Implement ETags

schoolsyst_api/etag.py

@@ -0,0 +1,37 @@
+from hashlib import sha256
+from typing import Callable
+
+from fastapi.requests import Request
+from fastapi_etag import Etag
+from schoolsyst_api import database
+from schoolsyst_api.models import OBJECT_KEY_FORMAT
+
+
+def compute_for(collection_name: str) -> Callable[[Request], str]:
+    """
+    Returns an `Etag` with a function that takes a Request and returns a SHA256
+    hexdigest hash of the `updated_at` field of an object from `collection_name`
+    with a _key equal to a path parameter `{key}`'s value as the etag generation function.
+    """
+
+    async def compute(request: Request) -> str:
+        # Get the database
+        db = database.get()
+        # Get the key of the object from the path parameters from Request
+        key = request.path_params["key"]
+        # Get the collection name from the request path
+        collection_name = request.path.split("/")[1].replace("-", "_")
+        # Get the full key by getting the current user
+        # current_user_key = parse(auth.JWT_SUB_FORMAT, request.auth)
+        full_key = OBJECT_KEY_FORMAT.format(object=key, owner="current_user.key")
+        # Get the document from collection collection_name with _key key
+        document = db.collection(collection_name).get(full_key)
+        # Get the updated_at date
+        updated_at = document["updated_at"]
+        # Compute a hash of thet updated_at date
+        sha256hash = sha256(updated_at)
+        # Get the hexdigest of that hash (which is a `str`)
+        hexdigest = sha256hash.hexdigest()
+        return hexdigest
+
+    return Etag(compute)

schoolsyst_api/main.py

@@ -1,5 +1,6 @@
 from pathlib import Path
 
+import fastapi_etag
 import typed_dotenv
 import uvicorn
 from fastapi import FastAPI
@@ -20,6 +21,8 @@
 typed_dotenv.load_into(EnvironmentVariables, Path(__file__).parent.parent / ".env")
 # Initialize the database
 api.add_event_handler("startup", database.initialize)
+# Handle Etags
+fastapi_etag.add_exception_handler(api)
 # Handle CORS
 api.add_middleware(**cors.middleware_params)
 # Include routes

schoolsyst_api/subjects.py

@@ -5,7 +5,7 @@
 from arango.database import StandardDatabase
 from fastapi import Depends, HTTPException, Response, status
 from fastapi_utils.inferring_router import InferringRouter
-from schoolsyst_api import database
+from schoolsyst_api import database, etag
 from schoolsyst_api.accounts.users import get_current_confirmed_user
 from schoolsyst_api.models import (
     OBJECT_KEY_FORMAT,
@@ -67,7 +67,7 @@ def update_a_subject(
     return db.collection("subjects").update(updated_subject, return_new=True)["new"]
 
 
-@router.get("/subjects/{key}")
+@router.get("/subjects/{key}", dependencies=[Depends(etag.compute_for("subjects"))])
 def get_a_subject(
     key: ObjectBareKey,
     current_user: User = Depends(get_current_confirmed_user),