fix: Profilbild-Upload auf JSON/Base64 umgestellt statt multipart

POST /profile/avatar schlug live mit net::ERR_FAILED fehl (Verbindung
abgebrochen, keine Antwort) - selbst bei einer winzigen Testdatei.
CORS-Preflight lief sauber durch, nur der eigentliche multipart-POST
nicht; passt zum bereits dokumentierten Cloudflare-Verhalten bei
multipart-Uploads (siehe .gitea/workflows/*-image.yml). Umgangen durch
Umstellung auf denselben JSON-Content-Type, der fuer alle anderen
Endpunkte nachweislich zuverlaessig funktioniert: Bild wird
clientseitig als data:-URL kodiert und im JSON-Body gesendet.
Globales JSON-Body-Limit auf 5mb angehoben (deckt 2MB-Bild plus
Base64-Overhead).

ApiCore-Backend/src/app.config.ts

@@ -10,6 +10,11 @@ export function configureApp(app: NestExpressApplication): void {
   // real client IP from X-Forwarded-For — required for per-client throttling
   // to work correctly rather than rate-limiting all traffic together.
   app.set('trust proxy', 1);
+  // Default 100kb JSON body limit is too small for the avatar upload, which
+  // sends the image as a base64 data: URL in the JSON body (not multipart -
+  // see profile/dto/upload-avatar.dto.ts for why) - 5mb comfortably covers
+  // the 2MB decoded size cap plus base64 overhead.
+  app.useBodyParser('json', { limit: '5mb' });
   app.use(helmet());
   app.use(cookieParser());
   app.use(requestLoggerMiddleware);

ApiCore-Backend/src/profile/avatar-mime-types.ts

@@ -1,3 +1,5 @@
+export const MAX_AVATAR_SIZE_BYTES = 2 * 1024 * 1024;
+
 export const ALLOWED_AVATAR_MIME_TYPES: Record<string, string> = {
   'image/jpeg': '.jpg',
   'image/png': '.png',

ApiCore-Backend/src/profile/dto/upload-avatar.dto.ts

@@ -0,0 +1,18 @@
+import { ApiProperty } from '@nestjs/swagger';
+import { IsString, MaxLength } from 'class-validator';
+
+// Base64 data: URL instead of multipart/form-data - some reverse-proxy
+// setups mishandle multipart uploads (seen with this deployment's own
+// container registry pushes, see .gitea/workflows/*-image.yml), while plain
+// JSON POSTs have proven reliable end to end. 3_000_000 chars covers the
+// 2 MB size cap (MAX_AVATAR_SIZE_BYTES) plus base64's ~33% overhead and the
+// data: URL prefix, with headroom.
+export class UploadAvatarDto {
+  @ApiProperty({
+    description:
+      'Bild als data: URL, z.B. "data:image/png;base64,...". Erlaubt: image/jpeg, image/png, image/webp.',
+  })
+  @IsString()
+  @MaxLength(3_000_000)
+  data!: string;
+}

ApiCore-Backend/src/profile/profile.controller.ts

@@ -1,5 +1,4 @@
 import {
-  BadRequestException,
   Body,
   Controller,
   Delete,
@@ -8,26 +7,21 @@ import {
   Patch,
   Post,
   Res,
-  UploadedFile,
-  UseInterceptors,
 } from '@nestjs/common';
-import { FileInterceptor } from '@nestjs/platform-express';
-import { ApiBearerAuth, ApiConsumes, ApiTags } from '@nestjs/swagger';
+import { ApiBearerAuth, ApiTags } from '@nestjs/swagger';
 import { Throttle } from '@nestjs/throttler';
 import type { Response } from 'express';
 import { CurrentUser } from '../auth/decorators/current-user.decorator';
 import type { AuthenticatedUser } from '../auth/types/authenticated-user';
 import { SENSITIVE_ACTION_THROTTLE } from '../auth/util/throttle';
-import { isAllowedAvatarMimeType } from './avatar-mime-types';
 import { ChangePasswordDto } from './dto/change-password.dto';
 import { DeactivateAccountDto } from './dto/deactivate-account.dto';
 import { DisableMfaDto } from './dto/disable-mfa.dto';
 import { MfaConfirmDto } from './dto/mfa-confirm.dto';
 import { UpdateProfileDto } from './dto/update-profile.dto';
+import { UploadAvatarDto } from './dto/upload-avatar.dto';
 import { ProfileService } from './profile.service';
 
-const MAX_AVATAR_SIZE_BYTES = 2 * 1024 * 1024;
-
 /**
  * Deliberately its own top-level path, not nested under /users/:id -
  * "/users/me" would collide with UsersController's PATCH/GET ":id" route
@@ -76,31 +70,12 @@ export class ProfileController {
   }
 
