NAME

Bifcode2 - encode and decode BIFCODE2 serialization format

VERSION

2.000_4 (2019-11-09)

SYNOPSIS

    use utf8;
    use boolean;
    use Bifcode2 qw( encode_bifcode2 decode_bifcode2 );

    my $bifcode = encode_bifcode2 {
        bools   => [ boolean::false, boolean::true, ],
        bytes   => \pack( 's<',       255 ),
        integer => 25,
        real    => 1.25e-5,
        null    => undef,
        utf8    => "Ελύτη",
    };

    # 7b 75 35 2e 62 6f 6f 6c 73 3a 5b 66 2c 74 2c    {u5.bools:[f,t,
    # 5d 75 35 2e 62 79 74 65 73 3a 62 32 2e ff  0    ]u5.bytes:b2...
    # 2c 75 37 2e 69 6e 74 65 67 65 72 3a 69 32 35    ,u7.integer:i25
    # 2c 75 34 2e 6e 75 6c 6c 3a 7e 2c 75 34 2e 72    ,u4.null:~,u4.r
    # 65 61 6c 3a 72 31 2e 32 35 65 2d 35 2c 75 34    eal:r1.25e-5,u4
    # 2e 75 74 66 38 3a 75 31 30 2e ce 95 ce bb cf    .utf8:u10......
    # 8d cf 84 ce b7 2c 7d                            .....,}

    my $decoded = decode_bifcode2 $bifcode;

DESCRIPTION

Bifcode2 implements the BIFCODE2 serialisation format, a mixed binary/text encoding with support for the following data types:

  • Primitive:

    • Undefined(null)

    • Booleans(true/false)

    • Integer numbers

    • Real numbers

    • UTF8 strings

    • Binary strings

  • Structured:

    • Arrays(lists)

    • Hashes(dictionaries)

The encoding is simple to construct and relatively easy to parse. There is no need to escape special characters in strings. It is not considered human readable, but as it is mostly text it can usually be visually debugged.

BIFCODE2 can only be constructed canonically; i.e. there is only one possible encoding per data structure. This property makes it suitable for comparing structures (using cryptographic hashes) across networks.

In terms of size the encoding is similar to minified JSON. In terms of speed this module compares well with other pure Perl encoding modules with the same features.

MOTIVATION

BIFCODE2 was created for a project because none of currently available serialization formats (Bencode, JSON, MsgPack, Netstrings, Sereal, YAML, etc) met the requirements of:

  • Support for undef

  • Support for binary data

  • Support for UTF8 strings

  • Universally-recognized canonical form for hashing

  • Trivial to construct on the fly from SQLite triggers

I have no lofty goals or intentions to promote this outside of my specific case, but would appreciate hearing about other uses or implementations.

SPECIFICATION

The encoding is defined as follows:

BIFCODE2_UNDEF

A null or undefined value correspond to "~,".

BIFCODE2_TRUE and BIFCODE2_FALSE

Boolean values are represented by "t," and "f,".

BIFCODE2_UTF8

A UTF8 string is "u" followed by the octet length of the encoded string as a base ten number followed by a "." and the encoded string followed by ",". For example the Perl string "\x{df}" (ß) corresponds to "u2.\x{c3}\x{9f},".

BIFCODE2_BYTES

Opaque data is 'b' followed by the octet length of the data as a base ten number followed by a "." and then the data itself followed by ",". For example a three-byte blob 'xyz' corresponds to 'b3.xyz,'.

BIFCODE2_INTEGER

Integers are represented by an 'i' followed by the number in base 10 followed by a ','. For example 'i3,' corresponds to 3 and 'i-3,' corresponds to -3. Integers have no size limitation. 'i-0,' is invalid. All encodings with a leading zero, such as 'i03,', are invalid, other than 'i0,', which of course corresponds to 0.

BIFCODE2_REAL

Real numbers are represented by an 'r' followed by a decimal number in base 10 followed by a 'e' followed by an exponent followed by a ','. For example 'r3.0e-1,' corresponds to 0.3 and 'r-0.1e0,' corresponds to -0.1. Reals have no size limitation. 'r-0.0e0,' is invalid. All encodings with an extraneous leading zero, such as 'r03.0e0,', or an extraneous trailing zero, such as 'r3.10e0,', are invalid.

