Resumable Browser Uploads for Crowded Event Networks

Event uploads fail differently from normal office uploads. A wedding guest may move between venue Wi-Fi and mobile data, lock the phone while a video is transferring, or close the browser as soon as the progress bar reaches 100%. Hundreds of devices can share one access point, and users rarely wait around to diagnose an error. The usual POST request plus optimistic success toast is not enough. A reliable browser flow needs a small protocol that distinguishes local preparation, network transfer, server acceptance, media processing, and final availability. This article describes a platform-neutral design for that protocol. The five states users actually experience Model each file as a durable state machine: selected -> preparing -> transferring -> accepted -> processing -> ready Add terminal or recoverable branches: preparing -> rejected_local transferring -> paused | retryable_error | expired accepted -> processing_error processing -> ready | processing_error The key distinction is between transferring and accepted . The browser may have sent every byte while the server has not yet committed the upload. Showing “done” at that boundary creates the most frustrating failure: the guest deletes the original, but the organizer never receives it. Give every file a client-generated identity Create an upload ID before the first network request. A UUID is sufficient when combined with the event identifier: const uploadId = crypto . randomUUID (); const uploadIntent = { uploadId , eventId , name : file . name , size : file . size , type : file . type , lastModified : file . lastModified , }; Send that identity when creating the server-side upload session. If the browser retries after a timeout, the server returns the existing session instead of creating a duplicate. This is idempotency at the workflow level. A guest can tap “retry” without having to understand whether the first request reached the server. Separate the control plane from file bytes Use a small JSON API for sessi