error: RpcError with custom client error

subxt/src/client/online_client.rs

@@ -74,7 +74,7 @@ impl<T: Config> OnlineClient<T> {
     pub async fn from_url(url: impl AsRef<str>) -> Result<OnlineClient<T>, Error> {
         let client = jsonrpsee_helpers::ws_client(url.as_ref())
             .await
-            .map_err(|e| crate::error::RpcError(e.to_string()))?;
+            .map_err(|e| crate::error::RpcError::ClientError(Box::new(e)))?;
         OnlineClient::from_rpc_client(Arc::new(client)).await
     }
 }

subxt/src/error.rs

@@ -102,10 +102,17 @@ impl From<DispatchError> for Error {
 }
 
 /// An RPC error. Since we are generic over the RPC client that is used,
-/// the error is any custom string.
+/// the error is boxed and could be casted.
 #[derive(Debug, thiserror::Error)]
 #[error("RPC error: {0}")]
-pub struct RpcError(pub String);
+pub enum RpcError {
+    // Dev note: We need the error to be safely sent between threads
+    // for `subscribe_to_block_headers_filling_in_gaps` and friends.
+    /// Error related to the RPC client.
+    ClientError(Box<dyn std::error::Error + Send + 'static>),
+    /// Custom error.
+    Custom(String),
+}
 
 /// This is our attempt to decode a runtime DispatchError. We either
 /// successfully decode it into a [`ModuleError`], or we fail and keep

subxt/src/rpc/jsonrpsee_impl.rs

@@ -35,7 +35,7 @@ impl RpcClientT for Client {
             let params = prep_params_for_jsonrpsee(params)?;
             let res = ClientT::request(self, method, Some(params))
                 .await
-                .map_err(|e| RpcError(e.to_string()))?;
+                .map_err(|e| RpcError::ClientError(Box::new(e)))?;
             Ok(res)
         })
     }
@@ -55,8 +55,8 @@ impl RpcClientT for Client {
                 unsub,
             )
             .await
-            .map_err(|e| RpcError(e.to_string()))?
-            .map_err(|e| RpcError(e.to_string()))
+            .map_err(|e| RpcError::ClientError(Box::new(e)))?
+            .map_err(|e| RpcError::ClientError(Box::new(e)))
             .boxed();
             Ok(sub)
         })
@@ -77,7 +77,7 @@ fn prep_params_for_jsonrpsee(
     let arr = match val {
         Value::Array(arr) => Ok(arr),
         _ => {
-            Err(RpcError(format!(
+            Err(RpcError::Custom(format!(
                 "RPC Params are expected to be an array but got {params}"
             )))
         }

subxt/src/tx/tx_progress.rs

@@ -107,7 +107,7 @@ where
                 _ => continue,
             }
         }
-        Err(RpcError("RPC subscription dropped".to_string()).into())
+        Err(RpcError::Custom("RPC subscription dropped".into()).into())
     }
 
     /// Wait for the transaction to be finalized, and return a [`TxInBlock`]
@@ -133,7 +133,7 @@ where
                 _ => continue,
             }
         }
-        Err(RpcError("RPC subscription dropped".to_string()).into())
+        Err(RpcError::Custom("RPC subscription dropped".into()).into())
     }
 
     /// Wait for the transaction to be finalized, and for the transaction events to indicate