codex/codex-rs/mcp-server/src/outgoing_message.rs

use std::collections::HashMap;
use std::sync::atomic::AtomicI64;
use std::sync::atomic::Ordering;

use codex_core::protocol::Event;
use mcp_types::JSONRPC_VERSION;
use mcp_types::JSONRPCError;
use mcp_types::JSONRPCErrorError;
use mcp_types::JSONRPCMessage;
use mcp_types::JSONRPCNotification;
use mcp_types::JSONRPCRequest;
use mcp_types::JSONRPCResponse;
use mcp_types::RequestId;
use mcp_types::Result;
use serde::Serialize;
use tokio::sync::Mutex;
use tokio::sync::mpsc;
use tokio::sync::oneshot;
use tracing::warn;

use crate::error_code::INTERNAL_ERROR_CODE;

/// Sends messages to the client and manages request callbacks.
pub(crate) struct OutgoingMessageSender {
    next_request_id: AtomicI64,
    sender: mpsc::Sender<OutgoingMessage>,
    request_id_to_callback: Mutex<HashMap<RequestId, oneshot::Sender<Result>>>,
}

impl OutgoingMessageSender {
    pub(crate) fn new(sender: mpsc::Sender<OutgoingMessage>) -> Self {
        Self {
            next_request_id: AtomicI64::new(0),
            sender,
            request_id_to_callback: Mutex::new(HashMap::new()),
        }
    }

    pub(crate) async fn send_request(
        &self,
        method: &str,
        params: Option<serde_json::Value>,
    ) -> oneshot::Receiver<Result> {
        let id = RequestId::Integer(self.next_request_id.fetch_add(1, Ordering::Relaxed));
        let outgoing_message_id = id.clone();
        let (tx_approve, rx_approve) = oneshot::channel();
        {
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.insert(id, tx_approve);
        }

        let outgoing_message = OutgoingMessage::Request(OutgoingRequest {
            id: outgoing_message_id,
            method: method.to_string(),
            params,
        });
        let _ = self.sender.send(outgoing_message).await;
        rx_approve
    }

    pub(crate) async fn notify_client_response(&self, id: RequestId, result: Result) {
        let entry = {
            let mut request_id_to_callback = self.request_id_to_callback.lock().await;
            request_id_to_callback.remove_entry(&id)
        };

        match entry {
            Some((id, sender)) => {
                if let Err(err) = sender.send(result) {
                    warn!("could not notify callback for {id:?} due to: {err:?}");
                }
            }
            None => {
                warn!("could not find callback for {id:?}");
            }
        }
    }

    pub(crate) async fn send_response<T: Serialize>(&self, id: RequestId, response: T) {
        match serde_json::to_value(response) {
            Ok(result) => {
                let outgoing_message = OutgoingMessage::Response(OutgoingResponse { id, result });
                let _ = self.sender.send(outgoing_message).await;
            }
            Err(err) => {
                self.send_error(
                    id,
                    JSONRPCErrorError {
                        code: INTERNAL_ERROR_CODE,
                        message: format!("failed to serialize response: {err}"),
                        data: None,
                    },
                )
                .await;
            }
        }
    }

    pub(crate) async fn send_event_as_notification(
        &self,
        event: &Event,
        meta: Option<OutgoingNotificationMeta>,
    ) {
        #[allow(clippy::expect_used)]
        let event_json = serde_json::to_value(event).expect("Event must serialize");

        let params = if let Ok(params) = serde_json::to_value(OutgoingNotificationParams {
            meta,
            event: event_json.clone(),
        }) {
            params
        } else {
            warn!("Failed to serialize event as OutgoingNotificationParams");
            event_json
        };

        self.send_notification(OutgoingNotification {
            method: "codex/event".to_string(),
            params: Some(params.clone()),
        })
        .await;

        self.send_event_as_notification_new_schema(event, Some(params.clone()))
            .await;
    }

    pub(crate) async fn send_notification(&self, notification: OutgoingNotification) {
        let outgoing_message = OutgoingMessage::Notification(notification);
        let _ = self.sender.send(outgoing_message).await;
    }

    // should be backwards compatible.
    // it will replace send_event_as_notification eventually.
    async fn send_event_as_notification_new_schema(
        &self,
        event: &Event,
        params: Option<serde_json::Value>,
    ) {
        let outgoing_message = OutgoingMessage::Notification(OutgoingNotification {
            method: event.msg.to_string(),
            params,
        });
        let _ = self.sender.send(outgoing_message).await;
    }
    pub(crate) async fn send_error(&self, id: RequestId, error: JSONRPCErrorError) {
        let outgoing_message = OutgoingMessage::Error(OutgoingError { id, error });
        let _ = self.sender.send(outgoing_message).await;
    }
}

