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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 $VERSION);
7a6a85bf 23
dcf2e277 24$VERSION = '2.09';
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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
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3641;
365__END__
366
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367=head1 NAME
368
f062ea6c 369Storable - persistence for Perl data structures
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370
371=head1 SYNOPSIS
372
373 use Storable;
374 store \%table, 'file';
375 $hashref = retrieve('file');
376
377 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
378
379 # Network order
380 nstore \%table, 'file';
381 $hashref = retrieve('file'); # There is NO nretrieve()
382
383 # Storing to and retrieving from an already opened file
384 store_fd \@array, \*STDOUT;
385 nstore_fd \%table, \*STDOUT;
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386 $aryref = fd_retrieve(\*SOCKET);
387 $hashref = fd_retrieve(\*SOCKET);
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388
389 # Serializing to memory
390 $serialized = freeze \%table;
391 %table_clone = %{ thaw($serialized) };
392
393 # Deep (recursive) cloning
394 $cloneref = dclone($ref);
395
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396 # Advisory locking
397 use Storable qw(lock_store lock_nstore lock_retrieve)
398 lock_store \%table, 'file';
399 lock_nstore \%table, 'file';
400 $hashref = lock_retrieve('file');
401
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402=head1 DESCRIPTION
403
f062ea6c 404The Storable package brings persistence to your Perl data structures
7a6a85bf 405containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
c261f00e 406conveniently stored to disk and retrieved at a later time.
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407
408It can be used in the regular procedural way by calling C<store> with
409a reference to the object to be stored, along with the file name where
410the image should be written.
775ecd75 411
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412The routine returns C<undef> for I/O problems or other internal error,
413a true value otherwise. Serious errors are propagated as a C<die> exception.
414
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415To retrieve data stored to disk, use C<retrieve> with a file name.
416The objects stored into that file are recreated into memory for you,
417and a I<reference> to the root object is returned. In case an I/O error
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418occurs while reading, C<undef> is returned instead. Other serious
419errors are propagated via C<die>.
420
421Since storage is performed recursively, you might want to stuff references
422to objects that share a lot of common data into a single array or hash
423table, and then store that object. That way, when you retrieve back the
424whole thing, the objects will continue to share what they originally shared.
425
426At the cost of a slight header overhead, you may store to an already
427opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 428from a file via C<fd_retrieve>. Those names aren't imported by default,
c261f00e 429so you will have to do that explicitly if you need those routines.
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430The file descriptor you supply must be already opened, for read
431if you're going to retrieve and for write if you wish to store.
432
433 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 434 $hashref = fd_retrieve(*STDIN);
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435
436You can also store data in network order to allow easy sharing across
437multiple platforms, or when storing on a socket known to be remotely
438connected. The routines to call have an initial C<n> prefix for I<network>,
439as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
440correctly restored so you don't have to know whether you're restoring
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441from native or network ordered data. Double values are stored stringified
442to ensure portability as well, at the slight risk of loosing some precision
443in the last decimals.
7a6a85bf 444
9e21b3d0 445When using C<fd_retrieve>, objects are retrieved in sequence, one
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446object (i.e. one recursive tree) per associated C<store_fd>.
447
448If you're more from the object-oriented camp, you can inherit from
449Storable and directly store your objects by invoking C<store> as
450a method. The fact that the root of the to-be-stored tree is a
451blessed reference (i.e. an object) is special-cased so that the
452retrieve does not provide a reference to that object but rather the
453blessed object reference itself. (Otherwise, you'd get a reference
454to that blessed object).
455
456=head1 MEMORY STORE
457
458The Storable engine can also store data into a Perl scalar instead, to
459later retrieve them. This is mainly used to freeze a complex structure in
460some safe compact memory place (where it can possibly be sent to another
461process via some IPC, since freezing the structure also serializes it in
462effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
463out and recreate the original complex structure in memory.
464
465Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
466If you wish to send out the frozen scalar to another machine, use
467C<nfreeze> instead to get a portable image.
