如何hook block

原生代码

- (void)viewDidLoad {
    [super viewDidLoad];
    [self sendRequest:^(NSString *str) {
        NSLog(@"%@",str);
    }];
}

- (void)sendRequest:(void (^)( NSString *))arg {
    arg(@"abcd");
}

hook 代码

%hook ViewController
- (void)sendRequest:(void (^)( NSString *))arg {
    void (^res)( NSString *) = arg;
    res = ^(NSString *str){
        NSLog(@"=====%@",str);
        str = @"1111111";
        arg(str);
    };
    %orig(res);
}
%end

日志打印

=====abcd
1111111