Storable(3perl) Perl Programmers Reference Guide Storable(3perl)
NAME
Storable - persistence for Perl data structures
SYNOPSIS
use Storable;
store \%table, 'file';
$hashref = retrieve('file');
use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
# Network order
nstore \%table, 'file';
$hashref = retrieve('file'); # There is NO nretrieve()
# Storing to and retrieving from an already opened file
store_fd \@array, \*STDOUT;
nstore_fd \%table, \*STDOUT;
$aryref = fd_retrieve(\*SOCKET);
$hashref = fd_retrieve(\*SOCKET);
# Serializing to memory
$serialized = freeze \%table;
%table_clone = %{ thaw($serialized) };
# Deep (recursive) cloning
$cloneref = dclone($ref);
# Advisory locking
use Storable qw(lock_store lock_nstore lock_retrieve)
lock_store \%table, 'file';
lock_nstore \%table, 'file';
$hashref = lock_retrieve('file');
DESCRIPTION
The Storable package brings persistence to your Perl data structures
containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
conveniently stored to disk and retrieved at a later time.
It can be used in the regular procedural way by calling "store" with a
reference to the object to be stored, along with the file name where the
image should be written.
The routine returns "undef" for I/O problems or other internal error, a
true value otherwise. Serious errors are propagated as a "die"
exception.
To retrieve data stored to disk, use "retrieve" with a file name. The
objects stored into that file are recreated into memory for you, and a
reference to the root object is returned. In case an I/O error occurs
while reading, "undef" is returned instead. Other serious errors are
propagated via "die".
Since storage is performed recursively, you might want to stuff
references to objects that share a lot of common data into a single
array or hash table, and then store that object. That way, when you
retrieve back the whole thing, the objects will continue to share what
they originally shared.
At the cost of a slight header overhead, you may store to an already
opened file descriptor using the "store_fd" routine, and retrieve from a
file via "fd_retrieve". Those names aren't imported by default, so you
will have to do that explicitly if you need those routines. The file
descriptor you supply must be already opened, for read if you're going
to retrieve and for write if you wish to store.
store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
$hashref = fd_retrieve(*STDIN);
You can also store data in network order to allow easy sharing across
multiple platforms, or when storing on a socket known to be remotely
connected. The routines to call have an initial "n" prefix for network,
as in "nstore" and "nstore_fd". At retrieval time, your data will be
correctly restored so you don't have to know whether you're restoring
from native or network ordered data. Double values are stored
stringified to ensure portability as well, at the slight risk of loosing
some precision in the last decimals.
When using "fd_retrieve", objects are retrieved in sequence, one object
(i.e. one recursive tree) per associated "store_fd".
If you're more from the object-oriented camp, you can inherit from
Storable and directly store your objects by invoking "store" as a
method. The fact that the root of the to-be-stored tree is a blessed
reference (i.e. an object) is special-cased so that the retrieve does
not provide a reference to that object but rather the blessed object
reference itself. (Otherwise, you'd get a reference to that blessed
object).
MEMORY STORE
The Storable engine can also store data into a Perl scalar instead, to
later retrieve them. This is mainly used to freeze a complex structure
in some safe compact memory place (where it can possibly be sent to
another process via some IPC, since freezing the structure also
serializes it in effect). Later on, and maybe somewhere else, you can
thaw the Perl scalar out and recreate the original complex structure in
memory.
Surprisingly, the routines to be called are named "freeze" and "thaw".
If you wish to send out the frozen scalar to another machine, use
"nfreeze" instead to get a portable image.
Note that freezing an object structure and immediately thawing it
actually achieves a deep cloning of that structure:
dclone(.) = thaw(freeze(.))
Storable provides you with a "dclone" interface which does not create
that intermediary scalar but instead freezes the structure in some
internal memory space and then immediately thaws it out.
ADVISORY LOCKING
The "lock_store" and "lock_nstore" routine are equivalent to "store" and
"nstore", except that they get an exclusive lock on the file before
writing. Likewise, "lock_retrieve" does the same as "retrieve", but
also gets a shared lock on the file before reading.
As with any advisory locking scheme, the protection only works if you
systematically use "lock_store" and "lock_retrieve". If one side of
your application uses "store" whilst the other uses "lock_retrieve", you
will get no protection at all.
