Gracefully handle non-existent canvas error

diff --git a/src/main.rs b/src/main.rs
index 373a4012ec5cf518c1b827e080dac198f147e61f..9d1bd4496d5b6a7d87329c2929a62b2c1d03d610 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -40,6 +40,31 @@ impl ResponseError for ImageError {
     }
 }
 
+#[derive(Debug)]
+enum CanvasError {
+    NotExists
+}
+
+impl Display for CanvasError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Canvas Error: see error_response() for more details")
+    }
+}
+
+impl ResponseError for CanvasError {
+    fn status_code(&self) -> StatusCode {
+        match &self {
+            CanvasError::NotExists => StatusCode::NOT_FOUND
+        }
+    }
+
+    fn error_response(&self) -> HttpResponse<BoxBody> {
+        match &self {
+            CanvasError::NotExists => HttpResponse::NotFound().body("Canvas does not exist.")
+        }
+    }
+}
+
 struct ToRgbIter<'a, T> where T: AsPrimitive<u8> {
     iter: Box<&'a mut dyn Iterator<Item = T>>
 }
@@ -166,8 +191,8 @@ async fn img_pgen0(req: HttpRequest, canvas0: web::Data<Arc<Mutex<Option<Canvas>
     let tdim_y = 32 * scale;
     let img: RgbImage = {
         let canvas_option = &mut *canvas0.lock().unwrap();
-        let canvas = canvas_option.take();
-        let canvas = rgb_encode_to_canvas(canvas.expect("Canvas doesn't exist!"), percent_decode_str(&data).into_iter().borrow_mut())?;
+        let canvas = canvas_option.take().ok_or(CanvasError::NotExists)?;
+        let canvas = rgb_encode_to_canvas(canvas, percent_decode_str(&data).into_iter().borrow_mut())?;
         canvas_option.insert(canvas).img.clone()
     };
     let img = resize(&img, tdim_x, tdim_y, FilterType::Nearest);