--- CBOR-XS/README 2013/10/26 23:02:55 1.4 +++ CBOR-XS/README 2013/10/27 22:48:12 1.5 @@ -10,7 +10,17 @@ # OO-interface $coder = CBOR::XS->new; - #TODO + $binary_cbor_data = $coder->encode ($perl_value); + $perl_value = $coder->decode ($binary_cbor_data); + + # prefix decoding + + my $many_cbor_strings = ...; + while (length $many_cbor_strings) { + my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings); + # data was decoded + substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string + } DESCRIPTION WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA @@ -23,7 +33,8 @@ i.e. when you can represent something in JSON, you should be able to represent it in CBOR. - This makes it a faster and more compact binary alternative to JSON. + This makes it a faster and more compact binary alternative to JSON, with + the added ability of supporting serialising of perl objects. The primary goal of this module is to be *correct* and the secondary goal is to be *fast*. To reach the latter goal it was written in C. @@ -147,23 +158,33 @@ Perl array or hash, respectively. The keys of the map will be stringified during this process. - true, false - These CBOR values become "CBOR::XS::true" and "CBOR::XS::false", + null + CBOR null becomes "undef" in Perl. + + true, false, undefined + These CBOR values become "Types:Serialiser::true", + "Types:Serialiser::false" and "Types::Serialiser::error", respectively. They are overloaded to act almost exactly like the - numbers 1 and 0. You can check whether a scalar is a CBOR boolean by - using the "CBOR::XS::is_bool" function. + numbers 1 and 0 (for true and false) or to throw an exception on + access (for error). See the Types::Serialiser manpage for details. + + CBOR tag 256 (perl object) + The tag value 256 (TODO: pending iana registration) will be used to + deserialise a Perl object serialised with "FREEZE". See "OBJECT + SERIALISATION", below, for details. + + CBOR tag 55799 (magic header) + The tag 55799 is ignored (this tag implements the magic header). + + other CBOR tags + Tagged items consists of a numeric tag and another CBOR value. Tags + not handled internally are currently converted into a + CBOR::XS::Tagged object, which is simply a blessed array reference + consisting of the numeric tag value followed by the (decoded) CBOR + value. - null, undefined - CBOR null and undefined values becomes "undef" in Perl (in the - future, Undefined may raise an exception or something else). - - tags - Tagged items consists of a numeric tag and another CBOR value. The - tag 55799 is ignored (this tag implements the magic header). - - All other tags are currently converted into a CBOR::XS::Tagged - object, which is simply a blessed array reference consistsing of the - numeric tag value followed by the (decoded) BOR value. + In the future, support for user-supplied conversions might get + added. anything else Anything else (e.g. unsupported simple values) will raise a decoding @@ -195,14 +216,15 @@ value]" pair. The (numerical) tag will be encoded as a CBOR tag, the value will be encoded as appropriate for the value. - CBOR::XS::true, CBOR::XS::false - These special values become CBOR true and CBOR false values, - respectively. You can also use "\1" and "\0" directly if you want. - - blessed objects - Other blessed objects currently need to have a "TO_CBOR" method. It - will be called on every object that is being serialised, and must - return something that can be encoded in CBOR. + Types::Serialiser::true, Types::Serialiser::false, + Types::Serialiser::error + These special values become CBOR true, CBOR false and CBOR undefined + values, respectively. You can also use "\1", "\0" and "\undef" + directly if you want. + + other blessed objects + Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See + "OBJECT SERIALISATION", below, for details. simple scalars TODO Simple Perl scalars (any scalar that is not a reference) are @@ -247,7 +269,103 @@ than IEEE double to represent numerical values are supported, but might suffer loss of precision. - MAGIC HEADER + OBJECT SERIALISATION + 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 + directly (most of them), it will first look up the "TO_CBOR" method on + it. + + If it has a "TO_CBOR" method, it will call it with the object as only + argument, and expects exactly one return value, which it will then + substitute and encode it in the place of the object. + + Otherwise, it will look up the "FREEZE" method. If it exists, it will + call it with the object as first argument, and the constant string + "CBOR" as the second argument, to distinguish it from other serialisers. + + The "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. + + If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail + with an error. + + Objects encoded via "TO_CBOR" cannot be automatically decoded, but + objects encoded via "FREEZE" can be decoded using the following + protocol: + + When an encoded CBOR perl object is encountered by the decoder, it will + look up the "THAW" method, by using the stored classname, and will fail + if the method cannot be found. + + After the lookup it will call the "THAW" method with the stored + classname as first argument, the constant string "CBOR" as second + argument, and all values returned by "FREEZE" as remaining arguments. + + EXAMPLES + Here is an example "TO_CBOR" method: + + sub My::Object::TO_CBOR { + my ($obj) = @_; + + ["this is a serialised My::Object object", $obj->{id}] + } + + When a "My::Object" is encoded to CBOR, it will instead encode a simple + array with two members: a string, and the "object id". Decoding this + CBOR string will yield a normal perl array reference in place of the + object. + + A more useful and practical example would be a serialisation method for + the URI module. CBOR has a custom tag value for URIs, namely 32: + + sub URI::TO_CBOR { + my ($self) = @_; + my $uri = "$self"; # stringify uri + utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string + CBOR::XS::tagged 32, "$_[0]" + } + + This will encode URIs as a UTF-8 string with tag 32, which indicates an + URI. + + Decoding such an URI will not (currently) give you an URI object, but + instead a CBOR::XS::Tagged object with tag number 32 and the string - + exactly what was returned by "TO_CBOR". + + To serialise an object so it can automatically be deserialised, you need + to use "FREEZE" and "THAW". To take the URI module as example, this + would be a possible implementation: + + sub URI::FREEZE { + my ($self, $serialiser) = @_; + "$self" # encode url string + } + + sub URI::THAW { + my ($class, $serialiser, $uri) = @_; + + $class->new ($uri) + } + + Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For + example, a "FREEZE" method that returns "type", "id" and "variant" + values would cause an invocation of "THAW" with 5 arguments: + + sub My::Object::FREEZE { + my ($self, $serialiser) = @_; + + ($self->{type}, $self->{id}, $self->{variant}) + } + + sub My::Object::THAW { + my ($class, $serialiser, $type, $id, $variant) = @_; + + $class- $type, id => $id, variant => $variant) + } + +MAGIC HEADER 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 @@ -258,7 +376,7 @@ if present, so users can prepend this string as a "file type" indicator as required. - CBOR and JSON +CBOR and JSON CBOR is supposed to implement a superset of the JSON data model, and is, with some coercion, able to represent all JSON texts (something that other "binary JSON" formats such as BSON generally do not support). @@ -342,6 +460,9 @@ The JSON and JSON::XS modules that do similar, but human-readable, serialisation. + The Types::Serialiser module provides the data model for true, false and + error values. + AUTHOR Marc Lehmann http://home.schmorp.de/