work around box.com webdav rename bug

Apparently box.com renaming is just buggy. I tried a couple of fixes:

* In case the http Manager was opening multiple connections and reaching
  different backend servers, I tried limiting the number of connections
  to 1. Didn't help.
* To make sure it was not a http connection reuse problem, I tried
  rewriting how exportAction works, so that the same http connection
  is clearly open. Didn't help.

So, disable renaming of exports for box.com. It would be good to test it
with some other webdav server.

This commit was sponsored by John Peloquin on Patreon.

Remote/WebDAV.hs

@@ -201,9 +201,15 @@ checkPresentExportDav r mh _k loc = case mh of
 		either giveup return v
 
 renameExportDav :: Maybe DavHandle -> Key -> ExportLocation -> ExportLocation -> Annex Bool
-renameExportDav mh _k src dest = runExport mh $ \dav -> do
-	moveDAV (baseURL dav) (exportLocation src) (exportLocation dest)
-	return True
+renameExportDav Nothing _ _ _ = return False
+renameExportDav (Just h) _k src dest
+	-- box.com's DAV endpoint has buggy handling of renames,
+	-- so avoid renaming when using it.
+	| boxComUrl `isPrefixOf` baseURL h = return False
+	| otherwise = runExport (Just h) $ \dav -> do
+		maybe noop (void . mkColRecursive) (locationParent (exportLocation dest))
+		moveDAV (baseURL dav) (exportLocation src) (exportLocation dest)
+		return True
 
 runExport :: Maybe DavHandle -> (DavHandle -> DAVT IO Bool) -> Annex Bool
 runExport Nothing _ = return False
@@ -213,7 +219,10 @@ configUrl :: Remote -> Maybe URLString
 configUrl r = fixup <$> M.lookup "url" (config r)
   where
 	-- box.com DAV url changed
-	fixup = replace "https://www.box.com/dav/" "https://dav.box.com/dav/"
+	fixup = replace "https://www.box.com/dav/" boxComUrl
+
+boxComUrl :: URLString
+boxComUrl = "https://dav.box.com/dav/"
 
 type DavUser = B8.ByteString
 type DavPass = B8.ByteString