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Refactoring to Sv*_set() macros - patch #5
[perl5.git] / ext / Storable / Storable.pm
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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 $VERSION);
7a6a85bf 23
b162af07 24$VERSION = '2.15';
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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 $Fcntl::EXPORT_TAGS{'flock'}) {
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41 Fcntl->import(':flock');
42 } else {
43 eval q{
44 sub LOCK_SH () {1}
45 sub LOCK_EX () {2}
46 };
47 }
48}
49
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50sub CLONE {
51 # clone context under threads
52 Storable::init_perinterp();
53}
54
b8778c7c 55# Can't Autoload cleanly as this clashes 8.3 with &retrieve
9e21b3d0 56sub retrieve_fd { &fd_retrieve } # Backward compatibility
cb3d9de5 57
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58# By default restricted hashes are downgraded on earlier perls.
59
60$Storable::downgrade_restricted = 1;
e8189732 61$Storable::accept_future_minor = 1;
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62bootstrap Storable;
631;
64__END__
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65#
66# Use of Log::Agent is optional. If it hasn't imported these subs then
67# Autoloader will kindly supply our fallback implementation.
68#
69
70sub logcroak {
71 Carp::croak(@_);
72}
73
74sub logcarp {
75 Carp::carp(@_);
76}
b8778c7c 77
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78#
79# Determine whether locking is possible, but only when needed.
80#
81
530b72ba 82sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
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83 return $CAN_FLOCK if defined $CAN_FLOCK;
84 require Config; import Config;
85 return $CAN_FLOCK =
86 $Config{'d_flock'} ||
87 $Config{'d_fcntl_can_lock'} ||
88 $Config{'d_lockf'};
89}
90
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91sub show_file_magic {
92 print <<EOM;
93#
94# To recognize the data files of the Perl module Storable,
95# the following lines need to be added to the local magic(5) file,
96# usually either /usr/share/misc/magic or /etc/magic.
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97#
980 string perl-store perl Storable(v0.6) data
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99>4 byte >0 (net-order %d)
100>>4 byte &01 (network-ordered)
101>>4 byte =3 (major 1)
102>>4 byte =2 (major 1)
103
0a0da639 1040 string pst0 perl Storable(v0.7) data
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105>4 byte >0
106>>4 byte &01 (network-ordered)
107>>4 byte =5 (major 2)
108>>4 byte =4 (major 2)
109>>5 byte >0 (minor %d)
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110EOM
111}
112
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113sub read_magic {
114 my $header = shift;
115 return unless defined $header and length $header > 11;
116 my $result;
117 if ($header =~ s/^perl-store//) {
118 die "Can't deal with version 0 headers";
119 } elsif ($header =~ s/^pst0//) {
120 $result->{file} = 1;
121 }
122 # Assume it's a string.
123 my ($major, $minor, $bytelen) = unpack "C3", $header;
124
125 my $net_order = $major & 1;
126 $major >>= 1;
127 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
128
129 return $result if $net_order;
130
131 # I assume that it is rare to find v1 files, so this is an intentionally
132 # inefficient way of doing it, to make the rest of the code constant.
133 if ($major < 2) {
134 delete $result->{minor};
135 $header = '.' . $header;
136 $bytelen = $minor;
137 }
138
139 @$result{qw(byteorder intsize longsize ptrsize)} =
140 unpack "x3 A$bytelen C3", $header;
141
142 if ($major >= 2 and $minor >= 2) {
143 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
144 }
145 $result;
146}
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147
148#
149# store
150#
151# Store target object hierarchy, identified by a reference to its root.
152# The stored object tree may later be retrieved to memory via retrieve.
153# Returns undef if an I/O error occurred, in which case the file is
154# removed.
155#
156sub store {
dd19458b 157 return _store(\&pstore, @_, 0);
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158}
159
160#
161# nstore
162#
163# Same as store, but in network order.
164#
165sub nstore {
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166 return _store(\&net_pstore, @_, 0);
167}
168
169#
170# lock_store
171#
172# Same as store, but flock the file first (advisory locking).