468
469Note that freezing an object structure and immediately thawing it
470actually achieves a deep cloning of that structure:
471
472 dclone(.) = thaw(freeze(.))
473
474Storable provides you with a C<dclone> interface which does not create
475that intermediary scalar but instead freezes the structure in some
c261f00e 476internal memory space and then immediately thaws it out.
7a6a85bf 477
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478=head1 ADVISORY LOCKING
479
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480The C<lock_store> and C<lock_nstore> routine are equivalent to
481C<store> and C<nstore>, except that they get an exclusive lock on
482the file before writing. Likewise, C<lock_retrieve> does the same
483as C<retrieve>, but also gets a shared lock on the file before reading.
dd19458b 484
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485As with any advisory locking scheme, the protection only works if you
486systematically use C<lock_store> and C<lock_retrieve>. If one side of
487your application uses C<store> whilst the other uses C<lock_retrieve>,
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488you will get no protection at all.
489
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490The internal advisory locking is implemented using Perl's flock()
491routine. If your system does not support any form of flock(), or if
492you share your files across NFS, you might wish to use other forms
493of locking by using modules such as LockFile::Simple which lock a
494file using a filesystem entry, instead of locking the file descriptor.
dd19458b 495
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496=head1 SPEED
497
498The heart of Storable is written in C for decent speed. Extra low-level
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499optimizations have been made when manipulating perl internals, to
500sacrifice encapsulation for the benefit of greater speed.
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501
502=head1 CANONICAL REPRESENTATION
503
f062ea6c 504Normally, Storable stores elements of hashes in the order they are
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505stored internally by Perl, i.e. pseudo-randomly. If you set
506C<$Storable::canonical> to some C<TRUE> value, Storable will store
507hashes with the elements sorted by their key. This allows you to
508compare data structures by comparing their frozen representations (or
509even the compressed frozen representations), which can be useful for
510creating lookup tables for complicated queries.
511
f062ea6c 512Canonical order does not imply network order; those are two orthogonal
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513settings.
514
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515=head1 CODE REFERENCES
516
517Since Storable version 2.05, CODE references may be serialized with
518the help of L<B::Deparse>. To enable this feature, set
519C<$Storable::Deparse> to a true value. To enable deserializazion,
520C<$Storable::Eval> should be set to a true value. Be aware that
521deserialization is done through C<eval>, which is dangerous if the
522Storable file contains malicious data. You can set C<$Storable::Eval>
523to a subroutine reference which would be used instead of C<eval>. See
524below for an example using a L<Safe> compartment for deserialization
525of CODE references.
526
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527If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false
528values, then the value of C<$Storable::forgive_me> (see below) is
529respected while serializing and deserializing.
530
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531=head1 FORWARD COMPATIBILITY
532
533This release of Storable can be used on a newer version of Perl to
f062ea6c 534serialize data which is not supported by earlier Perls. By default,
c261f00e 535Storable will attempt to do the right thing, by C<croak()>ing if it
775ecd75 536encounters data that it cannot deserialize. However, the defaults
f062ea6c 537can be changed as follows:
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538
539=over 4
540
541=item utf8 data
542
543Perl 5.6 added support for Unicode characters with code points > 255,
544and Perl 5.8 has full support for Unicode characters in hash keys.
545Perl internally encodes strings with these characters using utf8, and
546Storable serializes them as utf8. By default, if an older version of
547Perl encounters a utf8 value it cannot represent, it will C<croak()>.
548To change this behaviour so that Storable deserializes utf8 encoded
549values as the string of bytes (effectively dropping the I<is_utf8> flag)
550set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
551data loss, because with C<$drop_utf8> true, it becomes impossible to tell
552whether the original data was the Unicode string, or a series of bytes
553that happen to be valid utf8.
554
555=item restricted hashes
556
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557Perl 5.8 adds support for restricted hashes, which have keys
558restricted to a given set, and can have values locked to be read only.
