Reapply "Improve fastapi perfs (antonputra#391)"

This reverts commit 19745b8.

lessons/232/python-app/main.py

@@ -7,7 +7,7 @@
 import orjson
 from asyncpg import PostgresError
 from fastapi import FastAPI, HTTPException
-from fastapi.responses import ORJSONResponse, PlainTextResponse
+from fastapi.responses import ORJSONResponse, PlainTextResponse, Response
 from prometheus_client import make_asgi_app
 from pydantic import BaseModel
 
@@ -25,12 +25,12 @@
 
 
 @app.get("/healthz", response_class=PlainTextResponse)
-def health():
-    return "OK"
+async def health():
+    return PlainTextResponse("OK")
 
 
 @app.get("/api/devices", response_class=ORJSONResponse)
-def get_devices():
+async def get_devices():
     devices = (
         {
             "id": 1,
@@ -58,15 +58,15 @@ def get_devices():
         },
     )
 
-    return devices
+    return ORJSONResponse(devices)
 
 
 class DeviceRequest(BaseModel):
     mac: str
     firmware: str
 
 
-@app.post("/api/devices", status_code=201, response_class=ORJSONResponse)
+@app.post("/api/devices", status_code=201, response_class=Response)
 async def create_device(
     device: DeviceRequest, conn: PostgresDep, cache_client: MemcachedDep
 ):
@@ -102,18 +102,20 @@ async def create_device(
             "updated_at": now,
         }
 
+        device_json = orjson.dumps(device_dict)
+
         # Measure cache operation
         start_time = time.perf_counter()
 
         await cache_client.set(
             device_uuid.hex.encode(),
-            orjson.dumps(device_dict),
+            device_json,
             exptime=20,
         )
 
         H.labels(op="set", db="memcache").observe(time.perf_counter() - start_time)
 
-        return device_dict
+        return Response(device_json, media_type="application/json")
 
     except PostgresError:
         logger.exception("Postgres error")
@@ -142,14 +144,14 @@ async def get_device_stats(cache_client: MemcachedDep):
         stats = await cache_client.stats()
         # H.labels(op="stats", db="memcache").observe(time.perf_counter() - start_time)
 
-        return {
+        return ORJSONResponse({
             "curr_items": stats.get(b"curr_items", 0),
             "total_items": stats.get(b"total_items", 0),
             "bytes": stats.get(b"bytes", 0),
             "curr_connections": stats.get(b"curr_connections", 0),
             "get_hits": stats.get(b"get_hits", 0),
             "get_misses": stats.get(b"get_misses", 0),
-        }
+        })
     except aiomcache.exceptions.ClientException:
         logger.exception("Memcached error")
         raise HTTPException(