944Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
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945
946Please e-mail us with problems, bug fixes, comments and complaints,
947although if you have complements you should send them to Raphael.
948Please don't e-mail Raphael with problems, as he no longer works on
949Storable, and your message will be delayed while he forwards it to us.
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950
951=head1 SEE ALSO
952
c261f00e 953L<Clone>.
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954
955=cut