Allow passing empty/nil params in case all are optional (#1078)

jsonrpc/server.go

@@ -363,11 +363,15 @@ func (s *Server) handleRequest(ctx context.Context, req *request) (*response, er
 
 func (s *Server) buildArguments(ctx context.Context, params any, method Method) ([]reflect.Value, error) {
 	if isNil(params) {
-		if len(method.Params) > 0 {
+		allParamsAreOptional := utils.All(method.Params, func(p Parameter) bool {
+			return p.Optional
+		})
+
+		if len(method.Params) > 0 && !allParamsAreOptional {
 			return nil, errors.New("missing non-optional param field")
 		}
 
-		return make([]reflect.Value, 0), nil
+		return s.buildDefaultArguments(ctx, method)
 	}
 
 	handlerType := reflect.TypeOf(method.Handler)
@@ -423,6 +427,20 @@ func (s *Server) buildArguments(ctx context.Context, params any, method Method)
 	return args, nil
 }
 
+func (s *Server) buildDefaultArguments(_ context.Context, method Method) ([]reflect.Value, error) {
+	handlerType := reflect.TypeOf(method.Handler)
+
+	numArgs := handlerType.NumIn()
+	args := make([]reflect.Value, 0, numArgs)
+
+	for i := 0; i < numArgs; i++ {
+		arg := reflect.New(handlerType.In(i)).Elem()
+		args = append(args, arg)
+	}
+
+	return args, nil
+}
+
 func (s *Server) parseParam(param any, t reflect.Type) (reflect.Value, error) {
 	handlerParam := reflect.New(t)
 	valueMarshaled, err := json.Marshal(param) // we have to marshal the value into JSON again

utils/slices.go

@@ -42,3 +42,8 @@ func IndexFunc[T comparable](slice []T, f func(T) bool) int {
 
 	return -1
 }
+
+// All returns true if all elements match the given predicate
+func All[T comparable](slice []T, f func(T) bool) bool {
+	return IndexFunc(slice, func(e T) bool { return !f(e) }) == -1
+}

utils/slices_test.go

@@ -65,3 +65,27 @@ func TestIndexFunc(t *testing.T) {
 		assert.Equal(t, 2, idx)
 	})
 }
+
+func TestAll(t *testing.T) {
+	t.Run("nil slice", func(t *testing.T) {
+		var input []int
+		allValue := All(input, func(int) bool {
+			return false
+		})
+		assert.True(t, allValue)
+	})
+	t.Run("no element matches the predicate", func(t *testing.T) {
+		input := []int{1, 2, 3, 4}
+		allEven := All(input, func(v int) bool {
+			return v%2 == 0
+		})
+		assert.False(t, allEven)
+	})
+	t.Run("all elements match the predicate", func(t *testing.T) {
+		input := []int{1, 3, 5, 7}
+		allOdd := All(input, func(v int) bool {
+			return v%2 != 0
+		})
+		assert.True(t, allOdd)
+	})
+}