feat: add tool call cancellation

Author: louis-jan

src-tauri/src/core/mcp/commands.rs

@@ -2,6 +2,7 @@ use rmcp::model::{CallToolRequestParam, CallToolResult};
 use serde_json::{Map, Value};
 use tauri::{AppHandle, Emitter, Runtime, State};
 use tokio::time::timeout;
+use tokio::sync::oneshot;
 
 use super::{
     constants::{DEFAULT_MCP_CONFIG, MCP_TOOL_CALL_TIMEOUT},
@@ -179,6 +180,7 @@ pub async fn get_tools(state: State<'_, AppState>) -> Result<Vec<ToolWithServer>
 /// * `state` - Application state containing MCP server connections
 /// * `tool_name` - Name of the tool to call
 /// * `arguments` - Optional map of argument names to values
+/// * `cancellation_token` - Optional token to allow cancellation from JS side
 ///
 /// # Returns
 /// * `Result<CallToolResult, String>` - Result of the tool call if successful, or error message if failed
@@ -187,13 +189,23 @@ pub async fn get_tools(state: State<'_, AppState>) -> Result<Vec<ToolWithServer>
 /// 1. Locks the MCP servers mutex to access server connections
 /// 2. Searches through all servers for one containing the named tool
 /// 3. When found, calls the tool on that server with the provided arguments
-/// 4. Returns error if no server has the requested tool
+/// 4. Supports cancellation via cancellation_token
+/// 5. Returns error if no server has the requested tool
 #[tauri::command]
 pub async fn call_tool(
     state: State<'_, AppState>,
     tool_name: String,
     arguments: Option<Map<String, Value>>,
+    cancellation_token: Option<String>,
 ) -> Result<CallToolResult, String> {
+    // Set up cancellation if token is provided
+    let (cancel_tx, cancel_rx) = oneshot::channel::<()>();
+    
+    if let Some(token) = &cancellation_token {
+        let mut cancellations = state.tool_call_cancellations.lock().await;
+        cancellations.insert(token.clone(), cancel_tx);
+    }
+
     let servers = state.mcp_servers.lock().await;
 
     // Iterate through servers and find the first one that contains the tool
@@ -209,25 +221,77 @@ pub async fn call_tool(
 
         println!("Found tool {} in server", tool_name);
 
-        // Call the tool with timeout
+        // Call the tool with timeout and cancellation support
         let tool_call = service.call_tool(CallToolRequestParam {
             name: tool_name.clone().into(),
             arguments,
         });
 
-        return match timeout(MCP_TOOL_CALL_TIMEOUT, tool_call).await {
-            Ok(result) => result.map_err(|e| e.to_string()),
-            Err(_) => Err(format!(
-                "Tool call '{}' timed out after {} seconds",
-                tool_name,
-                MCP_TOOL_CALL_TIMEOUT.as_secs()
-            )),
+        // Race between timeout, tool call, and cancellation
+        let result = if cancellation_token.is_some() {
+            tokio::select! {
+                result = timeout(MCP_TOOL_CALL_TIMEOUT, tool_call) => {
+                    match result {
+                        Ok(call_result) => call_result.map_err(|e| e.to_string()),
+                        Err(_) => Err(format!(
+                            "Tool call '{}' timed out after {} seconds",
+                            tool_name,
+                            MCP_TOOL_CALL_TIMEOUT.as_secs()
+                        )),
+                    }
+                }
+                _ = cancel_rx => {
+                    Err(format!("Tool call '{}' was cancelled", tool_name))
+                }
+            }
+        } else {
+            match timeout(MCP_TOOL_CALL_TIMEOUT, tool_call).await {
+                Ok(call_result) => call_result.map_err(|e| e.to_string()),
+                Err(_) => Err(format!(
+                    "Tool call '{}' timed out after {} seconds",
+                    tool_name,
+                    MCP_TOOL_CALL_TIMEOUT.as_secs()
+                )),
+            }
         };
+
+        // Clean up cancellation token
+        if let Some(token) = &cancellation_token {
+            let mut cancellations = state.tool_call_cancellations.lock().await;
+            cancellations.remove(token);
+        }
+
+        return result;
     }
 