173#
174sub lock_store {
175 return _store(\&pstore, @_, 1);
176}
177
178#
179# lock_nstore
180#
181# Same as nstore, but flock the file first (advisory locking).
182#
183sub lock_nstore {
184 return _store(\&net_pstore, @_, 1);
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185}
186
187# Internal store to file routine
188sub _store {
189 my $xsptr = shift;
190 my $self = shift;
dd19458b 191 my ($file, $use_locking) = @_;
7a6a85bf 192 logcroak "not a reference" unless ref($self);
b12202d0 193 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
7a6a85bf 194 local *FILE;
dd19458b 195 if ($use_locking) {
6e0ac6f5 196 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
862382c7 197 unless (&CAN_FLOCK) {
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198 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
199 return undef;
f567092b 200 }
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201 flock(FILE, LOCK_EX) ||
202 logcroak "can't get exclusive lock on $file: $!";
203 truncate FILE, 0;
204 # Unlocking will happen when FILE is closed
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205 } else {
206 open(FILE, ">$file") || logcroak "can't create $file: $!";
dd19458b 207 }
6e0ac6f5 208 binmode FILE; # Archaic systems...
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209 my $da = $@; # Don't mess if called from exception handler
210 my $ret;
211 # Call C routine nstore or pstore, depending on network order
212 eval { $ret = &$xsptr(*FILE, $self) };
213 close(FILE) or $ret = undef;
214 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
215 logcroak $@ if $@ =~ s/\.?\n$/,/;
216 $@ = $da;
217 return $ret ? $ret : undef;
218}
219
220#
221# store_fd
222#
223# Same as store, but perform on an already opened file descriptor instead.
224# Returns undef if an I/O error occurred.
225#
226sub store_fd {
227 return _store_fd(\&pstore, @_);
228}
229
230#
231# nstore_fd
232#
233# Same as store_fd, but in network order.
234#
235sub nstore_fd {
236 my ($self, $file) = @_;
237 return _store_fd(\&net_pstore, @_);
238}
239
240# Internal store routine on opened file descriptor
241sub _store_fd {
242 my $xsptr = shift;
243 my $self = shift;
244 my ($file) = @_;
245 logcroak "not a reference" unless ref($self);
246 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
247 my $fd = fileno($file);
248 logcroak "not a valid file descriptor" unless defined $fd;
249 my $da = $@; # Don't mess if called from exception handler
250 my $ret;
251 # Call C routine nstore or pstore, depending on network order
252 eval { $ret = &$xsptr($file, $self) };
253 logcroak $@ if $@ =~ s/\.?\n$/,/;
596596d5 254 local $\; print $file ''; # Autoflush the file if wanted
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255 $@ = $da;
256 return $ret ? $ret : undef;
257}
258
259#
260# freeze
261#
262# Store oject and its hierarchy in memory and return a scalar
263# containing the result.
264#
265sub freeze {
266 _freeze(\&mstore, @_);
267}
268
269#
270# nfreeze
271#
272# Same as freeze but in network order.
273#
274sub nfreeze {
275 _freeze(\&net_mstore, @_);
276}
277
278# Internal freeze routine
279sub _freeze {
280 my $xsptr = shift;
281 my $self = shift;
282 logcroak "not a reference" unless ref($self);
283 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
284 my $da = $@; # Don't mess if called from exception handler
285 my $ret;
286 # Call C routine mstore or net_mstore, depending on network order
287 eval { $ret = &$xsptr($self) };
288 logcroak $@ if $@ =~ s/\.?\n$/,/;
289 $@ = $da;
290 return $ret ? $ret : undef;
291}
292
293#
294# retrieve
295#
296# Retrieve object hierarchy from disk, returning a reference to the root
297# object of that tree.
298#
299sub retrieve {
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300 _retrieve($_[0], 0);
301}
302
303#
304# lock_retrieve
305#
306# Same as retrieve, but with advisory locking.
307#
308sub lock_retrieve {
309 _retrieve($_[0], 1);
310}
311
312# Internal retrieve routine
313sub _retrieve {
314 my ($file, $use_locking) = @_;
7a6a85bf 315 local *FILE;
dd19458b 316 open(FILE, $file) || logcroak "can't open $file: $!";
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317 binmode FILE; # Archaic systems...
