A file with a unique filename is transferred from a client computer to a server computer in chunks, which can be packaged into packets including metadata. The server computer can record indices of received chunks in a local metadata file associated with the file. Upon receiving the filename in a subsequent client request after a connection loss, the server computer can use the associated metadata file to determine whether portions of the file are missing. If so, the server computer can send indices corresponding to missing ranges instead of the client computer resending the whole file.