From 1326db231e4a76f844803a653ec8d44e4e649448 Mon Sep 17 00:00:00 2001
From: Jack Amadeo <jackamadeo@squareup.com>
Date: Fri, 13 Jun 2025 12:05:46 -0400
Subject: [PATCH] fix: handle JsonRPC error variants as responses (#2903)

---
 crates/mcp-client/examples/integration_test.rs | 6 ++++++
 crates/mcp-client/src/client.rs                | 3 ++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/crates/mcp-client/examples/integration_test.rs b/crates/mcp-client/examples/integration_test.rs
index b16af1be97..d4aa74751c 100644
--- a/crates/mcp-client/examples/integration_test.rs
+++ b/crates/mcp-client/examples/integration_test.rs
@@ -110,6 +110,12 @@ where
     let collected_events_after = events.lock().await.len();
     assert_eq!(collected_events_after - collected_eventes_before, n_steps);
 
+    let error_result = client
+        .call_tool("add", serde_json::json!({ "a": "foo", "b": "bar" }))
+        .await;
+    assert!(error_result.is_err());
+    println!("Error result: {error_result:#?}\n");
+
     // List resources
     let resources = client.list_resources(None).await?;
     println!("Resources: {resources:#?}\n");
diff --git a/crates/mcp-client/src/client.rs b/crates/mcp-client/src/client.rs
index 474592fdd7..e00e758f60 100644
--- a/crates/mcp-client/src/client.rs
+++ b/crates/mcp-client/src/client.rs
@@ -135,7 +135,8 @@ where
                     Ok(message) => {
                         tracing::info!("Received message: {:?}", message);
                         match message {
-                            JsonRpcMessage::Response(JsonRpcResponse { id: Some(id), .. }) => {
+                            JsonRpcMessage::Response(JsonRpcResponse { id: Some(id), .. })
+                            | JsonRpcMessage::Error(JsonRpcError { id: Some(id), .. }) => {
                                 service_ptr.respond(&id.to_string(), Ok(message)).await;
                             }
                             _ => {