559By default, when Storable encounters a restricted hash on a perl
560that doesn't support them, it will deserialize it as a normal hash,
561silently discarding any placeholder keys and leaving the keys and
562all values unlocked. To make Storable C<croak()> instead, set
563C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
564the default set it back to some C<TRUE> value.
c261f00e 565
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566=item files from future versions of Storable
567
568Earlier versions of Storable would immediately croak if they encountered
569a file with a higher internal version number than the reading Storable
570knew about. Internal version numbers are increased each time new data
571types (such as restricted hashes) are added to the vocabulary of the file
572format. This meant that a newer Storable module had no way of writing a
f062ea6c 573file readable by an older Storable, even if the writer didn't store newer
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574data types.
575
576This version of Storable will defer croaking until it encounters a data
577type in the file that it does not recognize. This means that it will
578continue to read files generated by newer Storable modules which are careful
579in what they write out, making it easier to upgrade Storable modules in a
580mixed environment.
581
582The old behaviour of immediate croaking can be re-instated by setting
f062ea6c 583C<$Storable::accept_future_minor> to some C<FALSE> value.
e8189732 584
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585=back
586
f062ea6c 587All these variables have no effect on a newer Perl which supports the
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588relevant feature.
589
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590=head1 ERROR REPORTING
591
592Storable uses the "exception" paradigm, in that it does not try to workaround
593failures: if something bad happens, an exception is generated from the
594caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
595those exceptions.
596
597When Storable croaks, it tries to report the error via the C<logcroak()>
598routine from the C<Log::Agent> package, if it is available.
599
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600Normal errors are reported by having store() or retrieve() return C<undef>.
601Such errors are usually I/O errors (or truncated stream errors at retrieval).
602
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603=head1 WIZARDS ONLY
604
605=head2 Hooks
606
607Any class may define hooks that will be called during the serialization
608and deserialization process on objects that are instances of that class.
609Those hooks can redefine the way serialization is performed (and therefore,
c261f00e 610how the symmetrical deserialization should be conducted).
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611
612Since we said earlier:
613
614 dclone(.) = thaw(freeze(.))
615
616everything we say about hooks should also hold for deep cloning. However,
617hooks get to know whether the operation is a mere serialization, or a cloning.
618
619Therefore, when serializing hooks are involved,
620
621 dclone(.) <> thaw(freeze(.))
622
623Well, you could keep them in sync, but there's no guarantee it will always
624hold on classes somebody else wrote. Besides, there is little to gain in
f062ea6c 625doing so: a serializing hook could keep only one attribute of an object,
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626which is probably not what should happen during a deep cloning of that
627same object.
628
629Here is the hooking interface:
630
bbc7dcd2 631=over 4
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632
633=item C<STORABLE_freeze> I<obj>, I<cloning>
634
635The serializing hook, called on the object during serialization. It can be
636inherited, or defined in the class itself, like any other method.
637
638Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
639whether we're in a dclone() or a regular serialization via store() or freeze().
640
641Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
642is the serialized form to be used, and the optional $ref1, $ref2, etc... are
643extra references that you wish to let the Storable engine serialize.
644
645At deserialization time, you will be given back the same LIST, but all the
646extra references will be pointing into the deserialized structure.
647
648The B<first time> the hook is hit in a serialization flow, you may have it
649return an empty list. That will signal the Storable engine to further
650discard that hook for this class and to therefore revert to the default
651serialization of the underlying Perl data. The hook will again be normally
652processed in the next serialization.
653
654Unless you know better, serializing hook should always say:
655
656 sub STORABLE_freeze {
657 my ($self, $cloning) = @_;
658 return if $cloning; # Regular default serialization
659 ....
660 }
661
662in order to keep reasonable dclone() semantics.
663
664=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
665
666The deserializing hook called on the object during deserialization.
f062ea6c 667But wait: if we're deserializing, there's no object yet... right?
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668
669Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
670you can view C<STORABLE_thaw> as an alternate creation routine.
671
672This means the hook can be inherited like any other method, and that
673I<obj> is your blessed reference for this particular instance.
674
675The other arguments should look familiar if you know C<STORABLE_freeze>:
676I<cloning> is true when we're part of a deep clone operation, I<serialized>
677is the serialized string you returned to the engine in C<STORABLE_freeze>,
678and there may be an optional list of references, in the same order you gave
679them at serialization time, pointing to the deserialized objects (which
680have been processed courtesy of the Storable engine).
