Split PanelJupyterExecutor into separate module (#4276)

* Split PanelJupyterExecutor into separate module

* Small fix

panel/io/jupyter_executor.py

@@ -0,0 +1,173 @@
+from __future__ import annotations
+
+import asyncio
+import weakref
+
+from dataclasses import dataclass
+from typing import (
+    Any, Dict, List, Union,
+)
+
+import tornado
+
+from bokeh.command.util import build_single_handler_application
+from bokeh.document import Document
+from bokeh.embed.bundle import extension_dirs
+from bokeh.protocol import Protocol
+from bokeh.protocol.receiver import Receiver
+from bokeh.server.connection import ServerConnection
+from bokeh.server.contexts import BokehSessionContext
+from bokeh.server.protocol_handler import ProtocolHandler
+from bokeh.server.session import ServerSession
+from bokeh.server.views.static_handler import StaticHandler
+from bokeh.server.views.ws import WSHandler
+from bokeh.util.token import get_session_id, get_token_payload
+from ipykernel.comm import Comm
+from IPython.display import HTML, publish_display_data
+
+from ..util import edit_readonly
+from .resources import Resources
+from .server import server_html_page_for_session
+from .state import set_curdoc, state
+
+
+@dataclass
+class _RequestProxy:
+
+    arguments: Dict[str, List[bytes]]
+    cookies: Dict[str, str]
+    headers: Dict[str, str | List[str]]
+
+
+class PanelExecutor(WSHandler):
+    """
+    The PanelExecutor is intended to be run inside a kernel where it
+    runs a Panel application renders the HTML and then establishes a
+    Jupyter Comm channel to communicate with the PanelWSProxy in order
+    to send and receive messages to and from the frontend.
+    """
+
+    def __init__(self, path, token, root_url):
+        self.path = path
+        self.token = token
+        self.root_url = root_url
+        self.payload = self._get_payload(token)
+        self.session_id = get_session_id(token)
+        self.comm = Comm(target_name=self.session_id)
+        self.comm.on_msg(self._receive_msg)
+        self.protocol = Protocol()
+        self.receiver = Receiver(self.protocol)
+        self.handler = ProtocolHandler()
+        self.write_lock = tornado.locks.Lock()
+        self._context = None
+
+        self.resources = Resources(
+            mode="server", root_url=self.root_url,
+            path_versioner=StaticHandler.append_version
+        )
+        self._set_state()
+        self.session = self._create_server_session()
+        self.connection = ServerConnection(self.protocol, self, None, self.session)
+
+    def _get_payload(self, token: str) -> Dict[str, Any]:
+        payload = get_token_payload(token)
+        if ('cookies' in payload and 'headers' in payload
+            and not 'Cookie' in payload['headers']):
+            # Restore Cookie header from cookies dictionary
+            payload['headers']['Cookie'] = '; '.join([
+                f'{k}={v}' for k, v in payload['cookies'].items()
+            ])
+        return payload
+
+    def _set_state(self):
+        state._jupyter_kernel_context = True
+        with edit_readonly(state):
+            state.base_url = self.root_url + '/'
+            state.rel_path = self.root_url
+
+    def _receive_msg(self, msg) -> None:
+        asyncio.ensure_future(self._receive_msg_async(msg))
+
+    async def _receive_msg_async(self, msg) -> None:
+        try:
+            message = await self._receive(msg['content']['data'])
+        except Exception as e:
+            # If you go look at self._receive, it's catching the
+            # expected error types... here we have something weird.
+            self._internal_error(f"server failed to parse a message: {e}")
+            message = None
+
+        try:
+            if message:
+                work = await self._handle(message)
+                if work:
+                    await self._schedule(work)
+        except Exception as e:
+            self._internal_error(f"server failed to handle a message: {e}")
+
+    def _internal_error(self, msg: str) -> None:
+        self.comm.send(msg, {'status': 'internal_error'})
+
+    def _protocol_error(self, msg: str) -> None:
+        self.comm.send(msg, {'status': 'protocol_error'})
+
+    def _create_server_session(self) -> ServerSession:
+        doc = Document()
+
+        self._context = session_context = BokehSessionContext(
+            self.session_id, None, doc
+        )
+
+        # using private attr so users only have access to a read-only property
+        session_context._request = _RequestProxy(
+            arguments={k: [v.encode('utf-8') for v in vs] for k, vs in self.payload.get('arguments', {})},
+            cookies=self.payload.get('cookies'),
+            headers=self.payload.get('headers')
+        )
+        session_context._token = self.token
+
+        # expose the session context to the document
+        # use the _attribute to set the public property .session_context
+        doc._session_context = weakref.ref(session_context)
+
+        if self.path.endswith('.yaml') or self.path.endswith('.yml'):
+            from lumen.command import (
+                build_single_handler_application as build_lumen_app,
+            )
+            app = build_lumen_app(self.path, argv=None)
+        else:
+            app = build_single_handler_application(self.path)
+        with set_curdoc(doc):
+            app.initialize_document(doc)
+
+        loop = tornado.ioloop.IOLoop.current()
+        session = ServerSession(self.session_id, doc, io_loop=loop, token=self.token)
+        session_context._set_session(session)
+        return session
+
+
+    async def write_message(
+        self, message: Union[bytes, str, Dict[str, Any]],
+        binary: bool = False, locked: bool = True
+    ) -> None:
+        metadata = {'binary': binary}
+        if binary:
+            self.comm.send({}, metadata=metadata, buffers=[message])
+        else:
+            self.comm.send(message, metadata=metadata)
+
+    def render(self) -> HTML:
+        """
+        Renders the application to an IPython.display.HTML object to
+        be served by the `PanelJupyterHandler`.
+        """
+        with set_curdoc(self.session.document):
+            html = server_html_page_for_session(
+                self.session,
+                resources=self.resources,
+                title=self.session.document.title,
+                template=self.session.document.template,
+                template_variables=self.session.document.template_variables
+            )
+        publish_display_data({'application/bokeh-extensions': extension_dirs})
+        return HTML(html)