The `chain::Access` trait (and the `chain::AccessError` enum) is a
bit strange - it only really makes sense if users import it via the
`chain` module, otherwise they're left with a trait just called
`Access`. Worse, for bindings users its always just called
`Access`, in part because many downstream languages don't have a
mechanism to import a module and then refer to it.
Further, its stuck dangling in the `chain` top-level mod.rs file,
sitting in a module that doesn't use it at all (it's only used in
`routing::gossip`).
Instead, we give it its full name - `UtxoLookup` (and rename the
error enum `UtxoLookupError`) and put it in the a new
`routing::utxo` module, next to `routing::gossip`.
NetGraphMsgHandler implements RoutingMessageHandler to handle gossip
messages defined in BOLT 7 and maintains a view of the network by
updating NetworkGraph. Rename it to P2PGossipSync, which better
describes its purpose, and to contrast with RapidGossipSync.
WatchEventProvider served as a means for replacing ChainWatchInterface.
However, it requires users to explicitly fetch WatchEvents, even if not
interested in them. Replace WatchEventProvider by chain::Filter, which
is an optional member of ChainMonitor. If set, interesting transactions
and output spends are registered such that blocks containing them can be
retrieved from a chain source in an efficient manner.
This is useful when the chain source is not a full node. For Electrum,
it allows for pre-filtered blocks. For BIP157/158, it serves as a means
to match against compact filters.
ManyChannelMonitor was renamed chain::Watch in the previous commit. Use
a more concise name for an implementation that monitors the chain for
channel activity. Future work will parameterize the struct to allow for
different varieties of persistence. Thus, users usually will be able to
use ChainMonitor directly rather than implementing a chain::Watch that
wraps it.
Rename ManyChannelMonitor to chain::Watch and move to chain/mod.rs,
where chain-related interfaces live. Update the documentation for
clarity and to conform to rustdoc formatting.
ChainWatchInterface was intended as an interface for watching rather
than accessing the chain. Remove get_chain_utxo and add chain::Access
trait for this behavior. Wrap it with an Option in NetGraphMsgHandler in
order to simplify the error interface.
Use of ChainWatchInterface was replaced with WatchEvent in the previous
commit. Remove it from the parameterization of SimpleManyChannelMonitor
since it is no longer needed.
