UploadLength

UploadLength is a term used in resumable file upload protocols, most prominently in the tus protocol. It denotes the total size, in bytes, of the file to be uploaded. The Upload-Length value is provided by the client during the creation of the upload resource, typically in a header named Upload-Length on the initial request to the upload endpoint.

In a typical tus workflow, the client first creates an upload resource by sending a POST request with Upload-Length indicating the final file size. The server responds with a URL for the new upload resource. The client then uploads data in chunks using PATCH requests to that URL, including a header called Upload-Offset to indicate how many bytes have already been received. The server responds with the updated offset, and the process continues until the uploaded offset matches the declared Upload-Length, signaling completion. The Upload-Length is used by the server to enforce size limits, allocate storage, and validate progress.

There are optional extensions in the protocol. For example, Upload-Metadata can accompany the creation request to carry information such as the filename or file type, encoded as metadata. Some implementations support deferring the length when the exact size is unknown at the outset; in such cases, the client may omit Upload-Length or use an extension header to indicate deferral, with the final length established later in the upload.

Use of UploadLength enables reliable pause-and-resume uploads, improves error recovery, and helps servers manage resources. It is, however, specific to the protocol in use and may have variations or optional extensions across implementations.