[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2018-10-29T17:51:27Z"
 content="""
Looking at the code, it addurl clearly *does* use the urls returned by
CHECKURL. In Command/AddUrl.hs:

        go deffile (Right (UrlMulti l))
                | isNothing (fileOption (downloadOptions o)) =
                        forM_ l $ \(u', sz, f) -> do
                                let f' = adjustFile o (deffile </> fromSafeFilePath f)
                                void $ commandAction $
                                        startRemote r o f' u' sz

`l` is the list of values it returns, and `u'` is individual urls from that list,
as opposed to `u` which is the url the user provided.
`u'` is passed to `startRemote`, and `u` is not.

Hmm, but in Remote/External.hs there is a special case:

                -- Treat a single item multi response specially to
                -- simplify the external remote implementation.
                CHECKURL_MULTI ((_, sz, f):[]) ->
                        result $ UrlContents sz $ Just $ mkSafeFilePath f
                CHECKURL_MULTI l -> result $ UrlMulti $ map mkmulti l

That does not have any kind of rationalle in [[!commit 8a17bcb0be91c345a52d78c08009285b0fcd6e3a]],
but the next commit added `doc/special_remotes/external/git-annex-remote-torrent`
and I think I can see why I felt it simplified things. That script always
replies with CHECKURL-MULTI, but a torrent often contains a single file, and
it would be perhaps bettter to use the original url provided to the user for such a
file from a torrent, rather than an url that asks for file "#1" from the torrent.
Although AFAICS either would work, and Remote/BitTorrent.hs contains just the kind
of special case for a single item torrent that I was wanting to avoid external
special remotes needing to worry about.

The other benefit to special casing UrlContents is that lets addurl --file specify
where to put the file, which the fileOption check in the first code block
above prevents for UrlMulti. But, that could just as well be handled by
adding a single file special case to the code in AddUrl.

I suppose changing this won't break anything, or if it does it was relying
on this undocumented behavior.
"""]]