681
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682When the Storable engine does not find any C<STORABLE_thaw> hook routine,
683it tries to load the class by requiring the package dynamically (using
684the blessed package name), and then re-attempts the lookup. If at that
685time the hook cannot be located, the engine croaks. Note that this mechanism
c261f00e 686will fail if you define several classes in the same file, but L<perlmod>
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687warned you.
688
f062ea6c 689It is up to you to use this information to populate I<obj> the way you want.
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690
691Returned value: none.
692
693=back
694
695=head2 Predicates
696
c261f00e 697Predicates are not exportable. They must be called by explicitly prefixing
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698them with the Storable package name.
699
bbc7dcd2 700=over 4
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701
702=item C<Storable::last_op_in_netorder>
703
704The C<Storable::last_op_in_netorder()> predicate will tell you whether
705network order was used in the last store or retrieve operation. If you
706don't know how to use this, just forget about it.
707
708=item C<Storable::is_storing>
709
710Returns true if within a store operation (via STORABLE_freeze hook).
711
712=item C<Storable::is_retrieving>
713
f062ea6c 714Returns true if within a retrieve operation (via STORABLE_thaw hook).
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715
716=back
717
718=head2 Recursion
719
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720With hooks comes the ability to recurse back to the Storable engine.
721Indeed, hooks are regular Perl code, and Storable is convenient when
722it comes to serializing and deserializing things, so why not use it
723to handle the serialization string?
7a6a85bf 724
f062ea6c 725There are a few things you need to know, however:
7a6a85bf 726
bbc7dcd2 727=over 4
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728
729=item *
730
731You can create endless loops if the things you serialize via freeze()
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732(for instance) point back to the object we're trying to serialize in
733the hook.
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734
735=item *
736
737Shared references among objects will not stay shared: if we're serializing
738the list of object [A, C] where both object A and C refer to the SAME object
739B, and if there is a serializing hook in A that says freeze(B), then when
740deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
741a deep clone of B'. The topology was not preserved.
742
743=back
744
745That's why C<STORABLE_freeze> lets you provide a list of references
746to serialize. The engine guarantees that those will be serialized in the
747same context as the other objects, and therefore that shared objects will
748stay shared.
749
750In the above [A, C] example, the C<STORABLE_freeze> hook could return:
751
752 ("something", $self->{B})
753
754and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
755would get back the reference to the B' object, deserialized for you.
756
757Therefore, recursion should normally be avoided, but is nonetheless supported.
758
759=head2 Deep Cloning
760
f062ea6c 761There is a Clone module available on CPAN which implements deep cloning
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762natively, i.e. without freezing to memory and thawing the result. It is
763aimed to replace Storable's dclone() some day. However, it does not currently
764support Storable hooks to redefine the way deep cloning is performed.
765
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766=head1 Storable magic
767
768Yes, there's a lot of that :-) But more precisely, in UNIX systems
769there's a utility called C<file>, which recognizes data files based on
770their contents (usually their first few bytes). For this to work,
8b793558 771a certain file called F<magic> needs to taught about the I<signature>
0a0da639 772of the data. Where that configuration file lives depends on the UNIX
f062ea6c 773flavour; often it's something like F</usr/share/misc/magic> or
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774F</etc/magic>. Your system administrator needs to do the updating of
775the F<magic> file. The necessary signature information is output to
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776STDOUT by invoking Storable::show_file_magic(). Note that the GNU
777implementation of the C<file> utility, version 3.38 or later,
778is expected to contain support for recognising Storable files
779out-of-the-box, in addition to other kinds of Perl files.
