How to pass an object by reference inside Rust Warp callback?

Question

I am pretty new to Rust programming and still trying to understand the concepts around memory and ownership.

I have this code.

#[tokio::main]
async fn main() {

    let file_root = String::from("test_dir/");
    let content_dir = String::from("posts_");
    let obj = msgnode::MsgNode::new(file_root.clone(), content_dir.clone());

    let node_filter = warp::any().map(move || obj.clone());

    // GET /hello/warp => 200 OK with body "Hello, warp!"
    let hello = warp::get()
        .and(warp::path("waservice"))
        .and(warp::path::end())
        .and(msg_body())
        .and(node_filter.clone())
        .and_then(store_wamsg);

    warp::serve(hello)
        .run(([127, 0, 0, 1], 3030))
        .await;
}

mod msgnode;

Everything is fine with that, except that I cannot work with cloned instance of MsgNode object. Inside the store_wamsg I am using the MsgNode object as following:

async fn store_wamsg(item: MsgItem, node : &msgnode::MsgNode) -> Result<impl warp::Reply, warp::Rejection> {
    
    let mut node2 = node.clone();

    node2.create_file(item.msg_content);
    
    Ok(warp::reply::with_status(
        "All good",
        http::StatusCode::OK,
    ))
}

My question is, if there is a way that I don't need to use multiple cloned instances of MsgNode object inside the main function, every time a new request is made to the service?

To be more precise I want to do something like this:

let node_filter = warp::any().map(move || &obj);

And somehow pass the reference inside the store_wamsg function. Right now when I do this I run into the following error:

116 |     let node_filter = warp::any().map(move || &obj);
    |                                       ------- ^^^^ returning this value requires that `'1` must outlive `'2`  
    |                                       |     |
    |                                       |     return type of closure is &'2 MsgNode
    |                                       lifetime `'1` represents this closure's body
    |
    = note: closure implements `Fn`, so references to captured variables can't escape the closure

Answer 1

You can enacapsulate msgnode in Arc Mutex to sync access:

use std::sync::{Arc, Mutex};

let obj = Arc::new(Mutex::new(msgnode::MsgNode::new(
    file_root.clone(),
    content_dir.clone(),
)));

let node_filter = warp::any().map(move || obj.clone());

Here, obj.clone() clones the atomic resouce counter, not msgnode. So that there is only one instance of MsgNode and threads coordinate their access to it with the help of Arc and Mutex.