Implemented the Retriever.
Unfortunately, it is a fileRetriever and not a byteRetriever.
It should be possible to convert this to a byteRetiever, but I got stuck:
The conduit sink needs to process individual chunks, but a byteRetriever
needs to pass a single L.ByteString to its callback for processing. I
looked into using unsafeInerlaveIO to build up the bytestring lazily,
but the sink is already operating under conduit's inversion of control,
and does not run directly in IO anyway.
On the plus side, no more memory leak..
Currently, initremote works, but not the other operations. They should be
fairly easy to add from this base.
Also, https://github.com/aristidb/aws/issues/119 blocks internet archive
support.
Note that since http-conduit is used, this also adds https support to S3.
Although git-annex encrypts everything anyway, so that may not be extremely
useful. It is not enabled by default, because existing S3 special remotes
have port=80 in their config. Setting port=443 will enable it.
This commit was sponsored by Daniel Brockman.
Reusing http connection when operating on chunks is not done yet,
I had to submit some patches to DAV to support that. However, this is no
slower than old-style chunking was.
Note that it's a fileRetriever and a fileStorer, despite DAV using
bytestrings that would allow streaming. As a result, upload/download of
encrypted files is made a bit more expensive, since it spools them to temp
files. This was needed to get the progress meters to work.
There are probably ways to avoid that.. But it turns out that the current
DAV interface buffers the whole file content in memory, and I have
sent in a patch to DAV to improve its interfaces. Using the new interfaces,
it's certainly going to need to be a fileStorer, in order to read the file
size from the file (getting the size of a bytestring would destroy
laziness). It should be possible to use the new interface to make it be a
byteRetriever, so I'll change that when I get to it.
This commit was sponsored by Andreas Olsson.
I tend to prefer moving toward explicit exception handling, not away from
it, but in this case, I think there are good reasons to let checkPresent
throw exceptions:
1. They can all be caught in one place (Remote.hasKey), and we know
every possible exception is caught there now, which we didn't before.
2. It simplified the code of the Remotes. I think it makes sense for
Remotes to be able to be implemented without needing to worry about
catching exceptions inside them. (Mostly.)
3. Types.StoreRetrieve.Preparer can only work on things that return a
Bool, which all the other relevant remote methods already did.
I do not see a good way to generalize that type; my previous attempts
failed miserably.
