implemented reload script injection

src/zona/server.py

@@ -1,3 +1,4 @@
+import io
 import os
 import signal
 import sys
@@ -7,22 +8,110 @@ from pathlib import Path
 from types import FrameType
 from typing import override
 
+from rich import print
 from watchdog.events import FileSystemEvent, FileSystemEventHandler
 from watchdog.observers import Observer
 
 from zona.builder import ZonaBuilder
 from zona.log import get_logger
+from zona.websockets import WebSocketServer
 
 logger = get_logger()
 
 
+def make_reload_script(host: str, port: int) -> str:
+    """Generates the JavaScript that must be injected into HTML pages for the live reloading to work."""
+    return f"""
+<script>
+const ws = new WebSocket("ws://{host}:{port}");
+ws.onmessage = event => {{
+    if (event.data === "reload") {{
+        location.reload();
+    }}
+}};
+</script>
+"""
+
+
+def make_handler_class(script: str):
+    """Build the live reload handler with the script as an attribute."""
+
+    class CustomHandler(LiveReloadHandler):
+        pass
+
+    CustomHandler.script = script
+    return CustomHandler
+
+
+class LiveReloadHandler(SimpleHTTPRequestHandler):
+    """
+    Request handler implementing live reloading.
+    All logs are suppressed.
+    HTML files have the reload script injected before </body>.
+    """
+
+    script: str = ""
+
+    @override
+    def log_message(self, format, *args):  # type: ignore
+        pass
+
+    @override
+    def send_head(self):
+        path = Path(self.translate_path(self.path))
+        # check if serving path/index.html
+        if path.is_dir():
+            index_path = path / "index.html"
+            if index_path.is_file():
+                path = index_path
+        # check if serving html file
+        if Path(path).suffix in {".html", ".htm"} and self.script != "":
+            try:
+                logger.debug("Injecting reload script")
+                # read the html
+                with open(path, "rb") as f:
+                    content = f.read().decode("utf-8")
+                # inject script at the end of body
+                if r"</body>" in content:
+                    content = content.replace(
+                        "</body>", self.script + "</body>"
+                    )
+                else:
+                    # if no </body>, add to the end
+                    content += self.script
+                # reencode, prepare headers, serve file
+                encoded = content.encode("utf-8")
+                self.send_response(200)
+                self.send_header(
+                    "Content-type", "text/html; charset=utf-8"
+                )
+                self.send_header("Content-Length", str(len(encoded)))
+                self.end_headers()
+                return io.BytesIO(encoded)
+            except Exception:
+                self.send_error(404, "File not found")
+                return None
+        return super().send_head()
+
+
 class QuietHandler(SimpleHTTPRequestHandler):
+    """SimpleHTTPRequestHandler with logs suppressed."""
+
     @override
     def log_message(self, format, *args):  # type: ignore
         pass
 
 
 class ZonaServer(ThreadingHTTPServer):
+    """HTTP server implementing live reloading via a WebSocket server.
+    Suppresses BrokenPipeError and ConnectionResetError.
+    """
+
+    ws_server: WebSocketServer | None = None
+
+    def set_ws_server(self, ws_server: WebSocketServer):
+        self.ws_server = ws_server
+
     @override
     def handle_error(self, request, client_address):  # type: ignore
         _, exc_value = sys.exc_info()[:2]
@@ -33,12 +122,33 @@ class ZonaServer(ThreadingHTTPServer):
 
 
 class ZonaReloadHandler(FileSystemEventHandler):
-    def __init__(self, builder: ZonaBuilder, output: Path):
+    """FileSystemEventHandler that rebuilds the website
+    and triggers the browser into refreshing over WebSocket."""
+
+    def __init__(
+        self,
+        builder: ZonaBuilder,
+        output: Path,
+        ws_server: WebSocketServer,
+    ):
         self.builder: ZonaBuilder = builder
         self.output: Path = output.resolve()
+        self.ws_server: WebSocketServer = ws_server
+
+    def _trigger_rebuild(self, event: FileSystemEvent):
+        # check if it's an event we care about
+        if not self._should_ignore(event):
+            logger.info(f"Modified: {event.src_path}, rebuilding...")
+            # rebuild static site
+            self.builder.build()
+            assert self.ws_server
+            # trigger browser refresh
+            self.ws_server.notify_all()
 
     def _should_ignore(self, event: FileSystemEvent) -> bool:
         path = Path(str(event.src_path)).resolve()
+        # ignore if the output directory has been changed
+        # to avoid infinite loop
         return (
             self.output in path.parents
             or path == self.output
@@ -47,26 +157,11 @@ class ZonaReloadHandler(FileSystemEventHandler):
 
