basic etag behavior

Author: devksingh4

cloudformation/iam.yml

@@ -88,9 +88,9 @@ Resources:
             Resource:
               - Fn::Sub: arn:aws:dynamodb:${AWS::Region}:${AWS::AccountId}:table/infra-core-api-cache
             Condition:
-              ForAllValues:StringEquals:
+              ForAllValues:StringLike:
                 dynamodb:LeadingKeys:
-                  - testing # add any keys that must be accessible
+                  - etag-events-* # add any keys that must be accessible
               ForAllValues:StringLike:
                 dynamodb:Attributes:
                   - primaryKey

src/api/functions/cache.ts

@@ -1,7 +1,10 @@
 import {
+  DeleteItemCommand,
   DynamoDBClient,
+  GetItemCommand,
   PutItemCommand,
   QueryCommand,
+  UpdateItemCommand,
 } from "@aws-sdk/client-dynamodb";
 import { genericConfig } from "../../common/config.js";
 import { marshall, unmarshall } from "@aws-sdk/util-dynamodb";
@@ -52,3 +55,79 @@ export async function insertItemIntoCache(
     }),
   );
 }
+
+export async function atomicIncrementCacheCounter(
+  dynamoClient: DynamoDBClient,
+  key: string,
+  amount: number,
+  returnOld: boolean = false,
+): Promise<number> {
+  const response = await dynamoClient.send(
+    new UpdateItemCommand({
+      TableName: genericConfig.CacheDynamoTableName,
+      Key: marshall({
+        primaryKey: key,
+      }),
+      UpdateExpression: "ADD #counterValue :increment",
+      ExpressionAttributeNames: {
+        "#counterValue": "counterValue",
+      },
+      ExpressionAttributeValues: marshall({
+        ":increment": amount,
+      }),
+      ReturnValues: returnOld ? "UPDATED_OLD" : "UPDATED_NEW",
+    }),
+  );
+
+  if (!response.Attributes) {
+    return returnOld ? 0 : amount;
+  }
+
+  const value = unmarshall(response.Attributes).counter;
+  return typeof value === "number" ? value : 0;
+}
+
+export async function getCacheCounter(
+  dynamoClient: DynamoDBClient,
+  key: string,
+  defaultValue: number = 0,
+): Promise<number> {
+  const response = await dynamoClient.send(
+    new GetItemCommand({
+      TableName: genericConfig.CacheDynamoTableName,
+      Key: marshall({
+        primaryKey: key,
+      }),
+      ProjectionExpression: "counterValue", // Only retrieve the value attribute
+    }),
+  );
+
+  if (!response.Item) {
+    return defaultValue;
+  }
+
+  const value = unmarshall(response.Item).counterValue;
+  return typeof value === "number" ? value : defaultValue;
+}
+
+export async function deleteCacheCounter(
+  dynamoClient: DynamoDBClient,
+  key: string,
+): Promise<number | null> {
+  const params = {
+    TableName: genericConfig.CacheDynamoTableName,
+    Key: marshall({
+      primaryKey: key,
+    }),
+    ReturnValue: "ALL_OLD",
+  };
+
+  const response = await dynamoClient.send(new DeleteItemCommand(params));
+
+  if (response.Attributes) {
+    const item = unmarshall(response.Attributes);
+    const value = item.counterValue;
+    return typeof value === "number" ? value : 0;
+  }
+  return null;
+}

src/api/routes/events.ts

@@ -24,6 +24,11 @@ import { randomUUID } from "crypto";
 import moment from "moment-timezone";
 import { IUpdateDiscord, updateDiscord } from "../functions/discord.js";
 import rateLimiter from "api/plugins/rateLimiter.js";
+import {
+  atomicIncrementCacheCounter,
+  deleteCacheCounter,
+  getCacheCounter,
+} from "api/functions/cache.js";
 
 const repeatOptions = ["weekly", "biweekly"] as const;
 const CLIENT_HTTP_CACHE_POLICY = `public, max-age=${EVENT_CACHED_DURATION}, stale-while-revalidate=420, stale-if-error=3600`;
@@ -137,6 +142,11 @@ const eventsPlugin: FastifyPluginAsync = async (fastify, _options) => {
               TableName: genericConfig.EventsDynamoTableName,
             });
           }
+          const etag = await getCacheCounter(
+            fastify.dynamoClient,
+            "events-etag-all",
+          );
+          reply.header("etag", etag);
           const response = await fastify.dynamoClient.send(command);
           const items = response.Items?.map((item) => unmarshall(item));
           const currentTimeChicago = moment().tz("America/Chicago");
@@ -277,6 +287,18 @@ const eventsPlugin: FastifyPluginAsync = async (fastify, _options) => {
           }
           throw new DiscordEventError({});
         }
+        await atomicIncrementCacheCounter(
+          fastify.dynamoClient,
+          `events-etag-${entryUUID}`,
+          1,
+          false,
+        );
+        await atomicIncrementCacheCounter(
+          fastify.dynamoClient,
+          "events-etag-all",
+          1,
+          false,
+        );
         reply.status(201).send({
           id: entryUUID,
           resource: `/api/v1/events/${entryUUID}`,
@@ -335,6 +357,7 @@ const eventsPlugin: FastifyPluginAsync = async (fastify, _options) => {
           message: "Failed to delete event from Dynamo table.",
         });
       }
+      await deleteCacheCounter(fastify.dynamoClient, `events-etag-${id}`);
       request.log.info(
         { type: "audit", actor: request.username, target: id },
         `deleted event "${id}"`,
@@ -372,7 +395,11 @@ const eventsPlugin: FastifyPluginAsync = async (fastify, _options) => {
         if (!ts) {
           reply.header("Cache-Control", CLIENT_HTTP_CACHE_POLICY);
         }
-        return reply.send(item);
+        const etag = await getCacheCounter(
+          fastify.dynamoClient,
+          `events-etag-${id}`,
+        );
+        return reply.header("etag", etag).send(item);
       } catch (e) {
         if (e instanceof BaseError) {
           throw e;