Erlpack

Erlpack is a fast encoder and decoder for the Erlang Term Format (version 131) for Python and JavaScript.

JavaScript

Things that can be packed:

• Null
• Booleans
• Strings
• Atoms
• Unicode Strings
• Floats
• Integers
• Longs
• Longs over 64 bits
• Objects
• Arrays
• Tuples
• PIDs
• Ports
• Exports
• References

How to pack:

let erlpack = require("erlpack");

packed = erlpack.pack({'a': true, 'list': ['of', 3, 'things', 'to', 'pack']});

How to unpack:

Note: Unpacking requires the binary data be a Uint8Array or Buffer. For those using electron/libchromium see the gotcha below.

let erlpack = require("erlpack");

let unpacked = null;
let packed = new Buffer('', 'binary');
try  {
    unpacked = erlpack.unpack(packed);
}
catch (e) {
    // got an exception parsing
}

Libchromium / Electron Gotcha

Some versions of libchromium replace the native data type backing TypedArrays with a custom data type called blink::WebArrayBuffer. To keep erlpack' dependencies simple this data type is not supported directly. If you're using Electron / Libchromium you need to convert the blink::WebArrayBuffer into a node::Buffer before passing to erlpack. You will need to add this code into your native package somewhere:

v8::Local<v8::Value> ConvertToNodeBuffer(const v8::Local<v8::Object>& blinkArray)
{
    if (node::Buffer::HasInstance(blinkArray)) {
        return blinkArray;
    }
    else if (blinkArray->IsArrayBufferView()) {
        auto byteArray = v8::ArrayBufferView::Cast(*blinkArray);
        return node::Buffer::Copy(v8::Isolate::GetCurrent(), (const char*)byteArray->Buffer()->GetContents().Data(), byteArray->ByteLength()).ToLocalChecked();
    }
    
    return v8::Local<v8::Primitive>(v8::Null(v8::Isolate::GetCurrent()));
}

Then in JavaScript something like:

let packed = NativeUtils.convertToNodeBuffer(new Uint8Array(binaryPayload));
// unpack now using erlpack.unpack(packed)

Python

Things that can be packed:

• None
• Booleans
• Strings
• Atoms
• Unicode Strings
• Floats
• Integers
• Longs
• Longs over 64 bits
• Dictionaries
• Lists
• Tuples
• User Types (via an encode hook)
• PIDs
• Ports
• Exports
• References

How to pack:

from erlpack import pack

packed = pack(["thing", "to", "pack"])

How to unpack:

from erlpack import unpack

unpacked = unpack(packed)

How to pack an atom:

from erlpack import Atom, pack

packed = pack(Atom('hello'))

How to use an encode hook.

from erlpack import ErlangTermEncoder

def encode_hook(obj):
    if isinstance(obj, datetime.datetime):
        return obj.isoformat()

encoder = ErlangTermEncoder(encode_hook=encode_hook)
packed = encoder.pack(datetime.datetime(2015, 12, 25, 12, 23, 55))

How to make custom types packable.

from erlpack import pack, Atom

class User(object):
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __erlpack__(self):
        return {
            Atom('name'): self.name,
            Atom('age'): self.age
        }

u = User(name='Jake', age=23)
packed = pack(u)

Go (golang)

Discord has moved away from Go internally and so we do not maintain a version of erlpack in Go ourselves. However, all is not lost!, please check out: https://github.com/JakeMakesStuff/go-erlpack

Building

Python

Generating the new .cpp files can be accomplished by running python setup.py --use-cython build_ext --inplace.

cython must be installed for this to work.

Testing

1. Install the development version of erlpack with python setup.py develop.
2. Install pytest.
3. Execute pytest py/tests.