The internal advisory locking is implemented using Perl's flock()
routine. If your system does not support any form of flock(), or if you
share your files across NFS, you might wish to use other forms of
locking by using modules such as LockFile::Simple which lock a file
using a filesystem entry, instead of locking the file descriptor.
SPEED
The heart of Storable is written in C for decent speed. Extra low-level
optimizations have been made when manipulating perl internals, to
sacrifice encapsulation for the benefit of greater speed.
CANONICAL REPRESENTATION
Normally, Storable stores elements of hashes in the order they are
stored internally by Perl, i.e. pseudo-randomly. If you set
$Storable::canonical to some "TRUE" value, Storable will store hashes
with the elements sorted by their key. This allows you to compare data
structures by comparing their frozen representations (or even the
compressed frozen representations), which can be useful for creating
lookup tables for complicated queries.
Canonical order does not imply network order; those are two orthogonal
settings.
CODE REFERENCES
Since Storable version 2.05, CODE references may be serialized with the
help of B::Deparse. To enable this feature, set $Storable::Deparse to a
true value. To enable deserialization, $Storable::Eval should be set to
a true value. Be aware that deserialization is done through "eval",
which is dangerous if the Storable file contains malicious data. You can
set $Storable::Eval to a subroutine reference which would be used
instead of "eval". See below for an example using a Safe compartment for
deserialization of CODE references.
If $Storable::Deparse and/or $Storable::Eval are set to false values,
then the value of $Storable::forgive_me (see below) is respected while
serializing and deserializing.
FORWARD COMPATIBILITY
This release of Storable can be used on a newer version of Perl to
serialize data which is not supported by earlier Perls. By default,
Storable will attempt to do the right thing, by croak()ing if it
encounters data that it cannot deserialize. However, the defaults can
be changed as follows:
utf8 data
Perl 5.6 added support for Unicode characters with code points >
255, and Perl 5.8 has full support for Unicode characters in hash
keys. Perl internally encodes strings with these characters using
utf8, and Storable serializes them as utf8. By default, if an older
version of Perl encounters a utf8 value it cannot represent, it will
croak(). To change this behaviour so that Storable deserializes
utf8 encoded values as the string of bytes (effectively dropping the
is_utf8 flag) set $Storable::drop_utf8 to some "TRUE" value. This
is a form of data loss, because with $drop_utf8 true, it becomes
impossible to tell whether the original data was the Unicode string,
or a series of bytes that happen to be valid utf8.
restricted hashes
Perl 5.8 adds support for restricted hashes, which have keys
restricted to a given set, and can have values locked to be read
only. By default, when Storable encounters a restricted hash on a
perl that doesn't support them, it will deserialize it as a normal
hash, silently discarding any placeholder keys and leaving the keys
and all values unlocked. To make Storable croak() instead, set
$Storable::downgrade_restricted to a "FALSE" value. To restore the
default set it back to some "TRUE" value.
The cperl PERL_PERTURB_KEYS_TOP hash strategy has a known problem
with restricted hashes.
huge objects
On 64bit systems some data structures may exceed the 2G (i.e.
I32_MAX) limit. On 32bit systems also strings between I32 and U32
(2G-4G). Since Storable 3.00 (not in perl5 core) we are able to
store and retrieve these objects, even if perl5 itself is not able
to handle them. These are strings longer then 4G, arrays with more
then 2G elements and hashes with more then 2G elements. cperl
forbids hashes with more than 2G elements, but this fail in cperl
then. perl5 itself at least until 5.26 allows it, but cannot iterate
over them. Note that creating those objects might cause out of
memory exceptions by the operating system before perl has a chance
to abort.
files from future versions of Storable
Earlier versions of Storable would immediately croak if they
encountered a file with a higher internal version number than the
reading Storable knew about. Internal version numbers are increased
each time new data types (such as restricted hashes) are added to
the vocabulary of the file format. This meant that a newer Storable
module had no way of writing a file readable by an older Storable,
even if the writer didn't store newer data types.
This version of Storable will defer croaking until it encounters a
data type in the file that it does not recognize. This means that
it will continue to read files generated by newer Storable modules
which are careful in what they write out, making it easier to
upgrade Storable modules in a mixed environment.
The old behaviour of immediate croaking can be re-instated by
setting $Storable::accept_future_minor to some "FALSE" value.
All these variables have no effect on a newer Perl which supports the
relevant feature.
ERROR REPORTING
Storable uses the "exception" paradigm, in that it does not try to
workaround failures: if something bad happens, an exception is generated
from the caller's perspective (see Carp and croak()). Use eval {} to
trap those exceptions.