BIFCODE2_LIST

Lists are encoded as a '[' followed by their elements (also BIFCODE2 encoded) followed by a ']'. For example '[u4.spam,u4.eggs,]' corresponds to ['spam', 'eggs'].

BIFCODE2_DICT

Dictionaries are encoded as a '{' followed by a list of alternating keys and their corresponding values followed by a '}'. Keys must be of type BIFCODE2_UTF8 or BIFCODE2_BYTES and are encoded with a ":" as the last character instead of ",".

For example, '{u3.cow:u3.moo,u4.spam:u4.eggs,}' corresponds to {'cow': 'moo', 'spam': 'eggs'} and '{u4.spam:[u1.a,u1.b,]}' corresponds to {'spam'. ['a', 'b']}. Keys must appear in sorted order (sorted as raw strings, not alphanumerics).

BIFCODE2_BIFCODE2

A Bifcode string is "B" followed by the octet length of the encoded string as a base ten number followed by a "." and the encoded string followed by ",". This is typically used to frame Bifcode structures over a network.

INTERFACE

encode_bifcode2( $datastructure )

Takes a single argument which may be a scalar, or may be a reference to either a scalar, an array, a hash or a Bifcode2::BIFCODE2 object. Arrays and hashes may in turn contain values of these same types. Returns a byte string blessed as Bifcode2::BIFCODE2.

The mapping from Perl to BIFCODE2 is as follows:

  • 'undef' maps directly to BIFCODE2_UNDEF.

  • The true and false values from the boolean distribution encode to BIFCODE2_TRUE and BIFCODE2_FALSE.

  • A plain scalar is treated as follows:

    • BIFCODE2_UTF8 if utf8::is_utf8 returns true; or

    • BIFCODE2_INTEGER if it looks like a canonically represented integer; or

    • BIFCODE2_REAL if it looks like a real number; or

    • BIFCODE2_UTF8 if it only contains ASCII characters; or

    • BIFCODE2_BYTES when none of the above applies.

    You can force scalars to be encoded a particular way by passing a reference to them blessed as Bifcode2::BYTES, Bifcode2::INTEGER, Bifcode2::REAL or Bifcode2::UTF8. The force_bifcode2 function below can help with creating such references.

  • SCALAR references become BIFCODE2_BYTES.

  • ARRAY references become BIFCODE2_LIST.

  • HASH references become BIFCODE2_DICT.

  • Bifcode2::BIFCODE2 references become BIFCODE2_BIFCODE2.

This subroutine croaks on unhandled data types.

decode_bifcode2( $string [, $max_depth ] )

Takes a byte string and returns the corresponding deserialised data structure.

If you pass an integer for the second option, it will croak when attempting to parse dictionaries nested deeper than this level, to prevent DoS attacks using maliciously crafted input.

BIFCODE2 types are mapped back to Perl in the reverse way to the encode_bifcode2 function, except for:

  • Any scalars which were "forced" to a particular type (using blessed references) will decode as plain scalars.

  • BIFCODE2_BIFCODE2 types are fully inflated into Perl structures, and not the intermediate BIFCODE2 string.

Croaks on malformed data.

force_bifcode2( $scalar, $type )

Returns a reference to $scalar blessed as Bifcode2::$TYPE. The value of $type is not checked, but the encode_bifcode2 function will only accept the resulting reference where $type is one of 'bytes', 'real', 'integer' or 'utf8'.

diff_bifcode2( $bc1, $bc2, [$diff_args] )

Returns a string representing the difference between two bifcodes. The inputs do not need to be valid Bifcode2; they are only expanded with a very simple regex before the diff is done. The third argument ($diff_args) is passed directly to Text::Diff.

Croaks if Text::Diff is not installed.

