fix: ensure jsonrpc field is serialized as "2.0"

codex-rs/mcp-types/generate_mcp_types.py

@@ -13,6 +13,8 @@ from pathlib import Path
 # Helper first so it is defined when other functions call it.
 from typing import Any, Literal
 
+SCHEMA_VERSION = "2025-03-26"
+JSONRPC_VERSION = "2.0"
 
 STANDARD_DERIVE = "#[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]\n"
 
@@ -30,7 +32,7 @@ def main() -> int:
     num_args = len(sys.argv)
     if num_args == 1:
         schema_file = (
-            Path(__file__).resolve().parent / "schema" / "2025-03-26" / "schema.json"
+            Path(__file__).resolve().parent / "schema" / SCHEMA_VERSION / "schema.json"
         )
     elif num_args == 2:
         schema_file = Path(sys.argv[1])
@@ -61,6 +63,9 @@ use serde::Serialize;
 use serde::de::DeserializeOwned;
 use std::convert::TryFrom;
 
+pub const MCP_SCHEMA_VERSION: &str = "{SCHEMA_VERSION}";
+pub const JSONRPC_VERSION: &str = "{JSONRPC_VERSION}";
+
 /// Paired request/response types for the Model Context Protocol (MCP).
 pub trait ModelContextProtocolRequest {
     const METHOD: &'static str;
@@ -74,6 +79,8 @@ pub trait ModelContextProtocolNotification {
     type Params: DeserializeOwned + Serialize + Send + Sync + 'static;
 }
 
+fn default_jsonrpc() -> String {{ JSONRPC_VERSION.to_owned() }}
+
 """
     ]
     definitions = schema_json["definitions"]
@@ -245,10 +252,6 @@ class StructField:
     serde: str | None = None
 
     def append(self, out: list[str], supports_const: bool) -> None:
-        # Omit these for now.
-        if self.name == "jsonrpc":
-            return
-
         if self.serde:
             out.append(f"    {self.serde}\n")
         if self.viz == "const":
@@ -273,6 +276,16 @@ def define_struct(
         if prop_name == "_meta":
             # TODO?
             continue
+        elif prop_name == "jsonrpc":
+            fields.append(
+                StructField(
+                    "pub",
+                    "jsonrpc",
+                    "String",  # cannot use `&'static str` because of Deserialize
+                    '#[serde(rename = "jsonrpc", default = "default_jsonrpc")]',
+                )
+            )
+            continue
 
         prop_type = map_type(prop, prop_name, name)
         if prop_name not in required_props:

codex-rs/mcp-types/src/lib.rs

@@ -10,6 +10,9 @@ use serde::Deserialize;
 use serde::Serialize;
 use std::convert::TryFrom;
 
+pub const MCP_SCHEMA_VERSION: &str = "2025-03-26";
+pub const JSONRPC_VERSION: &str = "2.0";
+
 /// Paired request/response types for the Model Context Protocol (MCP).
 pub trait ModelContextProtocolRequest {
     const METHOD: &'static str;
@@ -23,6 +26,10 @@ pub trait ModelContextProtocolNotification {
     type Params: DeserializeOwned + Serialize + Send + Sync + 'static;
 }
 
+fn default_jsonrpc() -> String {
+    JSONRPC_VERSION.to_owned()
+}
+
 /// Optional annotations for the client. The client can use annotations to inform how objects are used or displayed
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
 pub struct Annotations {
@@ -370,6 +377,8 @@ pub type JSONRPCBatchResponse = Vec<JSONRPCBatchResponseItem>;
 pub struct JSONRPCError {
     pub error: JSONRPCErrorError,
     pub id: RequestId,
+    #[serde(rename = "jsonrpc", default = "default_jsonrpc")]
+    pub jsonrpc: String,
 }
 
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
@@ -394,6 +403,8 @@ pub enum JSONRPCMessage {
 /// A notification which does not expect a response.
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
 pub struct JSONRPCNotification {
+    #[serde(rename = "jsonrpc", default = "default_jsonrpc")]
+    pub jsonrpc: String,
     pub method: String,
     pub params: Option<serde_json::Value>,
 }
@@ -402,6 +413,8 @@ pub struct JSONRPCNotification {
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
 pub struct JSONRPCRequest {
     pub id: RequestId,
+    #[serde(rename = "jsonrpc", default = "default_jsonrpc")]
+    pub jsonrpc: String,
     pub method: String,
     pub params: Option<serde_json::Value>,
 }
@@ -410,6 +423,8 @@ pub struct JSONRPCRequest {
 #[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
 pub struct JSONRPCResponse {
     pub id: RequestId,
+    #[serde(rename = "jsonrpc", default = "default_jsonrpc")]
+    pub jsonrpc: String,
     pub result: Result,
 }
 

codex-rs/mcp-types/tests/initialize.rs

@@ -5,6 +5,7 @@ use mcp_types::InitializeRequestParams;
 use mcp_types::JSONRPCMessage;
 use mcp_types::JSONRPCRequest;
 use mcp_types::RequestId;
+use mcp_types::JSONRPC_VERSION;
 use serde_json::json;
 
 #[test]
@@ -30,6 +31,7 @@ fn deserialize_initialize_request() {
     };
 
     let expected_req = JSONRPCRequest {
+        jsonrpc: JSONRPC_VERSION.into(),
         id: RequestId::Integer(1),
         method: "initialize".into(),
         params: Some(json!({