From 6d376fed1576e036d8a4ceb687493e647f3d8c0d Mon Sep 17 00:00:00 2001
From: Kevin Morris <kevr@0cost.org>
Date: Fri, 29 Oct 2021 23:10:20 -0700
Subject: [PATCH] feat(rpc): add ETag header with md5 hash content

The ETag header can be used for client-side caching.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag

Signed-off-by: Kevin Morris <kevr@0cost.org>
---
 aurweb/routers/rpc.py | 25 +++++++++++++++++++++++--
 aurweb/rpc.py         |  6 ++----
 test/test_rpc.py      |  8 ++++++++
 3 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/aurweb/routers/rpc.py b/aurweb/routers/rpc.py
index 0616326b..0c52404c 100644
--- a/aurweb/routers/rpc.py
+++ b/aurweb/routers/rpc.py
@@ -1,8 +1,12 @@
+import hashlib
+
 from http import HTTPStatus
 from typing import List, Optional
 from urllib.parse import unquote
 
-from fastapi import APIRouter, Query, Request
+import orjson
+
+from fastapi import APIRouter, Query, Request, Response
 from fastapi.responses import JSONResponse
 
 from aurweb.ratelimit import check_ratelimit
@@ -74,4 +78,21 @@ async def rpc(request: Request,
     # Prepare list of arguments for input. If 'arg' was given, it'll
     # be a list with one element.
     arguments = parse_args(request)
-    return JSONResponse(rpc.handle(arguments))
+    data = rpc.handle(arguments)
+
+    # Serialize `data` into JSON in a sorted fashion. This way, our
+    # ETag header produced below will never end up changed.
+    output = orjson.dumps(data, option=orjson.OPT_SORT_KEYS)
+
+    # Produce an md5 hash based on `output`.
+    md5 = hashlib.md5()
+    md5.update(output)
+    etag = md5.hexdigest()
+
+    # Finally, return our JSONResponse with the ETag header.
+    # The ETag header expects quotes to surround any identifier.
+    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag
+    return Response(output.decode(), headers={
+        "Content-Type": "application/json",
+        "ETag": f'"{etag}"'
+    })
diff --git a/aurweb/rpc.py b/aurweb/rpc.py
index e92f9c70..87700a2f 100644
--- a/aurweb/rpc.py
+++ b/aurweb/rpc.py
@@ -99,8 +99,7 @@ class RPC:
                              data: Dict[str, Any]):
         # Walk through all related PackageDependencies and produce
         # the appropriate dict entries.
-        depends = package.package_dependencies
-        for dep in depends:
+        for dep in package.package_dependencies:
             if dep.DepTypeID in DEP_TYPES:
                 key = DEP_TYPES.get(dep.DepTypeID)
 
@@ -114,8 +113,7 @@ class RPC:
                                data: Dict[str, Any]):
         # Walk through all related PackageRelations and produce
         # the appropriate dict entries.
-        relations = package.package_relations
-        for rel in relations:
+        for rel in package.package_relations:
             if rel.RelTypeID in REL_TYPES:
                 key = REL_TYPES.get(rel.RelTypeID)
 
diff --git a/test/test_rpc.py b/test/test_rpc.py
index 9400ee06..00703c23 100644
--- a/test/test_rpc.py
+++ b/test/test_rpc.py
@@ -488,3 +488,11 @@ def test_rpc_ratelimit(getint: mock.MagicMock, pipeline: Pipeline):
     # The new first request should be good.
     response = make_request("/rpc?v=5&type=suggest-pkgbase&arg=big")
     assert response.status_code == int(HTTPStatus.OK)
+
+
+def test_rpc_etag():
+    response1 = make_request("/rpc?v=5&type=suggest-pkgbase&arg=big")
+    response2 = make_request("/rpc?v=5&type=suggest-pkgbase&arg=big")
+    assert response1.headers.get("ETag") is not None
+    assert response1.headers.get("ETag") != str()
+    assert response1.headers.get("ETag") == response2.headers.get("ETag")