CStruct-Packing-raku

Description

CStruct::Packing is a simple solution for structured reading and writing of CStructs as binary numerical data.

The module is an alternative to Native::Packing. It requires all structures to be native CStructs, but can be signficantly faster.

Example

use v6;
use CStruct::Packing :Endian;

# open a GIF read the header
my class LogicalDescriptor
    is repr('CStruct')
    does CStruct::Packing[VaxEndian] {

    has uint16 $.width;
    has uint16 $.height;
    has uint8  $.flags;
    has uint8  $.bgColorIndex;
    has uint8  $.aspect;
}

my $fh = "t/lightbulb.gif".IO.open( :r, :bin);
my $offset = 6;  # skip GIF header

my LogicalDescriptor $screen .= read: $fh, :$offset;
say "GIF has size {$screen.width} X {$screen.height}";

It currently handles records containing native integers (int8, uint8, int16, etc), numerics (num32, num64) and inlined CStruct sub-records.

Data may read be and written to binary files, via the read and write methods
Or read and written to buffers via the unpack and pack methods.

Endianess

The two fixed modes are:

VaxEndian (or LittleEndian) - least significant byte written first
NetworkEndian (or BigEndian) - most significant byte written first

There is also a platform-dependant HostEndian mode. This will read and write binary data in the same endianess as the host computer.

Endian Examples:

use CStruct::Packing :Endian;

class C is repr('CStruct') { has int16 $.a }
class C-vax  is repr('CStruct') is C does CStruct::Packing[VaxEndian] {}
class C-net  is repr('CStruct') is C does CStruct::Packing[NetworkEndian] {}
class C-host is repr('CStruct') is C does CStruct::Packing[HostEndian] {}

say C-vax.new(:a(42)).pack;    # Buf[uint8]:0x<2a 00>
say C-net.new(:a(42)).pack;    # Buf[uint8]:0x<00 2a>
say C-host.new(:a(42)).pack;   # Depends on your host

Methods

pack

method pack(Any:D: Blob $buf?, :$layout --> Blob)

Returns a packed representation of the CStruct as a Blob.

unpack

method unpack(Blob:D $buf, :$layout --> Any:D)

Unpacks the buffer. If this method is called from an object, the object's contents are replaced. Otherwise a new object is returned.

read

method read(IO::Handle \fh, UInt :$offset, :$layout -> Any:D)

Utility method to read and unpack a structure from a file handle.

write

method read(IO::Handle \fh, UInt :$offset, :$layout)

Uitility method to pack and write a structure to a file handle.

packing-layout

method packing-layout(--> CArray)

Precomputes the memory layout and endian conversionsfor a structure.

my $layout = Rec.packing-layout; # precompute layout
my @recs = 100 xx Rec.read($fh, :$layout);

packed-size

method packed-size(--> size_t)

Returns the size of the packed structure

unpacked-size

method unpacked-size(--> size_t)

Returns the size of the packed structure. S.unpacked-size should be equal to nativesizeof(S).

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