improve compatibility with multipart/form-data mastodon API requests

1 files changed, 141 insertions, 0 deletions

diff --git a/packages/backend/src/server/ServerUtilityService.ts b/packages/backend/src/server/ServerUtilityService.ts
new file mode 100644
index 0000000000..f2900fad4f
--- /dev/null
+++ b/packages/backend/src/server/ServerUtilityService.ts
@@ -0,0 +1,141 @@
+/*
+ * SPDX-FileCopyrightText: hazelnoot and other Sharkey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import querystring from 'querystring';
+import multipart from '@fastify/multipart';
+import { Inject, Injectable } from '@nestjs/common';
+import { FastifyInstance } from 'fastify';
+import { DI } from '@/di-symbols.js';
+import type { Config } from '@/config.js';
+
+@Injectable()
+export class ServerUtilityService {
+	constructor(
+		@Inject(DI.config)
+		private readonly config: Config,
+	) {}
+
+	public addMultipartFormDataContentType(fastify: FastifyInstance): void {
+		fastify.register(multipart, {
+			limits: {
+				fileSize: this.config.maxFileSize,
+				files: 1,
+			},
+		});
+
+		// Default behavior saves files to memory - we don't want that!
+		// Store to temporary file instead, and copy the body fields while we're at it.
+		fastify.addHook<{ Body?: Record<string, string | string[] | undefined> }>('onRequest', async request => {
+			if (request.isMultipart()) {
+				const body = request.body ??= {};
+
+				// Save upload to temp directory.
+				// These are attached to request.savedRequestFiles
+				await request.saveRequestFiles();
+
+				// Copy fields to body
+				const formData = await request.formData();
+				formData.forEach((v, k) => {
+					// This can be string or File, and we handle files above.
+					if (typeof(v) === 'string') {
+						// This is just progressive conversion from undefined -> string -> string[]
+						if (body[k]) {
+							if (Array.isArray(body[k])) {
+								body[k].push(v);
+							} else {
+								body[k] = [body[k], v];
+							}
+						} else {
+							body[k] = v;
+						}
+					}
+				});
+			}
+		});
+	}
+
+	public addFormUrlEncodedContentType(fastify: FastifyInstance) {
+		fastify.addContentTypeParser('application/x-www-form-urlencoded', (_, payload, done) => {
+			let body = '';
+			payload.on('data', (data) => {
+				body += data;
+			});
+			payload.on('end', () => {
+				try {
+					const parsed = querystring.parse(body);
+					done(null, parsed);
+				} catch (e) {
+					done(e as Error);
+				}
+			});
+			payload.on('error', done);
+		});
+	}
+
+	public addCORS(fastify: FastifyInstance) {
+		fastify.addHook('onRequest', (_, reply, done) => {
+			// Allow web-based clients to connect from other origins.
+			reply.header('Access-Control-Allow-Origin', '*');
+
+			// Mastodon uses all types of request methods.
+			reply.header('Access-Control-Allow-Methods', '*');
+
+			// Allow web-based clients to access Link header - required for mastodon pagination.
+			// https://stackoverflow.com/a/54928828
+			// https://docs.joinmastodon.org/api/guidelines/#pagination
+			// https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Access-Control-Expose-Headers
+			reply.header('Access-Control-Expose-Headers', 'Link');
+
+			// Cache to avoid extra pre-flight requests
+			// https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Access-Control-Max-Age
+			reply.header('Access-Control-Max-Age', 60 * 60 * 24); // 1 day in seconds
+
+			done();
+		});
+	}
+
+	public addFlattenedQueryType(fastify: FastifyInstance) {
+		// Remove trailing "[]" from query params
+		fastify.addHook<{ Querystring?: Record<string, string | string[] | undefined> }>('preValidation', (request, _reply, done) => {
+			if (!request.query || typeof(request.query) !== 'object') {
+				return done();
+			}
+
+			for (const key of Object.keys(request.query)) {
+				if (!key.endsWith('[]')) {
+					continue;
+				}
+				if (request.query[key] == null) {
+					continue;
+				}
+
+				const newKey = key.substring(0, key.length - 2);
+				const newValue = request.query[key];
+				const oldValue = request.query[newKey];
+
+				// Move the value to the correct key
+				if (oldValue != null) {
+					if (Array.isArray(oldValue)) {
+						// Works for both array and single values
+						request.query[newKey] = oldValue.concat(newValue);
+					} else if (Array.isArray(newValue)) {
+						// Preserve order
+						request.query[newKey] = [oldValue, ...newValue];
+					} else {
+						// Preserve order
+						request.query[newKey] = [oldValue, newValue];
+					}
+				} else {
+					request.query[newKey] = newValue;
+				}
+
+				// Remove the invalid key
+				delete request.query[key];
+			}
+
+			return done();
+		});
+	}
+}