Iron Handler: Missing Lifetime Specifiers

Question

I'm trying to implement an Iron handler that contains a reference to another struct. That struct holds the data and does all operations on the data.

[package]
name = "testcrate"
version = "0.1.0"
authors = ["me"]

[dependencies]
iron = "^0.2"

This is the code:

//! Handlers for the server.
extern crate iron;

use iron::{status, middleware};
use iron::IronResult;
use iron::prelude::Set;
use iron::request::Request;
use iron::response::Response;

/// The MyServer struct holds the data and provides methods
/// to manipulate or retrieve that data.
struct MyServer;
impl MyServer {
    pub fn build_response() -> String {
        "response".to_string()
    }   
}

/// The ReadHandler handles the creation of HTTP responses.
pub struct ReadHandler {
    pub server: &MyServer,
}
impl middleware::Handler for ReadHandler {                                                                                         

    /// Return the current status JSON.
    fn handle(&self, req: &mut Request) -> IronResult<Response> {
        let body = self.server.build_response();
        let response = Response::with((status::Ok, body));
        Ok(response)
    }   
}

Unfortunately I'm getting errors about missing lifetime specifiers:

src/lib.rs:22:17: 22:26 error: missing lifetime specifier [E0106]
src/lib.rs:22     pub server: &MyServer,
                              ^~~~~~~~~
src/lib.rs:22:17: 22:26 help: run `rustc --explain E0106` to see a detailed explanation

But when I add lifetime specifiers (which I didn't fully understand yet)...

pub struct ReadHandler<'a> {
    pub server: &'a MyServer,
}
impl<'a> middleware::Handler for ReadHandler<'a> {
    // ...
}

...I get another error message:

src/lib.rs:24:1: 32:2 error: the type `ReadHandler<'a>` does not fulfill the required lifetime
src/lib.rs:24 impl<'a> middleware::Handler for ReadHandler<'a> {
src/lib.rs:25 
src/lib.rs:26     /// Return the current status JSON.
src/lib.rs:27     fn handle(&self, req: &mut Request) -> IronResult<Response> {
src/lib.rs:28         let body = self.server.build_response();
src/lib.rs:29         let response = Response::with((status::Ok, body));
              ...
note: type must outlive the static lifetime

There will be other handlers that will access the MyServer in a read-only or read-write mode.

What would be the correct way to add lifetime specifiers? Or do I maybe need a structure like an Arc?

Answer 1

The Handler trait is a subtrait of Any:

pub trait Handler: Send + Sync + Any {
    fn handle(&self, &mut Request) -> IronResult<Response>;
}

And the Any trait has a 'static lifetime bound:

pub trait Any: Reflect + 'static {
    fn get_type_id(&self) -> TypeId;
}

The 'static bound means that your struct cannot contain references. You'll have to use another type of pointer. Since Handler is also a subtrait of Send and Sync, you'll need to use Arc, since Rc is neither Send nor Sync.