--- CBOR-XS/XS.pm 2013/10/29 15:13:50 1.12 +++ CBOR-XS/XS.pm 2013/11/20 02:03:08 1.20 @@ -48,6 +48,14 @@ often compresses better than CBOR though, so if you plan to compress the data later you might want to compare both formats first). +To give you a general idea about speed, with texts in the megabyte range, +C usually encodes roughly twice as fast as L or +L and decodes about 15%-30% faster than those. The shorter the +data, the worse L performs in comparison. + +As for compactness, C encoded data structures are usually about +20% smaller than the same data encoded as (compact) JSON or L. + The primary goal of this module is to be I and the secondary goal is to be I. To reach the latter goal it was written in C. @@ -60,7 +68,7 @@ use common::sense; -our $VERSION = 0.05; +our $VERSION = 0.08; our @ISA = qw(Exporter); our @EXPORT = qw(encode_cbor decode_cbor); @@ -151,6 +159,52 @@ See SECURITY CONSIDERATIONS, below, for more info on why this is useful. +=item $cbor = $cbor->allow_unknown ([$enable]) + +=item $enabled = $cbor->get_allow_unknown + +If C<$enable> is true (or missing), then C will I throw an +exception when it encounters values it cannot represent in CBOR (for +example, filehandles) but instead will encode a CBOR C value. + +If C<$enable> is false (the default), then C will throw an +exception when it encounters anything it cannot encode as CBOR. + +This option does not affect C in any way, and it is recommended to +leave it off unless you know your communications partner. + +=item $cbor = $cbor->allow_sharing ([$enable]) + +=item $enabled = $cbor->get_allow_sharing + +If C<$enable> is true (or missing), then C will not double-encode +values that have been referenced before (e.g. when the same object, such +as an array, is referenced multiple times), but instead will emit a +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. + +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. + +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 string, which are hard but +not impossible to create in Perl, are not supported (this is the same as +for L). + +If C<$enable> is false (the default), then C will encode +exception when it encounters anything it cannot encode as CBOR. + +This option does not affect C in any way - shared values and +references will always be decoded properly if present. It is recommended +to leave it off unless you know your communications partner supports the +value sharing extensions to CBOR (http://cbor.schmorp.de/value-sharing). + =item $cbor_data = $cbor->encode ($perl_scalar) Converts the given Perl data structure (a scalar value) to its CBOR @@ -285,8 +339,9 @@ =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. +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 to +create such objects. =item Types::Serialiser::true, Types::Serialiser::false, Types::Serialiser::error @@ -448,10 +503,10 @@ There is no way to distinguish CBOR from other formats programmatically. To make it easier to distinguish CBOR from other formats, the CBOR specification has a special "magic string" that can be -prepended to any CBOR string without changing it's meaning. +prepended to any CBOR string without changing its meaning. This string is available as C<$CBOR::XS::MAGIC>. This module does not -prepend this string tot he CBOR data it generates, but it will ignroe it +prepend this string to the CBOR data it generates, but it will ignore it if present, so users can prepend this string as a "file type" indicator as required. @@ -518,6 +573,71 @@ $_[0][1] } +=head2 EXAMPLES + +Here are some examples of C uses to tag objects. + +You can look up CBOR tag value and emanings in the IANA registry at +L. + +Prepend a magic header (C<$CBOR::XS::MAGIC>): + + my $cbor = encode_cbor CBOR::XS::tag 55799, $value; + # same as: + my $cbor = $CBOR::XS::MAGIC . encode_cbor $value; + +Serialise some URIs and a regex in an array: + + my $cbor = encode_cbor [ + (CBOR::XS::tag 32, "http://www.nethype.de/"), + (CBOR::XS::tag 32, "http://software.schmorp.de/"), + (CBOR::XS::tag 35, "^[Pp][Ee][Rr][lL]\$"), + ]; + +Wrap CBOR data in CBOR: + + my $cbor_cbor = encode_cbor + CBOR::XS::tag 24, + encode_cbor [1, 2, 3]; + +=head1 TAG HANDLING AND EXTENSIONS + +This section describes how this module handles specific tagged values and +extensions. If a tag is not mentioned here, then the default handling +applies (creating a CBOR::XS::Tagged object on decoding, and only encoding +the tag when explicitly requested). + +Future versions of this module reserve the right to special case +additional tags (such as bigfloat or base64url). + +=over 4 + +=item (perl-object, L) + +These tags are automatically created for serialisable objects using the +C methods (the L object serialisation +protocol). + +=item , (sharable, sharedref, L ) + +These tags are automatically decoded when encountered, resulting in +shared values in the decoded object. They are only encoded, however, when +C is enabled. + +=item 22098 (indirection, L) + +This tag is automatically generated when a reference are encountered (with +the exception of hash and array refernces). It is converted to a reference +when decoding. + +=item 55799 (self-describe CBOR, RFC 7049) + +This value is not generated on encoding (unless explicitly requested by +the user), and is simply ignored when decoding. + +=back + + =head1 CBOR and JSON CBOR is supposed to implement a superset of the JSON data model, and is,