When Storable croaks, it tries to report the error via the logcroak()
routine from the "Log::Agent" package, if it is available.
Normal errors are reported by having store() or retrieve() return
"undef". Such errors are usually I/O errors (or truncated stream errors
at retrieval).
When Storable throws the "Max. recursion depth with nested structures
exceeded" error we are already out of stack space. Unfortunately on some
earlier perl versions cleaning up a recursive data structure recurses
into the free calls, which will lead to stack overflows in the cleanup.
This data structure is not properly cleaned up then, it will only be
destroyed during global destruction.
WIZARDS ONLY
Hooks
Any class may define hooks that will be called during the serialization
and deserialization process on objects that are instances of that class.
Those hooks can redefine the way serialization is performed (and
therefore, how the symmetrical deserialization should be conducted).
Since we said earlier:
dclone(.) = thaw(freeze(.))
everything we say about hooks should also hold for deep cloning.
However, hooks get to know whether the operation is a mere
serialization, or a cloning.
Therefore, when serializing hooks are involved,
dclone(.) <> thaw(freeze(.))
Well, you could keep them in sync, but there's no guarantee it will
always hold on classes somebody else wrote. Besides, there is little to
gain in doing so: a serializing hook could keep only one attribute of an
object, which is probably not what should happen during a deep cloning
of that same object.
Here is the hooking interface:
"STORABLE_freeze" obj, cloning
The serializing hook, called on the object during serialization. It
can be inherited, or defined in the class itself, like any other
method.
Arguments: obj is the object to serialize, cloning is a flag
indicating whether we're in a dclone() or a regular serialization
via store() or freeze().
Returned value: A LIST "($serialized, $ref1, $ref2, ...)" where
$serialized is the serialized form to be used, and the optional
$ref1, $ref2, etc... are extra references that you wish to let the
Storable engine serialize.
At deserialization time, you will be given back the same LIST, but
all the extra references will be pointing into the deserialized
structure.
The first time the hook is hit in a serialization flow, you may have
it return an empty list. That will signal the Storable engine to
further discard that hook for this class and to therefore revert to
the default serialization of the underlying Perl data. The hook
will again be normally processed in the next serialization.
Unless you know better, serializing hook should always say:
sub STORABLE_freeze {
my ($self, $cloning) = @_;
return if $cloning; # Regular default serialization
....
}
in order to keep reasonable dclone() semantics.
"STORABLE_thaw" obj, cloning, serialized, ...
The deserializing hook called on the object during deserialization.
But wait: if we're deserializing, there's no object yet... right?
Wrong: the Storable engine creates an empty one for you. If you
know Eiffel, you can view "STORABLE_thaw" as an alternate creation
routine.
This means the hook can be inherited like any other method, and that
obj is your blessed reference for this particular instance.
The other arguments should look familiar if you know
"STORABLE_freeze": cloning is true when we're part of a deep clone
operation, serialized is the serialized string you returned to the
engine in "STORABLE_freeze", and there may be an optional list of
references, in the same order you gave them at serialization time,
pointing to the deserialized objects (which have been processed
courtesy of the Storable engine).
When the Storable engine does not find any "STORABLE_thaw" hook
routine, it tries to load the class by requiring the package
dynamically (using the blessed package name), and then re-attempts
the lookup. If at that time the hook cannot be located, the engine
croaks. Note that this mechanism will fail if you define several
classes in the same file, but perlmod warned you.
It is up to you to use this information to populate obj the way you
want.
Returned value: none.
"STORABLE_attach" class, cloning, serialized
While "STORABLE_freeze" and "STORABLE_thaw" are useful for classes
where each instance is independent, this mechanism has difficulty
(or is incompatible) with objects that exist as common process-level
or system-level resources, such as singleton objects, database
pools, caches or memoized objects.
The alternative "STORABLE_attach" method provides a solution for
these shared objects. Instead of "STORABLE_freeze" -->
"STORABLE_thaw", you implement "STORABLE_freeze" -->
"STORABLE_attach" instead.
Arguments: class is the class we are attaching to, cloning is a flag
indicating whether we're in a dclone() or a regular de-serialization
via thaw(), and serialized is the stored string for the resource
object.
