Added a comment: progress?

doc/todo/borg_special_remote/comment_2_cec11f364d0c1e62d05c4205b3bf2a2d._comment

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+[[!comment format=mdwn
+ username="anarcat"
+ avatar="http://cdn.libravatar.org/avatar/4ad594c1e13211c1ad9edb81ce5110b7"
+ subject="progress?"
+ date="2018-11-27T06:47:26Z"
+ content="""
+How's that remote going, RonnyPfannschmidt? :) I can't tell from the [homepage](https://github.com/RonnyPfannschmidt/git-annex-borg/) but from the source code, it looks like initremote is supported so far, but not much else...
+
+From what I remember, borg supports storing arbitrary blobs with the `borg debug-put-obj` function, and retrieve one with `borg debug-get-obj`. Here's an example of how this could work:
+
+    [1145]anarcat@angela:test$ sha256sum /etc/motd 
+    a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921  /etc/motd
+    [1146]anarcat@angela:test$ borg init -e none repo
+    [1147]anarcat@angela:test$ borg debug-put-obj repo /etc/motd
+    object a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921 put.
+    [1148]anarcat@angela:test$ borg debug-get-obj repo a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921 tmp
+    object a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921 fetched.
+    [1149]anarcat@angela:test$ sha256sum tmp
+    a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921  tmp
+
+This assumes the underlying blob ID in borg is a SHA256 hash, but that
+seems like a fair assumption to make. Naturally, this could cause
+problems with git-annex, which supports multiple hashing algorithms
+thanks to the multiple [[backends]] support. But maybe this can just
+work this out by refusing to store non-matchin backends.
+
+That is, if borg actually worked that way. Unfortunately, while the
+above actually works, the resulting repository is not quite right:
+
+    $ borg debug dump-repo-objs .
+    Dumping 000000_0000000000000000000000000000000000000000000000000000000000000000.obj
+    Data integrity error: Chunk a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921: Invalid encryption envelope
+
+So borg does not like the repository at all... I'm not sure why, but
+it sure looks like borg \"objects\" are not as transparent as I
+hoped and that this low-level interface will not be suitable for
+git-annex.
+
+The higher level interface is \"archives\", which have (more or less) a
+CRUD interface (without the U, really) through the
+\"create/list/extract/prune\" interface. It's far from what we need:
+items are deplicated across archives so it means it is impossible to
+reliably delete a key unless we walk (and modify!) the entire archive list, which is
+slow and impractical. But it *could* definitely be used to add keys to
+a repository, using:
+
+    $ time borg create --stdin-name SHA256-a378977155fb42bb006496321cbe31f74cbda803c3f6ca590f30e76d1afad921 .::'{utcnow}' - < /etc/motd
+    1.30user 0.10system 0:01.62elapsed 86%CPU (0avgtext+0avgdata 81464maxresident)k
+    72inputs+1496outputs (0major+31135minor)pagefaults 0swaps
+
+As you can see, however, that is *slow* (although arguably not slower
+than `debug-put-obj` which is surprising).
+
+But even worse, that blob is now hidden behind that archive - you'd
+need to list all archives (which is also expensive) to find it.
+
+So I hit a dead end so I'm curious to hear how you were planning to
+implement this, Ronny. :) Presumably there should be a way to generate
+an object compatible with `debug-put-obj`, but that interface seems
+very brittle and has all sorts of warnings all around it... And on the
+other hand, the archive interface is clunky and slow... I wish there
+was a better way, and suspect it might be worth talking with upstream
+(which I'm not anymore) to see if there's a better way to work this
+problem. -- [[anarcat]]
+"""]]