Reduce app-server JSON serialization overhead (#34761)

## What changed

- Decode `JSONRPCRequest` into `ClientRequest` without serializing the entire request back into an intermediate JSON value.
- Define every client method's wire name explicitly and use it directly for request, response, and tracing method lookups.
- Serialize outgoing transport messages directly to JSON strings instead of first building a `serde_json::Value`.

## Testing

- Add regression coverage that compares direct request conversion with Serde decoding, including omitted and null parameters, legacy methods, and unknown methods.
- Verify that direct outgoing-message serialization preserves the notification wire shape.

GitOrigin-RevId: 304e14bcaea24e32743bf852a60a208e2f273db3

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -200,7 +200,7 @@ macro_rules! client_request_definitions {
         $(
             $(#[experimental($reason:expr)])?
             $(#[doc = $variant_doc:literal])*
-            $variant:ident $(=> $wire:literal)? {
+            $variant:ident => $wire:literal {
                 params: $(#[$params_meta:meta])* $params:ty,
                 $(inspect_params: $inspect_params:tt,)?
                 serialization: $serialization:ident $( ( $($serialization_args:tt)* ) )?,
@@ -215,7 +215,8 @@ macro_rules! client_request_definitions {
         pub enum ClientRequest {
             $(
                 $(#[doc = $variant_doc])*
-                $(#[serde(rename = $wire)] #[ts(rename = $wire)])?
+                #[serde(rename = $wire)]
+                #[ts(rename = $wire)]
                 $variant {
                     #[serde(rename = "id")]
                     request_id: RequestId,
@@ -232,16 +233,14 @@ macro_rules! client_request_definitions {
                 }
             }
 
+            pub const fn method_name(&self) -> &'static str {
+                match self {
+                    $(Self::$variant { .. } => $wire,)*
+                }
+            }
+
             pub fn method(&self) -> String {
-                serde_json::to_value(self)
-                    .ok()
-                    .and_then(|value| {
-                        value
-                            .get("method")
-                            .and_then(serde_json::Value::as_str)
-                            .map(str::to_owned)
-                    })
-                    .unwrap_or_else(|| "<unknown>".to_string())
+                self.method_name().to_string()
             }
 
             pub fn serialization_scope(&self) -> Option<ClientRequestSerializationScope> {
@@ -258,6 +257,26 @@ macro_rules! client_request_definitions {
             }
         }
 
+        impl TryFrom<JSONRPCRequest> for ClientRequest {
+            type Error = serde_json::Error;
+
+            fn try_from(request: JSONRPCRequest) -> Result<Self, Self::Error> {
+                let JSONRPCRequest {
+                    id: request_id,
+                    method,
+                    params,
+                    trace: _,
+                } = request;
+                let mut request = serde_json::Map::new();
+                request.insert("id".to_string(), serde_json::to_value(request_id)?);
+                request.insert("method".to_string(), serde_json::Value::String(method));
+                if let Some(params) = params {
+                    request.insert("params".to_string(), params);
+                }
+                serde_json::from_value(serde_json::Value::Object(request))
+            }
+        }
+
         /// Typed response from the server to the client.
         #[derive(Serialize, Deserialize, Debug, Clone)]
         #[allow(clippy::large_enum_variant)]
@@ -265,7 +284,7 @@ macro_rules! client_request_definitions {
         pub enum ClientResponse {
             $(
                 $(#[doc = $variant_doc])*
-                $(#[serde(rename = $wire)])?
+                #[serde(rename = $wire)]
                 $variant {
                     #[serde(rename = "id")]
                     request_id: RequestId,
@@ -282,15 +301,9 @@ macro_rules! client_request_definitions {
             }
 
             pub fn method(&self) -> String {
-                serde_json::to_value(self)
-                    .ok()
-                    .and_then(|value| {
-                        value
-                            .get("method")
-                            .and_then(serde_json::Value::as_str)
-                            .map(str::to_owned)
-                    })
-                    .unwrap_or_else(|| "<unknown>".to_string())
+                match self {
+                    $(Self::$variant { .. } => $wire.to_string(),)*
+                }
             }
 
             pub fn into_jsonrpc_parts(
@@ -405,7 +418,7 @@ macro_rules! client_request_definitions {
 
