node-formidable/formidable

formidable is a Node.js library that parses incoming form data, especially file uploads. When a browser submits a form with files attached, the data arrives in a format called multipart/form-data. Parsing this correctly, handling large files, and writing them somewhere without exhausting memory requires a dedicated library, and that is what formidable does. The library processes the incoming request as a stream, handling data as it arrives rather than loading the entire upload into memory. Parsed files can be written to the local filesystem automatically, streamed to Amazon S3, Azure Blob Storage, Google Cloud Storage, or any custom destination through a plugin interface. You get back the parsed form fields and file metadata once processing is complete. formidable works directly with Node.js's built-in HTTP module, and also integrates with frameworks like Express and Koa without requiring a separate middleware package. It includes configurable limits for file sizes and field counts, and handles errors gracefully when those limits are exceeded. The library has a plugin system for adding custom parsers or upload targets. The README reports parsing speeds in the range of 900 to 2500 megabytes per second and describes memory footprint as low because of the streaming architecture. The project was originally written for Transloadit, a service that processes uploaded images and videos, and has been tested against hundreds of gigabytes of uploads from varied clients over many years. The README cautions that versions v1 and v2 are still widely installed but have been deprecated for years and may have security issues if not configured carefully. Version 3 is the current recommended release and requires Node.js 20 or newer. A minimal experimental variant called formidable-mini is mentioned as a possible basis for a future version built on web-standard APIs. The full README is longer than what was shown.