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# 7 8require DynaLoader; 9require Exporter; 10package Storable; @ISA = qw(Exporter DynaLoader); 11 12@EXPORT = qw(store retrieve); 13@EXPORT_OK = qw( 14 nstore store_fd nstore_fd fd_retrieve 15 freeze nfreeze thaw 16 dclone 17 retrieve_fd 18 lock_store lock_nstore lock_retrieve 19); 20 21use AutoLoader; 22use vars qw($canonical $forgive_me $VERSION); 23 24$VERSION = '2.12'; 25*AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr... 26 27# 28# Use of Log::Agent is optional 29# 30 31eval "use Log::Agent"; 32 33require Carp; 34 35# 36# They might miss :flock in Fcntl 37# 38 39BEGIN { 40 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) { 41 Fcntl->import(':flock'); 42 } else { 43 eval q{ 44 sub LOCK_SH () {1} 45 sub LOCK_EX () {2} 46 }; 47 } 48} 49 50sub CLONE { 51 # clone context under threads 52 Storable::init_perinterp(); 53} 54 55# Can't Autoload cleanly as this clashes 8.3 with &retrieve 56sub retrieve_fd { &fd_retrieve } # Backward compatibility 57 58# By default restricted hashes are downgraded on earlier perls. 59 60$Storable::downgrade_restricted = 1; 61$Storable::accept_future_minor = 1; 62bootstrap Storable; 631; 64__END__ 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} 77 78# 79# Determine whether locking is possible, but only when needed. 80# 81 82sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK { 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 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. 97# 980 string perl-store perl Storable(v0.6) data 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 1040 string pst0 perl Storable(v0.7) data 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) 110EOM 111} 112 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} 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 { 157 return _store(\&pstore, @_, 0); 158} 159 160# 161# nstore 162# 163# Same as store, but in network order. 164# 165sub nstore { 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); 185} 186 187# Internal store to file routine 188sub _store { 189 my $xsptr = shift; 190 my $self = shift; 191 my ($file, $use_locking) = @_; 192 logcroak "not a reference" unless ref($self); 193 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist 194 local *FILE; 195 if ($use_locking) { 196 open(FILE, ">>$file") || logcroak "can't write into $file: $!"; 197 unless (&CAN_FLOCK) { 198 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; 199 return undef; 200 } 201 flock(FILE, LOCK_EX) || 202 logcroak "can't get exclusive lock on $file: $!"; 203 truncate FILE, 0; 204 # Unlocking will happen when FILE is closed 205 } else { 206 open(FILE, ">$file") || logcroak "can't create $file: $!"; 207 } 208 binmode FILE; # Archaic systems... 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 $@ =~ s/\.?\n$/,/; 254 local $\; print $file ''; # Autoflush the file if wanted 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 ? $ret : undef; 291} 292 293# 294# retrieve 295# 296# Retrieve object hierarchy from disk, returning a reference to the root 297# object of that tree. 298# 299sub retrieve { 300 _retrieve($_[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) = @_; 315 local *FILE; 316 open(FILE, $file) || logcroak "can't open $file: $!"; 317 binmode FILE; # Archaic systems... 318 my $self; 319 my $da = $@; # Could be from exception handler 320 if ($use_locking) { 321 unless (&CAN_FLOCK) { 322 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O"; 323 return undef; 324 } 325 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!"; 326 # Unlocking will happen when FILE is closed 327 } 328 eval { $self = pretrieve(*FILE) }; # Call C routine 329 close(FILE); 330 logcroak $@ if $@ =~ s/\.?\n$/,/; 331 $@ = $da; 332 return $self; 333} 334 335# 336# fd_retrieve 337# 338# Same as retrieve, but perform from an already opened file descriptor instead. 339# 340sub fd_retrieve { 341 my ($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 3691; 370__END__ 371 372=head1 NAME 373 374Storable - persistence for Perl data structures 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; 391 $aryref = fd_retrieve(\*SOCKET); 392 $hashref = fd_retrieve(\*SOCKET); 393 394 # Serializing to memory 395 $serialized = freeze \%table; 396 %table_clone = %{ thaw($serialized) }; 397 398 # Deep (recursive) cloning 399 $cloneref = dclone($ref); 400 401 # 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'); 406 407=head1 DESCRIPTION 408 409The Storable package brings persistence to your Perl data structures 410containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be 411conveniently stored to disk and retrieved at a later time. 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. 416 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 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 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 433from a file via C<fd_retrieve>. Those names aren't imported by default, 434so you will have to do that explicitly if you need those routines. 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"; 439 $hashref = fd_retrieve(*STDIN); 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 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. 449 450When using C<fd_retrieve>, objects are retrieved in sequence, one 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 481internal memory space and then immediately thaws it out. 482 483=head1 ADVISORY LOCKING 484 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. 489 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>, 493you will get no protection at all. 494 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. 500 501=head1 SPEED 502 503The heart of Storable is written in C for decent speed. Extra low-level 504optimizations have been made when manipulating perl internals, to 505sacrifice encapsulation for the benefit of greater speed. 506 507=head1 CANONICAL REPRESENTATION 508 509Normally, Storable stores elements of hashes in the order they are 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 517Canonical order does not imply network order; those are two orthogonal 518settings. 519 520=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<$Storable::Eval> 528to a subroutine reference which would be used instead of C<eval>. See 529below for an example using a L<Safe> compartment for deserialization 530of CODE references. 531 532If C<$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. 535 536=head1 FORWARD COMPATIBILITY 537 538This release of Storable can be used on a newer version of Perl to 539serialize data which is not supported by earlier Perls. By default, 540Storable will attempt to do the right thing, by C<croak()>ing if it 541encounters data that it cannot deserialize. However, the defaults 542can be changed as follows: 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 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<$Storable::downgrade_restricted> to a C<FALSE> value. To restore 569the default set it back to some C<TRUE> value. 