git-annex/doc/todo/cloning_direct_mode_repo_over_http.mdwn

Indirect mode repos can be cloned over http, and just work. But, direct
mode repos don't currently work; while git can clone them ok, git-annex get
doesn't know where to get the file contents from.

To support this, git-annex would have to check if the remote is in direct
mode, and when it is, it would need to download the direct mode mapping
file, to find out which file has the content of a key. Then, after
downloading the a file, it would need to make sure to checksum it, since
nothing prevents a direct mode file from being modified at the same time
it's downloaded.

All seems doable. However.. [[design/caching_database]] wants to switch the
direct mode mapping files from simple flat text files to a sqlite database.
Which would complicate this a lot. Can sqlite databases be accessed over
http, or would the whole, possibly large database need to be downloaded?
If so, what to do when the database changes? Re-downloading a possibly
large db is not good.

---

Alternatively, the direct mode mapping files of the remote could be
bypassed. Instead, look at what the remote HEAD branch is, and look at that
branch locally. Create local direct mode mappings for the remote HEAD
branch, and use them when downloading.

This approach would mean that, if the remote's HEAD changes and we haven't
noticed, we might download the wrong file (that has eg, been moved).
checksumming would detect this, but it does make it more fragile.

Also, creating the direct mode mappings for a remote HEAD would currently
be pretty slow. Probably implementing the caching database for direct mode
mappings would lead to faster code. So, this feature seems best blocked on
the direct mode database either way!

--[[Joey]]
[[!meta tag=deprecateddirectmode]]