+
+/// The `Access` trait defines behavior for accessing chain data and state, such as blocks and
+/// UTXOs.
+pub trait Access: Send + Sync {
+ /// Returns the transaction output of a funding transaction encoded by [`short_channel_id`].
+ /// Returns an error if `genesis_hash` is for a different chain or if such a transaction output
+ /// is unknown.
+ ///
+ /// [`short_channel_id`]: https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md#definition-of-short_channel_id
+ fn get_utxo(&self, genesis_hash: &BlockHash, short_channel_id: u64) -> Result<TxOut, AccessError>;
+}
+
+/// An error when accessing the chain via [`Access`].
+///
+/// [`Access`]: trait.Access.html
+#[derive(Clone)]
+pub enum AccessError {
+ /// The requested chain is unknown.
+ UnknownChain,
+
+ /// The requested transaction doesn't exist or hasn't confirmed.
+ UnknownTx,
+}
+
+/// An interface for providing [`WatchEvent`]s.
+///
+/// [`WatchEvent`]: enum.WatchEvent.html
+pub trait WatchEventProvider {
+ /// Releases events produced since the last call. Subsequent calls must only return new events.
+ fn release_pending_watch_events(&self) -> Vec<WatchEvent>;
+}
+
+/// An event indicating on-chain activity to watch for pertaining to a channel.
+pub enum WatchEvent {
+ /// Watch for a transaction with `txid` and having an output with `script_pubkey` as a spending
+ /// condition.
+ WatchTransaction {
+ /// Identifier of the transaction.
+ txid: Txid,
+
+ /// Spending condition for an output of the transaction.
+ script_pubkey: Script,
+ },
+ /// Watch for spends of a transaction output identified by `outpoint` having `script_pubkey` as
+ /// the spending condition.
+ WatchOutput {
+ /// Identifier for the output.
+ outpoint: OutPoint,
+
+ /// Spending condition for the output.
+ script_pubkey: Script,
+ }
+}