Because these resource objects are considered to be owned by the
entire process/system, and not the "property" of whatever is being
serialized, no references underneath the object should be included
in the serialized string. Thus, in any class that implements
"STORABLE_attach", the "STORABLE_freeze" method cannot return any
references, and "Storable" will throw an error if "STORABLE_freeze"
tries to return references.
All information required to "attach" back to the shared resource
object must be contained only in the "STORABLE_freeze" return
string. Otherwise, "STORABLE_freeze" behaves as normal for
"STORABLE_attach" classes.
Because "STORABLE_attach" is passed the class (rather than an
object), it also returns the object directly, rather than modifying
the passed object.
Returned value: object of type "class"
Predicates
Predicates are not exportable. They must be called by explicitly
prefixing them with the Storable package name.
"Storable::last_op_in_netorder"
The Storable::last_op_in_netorder() predicate will tell you whether
network order was used in the last store or retrieve operation. If
you don't know how to use this, just forget about it.
"Storable::is_storing"
Returns true if within a store operation (via STORABLE_freeze hook).
"Storable::is_retrieving"
Returns true if within a retrieve operation (via STORABLE_thaw
hook).
Recursion
With hooks comes the ability to recurse back to the Storable engine.
Indeed, hooks are regular Perl code, and Storable is convenient when it
comes to serializing and deserializing things, so why not use it to
handle the serialization string?
There are a few things you need to know, however:
• From Storable 3.05 to 3.13 we probed for the stack recursion limit
for references, arrays and hashes to a maximal depth of ~1200-35000,
otherwise we might fall into a stack-overflow. On JSON::XS this
limit is 512 btw. With references not immediately referencing each
other there's no such limit yet, so you might fall into such a
stack-overflow segfault.
This probing and the checks we performed have some limitations:
• the stack size at build time might be different at run time, eg.
the stack size may have been modified with ulimit(1). If it's
larger at run time Storable may fail the freeze() or thaw()
unnecessarily. If it's larger at build time Storable may
segmentation fault when processing a deep structure at run time.
• the stack size might be different in a thread.
• array and hash recursion limits are checked separately against
the same recursion depth, a frozen structure with a large
sequence of nested arrays within many nested hashes may exhaust
the processor stack without triggering Storable's recursion
protection.
So these now have simple defaults rather than probing at build-time.
You can control the maximum array and hash recursion depths by
modifying $Storable::recursion_limit and
$Storable::recursion_limit_hash respectively. Either can be set to
-1 to prevent any depth checks, though this isn't recommended.
If you want to test what the limits are, the stacksize tool is
included in the "Storable" distribution.
• You can create endless loops if the things you serialize via
freeze() (for instance) point back to the object we're trying to
serialize in the hook.
• Shared references among objects will not stay shared: if we're
serializing the list of object [A, C] where both object A and C
refer to the SAME object B, and if there is a serializing hook in A
that says freeze(B), then when deserializing, we'll get [A', C']
where A' refers to B', but C' refers to D, a deep clone of B'. The
topology was not preserved.
• The maximal stack recursion limit for your system is returned by
stack_depth() and stack_depth_hash(). The hash limit is usually half
the size of the array and ref limit, as the Perl hash API is not
optimal.
That's why "STORABLE_freeze" lets you provide a list of references to
serialize. The engine guarantees that those will be serialized in the
same context as the other objects, and therefore that shared objects
will stay shared.
In the above [A, C] example, the "STORABLE_freeze" hook could return:
("something", $self->{B})
and the B part would be serialized by the engine. In "STORABLE_thaw",
you would get back the reference to the B' object, deserialized for you.
Therefore, recursion should normally be avoided, but is nonetheless
supported.
Deep Cloning
There is a Clone module available on CPAN which implements deep cloning
natively, i.e. without freezing to memory and thawing the result. It is
aimed to replace Storable's dclone() some day. However, it does not
currently support Storable hooks to redefine the way deep cloning is
performed.
Storable magic
Yes, there's a lot of that :-) But more precisely, in UNIX systems
there's a utility called "file", which recognizes data files based on
their contents (usually their first few bytes). For this to work, a
certain file called magic needs to taught about the signature of the
data. Where that configuration file lives depends on the UNIX flavour;
often it's something like /usr/share/misc/magic or /etc/magic. Your
system administrator needs to do the updating of the magic file. The
necessary signature information is output to STDOUT by invoking
Storable::show_file_magic(). Note that the GNU implementation of the
"file" utility, version 3.38 or later, is expected to contain support
for recognising Storable files out-of-the-box, in addition to other
kinds of Perl files.
