feat(misskey-js): multipart/form-dataのリクエストに対応 (#14147)

* feat(misskey-js): multipart/form-dataのリクエストに対応

* lint

* add test

* Update Changelog

* テストを厳しくする

* lint

* multipart/form-dataではnullのプロパティを弾くように

packages/misskey-js/src/api.ts

@@ -1,7 +1,7 @@
 import './autogen/apiClientJSDoc.js';
 
-import { SwitchCaseResponseType } from './api.types.js';
-import type { Endpoints } from './api.types.js';
+import { endpointReqTypes } from './autogen/endpoint.js';
+import type { SwitchCaseResponseType, Endpoints } from './api.types.js';
 
 export type {
 	SwitchCaseResponseType,
@@ -23,7 +23,7 @@ export function isAPIError(reason: Record<PropertyKey, unknown>): reason is APIE
 
 export type FetchLike = (input: string, init?: {
 	method?: string;
-	body?: string;
+	body?: Blob | FormData | string;
 	credentials?: RequestCredentials;
 	cache?: RequestCache;
 	headers: { [key in string]: string }
@@ -49,20 +49,55 @@ export class APIClient {
 		this.fetch = opts.fetch ?? ((...args) => fetch(...args));
 	}
 
+	private assertIsRecord<T>(obj: T): obj is T & Record<string, any> {
+		return obj !== null && typeof obj === 'object' && !Array.isArray(obj);
+	}
+
 	public request<E extends keyof Endpoints, P extends Endpoints[E]['req']>(
 		endpoint: E,
 		params: P = {} as P,
 		credential?: string | null,
 	): Promise<SwitchCaseResponseType<E, P>> {
 		return new Promise((resolve, reject) => {
-			this.fetch(`${this.origin}/api/${endpoint}`, {
-				method: 'POST',
-				body: JSON.stringify({
+			let mediaType = 'application/json';
+			if (endpoint in endpointReqTypes) {
+				mediaType = endpointReqTypes[endpoint];
+			}
+			let payload: FormData | string = '{}';
+
+			if (mediaType === 'application/json') {
+				payload = JSON.stringify({
 					...params,
 					i: credential !== undefined ? credential : this.credential,
-				}),
+				});
+			} else if (mediaType === 'multipart/form-data') {
+				payload = new FormData();
+				const i = credential !== undefined ? credential : this.credential;
+				if (i != null) {
+					payload.append('i', i);
+				}
+				if (this.assertIsRecord(params)) {
+					for (const key in params) {
+						const value = params[key];
+
+						if (value == null) continue;
+
+						if (value instanceof File || value instanceof Blob) {
+							payload.append(key, value);
+						} else if (typeof value === 'object') {
+							payload.append(key, JSON.stringify(value));
+						} else {
+							payload.append(key, value);
+						}
+					}
+				}
+			}
+
+			this.fetch(`${this.origin}/api/${endpoint}`, {
+				method: 'POST',
+				body: payload,
 				headers: {
-					'Content-Type': 'application/json',
+					'Content-Type': endpointReqTypes[endpoint],
 				},
 				credentials: 'omit',
 				cache: 'no-cache',