         pub(crate) const EXPERIMENTAL_CLIENT_METHODS: &[&str] = &[
             $(
-                experimental_method_entry!($(#[experimental($reason)])? $(=> $wire)?),
+                experimental_method_entry!($(#[experimental($reason)])? => $wire),
             )*
         ];
         pub(crate) const EXPERIMENTAL_CLIENT_METHOD_PARAM_TYPES: &[&str] = &[
@@ -470,7 +483,7 @@ macro_rules! client_response_payload_from_impl {
 }
 
 client_request_definitions! {
-    Initialize {
+    Initialize => "initialize" {
         params: v1::InitializeParams,
         serialization: None,
         response: v1::InitializeResponse,
@@ -1177,25 +1190,25 @@ client_request_definitions! {
     },
 
     /// DEPRECATED APIs below
-    GetConversationSummary {
+    GetConversationSummary => "getConversationSummary" {
         params: v1::GetConversationSummaryParams,
         serialization: None,
         response: v1::GetConversationSummaryResponse,
     },
-    GitDiffToRemote {
+    GitDiffToRemote => "gitDiffToRemote" {
         params: v1::GitDiffToRemoteParams,
         serialization: None,
         response: v1::GitDiffToRemoteResponse,
     },
     /// DEPRECATED in favor of GetAccount
-    GetAuthStatus {
+    GetAuthStatus => "getAuthStatus" {
         params: v1::GetAuthStatusParams,
         serialization: global("account-auth"),
         response: v1::GetAuthStatusResponse,
     },
     // Legacy fuzzy search cancellation is intentionally concurrent: clients reuse a
     // cancellation token so a newer request can cancel an older in-flight search.
-    FuzzyFileSearch {
+    FuzzyFileSearch => "fuzzyFileSearch" {
         params: FuzzyFileSearchParams,
         serialization: None,
         response: FuzzyFileSearchResponse,
@@ -1798,6 +1811,81 @@ mod tests {
         RequestId::Integer(REQUEST_ID)
     }
 
+    fn decode_client_request_through_json(
+        request: &JSONRPCRequest,
+    ) -> std::result::Result<ClientRequest, String> {
+        serde_json::to_value(request)
+            .and_then(serde_json::from_value)
+            .map_err(|err| err.to_string())
+    }
+
+    #[test]
+    fn jsonrpc_request_conversion_preserves_serde_enum_decoding() {
+        let requests = [
+            JSONRPCRequest {
+                id: RequestId::Integer(1),
+                method: "thread/archive".to_string(),
+                params: Some(json!({"threadId": "thread-1"})),
+                trace: Some(codex_protocol::protocol::W3cTraceContext {
+                    traceparent: Some("traceparent".to_string()),
+                    tracestate: Some("tracestate".to_string()),
+                }),
+            },
+            // Required params preserve distinct omitted and explicit-null errors.
+            JSONRPCRequest {
+                id: RequestId::Integer(2),
+                method: "thread/archive".to_string(),
+                params: None,
+                trace: None,
+            },
+            JSONRPCRequest {
+                id: RequestId::Integer(3),
+                method: "thread/archive".to_string(),
+                params: Some(serde_json::Value::Null),
+                trace: None,
+            },
+            // Optional unit params preserve omitted, null, and empty-object behavior.
+            JSONRPCRequest {
+                id: RequestId::Integer(4),
+                method: "memory/reset".to_string(),
+                params: None,
+                trace: None,
+            },
+            JSONRPCRequest {
+                id: RequestId::Integer(5),
+                method: "memory/reset".to_string(),
+                params: Some(serde_json::Value::Null),
+                trace: None,
+            },
+            JSONRPCRequest {
+                id: RequestId::Integer(6),
+                method: "memory/reset".to_string(),
+                params: Some(json!({})),
+                trace: None,
+            },
+            JSONRPCRequest {
+                id: RequestId::Integer(7),
+                method: "getConversationSummary".to_string(),
+                params: Some(json!({
+                    "conversationId": "67e55044-10b1-426f-9247-bb680e5fe0c8"
+                })),
+                trace: None,
+            },
+            JSONRPCRequest {
+                id: RequestId::Integer(8),
+                method: "unknown/method".to_string(),
+                params: Some(json!({})),
+                trace: None,
+            },
+        ];
+
+        for request in requests {
+            let expected = decode_client_request_through_json(&request);
+            let actual = ClientRequest::try_from(request).map_err(|err| err.to_string());
+            assert_eq!(actual, expected);
+        }
+    }
+
     #[test]
     fn client_request_serialization_scope_covers_keyed_families() {
         let thread_id = "thread-1".to_string();

