Allow ElectrumSyncClient to reuse a preexisting client

Previously, our API would only allow users to have `ElectrumSyncClient`
a) construct an entirely `new` `electrum_client::Client` or b) take an
owened client via `from_client`.

Here, we change `ElectrumSyncClient::from_client` to accept an
`Arc<ElectrumClient>`, allowing to reuse a pre-existing client without
owning it. This is important as it will allow us to reuse the same
connection instead of forcing users to establish multiple connections if
they need something beyond syncing LDK.

Author: tnull

lightning-transaction-sync/src/electrum.rs

@@ -22,7 +22,7 @@ use bitcoin::{BlockHash, Script, Transaction, Txid};
 
 use std::collections::HashSet;
 use std::ops::Deref;
-use std::sync::Mutex;
+use std::sync::{Arc, Mutex};
 use std::time::Instant;
 
 /// Synchronizes LDK with a given Electrum server.
@@ -43,7 +43,7 @@ where
 {
 	sync_state: Mutex<SyncState>,
 	queue: Mutex<FilterQueue>,
-	client: ElectrumClient,
+	client: Arc<ElectrumClient>,
 	logger: L,
 }
 
@@ -53,18 +53,18 @@ where
 {
 	/// Returns a new [`ElectrumSyncClient`] object.
 	pub fn new(server_url: String, logger: L) -> Result<Self, TxSyncError> {
-		let client = ElectrumClient::new(&server_url).map_err(|e| {
+		let client = Arc::new(ElectrumClient::new(&server_url).map_err(|e| {
 			log_error!(logger, "Failed to connect to electrum server '{}': {}", server_url, e);
 			e
-		})?;
+		})?);
 
 		Self::from_client(client, logger)
 	}
 
 	/// Returns a new [`ElectrumSyncClient`] object using the given Electrum client.
 	///
 	/// This is not exported to bindings users as the underlying client from BDK is not exported.
-	pub fn from_client(client: ElectrumClient, logger: L) -> Result<Self, TxSyncError> {
+	pub fn from_client(client: Arc<ElectrumClient>, logger: L) -> Result<Self, TxSyncError> {
 		let sync_state = Mutex::new(SyncState::new());
 		let queue = Mutex::new(FilterQueue::new());
 
@@ -489,8 +489,8 @@ where
 	/// Returns a reference to the underlying Electrum client.
 	///
 	/// This is not exported to bindings users as the underlying client from BDK is not exported.
-	pub fn client(&self) -> &ElectrumClient {
-		&self.client
+	pub fn client(&self) -> Arc<ElectrumClient> {
+		Arc::clone(&self.client)
 	}
 }