Plz! How to safely modify MessageField in &mut T

[kingwingfly]

This is my proto:

message Bili {
    Headers headers = 1;
}

message Headers {
    string user_agent = 1;
    string referer = 2;
    map<string, string> cookies = 3;
}

This is what generated:

#[derive(PartialEq,Clone,Default,Debug)]
pub struct Bili {
    pub headers: ::protobuf::MessageField<Headers>,
    pub special_fields: ::protobuf::SpecialFields,
}


#[derive(PartialEq,Clone,Default,Debug)]
pub struct Headers {
    pub user_agent: ::std::string::String,
    pub referer: ::std::string::String,
    pub cookies: ::std::collections::HashMap<::std::string::String, ::std::string::String>,
    pub special_fields: ::protobuf::SpecialFields,
}

I want to modify cookies in Bili.headers.cookies with method signatured fn set_cookies(&mut self, cookies: HashMap<String, String>)

I tried:

// 1.
self.headers.cookies = cookies;    // => cannot assign to data in dereference of `MessageField<Headers>`
// 2.
self.headers.as_mut().unwrap().cookies = cookies; // => RuntimeErr: called `Option::unwrap()` on a `None` value

// test:
let mut bili = Bili::default();
let mut cookies = HashMap::new();
cookies.insert("1".to_string(), "1".to_string());
bili.extend_cookies(cookies);
assert_eq!(bili.cookies().len(), 1);
assert_eq!(bili.cookies().get("1").unwrap(), "1");

Below's how I did. any better way?

fn extend_cookies(&mut self, cookies: HashMap<String, String>) {
    match self.headers.as_mut() {
        Some(headers) => headers.cookies = cookies,
        None => {
            self.headers = MessageField::some(Headers {
                cookies,
                ..Default::default()
            })
        }
    }
}