[ViewVC] Diff of: cvs/CBOR-XS/XS.pm

Comparing CBOR-XS/XS.pm (file contents):
Revision 1.27 by root, Thu Nov 28 15:43:24 2013 UTC vs.
Revision 1.31 by root, Sat Nov 30 18:13:53 2013 UTC

     substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string
  }
 =head1 DESCRIPTION
-WARNING! This module is very new, and not very well tested (that's up
-to you to do). Furthermore, details of the implementation might change
-freely before version 1.0. And lastly, most extensions depend on an IANA
-assignment, and until that assignment is official, this implementation is
-not interoperable with other implementations (even future versions of this
-module) until the assignment is done.
-You are still invited to try out CBOR, and this module.
 This module converts Perl data structures to the Concise Binary Object
 Representation (CBOR) and vice versa. CBOR is a fast binary serialisation
-format that aims to use a superset of the JSON data model, i.e. when you
+format that aims to use an (almost) superset of the JSON data model, i.e.
-can represent something in JSON, you should be able to represent it in
+when you can represent something useful in JSON, you should be able to
-CBOR.
+represent it in CBOR.
-In short, CBOR is a faster and very compact binary alternative to JSON,
+In short, CBOR is a faster and quite compact binary alternative to JSON,
 with the added ability of supporting serialisation of Perl objects. (JSON
 often compresses better than CBOR though, so if you plan to compress the
-data later you might want to compare both formats first).
+data later and speed is less important you might want to compare both
+formats first).
 To give you a general idea about speed, with texts in the megabyte range,
 C<CBOR::XS> usually encodes roughly twice as fast as L<Storable> or
 L<JSON::XS> and decodes about 15%-30% faster than those. The shorter the
 data, the worse L<Storable> performs in comparison.
-As for compactness, C<CBOR::XS> encoded data structures are usually about
+Regarding compactness, C<CBOR::XS>-encoded data structures are usually
-20% smaller than the same data encoded as (compact) JSON or L<Storable>.
+about 20% smaller than the same data encoded as (compact) JSON or
+L<Storable>.
-In addition to the core CBOR data format, this module implements a number
+In addition to the core CBOR data format, this module implements a
-of extensions, to support cyclic and self-referencing data structures
+number of extensions, to support cyclic and shared data structures
-(see C<allow_sharing>), string deduplication (see C<pack_strings>) and
+(see C<allow_sharing> and C<allow_cycles>), string deduplication (see
-scalar references (always enabled).
+C<pack_strings>) and scalar references (always enabled).
 The primary goal of this module is to be I<correct> and the secondary goal
 is to be I<fast>. To reach the latter goal it was written in C.
 See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
 package CBOR::XS;
 use common::sense;
-our $VERSION = 0.09;
+our $VERSION = '1.0';
 our @ISA = qw(Exporter);
 our @EXPORT = qw(encode_cbor decode_cbor);
 use Exporter;
 reference to the earlier value.
 This means that such values will only be encoded once, and will not result
 in a deep cloning of the value on decode, in decoders supporting the value
 sharing extension. This also makes it possible to encode cyclic data
-structures.
+structures (which need C<allow_cycles> to ne enabled to be decoded by this
+module).
 It is recommended to leave it off unless you know your
 communication partner supports the value sharing extensions to CBOR
 (L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the
 resulting data structure might be unusable.
 Detecting shared values incurs a runtime overhead when values are encoded
 that have a reference counter large than one, and might unnecessarily
 increase the encoded size, as potentially shared values are encode as
-sharable whether or not they are actually shared.
+shareable whether or not they are actually shared.
 At the moment, only targets of references can be shared (e.g. scalars,
 arrays or hashes pointed to by a reference). Weirder constructs, such as
 an array with multiple "copies" of the I<same> string, which are hard but
 not impossible to create in Perl, are not supported (this is the same as