You can also use the following functions to extract the file header
information from Storable images:
$info = Storable::file_magic( $filename )
If the given file is a Storable image return a hash describing it.
If the file is readable, but not a Storable image return "undef".
If the file does not exist or is unreadable then croak.
The hash returned has the following elements:
"version"
This returns the file format version. It is a string like
"2.7".
Note that this version number is not the same as the version
number of the Storable module itself. For instance Storable
v0.7 create files in format v2.0 and Storable v2.15 create files
in format v2.7. The file format version number only increment
when additional features that would confuse older versions of
the module are added.
Files older than v2.0 will have the one of the version numbers
"-1", "0" or "1". No minor number was used at that time.
"version_nv"
This returns the file format version as number. It is a string
like "2.007". This value is suitable for numeric comparisons.
The constant function "Storable::BIN_VERSION_NV" returns a
comparable number that represents the highest file version
number that this version of Storable fully supports (but see
discussion of $Storable::accept_future_minor above). The
constant "Storable::BIN_WRITE_VERSION_NV" function returns what
file version is written and might be less than
"Storable::BIN_VERSION_NV" in some configurations.
"major", "minor"
This also returns the file format version. If the version is
"2.7" then major would be 2 and minor would be 7. The minor
element is missing for when major is less than 2.
"hdrsize"
The is the number of bytes that the Storable header occupies.
"netorder"
This is TRUE if the image store data in network order. This
means that it was created with nstore() or similar.
"byteorder"
This is only present when "netorder" is FALSE. It is the
$Config{byteorder} string of the perl that created this image.
It is a string like "1234" (32 bit little endian) or "87654321"
(64 bit big endian). This must match the current perl for the
image to be readable by Storable.
"intsize", "longsize", "ptrsize", "nvsize"
These are only present when "netorder" is FALSE. These are the
sizes of various C datatypes of the perl that created this
image. These must match the current perl for the image to be
readable by Storable.
The "nvsize" element is only present for file format v2.2 and
higher.
"file"
The name of the file.
$info = Storable::read_magic( $buffer )
$info = Storable::read_magic( $buffer, $must_be_file )
The $buffer should be a Storable image or the first few bytes of it.
If $buffer starts with a Storable header, then a hash describing the
image is returned, otherwise "undef" is returned.
The hash has the same structure as the one returned by
Storable::file_magic(). The "file" element is true if the image is
a file image.
If the $must_be_file argument is provided and is TRUE, then return
"undef" unless the image looks like it belongs to a file dump.
The maximum size of a Storable header is currently 21 bytes. If the
provided $buffer is only the first part of a Storable image it
should at least be this long to ensure that read_magic() will
recognize it as such.
EXAMPLES
Here are some code samples showing a possible usage of Storable:
use Storable qw(store retrieve freeze thaw dclone);
%color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
store(\%color, 'mycolors') or die "Can't store %a in mycolors!\n";
$colref = retrieve('mycolors');
die "Unable to retrieve from mycolors!\n" unless defined $colref;
printf "Blue is still %lf\n", $colref->{'Blue'};
$colref2 = dclone(\%color);
$str = freeze(\%color);
printf "Serialization of %%color is %d bytes long.\n", length($str);
$colref3 = thaw($str);
which prints (on my machine):
Blue is still 0.100000
Serialization of %color is 102 bytes long.
Serialization of CODE references and deserialization in a safe
compartment:
use Storable qw(freeze thaw);
use Safe;
use strict;
my $safe = new Safe;
# because of opcodes used in "use strict":
$safe->permit(qw(:default require));
local $Storable::Deparse = 1;
local $Storable::Eval = sub { $safe->reval($_[0]) };
my $serialized = freeze(sub { 42 });
my $code = thaw($serialized);
$code->() == 42;
SECURITY WARNING
Do not accept Storable documents from untrusted sources! There is no way
to configure Storable so that it can be used safely to process untrusted
data. While there are various options that can be used to mitigate
specific security issues these options do not comprise a complete safety
net for the user, and processing untrusted data may result in
segmentation faults, remote code execution, or privilege escalation.
The following lists some known features which represent security issues
that should be considered by users of this module.
