node: ConnectionPoolError

Introduced a ConnectionPoolError which appears when
we were unable to select a connection from the connection pool.

scylla-cql/src/errors.rs

@@ -37,6 +37,10 @@ pub enum QueryError {
     #[error("IO Error: {0}")]
     IoError(Arc<std::io::Error>),
 
+    /// Selected node's connection pool is in invalid state.
+    #[error("No connections in the pool: {0}")]
+    ConnectionPoolError(#[from] ConnectionPoolError),
+
     /// Unexpected message received
     #[error("Protocol Error: {0}")]
     ProtocolError(&'static str),
@@ -431,6 +435,10 @@ pub enum NewSessionError {
     #[error("IO Error: {0}")]
     IoError(Arc<std::io::Error>),
 
+    /// Selected node's connection pool is in invalid state.
+    #[error("No connections in the pool: {0}")]
+    ConnectionPoolError(#[from] ConnectionPoolError),
+
     /// Unexpected message received
     #[error("Protocol Error: {0}")]
     ProtocolError(&'static str),
@@ -474,6 +482,19 @@ pub enum BadKeyspaceName {
     IllegalCharacter(String, char),
 }
 
+/// An error that occurred when selecting a node connection
+/// to perform a request on.
+#[derive(Error, Debug, Clone)]
+#[non_exhaustive]
+pub enum ConnectionPoolError {
+    #[error("The pool is broken; Last connection failed with: {last_connection_error}")]
+    Broken { last_connection_error: String },
+    #[error("Pool is still being initialized")]
+    Initializing,
+    #[error("The node has been disabled by a host filter")]
+    NodeDisabledByHostFilter,
+}
+
 #[derive(Error, Debug, Clone)]
 #[error("Connection broken, reason: {0}")]
 pub struct BrokenConnectionError(Arc<dyn Error + Sync + Send>);
@@ -656,6 +677,7 @@ impl From<QueryError> for NewSessionError {
             QueryError::CqlResultParseError(e) => NewSessionError::CqlResultParseError(e),
             QueryError::CqlErrorParseError(e) => NewSessionError::CqlErrorParseError(e),
             QueryError::IoError(e) => NewSessionError::IoError(e),
+            QueryError::ConnectionPoolError(e) => NewSessionError::ConnectionPoolError(e),
             QueryError::ProtocolError(m) => NewSessionError::ProtocolError(m),
             QueryError::InvalidMessage(m) => NewSessionError::InvalidMessage(m),
             QueryError::TimeoutError => NewSessionError::TimeoutError,

scylla/src/transport/connection_pool.rs

@@ -20,6 +20,7 @@ use super::NodeAddr;
 use arc_swap::ArcSwap;
 use futures::{future::RemoteHandle, stream::FuturesUnordered, Future, FutureExt, StreamExt};
 use rand::Rng;
+use scylla_cql::errors::ConnectionPoolError;
 use std::convert::TryInto;
 use std::io::ErrorKind;
 use std::num::NonZeroUsize;
@@ -238,7 +239,7 @@ impl NodeConnectionPool {
     pub(crate) fn connection_for_shard(
         &self,
         shard: Shard,
-    ) -> Result<Arc<Connection>, std::io::Error> {
+    ) -> Result<Arc<Connection>, ConnectionPoolError> {
         trace!(shard = shard, "Selecting connection for shard");
         self.with_connections(|pool_conns| match pool_conns {
             PoolConnections::NotSharded(conns) => {
@@ -261,7 +262,7 @@ impl NodeConnectionPool {
         })
     }
 
-    pub(crate) fn random_connection(&self) -> Result<Arc<Connection>, std::io::Error> {
+    pub(crate) fn random_connection(&self) -> Result<Arc<Connection>, ConnectionPoolError> {
         trace!("Selecting random connection");
         self.with_connections(|pool_conns| match pool_conns {
             PoolConnections::NotSharded(conns) => {
@@ -345,7 +346,9 @@ impl NodeConnectionPool {
         }
     }
 
-    pub(crate) fn get_working_connections(&self) -> Result<Vec<Arc<Connection>>, std::io::Error> {
+    pub(crate) fn get_working_connections(
+        &self,
+    ) -> Result<Vec<Arc<Connection>>, ConnectionPoolError> {
         self.with_connections(|pool_conns| match pool_conns {
             PoolConnections::NotSharded(conns) => conns.clone(),
             PoolConnections::Sharded { connections, .. } => {
@@ -377,21 +380,14 @@ impl NodeConnectionPool {
     fn with_connections<T>(
         &self,
         f: impl FnOnce(&PoolConnections) -> T,
-    ) -> Result<T, std::io::Error> {
+    ) -> Result<T, ConnectionPoolError> {
         let conns = self.conns.load_full();
         match &*conns {
             MaybePoolConnections::Ready(pool_connections) => Ok(f(pool_connections)),
-            MaybePoolConnections::Broken(err) => Err(std::io::Error::new(
-                ErrorKind::Other,
-                format!(
-                    "No connections in the pool; last connection failed with: {}",
-                    err
-                ),
-            )),
-            MaybePoolConnections::Initializing => Err(std::io::Error::new(
-                ErrorKind::Other,
-                "No connections in the pool, pool is still being initialized",
-            )),
+            MaybePoolConnections::Broken(err) => Err(ConnectionPoolError::Broken {
+                last_connection_error: format!("{err}"),
+            }),
+            MaybePoolConnections::Initializing => Err(ConnectionPoolError::Initializing),
         }
     }
 }

scylla/src/transport/load_balancing/default.rs

@@ -2838,6 +2838,7 @@ mod latency_awareness {
                 // "fast" errors, i.e. ones that are returned quickly after the query begins
                 QueryError::BadQuery(_)
                 | QueryError::BrokenConnection(_)
+                | QueryError::ConnectionPoolError(_)
                 | QueryError::TooManyOrphanedStreamIds(_)
                 | QueryError::UnableToAllocStreamId
                 | QueryError::DbError(DbError::IsBootstrapping, _)

scylla/src/transport/node.rs

@@ -1,3 +1,4 @@
+use scylla_cql::errors::ConnectionPoolError;
 use tokio::net::lookup_host;
 use tracing::warn;
 use uuid::Uuid;
@@ -157,7 +158,7 @@ impl Node {
     pub(crate) async fn connection_for_shard(
         &self,
         shard: Shard,
-    ) -> Result<Arc<Connection>, std::io::Error> {
+    ) -> Result<Arc<Connection>, ConnectionPoolError> {
         self.get_pool()?.connection_for_shard(shard)
     }
 
@@ -186,7 +187,9 @@ impl Node {
         Ok(())
     }
 
-    pub(crate) fn get_working_connections(&self) -> Result<Vec<Arc<Connection>>, std::io::Error> {
+    pub(crate) fn get_working_connections(
+        &self,
+    ) -> Result<Vec<Arc<Connection>>, ConnectionPoolError> {
         self.get_pool()?.get_working_connections()
     }
 
@@ -196,14 +199,10 @@ impl Node {
         }
     }
 
-    fn get_pool(&self) -> Result<&NodeConnectionPool, std::io::Error> {
-        self.pool.as_ref().ok_or_else(|| {
-            std::io::Error::new(
-                std::io::ErrorKind::Other,
-                "No connections in the pool: the node has been disabled \
-                by the host filter",
-            )
-        })
+    fn get_pool(&self) -> Result<&NodeConnectionPool, ConnectionPoolError> {
+        self.pool
+            .as_ref()
+            .ok_or(ConnectionPoolError::NodeDisabledByHostFilter)
     }
 }