     Err(format!("Tool {} not found", tool_name))
 }
 
+/// Cancels a running tool call by its cancellation token
+///
+/// # Arguments
+/// * `state` - Application state containing cancellation tokens
+/// * `cancellation_token` - Token identifying the tool call to cancel
+///
+/// # Returns
+/// * `Result<(), String>` - Success if token found and cancelled, error otherwise
+#[tauri::command]
+pub async fn cancel_tool_call(
+    state: State<'_, AppState>,
+    cancellation_token: String,
+) -> Result<(), String> {
+    let mut cancellations = state.tool_call_cancellations.lock().await;
+    
+    if let Some(cancel_tx) = cancellations.remove(&cancellation_token) {
+        // Send cancellation signal - ignore if receiver is already dropped
+        let _ = cancel_tx.send(());
+        println!("Tool call with token {} cancelled", cancellation_token);
+        Ok(())
+    } else {
+        Err(format!("Cancellation token {} not found", cancellation_token))
+    }
+}
+
 #[tauri::command]
 pub async fn get_mcp_configs(app: AppHandle) -> Result<String, String> {
     let mut path = get_jan_data_folder_path(app);

src-tauri/src/core/state.rs

@@ -6,7 +6,7 @@ use rmcp::{
     service::RunningService,
     RoleClient, ServiceError,
 };
-use tokio::sync::Mutex;
+use tokio::sync::{Mutex, oneshot};
 use tokio::task::JoinHandle;
 
 /// Server handle type for managing the proxy server lifecycle
@@ -27,6 +27,7 @@ pub struct AppState {
     pub mcp_active_servers: Arc<Mutex<HashMap<String, serde_json::Value>>>,
     pub mcp_successfully_connected: Arc<Mutex<HashMap<String, bool>>>,
     pub server_handle: Arc<Mutex<Option<ServerHandle>>>,
+    pub tool_call_cancellations: Arc<Mutex<HashMap<String, oneshot::Sender<()>>>>,
 }
 
 impl RunningServiceEnum {

src-tauri/src/lib.rs

@@ -74,6 +74,7 @@ pub fn run() {
             // MCP commands
             core::mcp::commands::get_tools,
             core::mcp::commands::call_tool,
+            core::mcp::commands::cancel_tool_call,
             core::mcp::commands::restart_mcp_servers,
             core::mcp::commands::get_connected_servers,
             core::mcp::commands::save_mcp_configs,
@@ -105,6 +106,7 @@ pub fn run() {
             mcp_active_servers: Arc::new(Mutex::new(HashMap::new())),
             mcp_successfully_connected: Arc::new(Mutex::new(HashMap::new())),
             server_handle: Arc::new(Mutex::new(None)),
+            tool_call_cancellations: Arc::new(Mutex::new(HashMap::new())),
         })
         .setup(|app| {
             app.handle().plugin(

web-app/src/containers/ChatInput.tsx

@@ -46,8 +46,13 @@ const ChatInput = ({ model, className, initialMessage }: ChatInputProps) => {
   const textareaRef = useRef<HTMLTextAreaElement>(null)
   const [isFocused, setIsFocused] = useState(false)
   const [rows, setRows] = useState(1)
-  const { streamingContent, abortControllers, loadingModel, tools } =
-    useAppState()
+  const {
+    streamingContent,
+    abortControllers,
+    loadingModel,
+    tools,
+    cancelToolCall,
+  } = useAppState()
   const { prompt, setPrompt } = usePrompt()
   const { currentThreadId } = useThreads()
   const { t } = useTranslation()
@@ -161,8 +166,9 @@ const ChatInput = ({ model, className, initialMessage }: ChatInputProps) => {
   const stopStreaming = useCallback(
     (threadId: string) => {
       abortControllers[threadId]?.abort()
+      cancelToolCall?.()
     },
-    [abortControllers]
+    [abortControllers, cancelToolCall]
   )
 
   const fileInputRef = useRef<HTMLInputElement>(null)