318 my $self;
319 my $da = $@; # Could be from exception handler
dd19458b 320 if ($use_locking) {
862382c7 321 unless (&CAN_FLOCK) {
8be2b38b 322 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
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323 return undef;
324 }
8be2b38b 325 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
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326 # Unlocking will happen when FILE is closed
327 }
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328 eval { $self = pretrieve(*FILE) }; # Call C routine
329 close(FILE);
330 logcroak $@ if $@ =~ s/\.?\n$/,/;
331 $@ = $da;
332 return $self;
333}
334
335#
9e21b3d0 336# fd_retrieve
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337#
338# Same as retrieve, but perform from an already opened file descriptor instead.
339#
9e21b3d0 340sub fd_retrieve {
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341 my ($file) = @_;
342 my $fd = fileno($file);
343 logcroak "not a valid file descriptor" unless defined $fd;
344 my $self;
345 my $da = $@; # Could be from exception handler
346 eval { $self = pretrieve($file) }; # Call C routine
347 logcroak $@ if $@ =~ s/\.?\n$/,/;
348 $@ = $da;
349 return $self;
350}
351
352#
353# thaw
354#
355# Recreate objects in memory from an existing frozen image created
356# by freeze. If the frozen image passed is undef, return undef.
357#
358sub thaw {
359 my ($frozen) = @_;
360 return undef unless defined $frozen;
361 my $self;
362 my $da = $@; # Could be from exception handler
363 eval { $self = mretrieve($frozen) }; # Call C routine
364 logcroak $@ if $@ =~ s/\.?\n$/,/;
365 $@ = $da;
366 return $self;
367}
368
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3691;
370__END__
371
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372=head1 NAME
373
f062ea6c 374Storable - persistence for Perl data structures
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375
376=head1 SYNOPSIS
377
378 use Storable;
379 store \%table, 'file';
380 $hashref = retrieve('file');
381
382 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
383
384 # Network order
385 nstore \%table, 'file';
386 $hashref = retrieve('file'); # There is NO nretrieve()
387
388 # Storing to and retrieving from an already opened file
389 store_fd \@array, \*STDOUT;
390 nstore_fd \%table, \*STDOUT;
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391 $aryref = fd_retrieve(\*SOCKET);
392 $hashref = fd_retrieve(\*SOCKET);
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393
394 # Serializing to memory
395 $serialized = freeze \%table;
396 %table_clone = %{ thaw($serialized) };
397
398 # Deep (recursive) cloning
399 $cloneref = dclone($ref);
400
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401 # Advisory locking
402 use Storable qw(lock_store lock_nstore lock_retrieve)
403 lock_store \%table, 'file';
404 lock_nstore \%table, 'file';
405 $hashref = lock_retrieve('file');
406
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407=head1 DESCRIPTION
408
f062ea6c 409The Storable package brings persistence to your Perl data structures
7a6a85bf 410containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
c261f00e 411conveniently stored to disk and retrieved at a later time.
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412
413It can be used in the regular procedural way by calling C<store> with
414a reference to the object to be stored, along with the file name where
415the image should be written.
775ecd75 416
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417The routine returns C<undef> for I/O problems or other internal error,
418a true value otherwise. Serious errors are propagated as a C<die> exception.
419
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420To retrieve data stored to disk, use C<retrieve> with a file name.
421The objects stored into that file are recreated into memory for you,
422and a I<reference> to the root object is returned. In case an I/O error
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423occurs while reading, C<undef> is returned instead. Other serious
424errors are propagated via C<die>.
425
426Since storage is performed recursively, you might want to stuff references
427to objects that share a lot of common data into a single array or hash
428table, and then store that object. That way, when you retrieve back the
429whole thing, the objects will continue to share what they originally shared.
430
431At the cost of a slight header overhead, you may store to an already
432opened file descriptor using the C<store_fd> routine, and retrieve
9e21b3d0 433from a file via C<fd_retrieve>. Those names aren't imported by default,
c261f00e 434so you will have to do that explicitly if you need those routines.