0a0da639 780
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781=head1 EXAMPLES
782
783Here are some code samples showing a possible usage of Storable:
784
785 use Storable qw(store retrieve freeze thaw dclone);
786
787 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
788
789 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
790
791 $colref = retrieve('/tmp/colors');
792 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
793 printf "Blue is still %lf\n", $colref->{'Blue'};
794
795 $colref2 = dclone(\%color);
796
797 $str = freeze(\%color);
798 printf "Serialization of %%color is %d bytes long.\n", length($str);
799 $colref3 = thaw($str);
800
801which prints (on my machine):
802
803 Blue is still 0.100000
804 Serialization of %color is 102 bytes long.
805
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806Serialization of CODE references and deserialization in a safe
807compartment:
808
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809=for example begin
810
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811 use Storable qw(freeze thaw);
812 use Safe;
813 use strict;
814 my $safe = new Safe;
197b90bc 815 # because of opcodes used in "use strict":
d1e2299c 816 $safe->permit(qw(:default require));
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817 local $Storable::Deparse = 1;
818 local $Storable::Eval = sub { $safe->reval($_[0]) };
197b90bc 819 my $serialized = freeze(sub { 42 });
d2b96869 820 my $code = thaw($serialized);
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821 $code->() == 42;
822
823=for example end
824
825=for example_testing
826 is( $code->(), 42 );
d2b96869 827
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828=head1 WARNING
829
830If you're using references as keys within your hash tables, you're bound
f062ea6c 831to be disappointed when retrieving your data. Indeed, Perl stringifies
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832references used as hash table keys. If you later wish to access the
833items via another reference stringification (i.e. using the same
834reference that was used for the key originally to record the value into
835the hash table), it will work because both references stringify to the
836same string.
837
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838It won't work across a sequence of C<store> and C<retrieve> operations,
839however, because the addresses in the retrieved objects, which are
840part of the stringified references, will probably differ from the
841original addresses. The topology of your structure is preserved,
842but not hidden semantics like those.
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843
844On platforms where it matters, be sure to call C<binmode()> on the
845descriptors that you pass to Storable functions.
846
847Storing data canonically that contains large hashes can be
848significantly slower than storing the same data normally, as
c261f00e 849temporary arrays to hold the keys for each hash have to be allocated,
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850populated, sorted and freed. Some tests have shown a halving of the
851speed of storing -- the exact penalty will depend on the complexity of
852your data. There is no slowdown on retrieval.
853
854=head1 BUGS
855
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856You can't store GLOB, FORMLINE, etc.... If you can define semantics
857for those operations, feel free to enhance Storable so that it can
858deal with them.
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859
860The store functions will C<croak> if they run into such references
861unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
862case, the fatal message is turned in a warning and some
863meaningless string is stored instead.
864
865Setting C<$Storable::canonical> may not yield frozen strings that
866compare equal due to possible stringification of numbers. When the
f062ea6c 867string version of a scalar exists, it is the form stored; therefore,
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868if you happen to use your numbers as strings between two freezing
869operations on the same data structures, you will get different
870results.
871
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872When storing doubles in network order, their value is stored as text.
873However, you should also not expect non-numeric floating-point values
874such as infinity and "not a number" to pass successfully through a
875nstore()/retrieve() pair.
876
877As Storable neither knows nor cares about character sets (although it
878does know that characters may be more than eight bits wide), any difference
879in the interpretation of character codes between a host and a target
880system is your problem. In particular, if host and target use different
881code points to represent the characters used in the text representation
882of floating-point numbers, you will not be able be able to exchange
883floating-point data, even with nstore().
884
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885C<Storable::drop_utf8> is a blunt tool. There is no facility either to
886return B<all> strings as utf8 sequences, or to attempt to convert utf8
887data back to 8 bit and C<croak()> if the conversion fails.
888
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889Prior to Storable 2.01, no distinction was made between signed and
890unsigned integers on storing. By default Storable prefers to store a
891scalars string representation (if it has one) so this would only cause
892problems when storing large unsigned integers that had never been coverted
893to string or floating point. In other words values that had been generated
894by integer operations such as logic ops and then not used in any string or
895arithmetic context before storing.
896
897=head2 64 bit data in perl 5.6.0 and 5.6.1
898
899This section only applies to you if you have existing data written out
900by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
901has been configured with 64 bit integer support (not the default)
902If you got a precompiled perl, rather than running Configure to build
903your own perl from source, then it almost certainly does not affect you,
904and you can stop reading now (unless you're curious). If you're using perl
905on Windows it does not affect you.
