--- CBOR-XS/README 2013/10/26 10:41:12 1.2 +++ CBOR-XS/README 2013/11/22 16:18:59 1.9 @@ -10,15 +10,54 @@ # 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 - AND EAT YOUR CHILDREN! + 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 can represent something in JSON, you should be able to + represent it in CBOR. + + In short, CBOR is a faster and very 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). + + To give you a general idea about speed, with texts in the megabyte + range, "CBOR::XS" usually encodes roughly twice as fast as Storable or + JSON::XS and decodes about 15%-30% faster than those. The shorter the + data, the worse Storable performs in comparison. + + As for compactness, "CBOR::XS" encoded data structures are usually about + 20% smaller than the same data encoded as (compact) JSON or Storable. + + In addition to the core CBOR data format, this module implements a + number of extensions, to support cyclic and self-referencing data + structures (see "allow_sharing"), string deduplication (see + "allow_stringref") and scalar references (always enabled). - This module converts Perl data structures to CBOR and vice versa. Its - primary goal is to be *correct* and its secondary goal is to be *fast*. - To reach the latter goal it was written in C. + 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. See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and vice versa. @@ -47,7 +86,7 @@ The mutators for flags all return the CBOR object again and thus calls can be chained: - #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); + my $cbor = CBOR::XS->new->encode ({a => [1,2]}); $cbor = $cbor->max_depth ([$maximum_nesting_depth]) $max_depth = $cbor->get_max_depth @@ -88,6 +127,113 @@ See SECURITY CONSIDERATIONS, below, for more info on why this is useful. + $cbor = $cbor->allow_unknown ([$enable]) + $enabled = $cbor->get_allow_unknown + If $enable is true (or missing), then "encode" will *not* throw an + exception when it encounters values it cannot represent in CBOR (for + example, filehandles) but instead will encode a CBOR "error" value. + + If $enable is false (the default), then "encode" will throw an + exception when it encounters anything it cannot encode as CBOR. + + This option does not affect "decode" in any way, and it is + recommended to leave it off unless you know your communications + partner. + + $cbor = $cbor->allow_sharing ([$enable]) + $enabled = $cbor->get_allow_sharing + If $enable is true (or missing), then "encode" 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. + + It is recommended to leave it off unless you know your communication + partner supports the value sharing extensions to CBOR + (http://cbor.schmorp.de/value-sharing). + + 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 *same* + string, which are hard but not impossible to create in Perl, are not + supported (this is the same as for Storable). + + If $enable is false (the default), then "encode" will encode + exception when it encounters anything it cannot encode as CBOR. + + This option does not affect "decode" in any way - shared values and + references will always be decoded properly if present. + + $cbor = $cbor->allow_stringref ([$enable]) + $enabled = $cbor->get_allow_stringref + If $enable is true (or missing), then "encode" will try not to + encode the same string twice, but will instead encode a reference to + the string instead. Depending on your data format. this can save a + lot of space, but also results in a very large runtime overhead + (expect encoding times to be 2-4 times as high as without). + + It is recommended to leave it off unless you know your + communications partner supports the stringref extension to CBOR + (http://cbor.schmorp.de/stringref). + + If $enable is false (the default), then "encode" will encode + exception when it encounters anything it cannot encode as CBOR. + + This option does not affect "decode" in any way - string references + will always be decoded properly if present. + + $cbor = $cbor->filter ([$cb->($tag, $value)]) + $cb_or_undef = $cbor->get_filter + Sets or replaces the tagged value decoding filter (when $cb is + specified) or clears the filter (if no argument or "undef" is + provided). + + The filter callback is called only during decoding, when a + non-enforced tagged value has been decoded (see "TAG HANDLING AND + EXTENSIONS" for a list of enforced tags). For specific tags, it's + often better to provide a default converter using the + %CBOR::XS::FILTER hash (see below). + + The first argument is the numerical tag, the second is the (decoded) + value that has been tagged. + + The filter function should return either exactly one value, which + will replace the tagged value in the decoded data structure, or no + values, which will result in default handling, which currently means + the decoder creates a "CBOR::XS::Tagged" object to hold the tag and + the value. + + When the filter is cleared (the default state), the default filter + function, "CBOR::XS::default_filter", is used. This function simply + looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists + it must be a code reference that is called with tag and value, and + is responsible for decoding the value. If no entry exists, it + returns no values. + + Example: decode all tags not handled internally into + CBOR::XS::Tagged objects, with no other special handling (useful + when working with potentially "unsafe" CBOR data). + + CBOR::XS->new->filter (sub { })->decode ($cbor_data); + + Example: provide a global filter for tag 1347375694, converting the + value into some string form. + + $CBOR::XS::FILTER{1347375694} = sub { + my ($tag, $value); + + "tag 1347375694 value $value" + }; + $cbor_data = $cbor->encode ($perl_scalar) Converts the given Perl data structure (a scalar value) to its CBOR representation. @@ -120,14 +266,44 @@ refers to the abstract Perl language itself. CBOR -> PERL - True, False - These CBOR values become "CBOR::XS::true" and "CBOR::XS::false", - 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. + integers + CBOR integers become (numeric) perl scalars. On perls without 64 bit + support, 64 bit integers will be truncated or otherwise corrupted. + + byte strings + Byte strings will become octet strings in Perl (the byte values + 0..255 will simply become characters of the same value in Perl). + + UTF-8 strings + UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be + decoded into proper Unicode code points. At the moment, the validity + of the UTF-8 octets will not be validated - corrupt input will + result in corrupted Perl strings. + + arrays, maps + CBOR arrays and CBOR maps will be converted into references to a + Perl array or hash, respectively. The keys of the map will be + stringified during this process. null - A CBOR Null value becomes "undef" in Perl. + 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 (for true and false) or to throw an exception on + access (for error). See the Types::Serialiser manpage for details. + + tagged values + Tagged items consists of a numeric tag and another CBOR value. + + See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" + for details. + + anything else + Anything else (e.g. unsupported simple values) will raise a decoding + error. PERL -> CBOR The mapping from Perl to CBOR is slightly more difficult, as Perl is a @@ -139,29 +315,38 @@ ordering in hash keys (or CBOR maps), they will usually be encoded in a pseudo-random order. + Currently, tied hashes will use the indefinite-length format, while + normal hashes will use the fixed-length format. + array references - Perl array references become CBOR arrays. + Perl array references become fixed-length CBOR arrays. other references Other unblessed references are generally not allowed and will cause an exception to be thrown, except for references to the integers 0 - and 1, which get turned into "False" and "True" in CBOR. + and 1, which get turned into false and true in CBOR. - 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 - Blessed objects are not directly representable in CBOR. TODO See the - "allow_blessed" and "convert_blessed" methods on various options on - how to deal with this: basically, you can choose between throwing an - exception, encoding the reference as if it weren't blessed, or - provide your own serialiser method. + CBOR::XS::Tagged objects + Objects of this type must be arrays consisting of a single "[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 + "CBOR::XS::tag" to create such objects. + + 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 + "TAG HANDLING AND EXTENSIONS" for specific classes handled by this + module, and "OBJECT SERIALISATION" for generic object serialisation. simple scalars - TODO Simple Perl scalars (any scalar that is not a reference) are - the most difficult objects to encode: CBOR::XS will encode undefined - scalars as CBOR "Null" values, scalars that have last been used in a + Simple Perl scalars (any scalar that is not a reference) are the + most difficult objects to encode: CBOR::XS will encode undefined + scalars as CBOR null values, scalars that have last been used in a string context before encoding as CBOR strings, and anything else as number value: @@ -194,15 +379,270 @@ Tell me if you need this capability (but don't forget to explain why it's needed :). - Note that numerical precision has the same meaning as under Perl (so - binary to decimal conversion follows the same rules as in Perl, - which can differ to other languages). Also, your perl interpreter - might expose extensions to the floating point numbers of your - platform, such as infinities or NaN's - these cannot be represented - in CBOR, and it is an error to pass those in. - - CBOR and JSON - TODO + Perl values that seem to be integers generally use the shortest + possible representation. Floating-point values will use either the + IEEE single format if possible without loss of precision, otherwise + the IEEE double format will be used. Perls that use formats other + than IEEE double to represent numerical values are supported, but + might suffer loss of precision. + + 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 + CBOR string without changing its