   @Post('avatar')
-  @ApiConsumes('multipart/form-data')
-  @UseInterceptors(
-    FileInterceptor('file', {
-      limits: { fileSize: MAX_AVATAR_SIZE_BYTES },
-      fileFilter: (_req, file, callback) => {
-        if (!isAllowedAvatarMimeType(file.mimetype)) {
-          callback(
-            new BadRequestException('Nicht unterstützter Dateityp'),
-            false,
-          );
-          return;
-        }
-        callback(null, true);
-      },
-    }),
-  )
   @HttpCode(204)
   uploadAvatar(
-    @UploadedFile() file: Express.Multer.File | undefined,
+    @Body() dto: UploadAvatarDto,
     @CurrentUser() actor: AuthenticatedUser,
   ) {
-    if (!file) {
-      throw new BadRequestException('No file uploaded');
-    }
-    return this.profileService.uploadAvatar(actor.id, file);
+    return this.profileService.uploadAvatar(actor.id, dto.data);
   }
 
   @Delete('avatar')

ApiCore-Backend/src/profile/profile.service.spec.ts

@@ -178,19 +178,25 @@ describe('ProfileService', () => {
   });
 
   describe('uploadAvatar', () => {
-    const file = {
-      buffer: Buffer.from('binary'),
-      originalname: 'me.jpg',
-      mimetype: 'image/jpeg',
-      size: 1234,
-    } as Express.Multer.File;
+    const dataUrl = `data:image/jpeg;base64,${Buffer.from('binary').toString('base64')}`;
+
+    it('rejects a value that is not a data: URL', async () => {
+      await expect(
+        service.uploadAvatar('user-1', 'not-a-data-url'),
+      ).rejects.toBeInstanceOf(BadRequestException);
+    });
 
     it('rejects an unsupported mime type', async () => {
+      const zipDataUrl = dataUrl.replace('image/jpeg', 'application/zip');
       await expect(
-        service.uploadAvatar('user-1', {
-          ...file,
-          mimetype: 'application/zip',
-        }),
+        service.uploadAvatar('user-1', zipDataUrl),
+      ).rejects.toBeInstanceOf(BadRequestException);
+    });
+
+    it('rejects a file larger than the 2 MB cap', async () => {
+      const oversized = `data:image/jpeg;base64,${Buffer.alloc(3 * 1024 * 1024).toString('base64')}`;
+      await expect(
+        service.uploadAvatar('user-1', oversized),
       ).rejects.toBeInstanceOf(BadRequestException);
     });
 
@@ -201,7 +207,7 @@ describe('ProfileService', () => {
       });
       prisma.user.update.mockResolvedValue({});
 
-      await service.uploadAvatar('user-1', file);
+      await service.uploadAvatar('user-1', dataUrl);
 
       expect(fs.writeFile).toHaveBeenCalled();
       expect(fs.unlink).toHaveBeenCalledWith('/uploads/avatars/old.jpg');

ApiCore-Backend/src/profile/profile.service.ts

@@ -16,6 +16,7 @@ import { PermissionResolverService } from '../auth/permissions/permission-resolv
 import { UsersService } from '../users/users.service';
 import {
   ALLOWED_AVATAR_MIME_TYPES,
+  MAX_AVATAR_SIZE_BYTES,
   mimeTypeForExtension,
 } from './avatar-mime-types';
 import { UpdateProfileDto } from './dto/update-profile.dto';
@@ -141,19 +142,28 @@ export class ProfileService {
     await this.usersService.deactivate(userId, userId);
   }
 
-  async uploadAvatar(userId: string, file: Express.Multer.File): Promise<void> {
-    if (!(file.mimetype in ALLOWED_AVATAR_MIME_TYPES)) {
+  async uploadAvatar(userId: string, dataUrl: string): Promise<void> {
+    const match = /^data:(image\/(?:jpeg|png|webp));base64,(.+)$/.exec(dataUrl);
+    if (!match) {
+      throw new BadRequestException('Ungültiges Bildformat');
+    }
+    const [, mimeType, base64] = match;
+    if (!(mimeType in ALLOWED_AVATAR_MIME_TYPES)) {
       throw new BadRequestException('Nicht unterstützter Dateityp');
     }
+    const buffer = Buffer.from(base64, 'base64');
+    if (buffer.length > MAX_AVATAR_SIZE_BYTES) {
+      throw new BadRequestException('Datei zu groß (max. 2 MB)');
+    }
     const user = await this.requireUser(userId);
-    const extension = ALLOWED_AVATAR_MIME_TYPES[file.mimetype];
+    const extension = ALLOWED_AVATAR_MIME_TYPES[mimeType];
     const directory = avatarStorageRoot();
     await fs.mkdir(directory, { recursive: true });
     const avatarPath = path.join(
       directory,
       `${crypto.randomUUID()}${extension}`,
     );
-    await fs.writeFile(avatarPath, file.buffer);
+    await fs.writeFile(avatarPath, buffer);
     if (user.avatarPath) {
       await fs.unlink(user.avatarPath).catch(() => undefined);
     }