suggestion from omar - 1

mm2src/coins/utxo/rpc_clients/electrum_rpc/client.rs

@@ -307,11 +307,11 @@ impl ElectrumClient {
         let request = (req_id, request);
         // Use the active connections for this request.
         let connections = self.connection_manager.get_active_connections().await;
-        // Maximum number of connections to establish or use in request concurrently.
-        // Could be up to connections.len().
-        let concurrency = 1;
+        // Maximum number of connections to establish or use in request concurrently. Could be up to connections.len().
+        let concurrency = if send_to_all { connections.len() as u32 } else { 1 };
+        let disconnect_immediately = false;
         match self
-            .send_request_using(&request, connections, send_to_all, concurrency)
+            .send_request_using(&request, connections, send_to_all, concurrency, disconnect_immediately)
             .await
         {
             Ok(response) => Ok(response),
@@ -322,8 +322,9 @@ impl ElectrumClient {
                 // which means we might break the max connections rule.
                 // We will at most we will break this rule by `1` (have `max_connected + 1` open connections).
                 let concurrency = 1;
+                let disconnect_immediately = true;
                 match self
-                    .send_request_using(&request, connections, send_to_all, concurrency)
+                    .send_request_using(&request, connections, send_to_all, concurrency, disconnect_immediately)
                     .await
                 {
                     Ok(response) => Ok(response),
@@ -353,6 +354,8 @@ impl ElectrumClient {
         let response = connection
             .electrum_request(json, request.rpc_id(), ELECTRUM_REQUEST_TIMEOUT)
             .await?;
+        // Inform the connection manager that the connection was queried and no longer needed now.
+        self.connection_manager.not_needed(&to_addr).await;
 
         Ok(response)
     }
@@ -368,6 +371,7 @@ impl ElectrumClient {
         connections: Vec<Arc<ElectrumConnection>>,
         send_to_all: bool,
         max_concurrency: u32,
+        disconnect_immediately: bool,
     ) -> Result<(JsonRpcRemoteAddr, JsonRpcResponseEnum), Vec<(JsonRpcRemoteAddr, JsonRpcErrorType)>> {
         let max_concurrency = max_concurrency.max(1) as usize;
         // Create the request
@@ -408,6 +412,14 @@ impl ElectrumClient {
                         if final_response.is_none() {
                             final_response = Some((address, response));
                         }
+                        if disconnect_immediately {
+                            connection
+                                .disconnect(Some(ElectrumConnectionErr::Temporary(
+                                    "Was used as a fallback and not needed now.".to_string(),
+                                )))
+                                .await;
+                            event_handlers.on_disconnected(connection.address()).ok();
+                        }
                         if !send_to_all {
                             return final_response.ok_or(errors);
                         }

mm2src/coins/utxo/rpc_clients/electrum_rpc/connection_manager/manager.rs

@@ -266,7 +266,7 @@ impl ConnectionManager {
         }
     }
 
-    // Handles the connection event.
+    /// Handles the connection event.
     pub fn on_connected(&self, server_address: &str) {
         let all_connections = self.read_connections();
         let connection_ctx = unwrap_or_return!(all_connections.get(server_address));
@@ -275,7 +275,7 @@ impl ConnectionManager {
         connection_ctx.connected();
     }
 
-    // Handles the disconnection event from an Electrum server.
+    /// Handles the disconnection event from an Electrum server.
     pub fn on_disconnected(&self, server_address: &str) {
         let all_connections = self.read_connections();
         let connection_ctx = unwrap_or_return!(all_connections.get(server_address));
@@ -296,6 +296,24 @@ impl ConnectionManager {
         client.subscribe_addresses(abandoned_subs).ok();
     }
 
+    /// A method that should be called after using a specific server for some request.
+    ///
+    /// Instead of disconnecting the connection right away, this method will only disconnect it
+    /// if it's not in the maintained connections set.
+    pub async fn not_needed(&self, server_address: &str) {
+        let (id, connection) = {
+            let all_connections = self.read_connections();
+            let connection_ctx = unwrap_or_return!(all_connections.get(server_address));
+            (connection_ctx.id, connection_ctx.connection.clone())
+        };
+        if !self.read_maintained_connections().contains_key(&id) {
+            connection
+                .disconnect(Some(ElectrumConnectionErr::Temporary("Not needed anymore".to_string())))
+                .await;
+            self.on_disconnected(connection.address());
+        }
+    }
+
     /// Remove a connection from the connection manager by its address.
     // TODO(feat): Add the ability to add a connection during runtime.
     pub async fn remove_connection(

mm2src/coins/utxo/rpc_clients/electrum_rpc/constants.rs

@@ -1,5 +1,5 @@
 /// The timeout for the electrum server to respond to a request.
-pub const ELECTRUM_REQUEST_TIMEOUT: f64 = 60.;
+pub const ELECTRUM_REQUEST_TIMEOUT: f64 = 20.;
 /// The default (can be overridden) maximum timeout to establish a connection with the electrum server.
 /// This included connecting to the server and querying the server version.
 pub const DEFAULT_CONNECTION_ESTABLISHMENT_TIMEOUT: f64 = 60.;

mm2src/coins/utxo/utxo_builder/utxo_coin_builder.rs

@@ -68,9 +68,6 @@ pub enum UtxoCoinBuildError {
     )]
     CoinDoesntSupportTrezor,
     BlockHeaderStorageError(BlockHeaderStorageError),
-    // TODO: this isn't used
-    #[display(fmt = "Error {} on getting the height of the latest block from rpc!", _0)]
-    CantGetBlockCount(String),
     #[display(fmt = "Internal error: {}", _0)]
     Internal(String),
     #[display(fmt = "SPV params verificaiton failed. Error: {_0}")]