NAME

Bifcode - simple serialization format

VERSION

1.002 (2018-09-23)

SYNOPSIS

    use boolean;
    use Bifcode qw( encode_bifcode decode_bifcode );

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

    # 7b 55 35 3a 62 6f 6f 6c 73 2c 5b 30    {U5:bools,[0
    # 31 5d 55 35 3a 62 79 74 65 73 2c 42    1]U5:bytes,B
    # 32 3a ff  0 2c 55 35 3a 66 6c 6f 61    2:..,U5:floa
    # 74 2c 46 31 2e 32 35 65 2d 35 2c 55    t,F1.25e-5,U
    # 37 3a 69 6e 74 65 67 65 72 2c 49 32    7:integer,I2
    # 35 2c 55 35 3a 75 6e 64 65 66 2c 7e    5,U5:undef,~
    # 55 34 3a 75 74 66 38 2c 55 32 3a c3    U4:utf8,U2:.
    # 9f 2c 7d                               .,}

    my $decoded = decode_bifcode $bifcode;

DESCRIPTION

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

  • Primitive:

    • Undefined(null)

    • Booleans(true/false)

    • Integer numbers

    • Floating point 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.

bifcode 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

bifcode 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:

BIFCODE_UNDEF

A null or undefined value correspond to "~".

BIFCODE_TRUE and BIFCODE_FALSE

Boolean values are represented by "1" and "0".

BIFCODE_UTF8

A UTF8 string is "U" followed by the octet length of the encoded string as a base ten number followed by a colon and the encoded string followed by ",". For example the Perl string "\x{df}" (ß) corresponds to "U2:\x{c3}\x{9f},".

BIFCODE_BYTES

Opaque data is 'B' followed by the octet length of the data as a base ten number followed by a colon and then the data itself followed by ",". For example a three-byte blob 'xyz' corresponds to 'B3:xyz,'.

BIFCODE_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.

BIFCODE_FLOAT

Floats are represented by an 'F' followed by a decimal number in base 10 followed by a 'e' followed by an exponent followed by a ','. For example 'F3.0e-1,' corresponds to 0.3 and 'F-0.1e0,' corresponds to -0.1. Floats have no size limitation. 'F-0.0e0,' is invalid. All encodings with an extraneous leading zero, such as 'F03.0e0,', or an extraneous trailing zero, such as 'F3.10e0,', are invalid.

BIFCODE_LIST

Lists are encoded as a '[' followed by their elements (also bifcode encoded) followed by a ']'. For example '[U4:spam,U4:eggs,]' corresponds to ['spam', 'eggs'].

BIFCODE_DICT

Dictionaries are encoded as a '{' followed by a list of alternating keys and their corresponding values followed by a '}'. 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 be BIFCODE_UTF8 or BIFCODE_BYTES and appear in sorted order (sorted as raw strings, not alphanumerics).

INTERFACE

encode_bifcode( $datastructure )

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

The mapping from Perl to bifcode is as follows:

  • 'undef' maps directly to BIFCODE_UNDEF.

  • The true and false functions from the boolean distribution encode to BIFCODE_TRUE and BIFCODE_FALSE.

  • Plain scalars are treated as BIFCODE_UTF8 unless:

    • They look like canonically represented integers in which case they are mapped to BIFCODE_INTEGER; or

    • They look like floats in which case they are mapped to BIFCODE_FLOAT.

  • SCALAR references become BIFCODE_BYTES.

  • ARRAY references become BIFCODE_LIST.

  • HASH references become BIFCODE_DICT.

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

This subroutine croaks on unhandled data types.

decode_bifcode( $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.

bifcode types are mapped back to Perl in the reverse way to the encode_bifcode function, with the exception that any scalars which were "forced" to a particular type (using blessed references) will decode as unblessed scalars.

Croaks on malformed data.

force_bifcode( $scalar, $type )

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

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

Returns a string representing the difference between two bifcodes. The inputs do not need to be valid Bifcode; 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.

DIAGNOSTICS

The following exceptions may be raised by Bifcode:

Bifcode::Error::Decode

Your data is malformed in a non-identifiable way.

Bifcode::Error::DecodeBytes

Your data contains a byte string with an invalid length.

Bifcode::Error::DecodeBytesTrunc

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

Bifcode::Error::DecodeBytesTerm

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

Bifcode::Error::DecodeDepth

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

Bifcode::Error::DecodeTrunc

Your data is truncated.

Bifcode::Error::DecodeFloat

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

Bifcode::Error::DecodeFloatTrunc

Your data contains a float that is truncated.

Bifcode::Error::DecodeInteger

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

Bifcode::Error::DecodeIntegerTrunc

Your data contains an integer that is truncated.

Bifcode::Error::DecodeKeyType

Your data violates the bifcode format constaint that all dict keys be BIFCODE_BYTES or BIFCODE_UTF8.

Bifcode::Error::DecodeKeyDuplicate

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

Bifcode::Error::DecodeKeyOrder

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

Bifcode::Error::DecodeKeyValue

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

Bifcode::Error::DecodeTrailing

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

Bifcode::Error::DecodeUTF8

Your data contained a UTF8 string with an invalid length.

Bifcode::Error::DecodeUTF8Trunc

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

Bifcode::Error::DecodeUTF8Term

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

Bifcode::Error::DecodeUsage

You called decode_bifcode() with invalid arguments.

Bifcode::Error::DiffUsage

You called diff_bifcode() with invalid arguments.

Bifcode::Error::EncodeBytesUndef

You attempted to encode undef as a byte string.

Bifcode::Error::EncodeFloat

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

Bifcode::Error::EncodeFloatUndef

You attempted to encode undef as a float.

Bifcode::Error::EncodeInteger

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

Bifcode::Error::EncodeIntegerUndef

You attempted to encode undef as an integer.

Bifcode::Error::EncodeUTF8Undef

You attempted to encode undef as a UTF8 string.

Bifcode::Error::EncodeUnhandled

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

Bifcode::Error::EncodeUsage

You called encode_bifcode() with invalid arguments.

Bifcode::Error::ForceUsage

You called force_bifcode() with invalid arguments.

BUGS AND LIMITATIONS

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

At the moment all Perl hash keys are encoded as BIFCODE_UTF8 as I have not yet had the need for BIFCODE_BYTES keys or found a cheap, obvious way to distinguish the two.

SEE ALSO

This distribution includes the diff-bifcode command-line utility for comparing Bifcodes 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

  • 2017-2018 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.