Re: [MirageOS-devel] Irmin-on-Mirage status

[Thomas Leonard <talex5@xxxxxxxxx>]

On 6 August 2015 at 17:01, Thomas Gazagnaire <thomas@xxxxxxxxxxxxxx> wrote:
>> The browser side uses irmin-indexeddb, which uses Irmin's native
>> (non-Git) format, so the server needs to use that too. Does this work
>> yet?
>>
>> I see that Irmin_fs requires an IO module that provides filesystem
>> operations, but it doesn't quite match the mirage FS type. Has anyone
>> made an adaptor already?
>
> Yes, I've started to make one for ocaml-git[1]. Should be the same signature 
> that Irmin_fs.IO (or at least not very far).
>
> I'm refactoring ocaml-git to be able to change the SHA implementation more 
> easily. So it's now possible to use a pure-OCaml implementation when 
> compiling to javascript (instead of unconditionally depend on nocrypto) so 
> you can use it in Cuepkeeper to be compatible with Git. The branch is almost 
> ready to merge, I'm fixing some last issues with make `ogit fetch` work 
> optimally.

That sounds useful! I'm looking at updating irmin-indexeddb to use the
Git format now. It looks like there are two ways I could do this:

1. Implement Git.FS.IO for IndexedDB and let ocaml-git use this
virtual filesystem. Then implement Git.Sync.IO and Irmin_git.LOCK and
use that with Irmin_git.FS.

2. Expose Irmin_git.XContents, XCommit and XNode and use that with Irmin.Make.

The first looks a bit ugly, especially regarding locking. It would
involve cross-tab notifications using HTML storage, atomic operations
using IndexedDB and some recovery mechanism for dealing with closed
tabs. All of which seems like overkill, since Irmin_git would only use
these primitives to implement database transactions, which we have
already (e.g. we'd be using a database transaction to create a
lock-file to protect a Git transaction).

So, does exposing Irmin_git.XContents, XCommit and XNode sound
reasonable? Irmin-IndexedDB would still be writing directly to the
"ao" database table as before, but the blobs would be in Git format,
so the SHA1 sums would match, and it should then be possible to sync
between the browser and a regular Git repository without rebasing
everything.


> Thomas
>
> [1]:  
> https://github.com/mirage/ocaml-git/blob/master/lib/mirage/git_mirage.ml#L27
> [2]: https://github.com/mirage/ocaml-git/pull/115
>
>
>>
>> --
>> Dr Thomas Leonard        http://roscidus.com/blog/
>> GPG: DA98 25AE CAD0 8975 7CDA  BD8E 0713 3F96 CA74 D8BA
>>
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>



-- 
Dr Thomas Leonard        http://roscidus.com/blog/
GPG: DA98 25AE CAD0 8975 7CDA  BD8E 0713 3F96 CA74 D8BA

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