Handling File Uploads in Next.js Server Actions

Server actions are great for form submissions, but the moment a file input gets involved, a few things need extra care — body size limits, streaming to storage, and validating file type before you ever touch disk.

The pattern I've settled on: validate on the client for instant feedback, re-validate on the server since client checks are trivially bypassed, then stream directly to object storage rather than buffering the whole file in memory.

One gotcha worth calling out: Next's default body size limit will silently reject larger files unless you explicitly raise it in your route config. That cost me an afternoon the first time I hit it.

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