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435The file descriptor you supply must be already opened, for read
436if you're going to retrieve and for write if you wish to store.
437
438 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
9e21b3d0 439 $hashref = fd_retrieve(*STDIN);
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440
441You can also store data in network order to allow easy sharing across
442multiple platforms, or when storing on a socket known to be remotely
443connected. The routines to call have an initial C<n> prefix for I<network>,
444as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
445correctly restored so you don't have to know whether you're restoring
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446from native or network ordered data. Double values are stored stringified
447to ensure portability as well, at the slight risk of loosing some precision
448in the last decimals.
7a6a85bf 449
9e21b3d0 450When using C<fd_retrieve>, objects are retrieved in sequence, one
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451object (i.e. one recursive tree) per associated C<store_fd>.
452
453If you're more from the object-oriented camp, you can inherit from
454Storable and directly store your objects by invoking C<store> as
455a method. The fact that the root of the to-be-stored tree is a
456blessed reference (i.e. an object) is special-cased so that the
457retrieve does not provide a reference to that object but rather the
458blessed object reference itself. (Otherwise, you'd get a reference
459to that blessed object).
460
461=head1 MEMORY STORE
462
463The Storable engine can also store data into a Perl scalar instead, to
464later retrieve them. This is mainly used to freeze a complex structure in
465some safe compact memory place (where it can possibly be sent to another
466process via some IPC, since freezing the structure also serializes it in
467effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
468out and recreate the original complex structure in memory.
469
470Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
471If you wish to send out the frozen scalar to another machine, use
472C<nfreeze> instead to get a portable image.
473
474Note that freezing an object structure and immediately thawing it
475actually achieves a deep cloning of that structure:
476
477 dclone(.) = thaw(freeze(.))
478
479Storable provides you with a C<dclone> interface which does not create
480that intermediary scalar but instead freezes the structure in some
c261f00e 481internal memory space and then immediately thaws it out.
7a6a85bf 482
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483=head1 ADVISORY LOCKING
484
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485The C<lock_store> and C<lock_nstore> routine are equivalent to
486C<store> and C<nstore>, except that they get an exclusive lock on
487the file before writing. Likewise, C<lock_retrieve> does the same
488as C<retrieve>, but also gets a shared lock on the file before reading.
dd19458b 489
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490As with any advisory locking scheme, the protection only works if you
491systematically use C<lock_store> and C<lock_retrieve>. If one side of
492your application uses C<store> whilst the other uses C<lock_retrieve>,
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493you will get no protection at all.
494
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495The internal advisory locking is implemented using Perl's flock()
496routine. If your system does not support any form of flock(), or if
497you share your files across NFS, you might wish to use other forms
498of locking by using modules such as LockFile::Simple which lock a
499file using a filesystem entry, instead of locking the file descriptor.
dd19458b 500
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501=head1 SPEED
502
503The heart of Storable is written in C for decent speed. Extra low-level
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504optimizations have been made when manipulating perl internals, to
505sacrifice encapsulation for the benefit of greater speed.
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506
507=head1 CANONICAL REPRESENTATION
508
f062ea6c 509Normally, Storable stores elements of hashes in the order they are
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510stored internally by Perl, i.e. pseudo-randomly. If you set
511C<$Storable::canonical> to some C<TRUE> value, Storable will store
512hashes with the elements sorted by their key. This allows you to
513compare data structures by comparing their frozen representations (or
514even the compressed frozen representations), which can be useful for
515creating lookup tables for complicated queries.
516
f062ea6c 517Canonical order does not imply network order; those are two orthogonal
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518settings.
519
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520=head1 CODE REFERENCES
521
522Since Storable version 2.05, CODE references may be serialized with
523the help of L<B::Deparse>. To enable this feature, set
524C<$Storable::Deparse> to a true value. To enable deserializazion,
525C<$Storable::Eval> should be set to a true value. Be aware that
526deserialization is done through C<eval>, which is dangerous if the
527Storable file contains malicious data. You can set C<$Storable::Eval>
528to a subroutine reference which would be used instead of C<eval>. See
529below for an example using a L<Safe> compartment for deserialization
530of CODE references.