570 571=item files from future versions of Storable 572 573Earlier versions of Storable would immediately croak if they encountered 574a file with a higher internal version number than the reading Storable 575knew about. Internal version numbers are increased each time new data 576types (such as restricted hashes) are added to the vocabulary of the file 577format. This meant that a newer Storable module had no way of writing a 578file readable by an older Storable, even if the writer didn't store newer 579data types. 580 581This version of Storable will defer croaking until it encounters a data 582type in the file that it does not recognize. This means that it will 583continue to read files generated by newer Storable modules which are careful 584in what they write out, making it easier to upgrade Storable modules in a 585mixed environment. 586 587The old behaviour of immediate croaking can be re-instated by setting 588C<$Storable::accept_future_minor> to some C<FALSE> value. 589 590=back 591 592All these variables have no effect on a newer Perl which supports the 593relevant feature. 594 595=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 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). 607 608=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, 615how the symmetrical deserialization should be conducted). 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 630doing so: a serializing hook could keep only one attribute of an object, 631which is probably not what should happen during a deep cloning of that 632same object. 633 634Here is the hooking interface: 635 636=over 4 637 638=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. 672But wait: if we're deserializing, there's no object yet... right? 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 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 691will fail if you define several classes in the same file, but L<perlmod> 692warned you. 693 694It is up to you to use this information to populate I<obj> the way you want. 695 696Returned value: none. 697 698=back 699 700=head2 Predicates 701 702Predicates are not exportable. They must be called by explicitly prefixing 703them with the Storable package name. 704 705=over 4 706 707=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 719Returns true if within a retrieve operation (via STORABLE_thaw hook). 720 721=back 722 723=head2 Recursion 724 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? 729 730There are a few things you need to know, however: 731 732=over 4 733 734=item * 735 736You can create endless loops if the things you serialize via freeze() 737(for instance) point back to the object we're trying to serialize in 738the hook. 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 766There is a Clone module available on CPAN which implements deep cloning 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. 770 771=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, 776a certain file called F<magic> needs to taught about the I<signature> 777of the data. Where that configuration file lives depends on the UNIX 778flavour; often it's something like F</usr/share/misc/magic> or 779F</etc/magic>. Your system administrator needs to do the updating of 780the F<magic> file. The necessary signature information is output to 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. 785 786=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); 793 794 store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n"; 795 796 $colref = retrieve('mycolors'); 797 die "Unable to retrieve from mycolors!\n" unless defined $colref; 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 811Serialization of CODE references and deserialization in a safe 812compartment: 813 814=for example begin 815 816 use Storable qw(freeze thaw); 817 use Safe; 818 use strict; 819 my $safe = new Safe; 820 # because of opcodes used in "use strict": 821 $safe->permit(qw(:default require)); 822 local $Storable::Deparse = 1; 823 local $Storable::Eval = sub { $safe->reval($_[0]) }; 824 my $serialized = freeze(sub { 42 }); 825 my $code = thaw($serialized); 826 $code->() == 42; 827 828=for example end 829 830=for example_testing 831 is( $code->(), 42 ); 832 833=head1 WARNING 834 835If you're using references as keys within your hash tables, you're bound 836to be disappointed when retrieving your data. Indeed, Perl stringifies 837references used as hash table keys. If you later wish to access the 838items via another reference stringification (i.e. using the same 839reference that was used for the key originally to record the value into 840the hash table), it will work because both references stringify to the 841same string. 842 843It won't work across a sequence of C<store> and C<retrieve> operations, 844however, because the addresses in the retrieved objects, which are 845part of the stringified references, will probably differ from the 846original addresses. The topology of your structure is preserved, 847but not hidden semantics like those. 848 849On platforms where it matters, be sure to call C<binmode()> on the 850descriptors that you pass to Storable functions. 851 852Storing data canonically that contains large hashes can be 853significantly slower than storing the same data normally, as 854temporary arrays to hold the keys for each hash have to be allocated, 855populated, sorted and freed. Some tests have shown a halving of the 856speed of storing -- the exact penalty will depend on the complexity of 857your data. There is no slowdown on retrieval. 858 859=head1 BUGS 860 861You can't store GLOB, FORMLINE, etc.... If you can define semantics 862for those operations, feel free to enhance Storable so that it can 863deal with them. 864 865The store functions will C<croak> if they run into such references 866unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that 867case, the fatal message is turned in a warning and some 868meaningless string is stored instead. 869 870Setting C<$Storable::canonical> may not yield frozen strings that 871compare equal due to possible stringification of numbers. When the 872string version of a scalar exists, it is the form stored; therefore, 873if you happen to use your numbers as strings between two freezing 874operations on the same data structures, you will get different 875results. 876 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 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 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. 956 957=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> 969 Justin Banks <justinb@wamnet.com> 970 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!) 971 Salvador Ortiz Garcia <sog@msg.com.mx> 972 Dominic Dunlop <domo@computer.org> 973 Erik Haugan <erik@solbors.no> 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 979a few misunderstandings of mine regarding the perl internals, 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 9830.6--older images are, of course, still properly understood). 984Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading 985and references to tied items support. 986 987=head1 AUTHOR 988 989Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>> 990Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>> 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. 996 997=head1 SEE ALSO 998 999L<Clone>. 1000 1001=cut 1002