meaning. + + This string is available as $CBOR::XS::MAGIC. This module does not + 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. + +THE CBOR::XS::Tagged CLASS + CBOR has the concept of tagged values - any CBOR value can be tagged + with a numeric 64 bit number, which are centrally administered. + + "CBOR::XS" handles a few tags internally when en- or decoding. You can + also create tags yourself by encoding "CBOR::XS::Tagged" objects, and + the decoder will create "CBOR::XS::Tagged" objects itself when it hits + an unknown tag. + + These objects are simply blessed array references - the first member of + the array being the numerical tag, the second being the value. + + You can interact with "CBOR::XS::Tagged" objects in the following ways: + + $tagged = CBOR::XS::tag $tag, $value + This function(!) creates a new "CBOR::XS::Tagged" object using the + given $tag (0..2**64-1) to tag the given $value (which can be any + Perl value that can be encoded in CBOR, including serialisable Perl + objects and "CBOR::XS::Tagged" objects). + + $tagged->[0] + $tagged->[0] = $new_tag + $tag = $tagged->tag + $new_tag = $tagged->tag ($new_tag) + Access/mutate the tag. + + $tagged->[1] + $tagged->[1] = $new_value + $value = $tagged->value + $new_value = $tagged->value ($new_value) + Access/mutate the tagged value. + + EXAMPLES + Here are some examples of "CBOR::XS::Tagged" uses to tag objects. + + You can look up CBOR tag value and emanings in the IANA registry at + . + + Prepend a magic header ($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]; + +TAG HANDLING AND EXTENSIONS + This section describes how this module handles specific tagged values + and extensions. If a tag is not mentioned here and no additional filters + are provided for it, then the default handling applies (creating a + CBOR::XS::Tagged object on decoding, and only encoding the tag when + explicitly requested). + + Tags not handled specifically 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. + + Future versions of this module reserve the right to special case + additional tags (such as base64url). + + ENFORCED TAGS + These tags are always handled when decoding, and their handling cannot + be overriden by the user. + + (perl-object, ) + These tags are automatically created (and decoded) for serialisable + objects using the "FREEZE/THAW" methods (the Types::Serialier object + serialisation protocol). See "OBJECT SERIALISATION" for details. + + , (sharable, sharedref, L + ) + These tags are automatically decoded when encountered, resulting in + shared values in the decoded object. They are only encoded, however, + when "allow_sharable" is enabled. + + , (stringref-namespace, stringref, L + ) + These tags are automatically decoded when encountered. They are only + encoded, however, when "allow_stringref" is enabled. + + 22098 (indirection, ) + 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. + + 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. + + NON-ENFORCED TAGS + These tags have default filters provided when decoding. Their handling + can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or + by providing a custom "filter" callback when decoding. + + When they result in decoding into a specific Perl class, the module + usually provides a corresponding "TO_CBOR" method as well. + + When any of these need to load additional modules that are not part of + the perl core distribution (e.g. URI), it is (currently) up to the user + to provide these modules. The decoding usually fails with an exception + if the required module cannot be loaded. + + 2, 3 (positive/negative bignum) + These tags are decoded into Math::BigInt objects. The corresponding + "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal + CBOR integers, and others into positive/negative CBOR bignums. + + 4, 5 (decimal fraction/bigfloat) + Both decimal fractions and bigfloats are decoded into Math::BigFloat + objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* + encodes into a decimal fraction. + + CBOR cannot represent bigfloats with *very* large exponents - + conversion of such big float objects is undefined. + + Also, NaN and infinities are not encoded properly. + + 21, 22, 23 (expected later JSON conversion) + CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore + these tags. + + 32 (URI) + These objects decode into URI objects. The corresponding + "URI::TO_CBOR" method again results in a CBOR URI value. + +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). + + CBOR implements some extra hints and support for JSON interoperability, + and the spec offers further guidance for conversion between CBOR and + JSON. None of this is currently implemented in CBOR, and the guidelines + in the spec do not result in correct round-tripping of data. If JSON + interoperability is improved in the future, then the goal will be to + ensure that decoded JSON data will round-trip encoding and decoding to + CBOR intact. SECURITY CONSIDERATIONS When you are using CBOR in a protocol, talking to untrusted potentially @@ -275,6 +715,9 @@ 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/