Set to show which bytes in the file you are uploading.
Content-Range: bytes 0-524287/2000000 shows that you are uploading the first 524,288 bytes (256 x 1024 x 2) in a 2,000,000 byte file.
If the total file size isn't known beforehand (for example, during streaming uploads that might perform processing on the stream), you can specify an unknown total size as:
Content-Range: bytes 0-524287/*
If you are resuming an interrupted upload and want to know its progress, set the left part of the range to a
* to signal that it is unknown. E.g.,
Content-Range: bytes */2000000