From e0fefc986f0e564ee2d7d7117b2d997e05b22b22 Mon Sep 17 00:00:00 2001
From: Laura Hausmann <laura@hausmann.dev>
Date: Fri, 29 Sep 2023 23:29:14 +0200
Subject: [PATCH] [mastodon-client] Respect idempotency-key for new posts

---
 .../server/api/mastodon/endpoints/status.ts   | 61 ++++++++++++++++---
 1 file changed, 52 insertions(+), 9 deletions(-)

diff --git a/packages/backend/src/server/api/mastodon/endpoints/status.ts b/packages/backend/src/server/api/mastodon/endpoints/status.ts
index 5331d2617..eacec8ffa 100644
--- a/packages/backend/src/server/api/mastodon/endpoints/status.ts
+++ b/packages/backend/src/server/api/mastodon/endpoints/status.ts
@@ -13,11 +13,13 @@ import { UserHelpers } from "@/server/api/mastodon/helpers/user.js";
 import { convertPaginationArgsIds, limitToInt, normalizeUrlQuery } from "@/server/api/mastodon/endpoints/timeline.js";
 import { PaginationHelpers } from "@/server/api/mastodon/helpers/pagination.js";
 import { UserConverter } from "@/server/api/mastodon/converters/user.js";
+import { Cache } from "@/misc/cache.js";
+import { redisClient } from "@/db/redis.js";
+import AsyncLock from "async-lock";
+import { ILocalUser } from "@/models/entities/user.js";
 
-function normalizeQuery(data: any) {
-	const str = querystring.stringify(data);
-	return qs.parse(str);
-}
+const postIdempotencyCache = new Cache<{status?: MastodonEntity.Status}>('postIdempotencyCache', 60 * 60);
+const postIdempotencyLocks = new AsyncLock();
 
 export function setupEndpointsStatus(router: Router): void {
 	router.post("/v1/statuses", async (ctx) => {
@@ -30,14 +32,26 @@ export function setupEndpointsStatus(router: Router): void {
 				return;
 			}
 
+			const key = getIdempotencyKey(ctx.headers, user);
+			if (key !== null) {
+				const result = await getFromIdempotencyCache(key);
+
+				if (result) {
+					ctx.body = result;
+					return;
+				}
+			}
+
 			let request = NoteHelpers.normalizeComposeOptions(ctx.request.body);
-			const note = await NoteHelpers.createNote(request, user)
-				.then(p => NoteConverter.encode(p, user));
-			ctx.body = convertStatus(note);
+			ctx.body = await NoteHelpers.createNote(request, user)
+				.then(p => NoteConverter.encode(p, user))
+				.then(p => convertStatus(p));
+
+			if (key !== null) postIdempotencyCache.set(key, {status: ctx.body});
 		} catch (e: any) {
 			console.error(e);
-			ctx.status = 401;
-			ctx.body = e.response.data;
+			ctx.status = 500;
+			ctx.body = { error: e.message };
 		}
 	});
 	router.put("/v1/statuses/:id", async (ctx) => {
@@ -621,3 +635,32 @@ export function setupEndpointsStatus(router: Router): void {
 		},
 	);
 }
+
+function normalizeQuery(data: any) {
+	const str = querystring.stringify(data);
+	return qs.parse(str);
+}
+
+function getIdempotencyKey(headers: any, user: ILocalUser): string | null {
+	if (headers["idempotency-key"] === undefined || headers["idempotency-key"] === null) return null;
+	return `${user.id}-${Array.isArray(headers["idempotency-key"]) ? headers["idempotency-key"].at(-1)! : headers["idempotency-key"]}`;
+}
+
+async function getFromIdempotencyCache(key: string): Promise<MastodonEntity.Status | undefined> {
+	return postIdempotencyLocks.acquire(key, async (): Promise<MastodonEntity.Status | undefined> => {
+		if (await postIdempotencyCache.get(key) !== undefined) {
+			let i = 5;
+			while ((await postIdempotencyCache.get(key))?.status === undefined) {
+				if (++i > 5) throw new Error('Post is duplicate but unable to resolve original');
+				await new Promise((resolve) => {
+					setTimeout(resolve, 500);
+				});
+			}
+
+			return (await postIdempotencyCache.get(key))?.status;
+		} else {
+			await postIdempotencyCache.set(key, {});
+			return undefined;
+		}
+	});
+}