tus

tus, short for the resumable upload protocol, is an open HTTP-based standard for uploading large files in a way that can be paused and resumed after interruptions. It was created to improve reliability of uploads on unstable networks and is supported by a range of servers and clients. The protocol is storage-agnostic and focuses on keeping upload state consistent across disconnects.

How it works: a client creates a new upload by sending a POST to the server with the Upload-Length header and optional Upload-Metadata. The server responds with 201 Created and a Location header pointing to the upload resource. The client then sends PATCH requests to that URL containing data chunks, each accompanied by the Upload-Offset header. The server stores the data and replies with 204 No Content and an updated Upload-Offset. If the connection drops, the client can resume by repeating PATCHes or querying the resource for the current offset. Completion occurs when the cumulative offset equals the Upload-Length. The protocol also supports metadata through Upload-Metadata and may include optional features such as Upload-Concat for concatenating uploads. The design aims to be simple to implement on various backends while providing robust recovery from network failures.

Implementation and ecosystem: multiple server implementations exist for languages such as Node.js, Go, PHP, and .NET, and clients are available for JavaScript, iOS, and Android. The central project site is tus.io, and the protocol is maintained by an open community with ongoing additions and interoperability testing.

History and status: tus originated with Transloadit and has since become a widely used standard for large-file uploads, particularly in cloud storage and content management workflows. It remains in active development with formal versioning and ongoing client and server support.