* This release is almost entirely focused on a new API in the
`lightning-invoice` crate - the `InvoicePayer`. `InvoicePayer` is a
struct which takes a reference to a `ChannelManager` and a `NetworkGraph`
and retries payments as paths fail. It limits retries to a configurable
number, but is not serialized to disk and may retry additional times across
a serialization/load. In order to learn about failed payments, it must
receive `Event`s directly from the `ChannelManager`, wrapping a
user-provided `EventHandler` which it provides all unhandled events to
(#1059).
* `get_route` has been renamed `find_route` (#1059) and now takes a `Payee`
struct in replacement of a number of its long list of arguments (#1134).
`Payee` is further stored in the `Route` object returned and provided in the
`RouteParameters` contained in `Event::PaymentPathFailed` (#1059).
* `ChannelMonitor`s must now be persisted after calls which provide new block
data, prior to `MonitorEvent`s being passed back to `ChannelManager` for
processing. If you are using a `ChainMonitor` this is handled for you.
The `Persist` API has been updated to `Option`ally take the
`ChannelMonitorUpdate` as persistence events that result from chain data no
longer have a corresponding update (#1108).
* `routing::Score` now has a `payment_path_failed` method which it can use to
learn which channels often fail payments. It is automatically called by
`InvoicePayer` for failed payment paths (#1144).
* The default `Scorer` implementation is now a type alias to a type generic
across different clocks and supports serialization to persist scoring data
across restarts (#1146).
* `Event::PaymentSent` now includes the full fee which was spent across all
payment paths which were fulfilled or pending when the payment was fulfilled
(#1142).
* `NetGraphMsgHandler` now takes a `Deref` to the `NetworkGraph`, allowing for
shared references to the graph data to make serialization and references to
the graph data in the `InvoicePayer`'s `Router` simpler (#1149).
* `routing::Score::channel_penalty_msat` has been updated to provide the
`NodeId` of both the source and destination nodes of a channel (#1133).
* Delay disconnecting peers if we receive messages from them even if it takes
a while to receive a pong from them. Further, avoid sending too many gossip
messages between pings to ensure we should always receive pongs in a timely
manner. Together, these should significantly reduce instances of us failing
to remain connected to a peer during initial gossip sync (#1137).
* If a payment is sent, creating an outbound HTLC and sending it to our
counterparty (implying the `ChannelMonitor` was persisted on disk), but the
`ChannelManager` was not persisted prior to shutdown/crash, no
`Event::PaymentPathFailed` event will be generated if the HTLC is eventually
failed on chain (#1104).
* All above new Events/fields are ignored by prior clients. All above new
Events/fields are not present when reading objects serialized by prior
versions of the library.
* Payments for which a `Route` was generated using a previous version or for
which the payment was originally sent by a previous version of the library
will not be retried by an `InvoicePayer`.
This release was singularly focused and some contributions by third parties
were delayed.
In total, this release features 38 files changed, 4414 insertions, and 969
deletions in 71 commits from 2 authors, in alphabetical order:
* Jeffrey Czyz
* Matt Corallo
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