Move config into module and improve error handling

src/config.rs

@@ -0,0 +1,26 @@
+use {std::env, thiserror::Error};
+
+const ENV_VAR_PREFIX: &str = "LOCALHUB_";
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("The environment variable \"{0}\" must be set.")]
+    MissingEnvironmentVariable(String),
+}
+
+pub struct Config {
+    pub database_url: String,
+    pub static_file_path: String,
+}
+
+fn get_config_string(variable: &str) -> Result<String, Error> {
+    let full_var = format!("{ENV_VAR_PREFIX}{variable}");
+    env::var(&full_var).map_err(|_| Error::MissingEnvironmentVariable(full_var))
+}
+
+pub fn get_config() -> Result<Config, Error> {
+    Ok(Config {
+        database_url: get_config_string("DATABASE_URL")?,
+        static_file_path: get_config_string("STATIC_FILE_PATH")?,
+    })
+}

src/main.rs

@@ -1,24 +1,47 @@
 use {
     askama::Template,
     axum::{extract::State, routing::get, Router},
-    std::env,
+    thiserror::Error,
     tower_http::services::ServeDir,
 };
 
+mod config;
 mod db;
+
+use config::get_config;
 use db::Database;
 
-#[tokio::main]
-async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let db_pool = Database::create_pool(&env::var("LOCALHUB_DATABASE_URL")?, 2)?;
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("Loading configuration: \"{0}\"")]
+    MissingConfigError(#[from] config::Error),
+
+    #[error("Database error: {0}")]
+    DatabaseError(#[from] db::Error),
+
+    #[error("{0}")]
+    IOError(#[from] std::io::Error),
+}
+
+fn main() {
+    let runtime = tokio::runtime::Runtime::new().unwrap();
+    std::process::exit(match runtime.block_on(localhub_main()) {
+        Ok(()) => 0,
+        Err(err) => {
+            eprintln!("ERROR: {}", err);
+            1},
+    })
+}
+
+async fn localhub_main() -> Result<(), Error> {
+    let config = get_config()?;
+
+    let db_pool = Database::create_pool(&config.database_url, 2)?;
 
     let app = Router::new()
         .route("/", get(root))
         .with_state(db_pool)
-        .nest_service(
-            "/static",
-            ServeDir::new(env::var("LOCALHUB_STATIC_FILE_PATH")?),
-        );
+        .nest_service("/static", ServeDir::new(&config.static_file_path));
 
     let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await?;
     axum::serve(listener, app).await?;