Trait CancellationHandler 

pub trait CancellationHandler:
    Send
    + Sync
    + Debug {
    // Required method
    fn handle_cancellation<'life0, 'async_trait>(
        &'life0 self,
        notification: CancelledNotification,
    ) -> Pin<Box<dyn Future<Output = HandlerResult<()>> + Send + 'async_trait>>
       where Self: 'async_trait,
             'life0: 'async_trait;
}

Cancellation handler for processing cancellation notifications

Per MCP 2025-06-18 specification, notifications/cancelled can be sent by either side to indicate cancellation of a previously-issued request.

When the server sends a cancellation notification, it indicates that a request the client sent is being cancelled and the result will be unused. The client SHOULD cease any associated processing.

MCP Specification

From the MCP spec:

• “The request SHOULD still be in-flight, but due to communication latency, it is always possible that this notification MAY arrive after the request has already finished.”
• “A client MUST NOT attempt to cancel its initialize request.”

Examples

use turbomcp_client::handlers::{CancellationHandler, CancelledNotification, HandlerResult};
use async_trait::async_trait;

#[derive(Debug)]
struct MyCancellationHandler;

#[async_trait]
impl CancellationHandler for MyCancellationHandler {
    async fn handle_cancellation(&self, notification: CancelledNotification) -> HandlerResult<()> {
        println!("Request {} was cancelled", notification.request_id);
        if let Some(reason) = &notification.reason {
            println!("Reason: {}", reason);
        }

        // In a real implementation:
        // - Look up the in-flight request by notification.request_id
        // - Signal cancellation (e.g., via CancellationToken)
        // - Clean up any resources

        Ok(())
    }
}

Required Methods

fn handle_cancellation<'life0, 'async_trait>( &'life0 self, notification: CancelledNotification, ) -> Pin<Box<dyn Future<Output = HandlerResult<()>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Handle a cancellation notification

This method is called when the server cancels a request that the client previously issued.

Arguments

• notification - The cancellation notification containing request ID and optional reason

Returns

Returns Ok(()) if the cancellation was processed successfully.

Implementors

impl CancellationHandler for LoggingCancellationHandler