assets_dir fix for deployments

src/main.rs

@@ -1,6 +1,9 @@
 #[macro_use]
 extern crate rocket;
 
+use std::env;
+use std::path::PathBuf;
+
 use auth::session;
 use db::migrate::run_migrations;
 use db::schema::DollTags;
@@ -18,6 +21,29 @@ pub mod routes;
 
 #[launch]
 fn rocket() -> _ {
+	// in dev., this is easy to get right, but in prod in special systems such as nixos, it's annoying to predict.
+	// instead, we can simply set it at runtime.
+	// Priority order:
+	// 1. environment variable
+	// 2. `[..]/bin/dolltags/../lib/assets` (folder containing `/bin/dolltags` and `/lib/assets`)
+	// 3. `/assets` relative to cargo manifest (dev env)
+	let assets_path = env::var("ASSETS_PATH")
+		.map(|v| PathBuf::from(v))
+		.ok()
+		.or_else(|| {
+			env::current_exe().ok().and_then(|path| {
+				// path = /bin/dolltags
+				// path.parent.parent = /
+				let assets_dir = path.parent()?.parent()?.join("lib/assets");
+				if assets_dir.exists() {
+					Some(assets_dir)
+				} else {
+					None
+				}
+			})
+		})
+		.unwrap_or_else(|| PathBuf::from(relative!("/assets")));
+
 	rocket::build()
 		.attach(pages::init_templates())
 		.attach(DollTags::init())
@@ -26,7 +52,7 @@ fn rocket() -> _ {
 			"/",
 			catchers![error_handlers::not_found, session::unauthorized],
 		)
-		.mount("/assets", FileServer::from(relative!("/assets")))
+		.mount("/assets", FileServer::from(assets_path))
 		.mount(
 			"/account",
 			routes![