Most obviously, the optional (off by default) CODE reference
serialization feature allows transfer of code to the deserializing
process. Furthermore, any serialized object will cause Storable to
helpfully load the module corresponding to the class of the object in
the deserializing module. For manipulated module names, this can load
almost arbitrary code. Finally, the deserialized object's destructors
will be invoked when the objects get destroyed in the deserializing
process. Maliciously crafted Storable documents may put such objects in
the value of a hash key that is overridden by another key/value pair in
the same hash, thus causing immediate destructor execution.
To disable blessing objects while thawing/retrieving remove the flag
"BLESS_OK" = 2 from $Storable::flags or set the 2nd argument for
thaw/retrieve to 0.
To disable tieing data while thawing/retrieving remove the flag "TIE_OK"
= 4 from $Storable::flags or set the 2nd argument for thaw/retrieve to
0.
With the default setting of $Storable::flags = 6, creating or destroying
random objects, even renamed objects can be controlled by an attacker.
See CVE-2015-1592 and its metasploit module.
If your application requires accepting data from untrusted sources, you
are best off with a less powerful and more-likely safe serialization
format and implementation. If your data is sufficiently simple,
Cpanel::JSON::XS or Data::MessagePack are fine alternatives. For more
complex data structures containing various Perl specific data types like
regular expressions or aliased data Sereal is the best alternative and
offers maximum interoperability. Note that Sereal is unsafe by default,
but you can configure the encoder and decoder to mitigate any security
issues.
WARNING
If you're using references as keys within your hash tables, you're bound
to be disappointed when retrieving your data. Indeed, Perl stringifies
references used as hash table keys. If you later wish to access the
items via another reference stringification (i.e. using the same
reference that was used for the key originally to record the value into
the hash table), it will work because both references stringify to the
same string.
It won't work across a sequence of "store" and "retrieve" operations,
however, because the addresses in the retrieved objects, which are part
of the stringified references, will probably differ from the original
addresses. The topology of your structure is preserved, but not hidden
semantics like those.
On platforms where it matters, be sure to call binmode() on the
descriptors that you pass to Storable functions.
Storing data canonically that contains large hashes can be significantly
slower than storing the same data normally, as temporary arrays to hold
the keys for each hash have to be allocated, populated, sorted and
freed. Some tests have shown a halving of the speed of storing -- the
exact penalty will depend on the complexity of your data. There is no
slowdown on retrieval.
REGULAR EXPRESSIONS
Storable now has experimental support for storing regular expressions,
but there are significant limitations:
• perl 5.8 or later is required.
• regular expressions with code blocks, ie "/(?{ ... })/" or "/(??{
... })/" will throw an exception when thawed.
• regular expression syntax and flags have changed over the history of
perl, so a regular expression that you freeze in one version of perl
may fail to thaw or behave differently in another version of perl.
• depending on the version of perl, regular expressions can change in
behaviour depending on the context, but later perls will bake that
behaviour into the regexp.
Storable will throw an exception if a frozen regular expression cannot
be thawed.
BUGS
You can't store GLOB, FORMLINE, etc.... If you can define semantics for
those operations, feel free to enhance Storable so that it can deal with
them.
The store functions will "croak" if they run into such references unless
you set $Storable::forgive_me to some "TRUE" value. In that case, the
fatal message is converted to a warning and some meaningless string is
stored instead.
Setting $Storable::canonical may not yield frozen strings that compare
equal due to possible stringification of numbers. When the string
version of a scalar exists, it is the form stored; therefore, if you
happen to use your numbers as strings between two freezing operations on
the same data structures, you will get different results.
When storing doubles in network order, their value is stored as text.
However, you should also not expect non-numeric floating-point values
such as infinity and "not a number" to pass successfully through a
nstore()/retrieve() pair.
As Storable neither knows nor cares about character sets (although it
does know that characters may be more than eight bits wide), any
difference in the interpretation of character codes between a host and a
target system is your problem. In particular, if host and target use
different code points to represent the characters used in the text
representation of floating-point numbers, you will not be able be able
to exchange floating-point data, even with nstore().
"Storable::drop_utf8" is a blunt tool. There is no facility either to
return all strings as utf8 sequences, or to attempt to convert utf8 data
back to 8 bit and croak() if the conversion fails.
Prior to Storable 2.01, no distinction was made between signed and
unsigned integers on storing. By default Storable prefers to store a
scalars string representation (if it has one) so this would only cause
problems when storing large unsigned integers that had never been
converted to string or floating point. In other words values that had
been generated by integer operations such as logic ops and then not used
in any string or arithmetic context before storing.
