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fix(mcp): return -32601 for unknown methods, and implement the spec-required ping #13

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fix(mcp): return -32601 for unknown methods, and implement the spec-required ping #13

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29 changes: 19 additions & 10 deletions src/mcp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -196,11 +196,24 @@ pub async fn serve() -> Result<()> {
///
/// Routes the request to the appropriate handler based on the method name.
async fn handle_request(request: JsonRpcRequest) -> JsonRpcResponse {
let result = match request.method.as_str() {
"initialize" => handle_initialize(request.params),
"tools/list" => handle_list_tools(),
"tools/call" => handle_call_tool(request.params).await,
_ => Err(anyhow!("Unknown method: {}", request.method)),
// JSON-RPC 2.0 reserves -32601 for an unimplemented method; -32603 ("Internal
// error") means the server itself failed. Reporting -32603 for a method we
// simply do not implement tells the client the server is broken, and strict
// clients drop the connection on it during capability probing.
const METHOD_NOT_FOUND: i32 = -32601;
const INTERNAL_ERROR: i32 = -32603;

let (result, err_code) = match request.method.as_str() {
"initialize" => (handle_initialize(request.params), INTERNAL_ERROR),
"tools/list" => (handle_list_tools(), INTERNAL_ERROR),
"tools/call" => (handle_call_tool(request.params).await, INTERNAL_ERROR),
// `ping` is REQUIRED by the MCP spec; an empty result is its success shape.
"ping" => (Ok(serde_json::json!({})), INTERNAL_ERROR),
// Clients probe these after initialize even when the capability is not
// advertised. Answer empty rather than erroring.
"resources/list" => (Ok(serde_json::json!({ "resources": [] })), INTERNAL_ERROR),
"prompts/list" => (Ok(serde_json::json!({ "prompts": [] })), INTERNAL_ERROR),
_ => (Err(anyhow!("Unknown method: {}", request.method)), METHOD_NOT_FOUND),
};

match result {
Expand All @@ -214,11 +227,7 @@ async fn handle_request(request: JsonRpcRequest) -> JsonRpcResponse {
jsonrpc: "2.0".to_string(),
id: request.id,
result: None,
error: Some(JsonRpcError {
code: -32603, // Internal error
message: e.to_string(),
data: None,
}),
error: Some(JsonRpcError { code: err_code, message: e.to_string(), data: None }),
},
}
}
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