API: validation: mention invalid method name (#8489)

src/nvim/api/private/dispatch.c

@@ -29,6 +29,8 @@ static void msgpack_rpc_add_method_handler(String method,
   map_put(String, MsgpackRpcRequestHandler)(methods, method, handler);
 }
 
+/// @param name API method name
+/// @param name_len name size (includes terminating NUL)
 MsgpackRpcRequestHandler msgpack_rpc_get_handler_for(const char *name,
                                                      size_t name_len)
 {

src/nvim/api/vim.c

@@ -16,6 +16,7 @@
 #include "nvim/api/private/dispatch.h"
 #include "nvim/api/buffer.h"
 #include "nvim/msgpack_rpc/channel.h"
+#include "nvim/msgpack_rpc/helpers.h"
 #include "nvim/lua/executor.h"
 #include "nvim/vim.h"
 #include "nvim/buffer.h"
@@ -1163,6 +1164,11 @@ Array nvim_call_atomic(uint64_t channel_id, Array calls, Error *err)
 
     MsgpackRpcRequestHandler handler = msgpack_rpc_get_handler_for(name.data,
                                                                    name.size);
+    if (handler.fn == msgpack_rpc_handle_missing_method) {
+      api_set_error(&nested_error, kErrorTypeException, "Invalid method: %s",
+                    name.size > 0 ? name.data : "<empty>");
+      break;
+    }
     Object result = handler.fn(channel_id, args, &nested_error);
     if (ERROR_SET(&nested_error)) {
       // error handled after loop

src/nvim/msgpack_rpc/channel.c

@@ -312,24 +312,30 @@ static void handle_request(Channel *channel, msgpack_object *request)
     api_clear_error(&error);
     return;
   }
+
   // Retrieve the request handler
   MsgpackRpcRequestHandler handler;
+  Array args = ARRAY_DICT_INIT;
   msgpack_object *method = msgpack_rpc_method(request);
 
   if (method) {
     handler = msgpack_rpc_get_handler_for(method->via.bin.ptr,
                                           method->via.bin.size);
+    if (handler.fn == msgpack_rpc_handle_missing_method) {
+      String m = method->via.bin.size > 0
+        ? cbuf_to_string(method->via.bin.ptr, method->via.bin.size)
+        : cstr_to_string("<empty>");
+      ADD(args, STRING_OBJ(m));
+      handler.async = true;
+    } else if (!msgpack_rpc_to_array(msgpack_rpc_args(request), &args)) {
+      handler.fn = msgpack_rpc_handle_invalid_arguments;
+      handler.async = true;
+    }
   } else {
     handler.fn = msgpack_rpc_handle_missing_method;
     handler.async = true;
   }
 
-  Array args = ARRAY_DICT_INIT;
-  if (!msgpack_rpc_to_array(msgpack_rpc_args(request), &args)) {
-    handler.fn = msgpack_rpc_handle_invalid_arguments;
-    handler.async = true;
-  }
-
   RequestEvent *evdata = xmalloc(sizeof(RequestEvent));
   evdata->channel = channel;
   evdata->handler = handler;

src/nvim/msgpack_rpc/helpers.c

@@ -493,7 +493,8 @@ Object msgpack_rpc_handle_missing_method(uint64_t channel_id,
                                          Array args,
                                          Error *error)
 {
-  api_set_error(error, kErrorTypeException, "Invalid method name");
+  api_set_error(error, kErrorTypeException, "Invalid method: %s",
+                args.size > 0 ? args.items[0].data.string.data : "?");
   return NIL;
 }