Pass Error status in /dev/reload stream (#8106)

* get error message

* Support multiple clients

* add changeset

* add changeset

* add changeset

* Display in UI

* console.error the python traceback

* lint

---------

Co-authored-by: gradio-pr-bot <gradio-pr-bot@users.noreply.github.com>

.changeset/slow-bats-sniff.md

@@ -0,0 +1,6 @@
+---
+"@gradio/app": patch
+"gradio": patch
+---
+
+feat:Pass Error status in /dev/reload stream

gradio/http_server.py

@@ -137,15 +137,12 @@ def start_server(
             )
             reloader = None
             if GRADIO_WATCH_DIRS:
-                change_event = threading.Event()
-                app.change_event = change_event
                 reloader = SourceFileReloader(
                     app=app,
                     watch_dirs=GRADIO_WATCH_DIRS,
                     watch_module_name=GRADIO_WATCH_MODULE_NAME,
                     demo_name=GRADIO_WATCH_DEMO_NAME,
                     stop_event=threading.Event(),
-                    change_event=change_event,
                     demo_file=GRADIO_WATCH_DEMO_PATH,
                 )
             server = Server(config=config, reloader=reloader)

gradio/routes.py

@@ -19,7 +19,6 @@
 import os
 import posixpath
 import secrets
-import threading
 import time
 import traceback
 from pathlib import Path
@@ -31,6 +30,7 @@
     Callable,
     Dict,
     List,
+    Literal,
     Optional,
     Type,
     Union,
@@ -173,7 +173,9 @@ def __init__(
         self.queue_token = secrets.token_urlsafe(32)
         self.startup_events_triggered = False
         self.uploaded_file_dir = get_upload_folder()
-        self.change_event: None | threading.Event = None
+        self.change_count: int = 0
+        self.change_type: Literal["reload", "error"] | None = None
+        self.reload_error_message: str | None = None
         self._asyncio_tasks: list[asyncio.Task] = []
         self.auth_dependency = auth_dependency
         self.api_info = None
@@ -284,14 +286,20 @@ async def reload_checker(request: fastapi.Request):
                 heartbeat_rate = 15
                 check_rate = 0.05
                 last_heartbeat = time.perf_counter()
+                current_count = app.change_count
 
                 while True:
                     if await request.is_disconnected():
                         return
 
-                    if app.change_event and app.change_event.is_set():
-                        app.change_event.clear()
-                        yield """event: reload\ndata: {}\n\n"""
+                    if app.change_count != current_count:
+                        current_count = app.change_count
+                        msg = (
+                            json.dumps(f"{app.reload_error_message}")
+                            if app.change_type == "error"
+                            else "{}"
+                        )
+                        yield f"""event: {app.change_type}\ndata: {msg}\n\n"""
 
                     await asyncio.sleep(check_rate)
                     if time.perf_counter() - last_heartbeat > heartbeat_rate:

gradio/utils.py

@@ -38,6 +38,7 @@
     Generic,
     Iterable,
     Iterator,
+    Literal,
     Optional,
     TypeVar,
 )
@@ -123,15 +124,13 @@ def __init__(
         watch_module_name: str,
         demo_file: str,
         stop_event: threading.Event,
-        change_event: threading.Event,
         demo_name: str = "demo",
     ) -> None:
         super().__init__()
         self.app = app
         self.watch_dirs = watch_dirs
         self.watch_module_name = watch_module_name
         self.stop_event = stop_event
-        self.change_event = change_event
         self.demo_name = demo_name
         self.demo_file = Path(demo_file)
 
@@ -145,16 +144,17 @@ def should_watch(self) -> bool:
     def stop(self) -> None:
         self.stop_event.set()
 
-    def alert_change(self):
-        self.change_event.set()
+    def alert_change(self, change_type: Literal["reload", "error"] = "reload"):
+        self.app.change_type = change_type
+        self.app.change_count += 1
 
     def swap_blocks(self, demo: Blocks):
         old_blocks = self.running_app.blocks
         super().swap_blocks(demo)
         if old_blocks:
             reassign_keys(old_blocks, demo)
         demo.config = demo.get_config_file()
-        self.alert_change()
+        self.alert_change("reload")
 
 
 NO_RELOAD = True
@@ -281,6 +281,8 @@ def iter_py_files() -> Iterator[Path]:
                 )
                 traceback.print_exc()
                 mtimes = {}
+                reloader.alert_change("error")
+                reloader.app.reload_error_message = traceback.format_exc()
                 continue
             demo = getattr(module, reloader.demo_name)
             reloader.swap_blocks(demo)

js/app/src/Blocks.svelte

@@ -154,6 +154,13 @@
 		};
 	}
 
+	export function add_new_message(
+		message: string,
+		type: ToastMessage["type"]
+	): void {
+		messages = [new_message(message, -1, type), ...messages];
+	}
+
 	let _error_id = -1;
 
 	let user_left_page = false;

js/app/src/Index.svelte

@@ -302,6 +302,11 @@
 				const { host } = new URL(api_url);
 				let url = new URL(`http://${host}/dev/reload`);
 				eventSource = new EventSource(url);
+				eventSource.addEventListener("error", async (e) => {
+					new_message_fn("Error reloading app", "error");
+					// @ts-ignore
+					console.error(JSON.parse(e.data));
+				});
 				eventSource.addEventListener("reload", async (event) => {
 					app.close();
 					app = await Client.connect(api_url, {
@@ -372,6 +377,8 @@
 		}
 	};
 
+	let new_message_fn: (message: string, type: string) => void;
+
 	onMount(async () => {
 		intersecting.register(_id, wrapper);
 	});
@@ -449,6 +456,7 @@
 			{autoscroll}
 			bind:ready
 			bind:render_complete
+			bind:add_new_message={new_message_fn}
 			show_footer={!is_embed}
 			{app_mode}
 			{version}