531
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532If C<$Storable::Deparse> and/or C<$Storable::Eval> are set to false
533values, then the value of C<$Storable::forgive_me> (see below) is
534respected while serializing and deserializing.
535
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536=head1 FORWARD COMPATIBILITY
537
538This release of Storable can be used on a newer version of Perl to
f062ea6c 539serialize data which is not supported by earlier Perls. By default,
c261f00e 540Storable will attempt to do the right thing, by C<croak()>ing if it
775ecd75 541encounters data that it cannot deserialize. However, the defaults
f062ea6c 542can be changed as follows:
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543
544=over 4
545
546=item utf8 data
547
548Perl 5.6 added support for Unicode characters with code points > 255,
549and Perl 5.8 has full support for Unicode characters in hash keys.
550Perl internally encodes strings with these characters using utf8, and
551Storable serializes them as utf8. By default, if an older version of
552Perl encounters a utf8 value it cannot represent, it will C<croak()>.
553To change this behaviour so that Storable deserializes utf8 encoded
554values as the string of bytes (effectively dropping the I<is_utf8> flag)
555set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
556data loss, because with C<$drop_utf8> true, it becomes impossible to tell
557whether the original data was the Unicode string, or a series of bytes
558that happen to be valid utf8.
559
560=item restricted hashes
561
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562Perl 5.8 adds support for restricted hashes, which have keys
563restricted to a given set, and can have values locked to be read only.
564By default, when Storable encounters a restricted hash on a perl
565that doesn't support them, it will deserialize it as a normal hash,
566silently discarding any placeholder keys and leaving the keys and
567all values unlocked. To make Storable C<croak()> instead, set
568C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
569the default set it back to some C<TRUE> value.
c261f00e 570
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571=item files from future versions of Storable
572
573Earlier versions of Storable would immediately croak if they encountered
574a file with a higher internal version number than the reading Storable
575knew about. Internal version numbers are increased each time new data
576types (such as restricted hashes) are added to the vocabulary of the file
577format. This meant that a newer Storable module had no way of writing a
f062ea6c 578file readable by an older Storable, even if the writer didn't store newer
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579data types.
580
581This version of Storable will defer croaking until it encounters a data
582type in the file that it does not recognize. This means that it will
583continue to read files generated by newer Storable modules which are careful
584in what they write out, making it easier to upgrade Storable modules in a
585mixed environment.
586
587The old behaviour of immediate croaking can be re-instated by setting
f062ea6c 588C<$Storable::accept_future_minor> to some C<FALSE> value.
e8189732 589
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590=back
591
f062ea6c 592All these variables have no effect on a newer Perl which supports the
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593relevant feature.
594
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595=head1 ERROR REPORTING
596
597Storable uses the "exception" paradigm, in that it does not try to workaround
598failures: if something bad happens, an exception is generated from the
599caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
600those exceptions.
601
602When Storable croaks, it tries to report the error via the C<logcroak()>
603routine from the C<Log::Agent> package, if it is available.
604
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605Normal errors are reported by having store() or retrieve() return C<undef>.
606Such errors are usually I/O errors (or truncated stream errors at retrieval).
607
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608=head1 WIZARDS ONLY
609
610=head2 Hooks
611
612Any class may define hooks that will be called during the serialization
613and deserialization process on objects that are instances of that class.
614Those hooks can redefine the way serialization is performed (and therefore,
c261f00e 615how the symmetrical deserialization should be conducted).
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616
617Since we said earlier:
618
619 dclone(.) = thaw(freeze(.))
620
621everything we say about hooks should also hold for deep cloning. However,
622hooks get to know whether the operation is a mere serialization, or a cloning.
623
624Therefore, when serializing hooks are involved,
625
626 dclone(.) <> thaw(freeze(.))