/// Outgoing message from the server to the client.
pub(crate) enum OutgoingMessage {
    Request(OutgoingRequest),
    Notification(OutgoingNotification),
    Response(OutgoingResponse),
    Error(OutgoingError),
}

impl From<OutgoingMessage> for JSONRPCMessage {
    fn from(val: OutgoingMessage) -> Self {
        use OutgoingMessage::*;
        match val {
            Request(OutgoingRequest { id, method, params }) => {
                JSONRPCMessage::Request(JSONRPCRequest {
                    jsonrpc: JSONRPC_VERSION.into(),
                    id,
                    method,
                    params,
                })
            }
            Notification(OutgoingNotification { method, params }) => {
                JSONRPCMessage::Notification(JSONRPCNotification {
                    jsonrpc: JSONRPC_VERSION.into(),
                    method,
                    params,
                })
            }
            Response(OutgoingResponse { id, result }) => {
                JSONRPCMessage::Response(JSONRPCResponse {
                    jsonrpc: JSONRPC_VERSION.into(),
                    id,
                    result,
                })
            }
            Error(OutgoingError { id, error }) => JSONRPCMessage::Error(JSONRPCError {
                jsonrpc: JSONRPC_VERSION.into(),
                id,
                error,
            }),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingRequest {
    pub id: RequestId,
    pub method: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub params: Option<serde_json::Value>,
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingNotification {
    pub method: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub params: Option<serde_json::Value>,
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingNotificationParams {
    #[serde(rename = "_meta", default, skip_serializing_if = "Option::is_none")]
    pub meta: Option<OutgoingNotificationMeta>,

    #[serde(flatten)]
    pub event: serde_json::Value,
}

// Additional mcp-specific data to be added to a [`codex_core::protocol::Event`] as notification.params._meta
// MCP Spec: https://modelcontextprotocol.io/specification/2025-06-18/basic#meta
// Typescript Schema: https://github.com/modelcontextprotocol/modelcontextprotocol/blob/0695a497eb50a804fc0e88c18a93a21a675d6b3e/schema/2025-06-18/schema.ts
#[derive(Debug, Clone, PartialEq, Serialize)]
#[serde(rename_all = "camelCase")]
pub(crate) struct OutgoingNotificationMeta {
    pub request_id: Option<RequestId>,
}

impl OutgoingNotificationMeta {
    pub(crate) fn new(request_id: Option<RequestId>) -> Self {
        Self { request_id }
    }
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingResponse {
    pub id: RequestId,
    pub result: Result,
}

#[derive(Debug, Clone, PartialEq, Serialize)]
pub(crate) struct OutgoingError {
    pub error: JSONRPCErrorError,
    pub id: RequestId,
}

#[cfg(test)]
mod tests {
    #![allow(clippy::unwrap_used)]

    use codex_core::protocol::EventMsg;
    use codex_core::protocol::SessionConfiguredEvent;
    use pretty_assertions::assert_eq;
    use serde_json::json;
    use uuid::Uuid;

    use super::*;

    #[tokio::test]
    async fn test_send_event_as_notification() {
        let (outgoing_tx, mut outgoing_rx) = mpsc::channel::<OutgoingMessage>(2);
        let outgoing_message_sender = OutgoingMessageSender::new(outgoing_tx);

        let event = Event {
            id: "1".to_string(),
            msg: EventMsg::SessionConfigured(SessionConfiguredEvent {
                session_id: Uuid::new_v4(),
                model: "gpt-4o".to_string(),
                history_log_id: 1,
                history_entry_count: 1000,
            }),
        };

        outgoing_message_sender
            .send_event_as_notification(&event, None)
            .await;

        let result = outgoing_rx.recv().await.unwrap();
        let OutgoingMessage::Notification(OutgoingNotification { method, params }) = result else {
            panic!("expected Notification for first message");
        };
        assert_eq!(method, "codex/event");

        let Ok(expected_params) = serde_json::to_value(&event) else {
            panic!("Event must serialize");
        };
        assert_eq!(params, Some(expected_params.clone()));

        let result2 = outgoing_rx.recv().await.unwrap();
        let OutgoingMessage::Notification(OutgoingNotification {
            method: method2,
            params: params2,
        }) = result2
        else {
            panic!("expected Notification for second message");
        };
        assert_eq!(method2, event.msg.to_string());
        assert_eq!(params2, Some(expected_params));
    }

    #[tokio::test]
    async fn test_send_event_as_notification_with_meta() {
        let (outgoing_tx, mut outgoing_rx) = mpsc::channel::<OutgoingMessage>(2);
        let outgoing_message_sender = OutgoingMessageSender::new(outgoing_tx);

        let session_configured_event = SessionConfiguredEvent {
            session_id: Uuid::new_v4(),
            model: "gpt-4o".to_string(),
            history_log_id: 1,
            history_entry_count: 1000,
        };
        let event = Event {
            id: "1".to_string(),
            msg: EventMsg::SessionConfigured(session_configured_event.clone()),
        };
        let meta = OutgoingNotificationMeta {
            request_id: Some(RequestId::String("123".to_string())),
        };

        outgoing_message_sender
            .send_event_as_notification(&event, Some(meta))
            .await;

        let result = outgoing_rx.recv().await.unwrap();
        let OutgoingMessage::Notification(OutgoingNotification { method, params }) = result else {
            panic!("expected Notification for first message");
        };
        assert_eq!(method, "codex/event");
        let expected_params = json!({
            "_meta": {
                "requestId": "123",
            },
            "id": "1",
            "msg": {
                "session_id": session_configured_event.session_id,
                "model": session_configured_event.model,
                "history_log_id": session_configured_event.history_log_id,
                "history_entry_count": session_configured_event.history_entry_count,
                "type": "session_configured",
            }
        });
        assert_eq!(params.unwrap(), expected_params);

        let result2 = outgoing_rx.recv().await.unwrap();
        let OutgoingMessage::Notification(OutgoingNotification {
            method: method2,
            params: params2,
        }) = result2
        else {
            panic!("expected Notification for second message");
        };
        assert_eq!(method2, event.msg.to_string());
        assert_eq!(params2.unwrap(), expected_params);
    }
}