Get checksum over http or ftp

Question

I am looking to provide a upload feature for my application that accepts a uri like http or ftp, which would be downloaded by the server and stored. I know that the files uploaded would be large (>1GB).

I was wondering if there was a way to do a checksum through one of the protocols without first having to download the actual file. Since the files are large and would be stored, I'd like to prevent downloading duplicate data.

Best I could find was this post regarding ftp and scp and and Content-MD5 header field for HTTP which the file server may or may not support.

Answer 1

No. Neither http nor ftp support this. (Indeed im unaware of any protocol that does, but ssh could be coerced to foing it and rsync and bittorrent can do something a little similar - theu dont help you here though)

You might be able to do something in html5/ajax to locally read and process the hash for the file before uploading it - but this is not protocol related - you are, in effect, writing a program to run client side, in the browser, rather then use thr protocol.