 structures cannot be encoded in this mode.
 This option does not affect C<decode> in any way - shared values and
 references will always be decoded properly if present.
+=item $cbor = $cbor->allow_cycles ([$enable])
+=item $enabled = $cbor->get_allow_cycles
+If C<$enable> is true (or missing), then C<decode> will happily decode
+self-referential (cyclic) data structures. By default these will not be
+decoded, as they need manual cleanup to avoid memory leaks, so code that
+isn't prepared for this will not leak memory.
+If C<$enable> is false (the default), then C<decode> will throw an error
+when it encounters a self-referential/cyclic data structure.
+This option does not affect C<encode> in any way - shared values and
+references will always be decoded properly if present.
 =item $cbor = $cbor->pack_strings ([$enable])
 =item $enabled = $cbor->get_pack_strings
 If C<$enable> is true (or missing), then C<encode> will try not to encode
 function, C<CBOR::XS::default_filter>, is used. This function simply looks
 up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists it must be
 a code reference that is called with tag and value, and is responsible for
 decoding the value. If no entry exists, it returns no values.
-Example: decode all tags not handled internally into CBOR::XS::Tagged
+Example: decode all tags not handled internally into C<CBOR::XS::Tagged>
 objects, with no other special handling (useful when working with
 potentially "unsafe" CBOR data).
    CBOR::XS->new->filter (sub { })->decode ($cbor_data);
 =item tagged values
 Tagged items consists of a numeric tag and another CBOR value.
 See L<TAG HANDLING AND EXTENSIONS> and the description of C<< ->filter >>
-for details.
+for details on which tags are handled how.
 =item anything else
 Anything else (e.g. unsupported simple values) will raise a decoding
 error.
 =head2 PERL -> CBOR
 The mapping from Perl to CBOR is slightly more difficult, as Perl is a
-truly typeless language, so we can only guess which CBOR type is meant by
+typeless language. That means this module can only guess which CBOR type
-a Perl value.
+is meant by a perl value.
 =over 4
 =item hash references
 Perl hash references become CBOR maps. As there is no inherent ordering in
 hash keys (or CBOR maps), they will usually be encoded in a pseudo-random
-order.
+order. This order can be different each time a hahs is encoded.
 Currently, tied hashes will use the indefinite-length format, while normal
 hashes will use the fixed-length format.
 =item array references
 Perl array references become fixed-length CBOR arrays.
 =item other references
-Other unblessed references are generally not allowed and will cause an
+Other unblessed references will be represented using
-exception to be thrown, except for references to the integers C<0> and
+the indirection tag extension (tag value C<22098>,
-C<1>, which get turned into false and true in CBOR.
+L<http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
+to be able to decode these values somehow, by either "doing the right
+thing", decoding into a generic tagged object, simply ignoring the tag, or
+something else.
 =item CBOR::XS::Tagged objects
 Objects of this type must be arrays consisting of a single C<[tag, value]>
 pair. The (numerical) tag will be encoded as a CBOR tag, the value will
-be encoded as appropriate for the value. You cna use C<CBOR::XS::tag> to
+be encoded as appropriate for the value. You must use C<CBOR::XS::tag> to
 create such objects.
 =item Types::Serialiser::true, Types::Serialiser::false, Types::Serialiser::error
 These special values become CBOR true, CBOR false and CBOR undefined
 =back
 =head2 OBJECT SERIALISATION
+This module implements both a CBOR-specific and the generic
+L<Types::Serialier> object serialisation protocol. The following
+subsections explain both methods.
+=head3 ENCODING
 This module knows two way to serialise a Perl object: The CBOR-specific
 way, and the generic way.
-Whenever the encoder encounters a Perl object that it cnanot serialise
+Whenever the encoder encounters a Perl object that it cannot serialise
 directly (most of them), it will first look up the C<TO_CBOR> method on
 it.
 If it has a C<TO_CBOR> method, it will call it with the object as only
