What's the best way of handling errors in main method of actix-web? - rust

Question

Is there a way to handle errors inside main method in actix-web?
I have the following code, as you can see there's three places in that function that can panic: the reference to the DATABASE_URL environment variable, the creation of the connection pool and the initialization of the template engine (tera).
#[actix_web::main]
async fn main() -> std::io::Result<()> {
dotenv().ok();
let database_url = std::env::var("DATABASE_URL").expect("DATABASE_URL must be set.");
let manager = ConnectionManager::<PgConnection>::new(database_url);
let pool = Pool::builder().build(manager).expect("Failed to create connection pool.");
HttpServer::new(move || {
let tera = Tera::new("templates/**/*").unwrap();
App::new()
.data(pool.clone())
.data(tera)
.route("/", web::get().to(index))
})
.bind("127.0.0.1:8000")?
.run()
.await
}
So, I tried to change the return type on that function and use a previously defined Enum in order to handle those errors:
async fn main() -> Result<HttpServer, ServerError> {
dotenv().ok();
let database_url = std::env::var("DATABASE_URL")?;
let manager = ConnectionManager::<PgConnection>::new(database_url);
let pool = Pool::builder().build(manager)?;
HttpServer::new(move || {
let tera = Tera::new("templates/**/*")?;
App::new()
.data(pool.clone())
.data(tera)
.route("/", web::get().to(index))
})
.bind("127.0.0.1:8000")?
.run()
.await
}
But the compiler shows this message:
[Running 'cargo run']
error[E0107]: missing generics for struct `HttpServer`
|
| async fn main() -> Result<HttpServer, ServerError> {
| ^^^^^^^^^^ expected 4 type arguments
|
note: struct defined here, with 4 type parameters: `F`, `I`, `S`, `B`
|
| pub struct HttpServer<F, I, S, B>
| ^^^^^^^^^^ - - - -
help: use angle brackets to add missing type arguments
|
| async fn main() -> Result<HttpServer<F, I, S, B>, ServerError> {
| ^^^^^^^^^^^^
error: aborting due to previous error
For more information about this error, try `rustc --explain E0107`.
error: could not compile
What's the best course of action that I can follow here? Should I handle this kind of errors within the main method?