906
907Storable writes a file header which contains the sizes of various C
908language types for the C compiler that built Storable (when not writing in
909network order), and will refuse to load files written by a Storable not
910on the same (or compatible) architecture. This check and a check on
911machine byteorder is needed because the size of various fields in the file
912are given by the sizes of the C language types, and so files written on
913different architectures are incompatible. This is done for increased speed.
914(When writing in network order, all fields are written out as standard
915lengths, which allows full interworking, but takes longer to read and write)
916
917Perl 5.6.x introduced the ability to optional configure the perl interpreter
918to use C's C<long long> type to allow scalars to store 64 bit integers on 32
919bit systems. However, due to the way the Perl configuration system
920generated the C configuration files on non-Windows platforms, and the way
921Storable generates its header, nothing in the Storable file header reflected
922whether the perl writing was using 32 or 64 bit integers, despite the fact
923that Storable was storing some data differently in the file. Hence Storable
924running on perl with 64 bit integers will read the header from a file
925written by a 32 bit perl, not realise that the data is actually in a subtly
926incompatible format, and then go horribly wrong (possibly crashing) if it
927encountered a stored integer. This is a design failure.
928
929Storable has now been changed to write out and read in a file header with
930information about the size of integers. It's impossible to detect whether
931an old file being read in was written with 32 or 64 bit integers (they have
932the same header) so it's impossible to automatically switch to a correct
933backwards compatibility mode. Hence this Storable defaults to the new,
934correct behaviour.
935
936What this means is that if you have data written by Storable 1.x running
937on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
938then by default this Storable will refuse to read it, giving the error
939I<Byte order is not compatible>. If you have such data then you you
940should set C<$Storable::interwork_56_64bit> to a true value to make this
941Storable read and write files with the old header. You should also
942migrate your data, or any older perl you are communicating with, to this
943current version of Storable.
944
945If you don't have data written with specific configuration of perl described
946above, then you do not and should not do anything. Don't set the flag -
947not only will Storable on an identically configured perl refuse to load them,
948but Storable a differently configured perl will load them believing them
949to be correct for it, and then may well fail or crash part way through
950reading them.
951
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952=head1 CREDITS
953
954Thank you to (in chronological order):
955
956 Jarkko Hietaniemi <jhi@iki.fi>
957 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
958 Benjamin A. Holzman <bah@ecnvantage.com>
959 Andrew Ford <A.Ford@ford-mason.co.uk>
960 Gisle Aas <gisle@aas.no>
961 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
962 Murray Nesbitt <murray@activestate.com>
963 Marc Lehmann <pcg@opengroup.org>
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964 Justin Banks <justinb@wamnet.com>
965 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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966 Salvador Ortiz Garcia <sog@msg.com.mx>
967 Dominic Dunlop <domo@computer.org>
968 Erik Haugan <erik@solbors.no>
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969
970for their bug reports, suggestions and contributions.
971
972Benjamin Holzman contributed the tied variable support, Andrew Ford
973contributed the canonical order for hashes, and Gisle Aas fixed
f062ea6c 974a few misunderstandings of mine regarding the perl internals,
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975and optimized the emission of "tags" in the output streams by
976simply counting the objects instead of tagging them (leading to
977a binary incompatibility for the Storable image starting at version
f062ea6c 9780.6--older images are, of course, still properly understood).
7a6a85bf 979Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
f062ea6c 980and references to tied items support.
7a6a85bf 981
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982=head1 AUTHOR
983
0ba8809e 984Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
775ecd75 985Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
0ba8809e
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986
987Please e-mail us with problems, bug fixes, comments and complaints,
988although if you have complements you should send them to Raphael.
989Please don't e-mail Raphael with problems, as he no longer works on
990Storable, and your message will be delayed while he forwards it to us.
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991
992=head1 SEE ALSO
993
c261f00e 994L<Clone>.
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995
996=cut