64 bit data in perl 5.6.0 and 5.6.1
This section only applies to you if you have existing data written out
by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux
which has been configured with 64 bit integer support (not the default)
If you got a precompiled perl, rather than running Configure to build
your own perl from source, then it almost certainly does not affect you,
and you can stop reading now (unless you're curious). If you're using
perl on Windows it does not affect you.
Storable writes a file header which contains the sizes of various C
language types for the C compiler that built Storable (when not writing
in network order), and will refuse to load files written by a Storable
not on the same (or compatible) architecture. This check and a check on
machine byteorder is needed because the size of various fields in the
file are given by the sizes of the C language types, and so files
written on different architectures are incompatible. This is done for
increased speed. (When writing in network order, all fields are written
out as standard lengths, which allows full interworking, but takes
longer to read and write)
Perl 5.6.x introduced the ability to optional configure the perl
interpreter to use C's "long long" type to allow scalars to store 64 bit
integers on 32 bit systems. However, due to the way the Perl
configuration system generated the C configuration files on non-Windows
platforms, and the way Storable generates its header, nothing in the
Storable file header reflected whether the perl writing was using 32 or
64 bit integers, despite the fact that Storable was storing some data
differently in the file. Hence Storable running on perl with 64 bit
integers will read the header from a file written by a 32 bit perl, not
realise that the data is actually in a subtly incompatible format, and
then go horribly wrong (possibly crashing) if it encountered a stored
integer. This is a design failure.
Storable has now been changed to write out and read in a file header
with information about the size of integers. It's impossible to detect
whether an old file being read in was written with 32 or 64 bit integers
(they have the same header) so it's impossible to automatically switch
to a correct backwards compatibility mode. Hence this Storable defaults
to the new, correct behaviour.
What this means is that if you have data written by Storable 1.x running
on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
then by default this Storable will refuse to read it, giving the error
Byte order is not compatible. If you have such data then you should set
$Storable::interwork_56_64bit to a true value to make this Storable read
and write files with the old header. You should also migrate your data,
or any older perl you are communicating with, to this current version of
Storable.
If you don't have data written with specific configuration of perl
described above, then you do not and should not do anything. Don't set
the flag - not only will Storable on an identically configured perl
refuse to load them, but Storable a differently configured perl will
load them believing them to be correct for it, and then may well fail or
crash part way through reading them.
CREDITS
Thank you to (in chronological order):
Jarkko Hietaniemi <jhi@iki.fi>
Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
Benjamin A. Holzman <bholzman@earthlink.net>
Andrew Ford <A.Ford@ford-mason.co.uk>
Gisle Aas <gisle@aas.no>
Jeff Gresham <gresham_jeffrey@jpmorgan.com>
Murray Nesbitt <murray@activestate.com>
Marc Lehmann <pcg@opengroup.org>
Justin Banks <justinb@wamnet.com>
Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
Salvador Ortiz Garcia <sog@msg.com.mx>
Dominic Dunlop <domo@computer.org>
Erik Haugan <erik@solbors.no>
Benjamin A. Holzman <ben.holzman@grantstreet.com>
Reini Urban <rurban@cpan.org>
Todd Rinaldo <toddr@cpanel.net>
Aaron Crane <arc@cpan.org>
for their bug reports, suggestions and contributions.
Benjamin Holzman contributed the tied variable support, Andrew Ford
contributed the canonical order for hashes, and Gisle Aas fixed a few
misunderstandings of mine regarding the perl internals, and optimized
the emission of "tags" in the output streams by simply counting the
objects instead of tagging them (leading to a binary incompatibility for
the Storable image starting at version 0.6--older images are, of course,
still properly understood). Murray Nesbitt made Storable thread-safe.
Marc Lehmann added overloading and references to tied items support.
Benjamin Holzman added a performance improvement for overloaded classes;
thanks to Grant Street Group for footing the bill. Reini Urban took
over maintenance from p5p, and added security fixes and huge object
support.
AUTHOR
Storable was written by Raphael Manfredi <Raphael_Manfredi@pobox.com>
Maintenance is now done by cperl <http://perl11.org/cperl>
Please e-mail us with problems, bug fixes, comments and complaints,
although if you have compliments you should send them to Raphael.
Please don't e-mail Raphael with problems, as he no longer works on
Storable, and your message will be delayed while he forwards it to us.
SEE ALSO
Clone.
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