Re: Proposal for "fetch-any-blob Git protocol" and server design
- Date: Wed, 15 Mar 2017 10:59:03 -0700
- From: Junio C Hamano <gitster@xxxxxxxxx>
- Subject: Re: Proposal for "fetch-any-blob Git protocol" and server design
Jonathan Tan <jonathantanmy@xxxxxxxxxx> writes:
> == Design
> A new endpoint "server" is created. The client will send a message in
> the following format:
> fbp-request = PKT-LINE("fetch-blob-pack")
> want = PKT-LINE("want" SP obj-id)
> The client may send one or more SHA-1s for which it wants blobs, then
> a flush-pkt.
By "SHA-1s for which it wants blobs", you mean that "want" only
allows one exact blob object name? I think it is necessary to
support that mode of operation as a base case, and it is a good
When you know
- you have a "partial" clone that initially asked to contain only
blobs that are smaller than 10MB, and
- you are now trying to do a "git checkout v1.0 -- this/directory"
so that the directory is fully populated
instead of enumerating all the missing blobs from the output of
"ls-tree -r v1.0 this/directory" on separate "want" requests, you
may want to say "I want all the blobs that are not smaller than 10MB
in this tree object $(git rev-parse v1.0:this/directory)".
I am not saying that you should add something like this right away,
but I am wondering how you would extend the proposed system to do
so. Would you add "fetch-size-limited-blob-in-tree-pack" that runs
parallel to "fetch-blob-pack" request? Would you add a new type of
request packet "want-blob-with-expression" for fbp-request, which is
protected by some "protocol capability" exchange?
If the former, how does a client discover if a particular server
already supports the new "fetch-size-limited-blob-in-tree-pack"
request, so that it does not have to send a bunch of "want" request
by enumerating the blobs itself? If the latter, how does a client
discover if a particular server's "fetch-blob-pack" already supports
the new "want-blob-with-expression" request packet?
> === Endpoint support for forward compatibility
> This "server" endpoint requires that the first line be understood, but
> will ignore any other lines starting with words that it does not
> understand. This allows new "commands" to be added (distinguished by
> their first lines) and existing commands to be "upgraded" with
> backwards compatibility.