627
628Well, you could keep them in sync, but there's no guarantee it will always
629hold on classes somebody else wrote. Besides, there is little to gain in
f062ea6c 630doing so: a serializing hook could keep only one attribute of an object,
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631which is probably not what should happen during a deep cloning of that
632same object.
633
634Here is the hooking interface:
635
bbc7dcd2 636=over 4
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637
638=item C<STORABLE_freeze> I<obj>, I<cloning>
639
640The serializing hook, called on the object during serialization. It can be
641inherited, or defined in the class itself, like any other method.
642
643Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
644whether we're in a dclone() or a regular serialization via store() or freeze().
645
646Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
647is the serialized form to be used, and the optional $ref1, $ref2, etc... are
648extra references that you wish to let the Storable engine serialize.
649
650At deserialization time, you will be given back the same LIST, but all the
651extra references will be pointing into the deserialized structure.
652
653The B<first time> the hook is hit in a serialization flow, you may have it
654return an empty list. That will signal the Storable engine to further
655discard that hook for this class and to therefore revert to the default
656serialization of the underlying Perl data. The hook will again be normally
657processed in the next serialization.
658
659Unless you know better, serializing hook should always say:
660
661 sub STORABLE_freeze {
662 my ($self, $cloning) = @_;
663 return if $cloning; # Regular default serialization
664 ....
665 }
666
667in order to keep reasonable dclone() semantics.
668
669=item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
670
671The deserializing hook called on the object during deserialization.
f062ea6c 672But wait: if we're deserializing, there's no object yet... right?
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673
674Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
675you can view C<STORABLE_thaw> as an alternate creation routine.
676
677This means the hook can be inherited like any other method, and that
678I<obj> is your blessed reference for this particular instance.
679
680The other arguments should look familiar if you know C<STORABLE_freeze>:
681I<cloning> is true when we're part of a deep clone operation, I<serialized>
682is the serialized string you returned to the engine in C<STORABLE_freeze>,
683and there may be an optional list of references, in the same order you gave
684them at serialization time, pointing to the deserialized objects (which
685have been processed courtesy of the Storable engine).
686
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687When the Storable engine does not find any C<STORABLE_thaw> hook routine,
688it tries to load the class by requiring the package dynamically (using
689the blessed package name), and then re-attempts the lookup. If at that
690time the hook cannot be located, the engine croaks. Note that this mechanism
c261f00e 691will fail if you define several classes in the same file, but L<perlmod>
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692warned you.
693
f062ea6c 694It is up to you to use this information to populate I<obj> the way you want.
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695
696Returned value: none.
697
698=back
699
700=head2 Predicates
701
c261f00e 702Predicates are not exportable. They must be called by explicitly prefixing
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703them with the Storable package name.
704
bbc7dcd2 705=over 4
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706
707=item C<Storable::last_op_in_netorder>
708
709The C<Storable::last_op_in_netorder()> predicate will tell you whether
710network order was used in the last store or retrieve operation. If you
711don't know how to use this, just forget about it.
712
713=item C<Storable::is_storing>
714
715Returns true if within a store operation (via STORABLE_freeze hook).
716
717=item C<Storable::is_retrieving>
718
f062ea6c 719Returns true if within a retrieve operation (via STORABLE_thaw hook).
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720
721=back
722
723=head2 Recursion
724
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725With hooks comes the ability to recurse back to the Storable engine.
726Indeed, hooks are regular Perl code, and Storable is convenient when
727it comes to serializing and deserializing things, so why not use it
728to handle the serialization string?
7a6a85bf 729
f062ea6c 730There are a few things you need to know, however:
7a6a85bf 731
bbc7dcd2 732=over 4
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733
734=item *
735
736You can create endless loops if the things you serialize via freeze()
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737(for instance) point back to the object we're trying to serialize in
738the hook.
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739
740=item *
741
742Shared references among objects will not stay shared: if we're serializing
743the list of object [A, C] where both object A and C refer to the SAME object
744B, and if there is a serializing hook in A that says freeze(B), then when
745deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
746a deep clone of B'. The topology was not preserved.
747
748=back
749
750That's why C<STORABLE_freeze> lets you provide a list of references
751to serialize. The engine guarantees that those will be serialized in the
752same context as the other objects, and therefore that shared objects will
753stay shared.
