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:

[X] Null
[X] Booleans
[X] Strings
Atoms
[X] Unicode Strings
[X] Floats
[X] Integers
Longs
Longs over 64 bits
[X] Objects
[X] 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:

[X] None
[X] Booleans
[X] Strings
[X] Atoms
[X] Unicode Strings
[X] Floats
[X] Integers
[X] Longs
Longs over 64 bits
[X] Dictionaries
[X] Lists
[X] Tuples
[X] 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

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