fix: navigate initialization phase before tools/list request in MCP client

codex-rs/mcp-client/src/main.rs

@@ -10,10 +10,17 @@
 //! program. The utility connects, issues a `tools/list` request and prints the
 //! server's response as pretty JSON.
 
+use std::time::Duration;
+
 use anyhow::Context;
 use anyhow::Result;
 use codex_mcp_client::McpClient;
+use mcp_types::ClientCapabilities;
+use mcp_types::Implementation;
+use mcp_types::InitializeRequest;
+use mcp_types::InitializeRequestParams;
 use mcp_types::ListToolsRequestParams;
+use mcp_types::MCP_SCHEMA_VERSION;
 
 #[tokio::main]
 async fn main() -> Result<()> {
@@ -33,6 +40,28 @@ async fn main() -> Result<()> {
         .await
         .with_context(|| format!("failed to spawn subprocess: {original_args:?}"))?;
 
+    let params = InitializeRequestParams {
+        capabilities: ClientCapabilities {
+            experimental: None,
+            roots: None,
+            sampling: None,
+        },
+        client_info: Implementation {
+            name: "codex-mcp-client".to_owned(),
+            version: env!("CARGO_PKG_VERSION").to_owned(),
+        },
+        protocol_version: MCP_SCHEMA_VERSION.to_owned(),
+    };
+    let timeout = Some(Duration::from_secs(10));
+    let response = client
+        .send_request::<InitializeRequest>(params, timeout)
+        .await?;
+    eprintln!("initialize response: {response:?}");
+
+    client
+        .send_notification::<mcp_types::InitializedNotification>(None)
+        .await?;
+
     // Issue `tools/list` request (no params).
     let timeout = None;
     let tools = client

codex-rs/mcp-client/src/mcp_client.rs

@@ -17,6 +17,7 @@ use std::sync::atomic::AtomicI64;
 use std::sync::atomic::Ordering;
 use std::time::Duration;
 
+use anyhow::Context;
 use anyhow::Result;
 use anyhow::anyhow;
 use mcp_types::CallToolRequest;
@@ -29,6 +30,7 @@ use mcp_types::JSONRPCResponse;
 use mcp_types::ListToolsRequest;
 use mcp_types::ListToolsRequestParams;
 use mcp_types::ListToolsResult;
+use mcp_types::ModelContextProtocolNotification;
 use mcp_types::ModelContextProtocolRequest;
 use mcp_types::RequestId;
 use serde::Serialize;
@@ -273,6 +275,34 @@ impl McpClient {
         }
     }
 
+    pub async fn send_notification<N>(&self, params: N::Params) -> Result<()>
+    where
+        N: ModelContextProtocolNotification,
+        N::Params: Serialize,
+    {
+        // Serialize params -> JSON. For many request types `Params` is
+        // `Option<T>` and `None` should be encoded as *absence* of the field.
+        let params_json = serde_json::to_value(&params)?;
+        let params_field = if params_json.is_null() {
+            None
+        } else {
+            Some(params_json)
+        };
+
+        let method = N::METHOD.to_string();
+        let jsonrpc_notification = JSONRPCNotification {
+            jsonrpc: JSONRPC_VERSION.to_string(),
+            method: method.clone(),
+            params: params_field,
+        };
+
+        let notification = JSONRPCMessage::Notification(jsonrpc_notification);
+        self.outgoing_tx
+            .send(notification)
+            .await
+            .with_context(|| format!("failed to send notification `{method}` to writer task"))
+    }
+
     /// Convenience wrapper around `tools/list`.
     pub async fn list_tools(
         &self,