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Author image Felipe Gasper
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NAME

CBOR::Free - Fast CBOR for everyone

SYNOPSIS

    $cbor = CBOR::Free::encode( $some_data_structure );

    $thing = CBOR::Free::decode( $cbor )

    my $tagged = CBOR::Free::tag( 1, '2019-01-02T00:01:02Z' );

Also see CBOR::Free::Decoder for an object-oriented interface to the decoder.

DESCRIPTION

This library implements CBOR via XS under a license that permits commercial usage with no “strings attached”.

STATUS

This distribution is an experimental effort. Its interface is still subject to change. If you decide to use CBOR::Free in your project, please always check the changelog before upgrading.

FUNCTIONS

$cbor = encode( $DATA, %OPTS )

Encodes a data structure or non-reference scalar to CBOR. The encoder recognizes and encodes integers, floats, byte and character strings, array and hash references, CBOR::Free::Tagged instances, Types::Serialiser booleans, and undef (encoded as null).

The encoder currently does not handle any other blessed references.

%OPTS may be:

  • canonical - A boolean that makes the encoder output CBOR in canonical form.

  • string_encode_mode - Decides the logic to use for CBOR encoding of strings and hash keys. (The word “string” in the below descriptions applies equally to hash keys.)

    Takes one of:

    • sv: The default mode of operation. If the string’s internal UTF8 flag is set, it will become a CBOR text string; otherwise, it will be CBOR binary. This is good for IPC with other Perl code but isn’t a very friendly default for working with other languages that probably expect more reliably-typed strings.

      This is (currently) the only way to output text and binary strings in a single CBOR document. Unfortunately, because Perl itself doesn’t reliably distinguish between text and binary strings, neither can CBOR::Free. If you want to try, though:

      • Be sure to use character-decoding logic that always sets the string’s UTF8 flag, even if the input is plain ASCII. (As of this writing, Encode and Unicode::UTF8 work this way.)

      • Whatever consumes your Perl-sourced CBOR should probably accept “mis-typed” strings.

    • encode_text: Treats all strings as unencoded characters. All CBOR strings will be text.

      This is probably what you want if you follow the receive-decode-process-encode-output workflow that perlunitut recommends (which you might be doing via use utf8) AND if you intend for your CBOR to contain exclusively text.

      Think of this option as: “All my strings are decoded.”

      (Perl internals note: if !SvUTF8, the CBOR will be the UTF8-upgraded version.)

    • as_text: Treats all strings as octets of UTF-8. Wide characters (i.e., code points above 255) are thus invalid input. All CBOR strings will be text.

      This is probably what you want if you forgo character decoding (and encoding), treating all input as octets, BUT you still intend for your CBOR to contain exclusively text.

      Think of this option as: “I’ve encoded all my strings as UTF-8.”

      (Perl internals note: if SvUTF8, the CBOR will be the downgraded version.)

    • as_binary: Like as_text, but outputs CBOR binary instead of text.

      This is probably what you want if your application is “all binary, all the time”.

      Think of this option as: “Just the bytes, ma’am.”

  • preserve_references - A boolean that makes the encoder encode multi-referenced values via CBOR’s “shared references” tags. This allows encoding of shared and circular references. It also incurs a performance penalty.

    (Take care that any circular references in your application don’t cause memory leaks!)

  • scalar_references - A boolean that makes the encoder accept scalar references (rather than reject them) and encode them via CBOR’s “indirection” tag. Most languages don’t use references as Perl does, so this option seems of little use outside all-Perl IPC contexts; it is arguably more useful, then, for general use to have the encoder reject data structures that most other languages cannot represent.

Notes on mapping Perl to CBOR:

  • The internal state of a Perl scalar (e.g., whether it’s an integer, float, string, etc.) determines its CBOR encoding.

  • Perl doesn’t currently provide reliable binary/character string types. The various string_encode_mode options (described above) provide ways to deal with this problem.

  • The above applies also to strings vs. numbers: whatever consumes your Perl-sourced CBOR MUST account for the prospect of numbers that are in CBOR as strings, or vice-versa.

  • Perl hash keys are serialized as strings, either binary or text (according to the string_encode_mode).

  • Types::Serialiser booleans are encoded as CBOR booleans. Perl undef is encoded as CBOR null. (NB: No Perl value encodes as CBOR undefined.)

  • Scalar references (including references to other references) are unhandled by default, which makes them trigger an exception. You can optionally tell CBOR::Free to encode them via the scalar_references flag.

