How to handle Node.js file uploads with Fastify

Fastify, a Node.js framework known for performance and plugin-based design, can handle file uploads through the @fastify/multipart plugin, which parses multipart/form-data requests required for HTML forms containing files. The tutorial builds a Fastify project, configures ES modules, registers the multipart plugin, and creates an /upload endpoint that accepts multiple uploaded files and saves them locally in an uploads directory. It uses Node.js streams with pipeline and createWriteStream to write incoming file data directly to disk without buffering entire files in memory, improving efficiency for large uploads and avoiding event-loop blocking. The endpoint can use request.files() when only files are expected or request.parts() to process both files and ordinary form fields, distinguishing them by checking whether a part contains a file stream. Uploads are tested with Tap, form-auto-content, and Fastify’s inject method, allowing multipart POST requests to be simulated without starting a live server and verifying that the endpoint returns a successful status code.

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