Fix integer underflow in try_range_response for empty files (#3566)

axum-extra/src/response/file_stream.rs

@@ -191,6 +191,10 @@ where
         let metadata = file.metadata().await?;
         let total_size = metadata.len();
 
+        if total_size == 0 {
+            return Ok((StatusCode::RANGE_NOT_SATISFIABLE, "Range Not Satisfiable").into_response());
+        }
+
         if end == 0 {
             end = total_size - 1;
         }
@@ -596,4 +600,52 @@ mod tests {
         }
         Some((start, end))
     }
+
+    #[tokio::test]
+    async fn response_range_empty_file() -> Result<(), Box<dyn std::error::Error>> {
+        let file = tempfile::NamedTempFile::new()?;
+        file.as_file().set_len(0)?;
+        let path = file.path().to_owned();
+
+        let app = Router::new().route(
+            "/range_empty",
+            get(move |headers: HeaderMap| {
+                let path = path.clone();
+                async move {
+                    let range_header = headers
+                        .get(header::RANGE)
+                        .and_then(|value| value.to_str().ok());
+
+                    let (start, end) = if let Some(range) = range_header {
+                        if let Some(range) = parse_range_header(range) {
+                            range
+                        } else {
+                            return (StatusCode::RANGE_NOT_SATISFIABLE, "Invalid Range")
+                                .into_response();
+                        }
+                    } else {
+                        (0, 0)
+                    };
+
+                    FileStream::<ReaderStream<File>>::try_range_response(path, start, end)
+                        .await
+                        .unwrap_or_else(|_| StatusCode::INTERNAL_SERVER_ERROR.into_response())
+                }
+            }),
+        );
+
+        let response = app
+            .oneshot(
+                Request::builder()
+                    .uri("/range_empty")
+                    .header(header::RANGE, "bytes=0-")
+                    .body(Body::empty())
+                    .unwrap(),
+            )
+            .await
+            .unwrap();
+
+        assert_eq!(response.status(), StatusCode::RANGE_NOT_SATISFIABLE);
+        Ok(())
+    }
 }