fix(jetsocat): missing newline after MCP proxy JSON-RPC responses (#1507)

Author: CBenoit

crates/mcp-proxy/src/lib.rs

@@ -51,8 +51,6 @@ impl JsonRpcResponse {
 
         if let Some(id) = self.id {
             obj.insert("id".to_owned(), tinyjson::JsonValue::Number(id as f64));
-        } else {
-            obj.insert("id".to_owned(), tinyjson::JsonValue::Null);
         }
 
         if let Some(result) = &self.result {
@@ -64,7 +62,7 @@ impl JsonRpcResponse {
         }
 
         let json_obj = tinyjson::JsonValue::Object(obj);
-        Ok(json_obj.stringify().unwrap())
+        json_obj.stringify().context("failed to stringify response")
     }
 }
 
@@ -184,6 +182,11 @@ impl McpProxy {
 
                 Ok(None)
             }
+            "logging/setLevel" => {
+                debug!("Received logging/setLevel with parameters {:?}", request.params);
+
+                Ok(None)
+            }
             "tools/list" => {
                 match &self.transport {
                     InnerTransport::Http { url, .. } => {

crates/mcp-proxy/tests/no_io.rs

@@ -2,7 +2,7 @@
 #![allow(clippy::unwrap_used)]
 
 use mcp_proxy::internal::{decode_content_texts, extract_sse_json_line, unwrap_json_rpc_inner_result};
-use mcp_proxy::{Config, JsonRpcRequest, McpProxy};
+use mcp_proxy::{Config, JsonRpcRequest, JsonRpcResponse, McpProxy};
 
 use std::collections::HashMap;
 
@@ -50,18 +50,18 @@ fn sse_no_data_is_none() {
 fn decode_escaped_texts_works() {
     let mut text_obj = HashMap::new();
     text_obj.insert(
-        "text".to_string(),
-        tinyjson::JsonValue::String("hello\\u0027world\\ncode:\\u003Ctag\\u003E".to_string()),
+        "text".to_owned(),
+        tinyjson::JsonValue::String("hello\\u0027world\\ncode:\\u003Ctag\\u003E".to_owned()),
     );
 
     let mut content_obj = HashMap::new();
     content_obj.insert(
-        "content".to_string(),
+        "content".to_owned(),
         tinyjson::JsonValue::Array(vec![tinyjson::JsonValue::Object(text_obj)]),
     );
 
     let mut result_obj = HashMap::new();
-    result_obj.insert("result".to_string(), tinyjson::JsonValue::Object(content_obj));
+    result_obj.insert("result".to_owned(), tinyjson::JsonValue::Object(content_obj));
 
     let mut v = tinyjson::JsonValue::Object(result_obj);
     decode_content_texts(&mut v);
@@ -75,10 +75,10 @@ fn decode_escaped_texts_works() {
 #[test]
 fn unwrap_json_rpc_inner_result_prefers_result() {
     let mut tools_obj = HashMap::new();
-    tools_obj.insert("tools".to_string(), tinyjson::JsonValue::Array(vec![]));
+    tools_obj.insert("tools".to_owned(), tinyjson::JsonValue::Array(vec![]));
 
     let mut v_obj = HashMap::new();
-    v_obj.insert("result".to_string(), tinyjson::JsonValue::Object(tools_obj.clone()));
+    v_obj.insert("result".to_owned(), tinyjson::JsonValue::Object(tools_obj.clone()));
 
     let v = tinyjson::JsonValue::Object(v_obj);
     let got = unwrap_json_rpc_inner_result(v);
@@ -90,7 +90,7 @@ fn unwrap_json_rpc_inner_result_prefers_result() {
 #[test]
 fn unwrap_json_rpc_inner_result_passthrough() {
     let mut v_obj = HashMap::new();
-    v_obj.insert("tools".to_string(), tinyjson::JsonValue::Array(vec![]));
+    v_obj.insert("tools".to_owned(), tinyjson::JsonValue::Array(vec![]));
 
     let v = tinyjson::JsonValue::Object(v_obj);
     let got = unwrap_json_rpc_inner_result(v.clone());
@@ -137,3 +137,40 @@ async fn unknown_method_is_32601() {
         .unwrap();
     assert_eq!(get_number_path(resp.error.as_ref().unwrap(), &["code"]), -32601.0);
 }
+
+#[test]
+fn response_omits_null_id() {
+    let response = JsonRpcResponse {
+        jsonrpc: "2.0".to_owned(),
+        id: None,
+        result: Some(tinyjson::JsonValue::String("test".to_owned())),
+        error: None,
+    };
+
+    let json_str = response.to_string().unwrap();
+    let parsed: tinyjson::JsonValue = json_str.parse().unwrap();
+    let obj = parsed.get::<HashMap<String, tinyjson::JsonValue>>().unwrap();
+
+    // The id field should not be present when None
+    assert!(!obj.contains_key("id"));
+    assert!(obj.contains_key("jsonrpc"));
+    assert!(obj.contains_key("result"));
+}
+
+#[test]
+fn response_includes_id_when_present() {
+    let response = JsonRpcResponse {
+        jsonrpc: "2.0".to_owned(),
+        id: Some(42),
+        result: Some(tinyjson::JsonValue::String("test".to_owned())),
+        error: None,
+    };
+
+    let json_str = response.to_string().unwrap();
+    let parsed: tinyjson::JsonValue = json_str.parse().unwrap();
+    let obj = parsed.get::<HashMap<String, tinyjson::JsonValue>>().unwrap();
+
+    // The id field should be present when Some
+    assert!(obj.contains_key("id"));
+    assert_eq!(obj.get("id").unwrap().get::<f64>().unwrap(), &42.0);
+}

jetsocat/src/mcp.rs

@@ -13,33 +13,37 @@ pub(crate) async fn run_mcp_proxy(pipe: Pipe, mut mcp_client: mcp_proxy::McpProx
     loop {
         line.clear();
 
-        match reader.read_line(&mut line).await? {
-            0 => break, // EOF
-            _ => {
-                let line = line.trim();
-
-                if line.is_empty() {
-                    continue;
-                }
-
-                trace!(request = %line, "Received request");
-
-                match mcp_client.handle_jsonrpc_request_str(line).await {
-                    Ok(Some(resp)) => {
-                        let response = resp.to_string()?;
-                        writer
-                            .write_all(response.as_bytes())
-                            .await
-                            .context("failed to write response")?;
-                    }
-                    Ok(None) => {} // Notification; no response.
-                    Err(e) => {
-                        error!(error = format!("{e:#}"), "failed to handle request");
-                    }
-                }
+        let n_read = reader.read_line(&mut line).await.context("read_line")?;
+
+        if n_read == 0 {
+            debug!("Pipe EOFed");
+            return Ok(());
+        }
+
+        let line = line.trim();
+
+        if line.is_empty() {
+            continue;
+        }
+
+        trace!(request = %line, "Received request");
+
+        match mcp_client.handle_jsonrpc_request_str(line).await {
+            Ok(Some(resp)) => {
+                let mut response = resp.to_string()?;
+                trace!(%response, "Sending response");
+                response.push('\n'); // Push a newline to delemitate the message.
+
+                writer
+                    .write_all(response.as_bytes())
+                    .await
+                    .context("failed to write response")?;
+                writer.flush().await.context("failed to flush writer")?;
+            }
+            Ok(None) => {} // Notification; no response.
+            Err(e) => {
+                error!(error = format!("{e:#}"), "failed to handle request");
             }
         }
     }
-
-    Ok(())
 }