database.rs
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database.rs
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	//! This module handles a database layer, mainly intended to be used
	//! with a web server or framework like Rocket or Iron.
	//!
	//! It leverages diesel and r2d2.
	//!
	//! Most code comes from the Rocket manual:
	//! <https://rocket.rs/guide/state/#databases>

	use diesel::Connection;
	use diesel::pg::PgConnection;
	use diesel::r2d2::ConnectionManager;
	use diesel::r2d2::Pool;
	use diesel::r2d2::PooledConnection;
	use ErrorResult;
	use r2d2::Error as PoolError;
	use rocket::http::Status;
	use rocket::Outcome;
	use rocket::request::FromRequest;
	use rocket::request::Outcome as RequestOutcome;
	use rocket::Request;
	use rocket::State;
	use std::ops::Deref;

	/* -------------------------------------------------------------
	Custom types
	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

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

	/* -------------------------------------------------------------
	DatabaseConnection

	:: FromRequest
	:: Deref
	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

	/// Represents an established working database connection from the pool
	pub struct DatabaseConnection(pub PooledConnection<ConnectionManager<PgConnection>>);

	impl<'a, 'r> FromRequest<'a, 'r> for DatabaseConnection {
	type Error = ();

	fn from_request(request: &'a Request<'r>) -> RequestOutcome<Self, Self::Error> {
	let pool = request.guard::<State<PostgreSQLPool>>()?;
	match pool.get() {
	Ok(connection) => Outcome::Success(DatabaseConnection(connection)),
	Err(error) => {
	warn!(target:"request", "Can't get a connection from the pool: {}", error);

	Outcome::Failure((Status::ServiceUnavailable, ()))
	},
	}
	}
	}

	impl Deref for DatabaseConnection {
	type Target = PgConnection;

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

	/* -------------------------------------------------------------
	Helper methods to get a database connection
	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

	/// Builds a r2d2 database pool, to be used in a request guard or a managed state.
	///
	/// # Examples
	///
	/// ```
	/// rocket::ignite()
	/// .manage(initialize_database_pool(String::from("postgres://::1/test"), 4)?)
	/// .mount("/", routes)
	/// .launch();
	/// ```
	pub fn initialize_database_pool(url: &str, max_size: u32) -> Result<PostgreSQLPool, PoolError> {
	let manager = ConnectionManager::<PgConnection>::new(url);

	Pool::builder()
	.max_size(max_size)
	.build(manager)
	}

	/// Allows to test if it's possible to establish a connection to the database.
	///
	/// The goal is to test early any issue with the connection, and loudly warn or fail
	/// if the database can't be reached.
	///
	/// # Examples
	///
	/// ```
	/// // Initial connection to test if the database configuration works
	/// {
	/// test_database_connection(&config.database_url)?;
	/// info!(target: "runner", "Connection to database established.");
	/// }
	/// ```
	pub fn test_database_connection(database_url: &str) -> ErrorResult<()> {
	PgConnection::establish(database_url)?;

	Ok(())
	}

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