Add kaya-session package for server-side HTTP session management

example/session.py

@@ -0,0 +1,45 @@
+from kaya.core import HttpContext, KayaApp
+from kaya.session import InMemorySessionStore, SessionMiddleware
+
+app = SessionMiddleware(KayaApp(), InMemorySessionStore())
+
+
+@app.GET('/')
+async def home(ctx: HttpContext) -> None:
+    visits = ctx.session.get('visits', 0) + 1
+    ctx.session['visits'] = visits
+    await ctx.send_str(200, f'visits: {visits}')
+
+
+@app.GET('/read')
+async def read(ctx: HttpContext) -> None:
+    visits = ctx.session.get('visits', 0)
+    await ctx.send_str(200, f'visits: {visits}')
+
+
+@app.GET('/clear')
+async def clear(ctx: HttpContext) -> None:
+    ctx.session.invalidate()
+    await ctx.send_str(200, 'session cleared')
+
+@app.websocket('/echo')
+async def echo(ws: WebSocket) -> None:
+    await ws.accept()
+    async for msg in ws:
+        if msg.kind == 'text':
+            await ws.send_text(f"echo: {msg.data}")
+        elif msg.kind == 'binary':
+            data = msg.data
+            assert isinstance(data, bytes)
+            await ws.send_bytes(data)
+
+@app.websocket('/ws/visits')
+async def ws_visits(ws: WebSocket) -> None:
+    # WebSocket handlers can read the existing session. Most ASGI servers
+    # (including Granian and Daphne) do not forward the `headers` field of the
+    # `websocket.accept` message into the HTTP 101 response, so a new session
+    # cookie cannot be set during the handshake. Use the HTTP `/` endpoint to
+    # set or refresh the session cookie before connecting here.
+    await ws.accept()
+    visits = ws.session.get('visits', 0)
+    await ws.send_text(f'visits: {visits}')