idea on how sessions might be implemented

src/idom/backend/sanic.py

@@ -3,7 +3,7 @@
 import asyncio
 import json
 import logging
-from dataclasses import dataclass
+from dataclasses import dataclass, replace
 from typing import Any, Dict, Tuple, Union
 from urllib import parse as urllib_parse
 from uuid import uuid4
@@ -14,7 +14,7 @@
 from sanic_cors import CORS
 from websockets.legacy.protocol import WebSocketCommonProtocol
 
-from idom.backend.types import Location
+from idom.backend.types import Location, SessionState
 from idom.core.hooks import Context, create_context, use_context
 from idom.core.layout import Layout, LayoutEvent
 from idom.core.serve import (
@@ -27,7 +27,12 @@
 from idom.core.types import RootComponentConstructor
 
 from ._asgi import serve_development_asgi
-from .utils import safe_client_build_dir_path, safe_web_modules_dir_path
+from .utils import (
+    SESSION_COOKIE_NAME,
+    SessionManager,
+    safe_client_build_dir_path,
+    safe_web_modules_dir_path,
+)
 
 
 logger = logging.getLogger(__name__)
@@ -47,7 +52,7 @@ def configure(
     _setup_common_routes(blueprint, options)
 
     # this route should take priority so set up it up first
-    _setup_single_view_dispatcher_route(blueprint, component)
+    _setup_single_view_dispatcher_route(blueprint, component, options)
 
     app.blueprint(blueprint)
 
@@ -129,6 +134,9 @@ class Options:
     url_prefix: str = ""
     """The URL prefix where IDOM resources will be served from"""
 
+    session: SessionManager[Any] | None = None
+    """Used to create session cookies to perserve client state"""
+
 
 def _setup_common_routes(blueprint: Blueprint, options: Options) -> None:
     cors_options = options.cors
@@ -164,22 +172,51 @@ async def web_module_files(
 
 
 def _setup_single_view_dispatcher_route(
-    blueprint: Blueprint, constructor: RootComponentConstructor
+    blueprint: Blueprint,
+    constructor: RootComponentConstructor,
+    options: Options,
 ) -> None:
     async def model_stream(
         request: request.Request, socket: WebSocketCommonProtocol, path: str = ""
     ) -> None:
+        root = ConnectionContext(constructor(), value=Connection(request, socket, path))
+
+        if options.session:
+            root = options.session.context(root, value=request.ctx.idom_sesssion_state)
+
         send, recv = _make_send_recv_callbacks(socket)
-        conn = Connection(request, socket, path)
-        await serve_json_patch(
-            Layout(ConnectionContext(constructor(), value=conn)),
-            send,
-            recv,
-        )
+        await serve_json_patch(Layout(root), send, recv)
 
     blueprint.add_websocket_route(model_stream, "/_api/stream")
     blueprint.add_websocket_route(model_stream, "/<path:path>/_api/stream")
 
+    if options.session:
+        session = options.session
+
+        @blueprint.on_request
+        async def set_session_on_request(request: request.Request) -> None:
+            if request.scheme not in ("http", "https"):
+                return
+            session_id = request.cookies.get(SESSION_COOKIE_NAME)
+            request.ctx.idom_session_state = await session.get_state(session_id)
+
+        @blueprint.on_response
+        async def set_session_cookie_header(
+            request: request.Request, response: response.ResponseStream
+        ):
+            session_state: SessionState[Any] = request.ctx.idom_session_state
+            # only set cookie if it has not been set before
+            if session_state.fresh:
+                # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie
+                response.cookies[SESSION_COOKIE_NAME] = session.sid
+                response.cookies[SESSION_COOKIE_NAME]["secure"] = True
+                response.cookies[SESSION_COOKIE_NAME]["httponly"] = True
+                response.cookies[SESSION_COOKIE_NAME]["samesite"] = "strict"
+                response.cookies[SESSION_COOKIE_NAME]["expires"] = session.expiry_date
+
+                await session.update_state(replace(session_state, fresh=False))
+                logger.info(f"Setting cookie {response.cookies[SESSION_COOKIE_NAME]}")
+
 
 def _make_send_recv_callbacks(
     socket: WebSocketCommonProtocol,

src/idom/backend/types.py

@@ -1,8 +1,9 @@
 from __future__ import annotations
 
 import asyncio
-from dataclasses import dataclass
-from typing import Any, MutableMapping, TypeVar
+from dataclasses import dataclass, field
+from datetime import datetime
+from typing import Any, Generic, MutableMapping, TypeVar
 
 from typing_extensions import Protocol, runtime_checkable
 
@@ -56,3 +57,14 @@ class Location:
 
     search: str = ""
     """A search or query string - a '?' followed by the parameters of the URL."""
+
+
+_State = TypeVar("_State")
+
+
+@dataclass
+class SessionState(Generic[_State]):
+    id: str
+    value: _State
+    expiry_date: datetime
+    fresh: bool = field(default_factory=lambda: True)

src/idom/backend/utils.py

@@ -5,15 +5,18 @@
 import os
 import socket
 from contextlib import closing
+from dataclasses import dataclass
+from datetime import datetime, timezone
 from importlib import import_module
 from pathlib import Path
-from typing import Any, Iterator
+from typing import Any, Awaitable, Callable, Generic, Iterator, TypeVar
 
 import idom
 from idom.config import IDOM_WEB_MODULES_DIR
+from idom.core.hooks import create_context, use_context
 from idom.types import RootComponentConstructor
 
-from .types import BackendImplementation
+from .types import BackendImplementation, SessionState
 
 
 logger = logging.getLogger(__name__)
@@ -28,6 +31,50 @@
 )
 
 
+SESSION_COOKIE_NAME = "IdomSessionId"
+
+
+_State = TypeVar("_State")
+
+
+class SessionManager(Generic[_State]):
+    def __init__(
+        self,
+        create_state: Callable[[], Awaitable[_State]],
+        read_state: Callable[[str], Awaitable[_State | None]],
+        update_state: Callable[[_State], Awaitable[None]],
+    ):
+        self.context = create_context(None)
+        self._create_state = create_state
+        self._read_state = read_state
+        self._update_state = update_state
+
+    def use_context(self) -> _State:
+        return use_context(self.context)
+
+    async def update_state(self, state: SessionState[_State]) -> None:
+        await self._update_state(state)
+        logger.info(f"Updated session {state.id}")
+
+    async def get_state(self, id: str | None = None) -> SessionState[_State] | None:
+        if id is None:
+            state = await self._create_state()
+            logger.info(f"Created new session {state.id!r}")
+        else:
+            state = await self._read_state(id)
+            if state is None:
+                logger.info(f"Could not load session {id!r}")
+                state = await self._create_state()
+                logger.info(f"Created new session {state.id!r}")
+            elif state.expiry_date < datetime.now(timezone.utc):
+                logger.info(f"Session {id!r} expired at {state.expiry_date}")
+                state = await self._create_state()
+                logger.info(f"Created new session {state.id!r}")
+            else:
+                logger.info(f"Loaded existing session {id!r}")
+        return state
+
+
 def run(
     component: RootComponentConstructor,
     host: str = "127.0.0.1",