 argument, and expects exactly one return value, which it will then
 The C<FREEZE> method can return any number of values (i.e. zero or
 more). These will be encoded as CBOR perl object, together with the
 classname.
+These methods I<MUST NOT> change the data structure that is being
+serialised. Failure to comply to this can result in memory corruption -
+and worse.
 If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail
 with an error.
+=head3 DECODING
-Objects encoded via C<TO_CBOR> cannot be automatically decoded, but
+Objects encoded via C<TO_CBOR> cannot (normally) be automatically decoded,
-objects encoded via C<FREEZE> can be decoded using the following protocol:
+but objects encoded via C<FREEZE> can be decoded using the following
+protocol:
 When an encoded CBOR perl object is encountered by the decoder, it will
 look up the C<THAW> method, by using the stored classname, and will fail
 if the method cannot be found.
 After the lookup it will call the C<THAW> method with the stored classname
 as first argument, the constant string C<CBOR> as second argument, and all
 values returned by C<FREEZE> as remaining arguments.
-=head4 EXAMPLES
+=head3 EXAMPLES
 Here is an example C<TO_CBOR> method:
    sub My::Object::TO_CBOR {
       my ($obj) = @_;
   sub URI::TO_CBOR {
      my ($self) = @_;
      my $uri = "$self"; # stringify uri
      utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
-     CBOR::XS::tagged 32, "$_[0]"
+     CBOR::XS::tag 32, "$_[0]"
   }
 This will encode URIs as a UTF-8 string with tag 32, which indicates an
 URI.
 These tags are automatically created (and decoded) for serialisable
 objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object
 serialisation protocol). See L<OBJECT SERIALISATION> for details.
-=item 28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
+=item 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
-These tags are automatically decoded when encountered, resulting in
+These tags are automatically decoded when encountered (and they do not
+result in a cyclic data structure, see C<allow_cycles>), resulting in
 shared values in the decoded object. They are only encoded, however, when
-C<allow_sharable> is enabled.
+C<allow_sharing> is enabled.
+Not all shared values can be successfully decoded: values that reference
+themselves will I<currently> decode as C<undef> (this is not the same
+as a reference pointing to itself, which will be represented as a value
+that contains an indirect reference to itself - these will be decoded
+properly).
+Note that considerably more shared value data structures can be decoded
+than will be encoded - currently, only values pointed to by references
+will be shared, others will not. While non-reference shared values can be
+generated in Perl with some effort, they were considered too unimportant
+to be supported in the encoder. The decoder, however, will decode these
+values as shared values.
 =item 256, 25 (stringref-namespace, stringref, L <http://cbor.schmorp.de/stringref>)
 These tags are automatically decoded when encountered. They are only
 encoded, however, when C<pack_strings> is enabled.
 Only the double data type is supported for NV data types - when Perl uses
 long double to represent floating point values, they might not be encoded
 properly. Half precision types are accepted, but not encoded.
 Strict mode and canonical mode are not implemented.
+=head1 LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
+On perls that were built without 64 bit integer support (these are rare
+nowadays, even on 32 bit architectures), support for any kind of 64 bit
+integer in CBOR is very limited - most likely, these 64 bit values will
+be truncated, corrupted, or otherwise not decoded correctly. This also
+includes string, array and map sizes that are stored as 64 bit integers.
 =head1 THREADS
 This module is I<not> guaranteed to be thread safe and there are no

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Comparing CBOR-XS/XS.pm (file contents): Revision 1.27 by root, Thu Nov 28 15:43:24 2013 UTC vs. Revision 1.31 by root, Sat Nov 30 18:13:53 2013 UTC

Diff Legend

Comparing CBOR-XS/XS.pm (file contents):
Revision 1.27 by root, Thu Nov 28 15:43:24 2013 UTC vs.
Revision 1.31 by root, Sat Nov 30 18:13:53 2013 UTC