     @override
     def on_modified(self, event: FileSystemEvent):
-        if not self._should_ignore(event):
+        self._trigger_rebuild(event)
-            logger.info(f"Modified: {event.src_path}, rebuilding...")
-            self.builder.build()
 
     @override
     def on_created(self, event: FileSystemEvent):
-        if not self._should_ignore(event):
+        self._trigger_rebuild(event)
-            logger.info(f"Modified: {event.src_path}, rebuilding...")
-            self.builder.build()
-
-
-def run_http_server(dir: Path, host: str = "localhost", port: int = 8000):
-    os.chdir(dir)
-    handler = QuietHandler
-    httpd = ZonaServer(
-        server_address=(host, port), RequestHandlerClass=handler
-    )
-    logger.info(f"Serving {dir} at http://{host}:{port}")
-    logger.info("Exit with <c-c>")
-    httpd.serve_forever()
 
 
 def serve(
@@ -76,28 +171,58 @@ def serve(
     host: str = "localhost",
     port: int = 8000,
 ):
+    """Serve preview website with live reload and automatic rebuild."""
     builder = ZonaBuilder(root, output, draft)
+    # initial site build
     builder.build()
+    # use discovered paths if none provided
     if output is None:
         output = builder.layout.output
     if root is None:
         root = builder.layout.root
 
+    # spin up websocket server for live reloading
+    ws_port = port + 1
+    ws_server = WebSocketServer(host, ws_port)
+    ws_server.start()
+    # generate reload script for injection
+    reload_script = make_reload_script(host, ws_port)
+    # serve the output directory
+    os.chdir(output)
+    # generate handler with reload script as attribute
+    handler = make_handler_class(reload_script)
+    # initialize http server
+    httpd = ZonaServer(
+        server_address=(host, port), RequestHandlerClass=handler
+    )
+    # link websocket server
+    httpd.set_ws_server(ws_server)
+    # provide link to user
+    print(f"Serving {output} at http://{host}:{port}")
+    print("Exit with <c-c>")
+
+    # start server in a thread
     server_thread = threading.Thread(
-        target=run_http_server, args=(output, host, port), daemon=True
+        target=httpd.serve_forever, daemon=True
     )
     server_thread.start()
 
-    event_handler = ZonaReloadHandler(builder, output)
+    # initialize reload handler
+    event_handler = ZonaReloadHandler(builder, output, ws_server)
     observer = Observer()
     observer.schedule(event_handler, path=str(root), recursive=True)
     observer.start()
 
+    # function to shut down gracefully
     def shutdown_handler(_a: int, _b: FrameType | None):
         logger.info("Shutting down...")
         observer.stop()
+        httpd.shutdown()
+        sys.exit(0)
 
+    # register shutdown handler
     signal.signal(signal.SIGINT, shutdown_handler)
     signal.signal(signal.SIGTERM, shutdown_handler)
 
+    # start file change watcher
     observer.join()

src/zona/websockets.py

@@ -0,0 +1,52 @@
+import asyncio
+from threading import Thread
+
+from websockets.legacy.server import WebSocketServerProtocol, serve
+
+
+class WebSocketServer:
+    host: str
+    port: int
+    clients: set[WebSocketServerProtocol]
+    loop: asyncio.AbstractEventLoop | None
+    thread: Thread | None
+
+    def __init__(self, host: str = "localhost", port: int = 8765):
+        self.host = host
+        self.port = port
+        self.clients = set()
+        self.loop = None
+        self.thread = None
+
+    async def _handler(self, ws: WebSocketServerProtocol):
+        self.clients.add(ws)
+        try:
+            await ws.wait_closed()
+        finally:
+            self.clients.remove(ws)
+
+    def start(self):
+        def run():
+            self.loop = asyncio.new_event_loop()
+            asyncio.set_event_loop(self.loop)
+            ws_server = serve(
+                ws_handler=self._handler, host=self.host, port=self.port
+            )
+            self.loop.run_until_complete(ws_server)
+            self.loop.run_forever()
+
+        self.thread = Thread(target=run, daemon=True)
+        self.thread.start()
+
+    async def _broadcast(self, message: str):
+        for ws in self.clients.copy():
+            try:
+                await ws.send(message)
+            except Exception:
+                self.clients.discard(ws)
+
+    def notify_all(self, message: str = "reload"):
+        if self.loop and self.clients:
+            asyncio.run_coroutine_threadsafe(
+                coro=self._broadcast(message), loop=self.loop
+            )