It almost sounds like you are talking about caching. If that's the case then there is no need at all to reinvent that particular wheel. See (eg) the If-Modified-Since and Cache-Control headers.

Sorry, but you seem to have not understood me at all. To clarify even more, the conversation might look like this:

Client: hash1?
Server: yes
Client: hash2?
Server: no
Client: hash3?
Server: yes
And so on, until the client knows the file completely, so has no more questions.

you seem to have not understood me at all

With all due respect, I think that's because you haven't been clear at all. Your question makes almost no sense.

And so on, until the client knows the file completely, so has no more questions

Why does the client need to ask the server questions in order to download a file? wtf are you even talking about? This does not sound like any client/server file download transaction I've ever heard of.

Sorry, but you seem to have not understood me at all.

And he is not alone.

You should perhaps start by telling us which protocol you are taling about. A client asking for a hash sounds like some peer-to-peer file sharing protocol, but rsync also uses a kind of hash. If it is not a common protocol, like HTTP, FTP, rsync, link to the protocol spec.

Then, don't invent new terminology, use the one from the protocol spec.

Alexander

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Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)