Retry Based on Remote Offset

[frankyn]

If your request is terminated prior to receiving a response from the server or if you receive an HTTP 503 response from the server, you can query the current status of the upload by issuing an empty PUT request on the unique upload URI.

The storage client should poll the server to determine which bytes it has received.

// Variables:
// chunk = getBuffer()
// localNextByteOffset == getPosition()
// chunkSize = getChunkSize()
//
// Case 1: localNextByteOffset == 0 && remoteNextByteOffset == 0:
// we are retrying from first chunk start from 0 offset.
//
// Case 2: localNextByteOffset == remoteNextByteOffset:
// Special case of Case 1 when a chunk is retried.
//
// Case 3: localNextByteOffset < remoteNextByteOffset
//             && driftOffset < chunkSize:
// Upload progressed and localNextByteOffset is not in-sync with
// remoteNextByteOffset and driftOffset is less than chunkSize.
// driftOffset must be less than chunkSize for it to retry using
// chunk maintained in memory.
// Find the driftOffset by subtracting localNextByteOffset from
// remoteNextByteOffset.
// Use driftOffset to determine where to restart from using the chunk in
// memory.
//
// Case 4: localNextByteOffset < remoteNextByteOffset
//            && driftOffset == chunkSize:
// Special case of Case 3.
// If chunkSize is equal to driftOffset then remoteNextByteOffset has moved on
// to the next chunk.
//
// Case 5: localNextByteOffset < remoteNextByteOffset
//            && driftOffset > chunkSize:
// Throw exception as remoteNextByteOffset has drifted beyond the retriable
// chunk maintained in memory. This is not possible unless there's multiple
// clients uploading to the same resumable upload session.
//
// Case 6: localNextByteOffset > remoteNextByteOffset:
// For completeness, this case is not possible because it would require retrying
// a 400 status code which is not allowed.