Structure

Crystal's answer to Python's struct and Ruby's Array.pack/unpack.

Installation

1. Add the dependency to your shard.yml:

   dependencies:
     structure:
       github: watzon/structure
   

2. Run shards install

Usage

require "structure"

s = Structure.from("2IB")
buf = s.pack(1, 2, 3)
# alternatively
buf = s.pack([1, 2, 3])

pp buf == Bytes[0, 0, 0, 1, 0, 0, 0, 2, 3]
# => true

pp s.unpack(buf)
# => [1u32, 2u32, 3u8]

You can also make use of pack_into and unpack_from if you would like to use an existing IO.

require "structure"

io = IO::Memory.new

s = Structure.from("2IB")
buf = s.pack_into(io, 1, 2, 3)
# alternatively
buf = s.pack_into(io, [1, 2, 3])

io2 = IO::Memory.new

pp s.unpack_from(io)
# => [1u32, 2u32, 3u8]

Format Strings

Endianness

By default, the endianness is big-endian. It could be determined by specifying one of the following characters at the beginning of the format:

Types

Any format character may be preceded by an integral repeat count. For example, the format string '4h' means exactly the same as 'hhhh'.

Differences from Python struct library

• Numbers' byte order is big-endian by default (e.g. u32, f64...).
• There is no alignment support.
• 32 bit integer format character is only 'I'/'i' (and not 'L'/'l').

Contributing

1. Fork it (https://github.com/watzon/structure/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Chris Watson - creator and maintainer