web-app/src/hooks/useAppState.ts

@@ -13,6 +13,7 @@ type AppState = {
   tokenSpeed?: TokenSpeed
   currentToolCall?: ChatCompletionMessageToolCall
   showOutOfContextDialog?: boolean
+  cancelToolCall?: () => void
   setServerStatus: (value: 'running' | 'stopped' | 'pending') => void
   updateStreamingContent: (content: ThreadMessage | undefined) => void
   updateCurrentToolCall: (
@@ -24,6 +25,7 @@ type AppState = {
   updateTokenSpeed: (message: ThreadMessage, increment?: number) => void
   resetTokenSpeed: () => void
   setOutOfContextDialog: (show: boolean) => void
+  setCancelToolCall: (cancel: (() => void) | undefined) => void
 }
 
 export const useAppState = create<AppState>()((set) => ({
@@ -34,6 +36,7 @@ export const useAppState = create<AppState>()((set) => ({
   abortControllers: {},
   tokenSpeed: undefined,
   currentToolCall: undefined,
+  cancelToolCall: undefined,
   updateStreamingContent: (content: ThreadMessage | undefined) => {
     const assistants = useAssistant.getState().assistants
     const currentAssistant = useAssistant.getState().currentAssistant
@@ -112,4 +115,9 @@ export const useAppState = create<AppState>()((set) => ({
       showOutOfContextDialog: show,
     }))
   },
+  setCancelToolCall: (cancel) => {
+    set(() => ({
+      cancelToolCall: cancel,
+    }))
+  },
 }))

web-app/src/lib/completion.ts

@@ -31,8 +31,9 @@ import { ulid } from 'ulidx'
 import { MCPTool } from '@/types/completion'
 import { CompletionMessagesBuilder } from './messages'
 import { ChatCompletionMessageToolCall } from 'openai/resources'
-import { callTool } from '@/services/mcp'
+import { callToolWithCancellation } from '@/services/mcp'
 import { ExtensionManager } from './extension'
+import { useAppState } from '@/hooks/useAppState'
 
 export type ChatCompletionResponse =
   | chatCompletion
@@ -381,13 +382,17 @@ export const postMessageProcessing = async (
             )
           : true)
 
+      const { promise, cancel } = callToolWithCancellation({
+        toolName: toolCall.function.name,
+        arguments: toolCall.function.arguments.length
+          ? JSON.parse(toolCall.function.arguments)
+          : {},
+      })
+
+      useAppState.getState().setCancelToolCall(cancel)
+
       let result = approved
-        ? await callTool({
-            toolName: toolCall.function.name,
-            arguments: toolCall.function.arguments.length
-              ? JSON.parse(toolCall.function.arguments)
-              : {},
-          }).catch((e) => {
+        ? await promise.catch((e) => {
             console.error('Tool call failed:', e)
             return {
               content: [

web-app/src/lib/service.ts

@@ -5,6 +5,7 @@ export const AppRoutes = [
   'installExtensions',
   'getTools',
   'callTool',
+  'cancelToolCall',
   'listThreads',
   'createThread',
   'modifyThread',

web-app/src/services/mcp.ts

@@ -56,3 +56,44 @@ export const callTool = (args: {
 }): Promise<{ error: string; content: { text: string }[] }> => {
   return window.core?.api?.callTool(args)
 }
+
+/**
+ * @description Enhanced function to invoke an MCP tool with cancellation support
+ * @param args - Tool call arguments
+ * @param cancellationToken - Optional cancellation token
+ * @returns Promise with tool result and cancellation function
+ */
+export const callToolWithCancellation = (args: {
+  toolName: string
+  arguments: object
+  cancellationToken?: string
+}): {
+  promise: Promise<{ error: string; content: { text: string }[] }>
+  cancel: () => Promise<void>
+  token: string
+} => {
+  // Generate a unique cancellation token if not provided
+  const token = args.cancellationToken ?? `tool_call_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`
+  
+  // Create the tool call promise with cancellation token
+  const promise = window.core?.api?.callTool({
+    ...args,
+    cancellationToken: token
+  })
+  
+  // Create cancel function
+  const cancel = async () => {
+    await window.core?.api?.cancelToolCall({ cancellationToken: token })
+  }
+  
+  return { promise, cancel, token }
+}
+
+/**
+ * @description This function cancels a running tool call
+ * @param cancellationToken - The token identifying the tool call to cancel
+ * @returns
+ */
+export const cancelToolCall = (cancellationToken: string): Promise<void> => {
+  return window.core?.api?.cancelToolCall({ cancellationToken })
+}