operations: fix accounting for server side copies

See: https://forum.rclone.org/t/b2-server-side-copy-doesnt-show-cumulative-progress/11154

fs/accounting/accounting.go

@@ -168,6 +168,28 @@ func (acc *Account) checkRead() (err error) {
 	return nil
 }
 
+// ServerSideCopyStart should be called at the start of a server side copy
+//
+// This pretends a transfer has started
+func (acc *Account) ServerSideCopyStart() {
+	acc.statmu.Lock()
+	// Set start time.
+	if acc.start.IsZero() {
+		acc.start = time.Now()
+	}
+	acc.statmu.Unlock()
+}
+
+// ServerSideCopyEnd accounts for a read of n bytes in a sever side copy
+func (acc *Account) ServerSideCopyEnd(n int64) {
+	// Update Stats
+	acc.statmu.Lock()
+	acc.bytes += n
+	acc.statmu.Unlock()
+
+	acc.stats.Bytes(n)
+}
+
 // Account the read and limit bandwidth
 func (acc *Account) accountRead(n int) {
 	// Update Stats

fs/operations/operations.go

@@ -302,11 +302,14 @@ func Copy(ctx context.Context, f fs.Fs, dst fs.Object, remote string, src fs.Obj
 			if fs.Config.MaxTransfer >= 0 && accounting.Stats(ctx).GetBytes() >= int64(fs.Config.MaxTransfer) {
 				return nil, accounting.ErrorMaxTransferLimitReached
 			}
+			in := tr.Account(nil) // account the transfer
+			in.ServerSideCopyStart()
 			newDst, err = doCopy(ctx, src, remote)
 			if err == nil {
 				dst = newDst
-				accounting.Stats(ctx).Bytes(dst.Size()) // account the bytes for the server side transfer
+				in.ServerSideCopyEnd(dst.Size()) // account the bytes for the server side transfer
 			}
+			err = in.Close()
 		} else {
 			err = fs.ErrorCantCopy
 		}