754
755In the above [A, C] example, the C<STORABLE_freeze> hook could return:
756
757 ("something", $self->{B})
758
759and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
760would get back the reference to the B' object, deserialized for you.
761
762Therefore, recursion should normally be avoided, but is nonetheless supported.
763
764=head2 Deep Cloning
765
f062ea6c 766There is a Clone module available on CPAN which implements deep cloning
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767natively, i.e. without freezing to memory and thawing the result. It is
768aimed to replace Storable's dclone() some day. However, it does not currently
769support Storable hooks to redefine the way deep cloning is performed.
770
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771=head1 Storable magic
772
773Yes, there's a lot of that :-) But more precisely, in UNIX systems
774there's a utility called C<file>, which recognizes data files based on
775their contents (usually their first few bytes). For this to work,
8b793558 776a certain file called F<magic> needs to taught about the I<signature>
0a0da639 777of the data. Where that configuration file lives depends on the UNIX
f062ea6c 778flavour; often it's something like F</usr/share/misc/magic> or
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779F</etc/magic>. Your system administrator needs to do the updating of
780the F<magic> file. The necessary signature information is output to
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781STDOUT by invoking Storable::show_file_magic(). Note that the GNU
782implementation of the C<file> utility, version 3.38 or later,
783is expected to contain support for recognising Storable files
784out-of-the-box, in addition to other kinds of Perl files.
0a0da639 785
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786=head1 EXAMPLES
787
788Here are some code samples showing a possible usage of Storable:
789
790 use Storable qw(store retrieve freeze thaw dclone);
791
792 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
793
2359510d 794 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
7a6a85bf 795
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796 $colref = retrieve('mycolors');
797 die "Unable to retrieve from mycolors!\n" unless defined $colref;
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798 printf "Blue is still %lf\n", $colref->{'Blue'};
799
800 $colref2 = dclone(\%color);
801
802 $str = freeze(\%color);
803 printf "Serialization of %%color is %d bytes long.\n", length($str);
804 $colref3 = thaw($str);
805
806which prints (on my machine):
807
808 Blue is still 0.100000
809 Serialization of %color is 102 bytes long.
810
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811Serialization of CODE references and deserialization in a safe
812compartment:
813
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814=for example begin
815
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816 use Storable qw(freeze thaw);
817 use Safe;
818 use strict;
819 my $safe = new Safe;
197b90bc 820 # because of opcodes used in "use strict":
d1e2299c 821 $safe->permit(qw(:default require));
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822 local $Storable::Deparse = 1;
823 local $Storable::Eval = sub { $safe->reval($_[0]) };
197b90bc 824 my $serialized = freeze(sub { 42 });
d2b96869 825 my $code = thaw($serialized);
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826 $code->() == 42;
827
828=for example end
829
830=for example_testing
831 is( $code->(), 42 );
d2b96869 832
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833=head1 WARNING
834
835If you're using references as keys within your hash tables, you're bound
f062ea6c 836to be disappointed 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
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843It won't work across a sequence of C<store> and C<retrieve> operations,
844however, because the addresses in the retrieved objects, which are
845part of the stringified references, will probably differ from the
846original addresses. The topology of your structure is preserved,
847but not hidden semantics like those.
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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
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861You can't store GLOB, FORMLINE, etc.... If you can define semantics
862for those operations, feel free to enhance Storable so that it can
863deal with them.
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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
f062ea6c 872string version of a scalar exists, it is the form stored; therefore,
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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
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894Prior to Storable 2.01, no distinction was made between signed and
895unsigned integers on storing. By default Storable prefers to store a
896scalars string representation (if it has one) so this would only cause
897problems when storing large unsigned integers that had never been coverted
898to string or floating point. In other words values that had been generated
899by integer operations such as logic ops and then not used in any string or
900arithmetic context before storing.
