Multipart Uploads with Multer Interceptors
Wire FileInterceptor and FilesInterceptor to accept single and multi-file uploads with size limits.
Why Multer for Uploads
HTTP file uploads use the multipart/form-data content type, which splits the request body into parts: text fields and binary file payloads separated by a boundary marker.
NestJS does not parse this format on its own. Instead it ships first-class wrappers around Multer, the de-facto Express middleware for multipart parsing. You consume Multer through interceptors rather than wiring middleware manually.
FileInterceptor— one file from a single fieldFilesInterceptor— many files from one fieldFileFieldsInterceptor— files across several named fields
This lesson focuses on the first two and on enforcing size limits.
Installing the Types
The interceptors live in @nestjs/platform-express, which is already present in a standard Nest app. You only need the Multer type definitions to type your handler parameters correctly.
Install the dev dependency so Express.Multer.File is recognized by TypeScript:
npm install -D @types/multer
// Now Express.Multer.File is available globally in TypeScript.
// It describes the in-memory/disk file object Multer attaches
// to the request, e.g. originalname, mimetype, size, buffer, path.All lessons in this course
- Multipart Uploads with Multer Interceptors
- Streaming Large Responses with StreamableFile
- Direct-to-S3 Uploads with Presigned URLs
- Image Processing Pipelines with Sharp