AnyEvent::Handle Support

Bifcode2 implements the AnyEvent::Handle anyevent_read_type and anyevent_write_type functions which allow you to do this:

    $handle->push_write( 'Bifcode2' => { your => 'structure here' } );

    $handle->push_read(
        'Bifcode2' => sub {
            my ( $hdl, $ref ) = @_;
            # do stuff with $ref
        },
        $maxdepth   # passed straight to decode_bifcode2()
    );

DIAGNOSTICS

The following exceptions may be raised by Bifcode2:

Bifcode2::Error::Decode

Your data is malformed in a non-identifiable way.

Bifcode2::Error::DecodeBytes

Your data contains a byte string with an invalid length.

Bifcode2::Error::DecodeBytesTrunc

Your data includes a byte string declared to be longer than the available data.

Bifcode2::Error::DecodeBytesTerm

Your data includes a byte string that is missing a "," terminator.

Bifcode2::Error::DecodeDepth

Your data contains dicts or lists that are nested deeper than the $max_depth passed to decode_bifcode2().

Bifcode2::Error::DecodeTrunc

Your data is truncated.

Bifcode2::Error::DecodeReal

Your data contained something that was supposed to be a real but didn't make sense.

Bifcode2::Error::DecodeRealTrunc

Your data contains a real that is truncated.

Bifcode2::Error::DecodeInteger

Your data contained something that was supposed to be an integer but didn't make sense.

Bifcode2::Error::DecodeIntegerTrunc

Your data contains an integer that is truncated.

Bifcode2::Error::DecodeKeyType

Your data violates the bifcode format constaint that all dict keys be BIFCODE2_BYTES or BIFCODE2_UTF8.

Bifcode2::Error::DecodeKeyDuplicate

Your data violates the bifcode format constaint that all dict keys must be unique.

Bifcode2::Error::DecodeKeyOrder

Your data violates the bifcode format constaint that dict keys must appear in lexical sort order.

Bifcode2::Error::DecodeKeyValue

Your data contains a dictionary with an odd number of elements.

Bifcode2::Error::DecodeTrailing

Your data does not end after the first bifcode-serialised item.

Bifcode2::Error::DecodeUTF8

Your data contained a UTF8 string with an invalid length.

Bifcode2::Error::DecodeUTF8Trunc

Your data includes a string declared to be longer than the available data.

Bifcode2::Error::DecodeUTF8Term

Your data includes a UTF8 string that is missing a "," terminator.

Bifcode2::Error::DecodeUsage

You called decode_bifcode2() with invalid arguments.

Bifcode2::Error::DiffUsage

You called diff_bifcode2() with invalid arguments.

Bifcode2::Error::EncodeBytesUndef

You attempted to encode undef as a byte string.

Bifcode2::Error::EncodeReal

You attempted to encode something as a real that isn't recognised as one.

Bifcode2::Error::EncodeRealUndef

You attempted to encode undef as a real.

Bifcode2::Error::EncodeInteger

You attempted to encode something as an integer that isn't recognised as one.

Bifcode2::Error::EncodeIntegerUndef

You attempted to encode undef as an integer.

Bifcode2::Error::EncodeUTF8Undef

You attempted to encode undef as a UTF8 string.

Bifcode2::Error::EncodeUnhandled

You are trying to serialise a data structure that contains a data type not supported by the bifcode format.

Bifcode2::Error::EncodeUsage

You called encode_bifcode2() with invalid arguments.

Bifcode2::Error::ForceUsage

You called force_bifcode2() with invalid arguments.

BUGS AND LIMITATIONS

Strings and numbers are practically indistinguishable in Perl, so encode_bifcode2() has to resort to a heuristic to decide how to serialise a scalar. This cannot be fixed.

SEE ALSO

This distribution includes the diff-bifcode command-line utility for comparing BIFCODE2 in files.

AUTHOR

Mark Lawrence <nomad@null.net>, heavily based on Bencode by Aristotle Pagaltzis <pagaltzis@gmx.de>

COPYRIGHT AND LICENSE

This software is copyright (c):

  • 2015 by Aristotle Pagaltzis

  • 2017-2019 by Mark Lawrence.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.