901
902=head2 64 bit data in perl 5.6.0 and 5.6.1
903
904This section only applies to you if you have existing data written out
905by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
906has been configured with 64 bit integer support (not the default)
907If you got a precompiled perl, rather than running Configure to build
908your own perl from source, then it almost certainly does not affect you,
909and you can stop reading now (unless you're curious). If you're using perl
910on Windows it does not affect you.
911
912Storable writes a file header which contains the sizes of various C
913language types for the C compiler that built Storable (when not writing in
914network order), and will refuse to load files written by a Storable not
915on the same (or compatible) architecture. This check and a check on
916machine byteorder is needed because the size of various fields in the file
917are given by the sizes of the C language types, and so files written on
918different architectures are incompatible. This is done for increased speed.
919(When writing in network order, all fields are written out as standard
920lengths, which allows full interworking, but takes longer to read and write)
921
922Perl 5.6.x introduced the ability to optional configure the perl interpreter
923to use C's C<long long> type to allow scalars to store 64 bit integers on 32
924bit systems. However, due to the way the Perl configuration system
925generated the C configuration files on non-Windows platforms, and the way
926Storable generates its header, nothing in the Storable file header reflected
927whether the perl writing was using 32 or 64 bit integers, despite the fact
928that Storable was storing some data differently in the file. Hence Storable
929running on perl with 64 bit integers will read the header from a file
930written by a 32 bit perl, not realise that the data is actually in a subtly
931incompatible format, and then go horribly wrong (possibly crashing) if it
932encountered a stored integer. This is a design failure.
933
934Storable has now been changed to write out and read in a file header with
935information about the size of integers. It's impossible to detect whether
936an old file being read in was written with 32 or 64 bit integers (they have
937the same header) so it's impossible to automatically switch to a correct
938backwards compatibility mode. Hence this Storable defaults to the new,
939correct behaviour.
940
941What this means is that if you have data written by Storable 1.x running
942on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
943then by default this Storable will refuse to read it, giving the error
944I<Byte order is not compatible>. If you have such data then you you
945should set C<$Storable::interwork_56_64bit> to a true value to make this
946Storable read and write files with the old header. You should also
947migrate your data, or any older perl you are communicating with, to this
948current version of Storable.
949
950If you don't have data written with specific configuration of perl described
951above, then you do not and should not do anything. Don't set the flag -
952not only will Storable on an identically configured perl refuse to load them,
953but Storable a differently configured perl will load them believing them
954to be correct for it, and then may well fail or crash part way through
955reading them.
956
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957=head1 CREDITS
958
959Thank you to (in chronological order):
960
961 Jarkko Hietaniemi <jhi@iki.fi>
962 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
963 Benjamin A. Holzman <bah@ecnvantage.com>
964 Andrew Ford <A.Ford@ford-mason.co.uk>
965 Gisle Aas <gisle@aas.no>
966 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
967 Murray Nesbitt <murray@activestate.com>
968 Marc Lehmann <pcg@opengroup.org>
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969 Justin Banks <justinb@wamnet.com>
970 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
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971 Salvador Ortiz Garcia <sog@msg.com.mx>
972 Dominic Dunlop <domo@computer.org>
973 Erik Haugan <erik@solbors.no>
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974
975for their bug reports, suggestions and contributions.
976
977Benjamin Holzman contributed the tied variable support, Andrew Ford
978contributed the canonical order for hashes, and Gisle Aas fixed
f062ea6c 979a few misunderstandings of mine regarding the perl internals,
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980and optimized the emission of "tags" in the output streams by
981simply counting the objects instead of tagging them (leading to
982a binary incompatibility for the Storable image starting at version
f062ea6c 9830.6--older images are, of course, still properly understood).
7a6a85bf 984Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
f062ea6c 985and references to tied items support.
7a6a85bf 986
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987=head1 AUTHOR
988
0ba8809e 989Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
775ecd75 990Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
0ba8809e
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991
992Please e-mail us with problems, bug fixes, comments and complaints,
993although if you have complements you should send them to Raphael.
994Please don't e-mail Raphael with problems, as he no longer works on
995Storable, and your message will be delayed while he forwards it to us.
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996
997=head1 SEE ALSO
998
c261f00e 999L<Clone>.
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1000
1001=cut