Fenrir

Fenrir - 2020-12-18

Support for on-chain progression of app channels.

Added

• On-chain progression: The channel watcher is now interactive and informs the
  client when a channel has been registered on-chain. If the channel has a
  defined app logic with a valid state transition logic, clients can
  individually progress the app state on-chain according to the defined state
  transition logic by calling ProgressBy on the channel object.
• Settle with sub-channel disputes: Ledger channels can now be settled with
  funds locked in disputed sub-channels if the corresponding sub-channels have
  been registered and the disputes have been resolved on-chain.

Changed

• The channel watcher logic changed. The channel watcher now takes as input an
  event handler which gets notified about on-chain channel events. Before, the
  watcher automatically settled a channel in case of a dispute. Now, the watcher
  will automatically detect if an old state has been registered, refute with the
  most recent one, and notify the user. If the channel has a defined application
  logic, the user can further progress the channel on-chain. It is within the
  responsibility of the framework user to finally settle the channel and
  withdraw the funds.
• The channel settling logic changed. Before, a call to Settle on a channel
  object automatically registered the channel, concluded it, and withdrew the
  funds. Now, to accomodate on-chain progression functionality, the user must
  call Register independetly before being able to settle the channel.
  Afterwards, for app channels, the user has the opportunity to progress the
  channel state on-chain by calling ProgressBy. Finally, the user can settle
  the channel by calling Settle.
• ContractBackend.NewTransactor now sets the context on TransactOpts.
  Furthermore, parameter value has been removed.

Fixed

• Persistence: Sub-channels are now persisted and restored properly.