Venice core

This project aims at providing a unified abstract interface to exchange data between devices using different technologies.

Data exchanges do work as follow:

File exchange is done between a sender and a receiver;
Multiple (one or several) channels link sender and receiver;
Sender-side, a scheduler sends file chunks on channels as it sees fit;
Receiver-side, an aggregator reconstructs file from received file chunks.

General architecture

Channels

A channel is charged with transmitting data from sender end to receiver end. That's it!

This package provides a arbitrary-abstract Channel interface for other packages to implement, the idea being that you can implement a channel with whatever you want: Wi-Fi, Bluetooth...

Any technology able to carry data can be implemented into a channel! Yeah, even sound! (don't try this at home)

There are two types of channel:

DataChannel: they are used to transfer file chunks between devices;
BootstrapChannel: they are used to communicate about DataChannel credentials.

Implementation

Channel implementation

Bootstrap channel

abstract class BootstrapChannel {
  /// Provides information to sending and receiving ends about what's happening
  /// in the current channel.
  late Function(BootstrapChannelEvent event, dynamic data) on;

  /// Initializes current channel, and returns when it is ready to send data.
  Future<void> initSender();

  /// Initializes current channel, and returns when it is ready to receive data.
  Future<void> initReceiver();

  /// Sends file metadata to receiving end.
  Future<void> sendFileMetadata(FileMetadata data);

  /// Sends channel metadata to receiving end, for it to initialize data
  /// channels before starting file exchange.
  Future<void> sendChannelMetadata(ChannelMetadata data);
}

Your custom bootstrap channel must implement those four methods:

initSender will be called by the scheduler: you should include in there all code relative to socket opening;
initReceiver will be called by the receiver: it should establish connection with connection-opening code contained in initSender;
sendFileMetadata and sendChannelMetadata will be called by the sending end to transmit information to receiving end.

Data channel

abstract class DataChannel {
  /// Provides information to sending and receiving ends about what's happening
  /// in the current channel.
  late Function(DataChannelEvent event, dynamic data) on;

  /// Initializes current channel, and returns when it is ready to send data.
  /// Once sockets are ready, this must send information about them through
  /// provided bootstrap channel.
  Future<void> initSender(BootstrapChannel channel);

  /// Initializes current channel from provided channel metadata, and returns
  /// when it is ready to receive data.
  Future<void> initReceiver(ChannelMetadata data);

  /// Sends a file piece through current channel, and returns after successful
  /// sending; this doesn't check if message was received.
  Future<void> sendMessage(VeniceMessage msg);
}

Your custom data channel must implement those three methods:

initSender will be called by the scheduler: you should include in there all code relative to socket opening;
initReceiver will be called by the receiver: it should establish connection with connection-opening code contained in initSender;
sendMessage will be called by scheduler sender-side; it should send chunk's data over previously-opened socket.

Implementation strategy

As said previously, the Channel interface provided by this package is as abstract as possible to let people implement it the way they want.

It is written in Dart, and thus can be used on a variety of platforms: Android, iOS, Linux, Windows and macOS.

There are two ways to implement a channel: you must create either a package or a plugin.

Package implementation

If you can use Dart or Flutter packages to create your implementation, then package is the way to go. It only requires you to implement Channel interface using third-party packages.

Plugin implementation

However, if you need to write channel implementation for each platforms, you'll have to create a Flutter plugin, which invokes native code through a method channel.

Venice-D2D/venice_core