codex-rs/app-server-transport/src/transport/mod.rs

@@ -256,14 +256,7 @@ async fn enqueue_incoming_message(
 }
 
 fn serialize_outgoing_message(outgoing_message: OutgoingMessage) -> Option<String> {
-    let value = match serde_json::to_value(outgoing_message) {
-        Ok(value) => value,
-        Err(err) => {
-            error!("Failed to convert OutgoingMessage to JSON value: {err}");
-            return None;
-        }
-    };
-    match serde_json::to_string(&value) {
+    match serde_json::to_string(&outgoing_message) {
         Ok(json) => Some(json),
         Err(err) => {
             error!("Failed to serialize JSONRPCMessage: {err}");
@@ -295,6 +288,32 @@ mod tests {
         );
     }
 
+    #[test]
+    fn serialize_outgoing_message_preserves_wire_shape() {
+        let message = OutgoingMessage::AppServerNotification(ServerNotificationEnvelope {
+            notification: ServerNotification::ConfigWarning(ConfigWarningNotification {
+                summary: "summary".to_string(),
+                details: None,
+                path: None,
+                range: None,
+            }),
+            emitted_at_ms: Some(1_234),
+        });
+
+        let json = serialize_outgoing_message(message).expect("message should serialize");
+        assert_eq!(
+            serde_json::from_str::<serde_json::Value>(&json).expect("message should be valid JSON"),
+            json!({
+                "method": "configWarning",
+                "params": {
+                    "summary": "summary",
+                    "details": null,
+                },
+                "emittedAtMs": 1_234,
+            })
+        );
+    }
+
     #[tokio::test]
     async fn enqueue_incoming_request_returns_overload_error_when_queue_is_full() {
         let connection_id = ConnectionId(42);

codex-rs/app-server/src/app_server_tracing.rs

@@ -64,8 +64,8 @@ pub(crate) fn typed_request_span(
     connection_id: ConnectionId,
     session: &ConnectionSessionState,
 ) -> Span {
-    let method = request.method();
-    let span = app_server_request_span_template(&method, "in-process", request.id(), connection_id);
+    let method = request.method_name();
+    let span = app_server_request_span_template(method, "in-process", request.id(), connection_id);
 
     let client_info = initialize_client_info_from_typed_request(request);
     record_client_info(
@@ -78,7 +78,7 @@ pub(crate) fn typed_request_span(
             .or(session.client_version()),
     );
 
-    attach_parent_context(&span, &method, request.id(), /*parent_trace*/ None);
+    attach_parent_context(&span, method, request.id(), /*parent_trace*/ None);
     span
 }
 

codex-rs/app-server/src/message_processor.rs

@@ -88,15 +88,9 @@ use crate::models_refresh_worker::ModelsRefreshWorker;
 
 const CONNECTION_RPC_DRAIN_TIMEOUT: Duration = Duration::from_secs(/*secs*/ 30);
 
-fn deserialize_client_request(
-    request: &JSONRPCRequest,
-) -> Result<ClientRequest, JSONRPCErrorError> {
-    serde_json::to_value(request)
+fn deserialize_client_request(request: JSONRPCRequest) -> Result<ClientRequest, JSONRPCErrorError> {
+    ClientRequest::try_from(request)
         .map_err(|err| invalid_request(format!("Invalid request: {err}")))
-        .and_then(|request_json| {
-            serde_json::from_value(request_json)
-                .map_err(|err| invalid_request(format!("Invalid request: {err}")))
-        })
 }
 
 pub(crate) struct MessageProcessor {
@@ -543,7 +537,7 @@ impl MessageProcessor {
             Arc::clone(&self.outgoing),
             request_context.clone(),
             async {
-                let codex_request = deserialize_client_request(&request);
+                let codex_request = deserialize_client_request(request);
                 let result = match codex_request {
                     Ok(codex_request) => {
                         // Websocket callers finalize outbound readiness in lib.rs after mirroring