HTTP headers / response header
Content-Range: bytes 0-1023/146515
Labels which slice of the full resource this 206 response carries, and the total size after the slash.
On 416 it reports just the total (bytes */146515) so the client can restart sanely.
The fastest way to see what Content-Range is actually doing is to send the request and read both sides raw — ReqPad shows auto-generated and custom headers for every request, on all six protocols, with history. Related references: status codes · WWW-Authenticate · Content-Encoding · Transfer-Encoding · ETag · Last-Modified · Expires
Build the request, send it, read raw headers and timing — from your iPhone. Free to start.