  • Via the optional preserve_references flag, circular and shared references may be preserved. Without this flag, circular references cause an exception, and other shared references are not preserved.

  • Instances of CBOR::Free::Tagged are encoded as tagged values.

An error is thrown on excess recursion or an unrecognized object.

$data = decode( $CBOR )

Decodes a data structure from CBOR. Errors are thrown to indicate invalid CBOR. A warning is thrown if $CBOR is longer than is needed for $data.

Notes on mapping CBOR to Perl:

  • decode() decodes CBOR text strings as UTF-8-decoded Perl strings. CBOR binary strings become undecoded Perl strings.

    (See CBOR::Free::Decoder and CBOR::Free::SequenceDecoder for more character-decoding options.)

    Notes:

    • Invalid UTF-8 in a CBOR text string is usually considered invalid input and will thus prompt a thrown exception. (See CBOR::Free::Decoder and CBOR::Free::SequenceDecoder if you want to tolerate invalid UTF-8.)

    • You can reliably use utf8::is_utf8() to determine if a given Perl string came from CBOR text or binary, but ONLY if you test the scalar as it appears in the newly-decoded data structure itself. Generally Perl code should avoid is_utf8(), but with CBOR::Free-created strings this limited use case is legitimate and potentially gainful.

  • The only map keys that decode() accepts are integers and strings. An exception is thrown if the decoder finds anything else as a map key. Note that, because Perl does not distinguish between binary and text strings, if two keys of the same map contain the same bytes, Perl will consider these a duplicate key and prefer the latter.

  • CBOR booleans become the corresponding Types::Serialiser values. Both CBOR null and undefined become Perl undef.

  • CBOR’s “indirection” tag is interpreted as a scalar reference. This behavior is always active; unlike with the encoder, there is no need to enable it manually.

  • preserve_references() mode complements the same flag given to the encoder.

  • This function does not interpret any other tags. If you need to decode other tags, look at CBOR::Free::Decoder. Any unhandled tags that this function sees prompt a warning but are otherwise ignored.

$obj = tag( $NUMBER, $DATA )

Tags an item for encoding so that its CBOR encoding will preserve the tag number. (Include $obj, not $DATA, in the data structure that encode() receives.)

BOOLEANS

CBOR::Free::true() and CBOR::Free::false() are defined as convenience aliases for the equivalent Types::Serialiser functions. (Note that there are no equivalent scalar aliases.)

FRACTIONAL (FLOATING-POINT) NUMBERS

Floating-point numbers are encoded in CBOR as IEEE 754 half-, single-, or double-precision. If your Perl is compiled to use anything besides IEEE 754 double-precision to represent floating-point values (e.g., “long double” or “quadmath” compilation options), you may see rounding errors when converting to/from CBOR. If that’s a problem for you, append an empty string to your floating-point numbers, which will cause CBOR::Free to encode them as strings.

INTEGER LIMITS

CBOR handles up to 64-bit positive and negative integers. Most Perls nowadays can handle 64-bit integers, but if yours can’t then you’ll get an exception whenever trying to parse an integer that can’t be represented with 32 bits. This means:

  • Anything greater than 0xffff_ffff (4,294,967,295)

  • Anything less than -0x8000_0000 (2,147,483,648)

Note that even 64-bit Perls can’t parse negatives that are less than -0x8000_0000_0000_0000 (-9,223,372,036,854,775,808); these also prompt an exception since Perl can’t handle them. (It would be possible to load Math::BigInt to handle these; if that’s desirable for you, file a feature request.)

ERROR HANDLING

Most errors are represented via instances of subclasses of CBOR::Free::X, which subclasses X::Tiny::Base.

SPEED

CBOR::Free is pretty snappy. I find that it keeps pace with or surpasses CBOR::XS, Cpanel::JSON::XS, JSON::XS, Sereal, and Data::MessagePack.

It’s also quite light. Its only “heavy” dependency is Types::Serialiser, which is only loaded when you actually need it. This keeps memory usage low for when, e.g., you’re using CBOR for IPC between Perl processes and have no need for true booleans.

AUTHOR

Gasper Software Consulting (FELIPE)

LICENSE

This code is licensed under the same license as Perl itself.

SEE ALSO

CBOR::PP is a pure-Perl CBOR library.

CBOR::XS is an older CBOR module on CPAN. It’s got more bells and whistles, so check it out if CBOR::Free lacks a feature you’d like. Note that its maintainer has abandoned support for Perl versions from 5.22 onward, though, and its GPL license limits its usefulness in commercial perlcc applications.