Plume/plume-models/src/db_conn.rs

use diesel::{
    pg::PgConnection,
    r2d2::{ConnectionManager, Pool, PooledConnection}
};
use rocket::{Request, State, Outcome, http::Status, request::{self, FromRequest}};
use std::ops::Deref;

pub type PgPool = Pool<ConnectionManager<PgConnection>>;

// From rocket documentation

// Connection request guard type: a wrapper around an r2d2 pooled connection.
pub struct DbConn(pub PooledConnection<ConnectionManager<PgConnection>>);

/// Attempts to retrieve a single connection from the managed database pool. If
/// no pool is currently managed, fails with an `InternalServerError` status. If
/// no connections are available, fails with a `ServiceUnavailable` status.
impl<'a, 'r> FromRequest<'a, 'r> for DbConn {
    type Error = ();

    fn from_request(request: &'a Request<'r>) -> request::Outcome<Self, Self::Error> {
        let pool = request.guard::<State<PgPool>>()?;
        match pool.get() {
            Ok(conn) => Outcome::Success(DbConn(conn)),
            Err(_) => Outcome::Failure((Status::ServiceUnavailable, ()))
        }
    }
}

// For the convenience of using an &DbConn as an &PgConnection.
impl Deref for DbConn {
    type Target = PgConnection;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}