* Fix WebDAV by requesting new ETag conditionally
For me. this was saving only the first time and subsequently failing.
Having revised the requests, I noticed it didn't get a new ETag after saving.
Seems not all WebDAV implementations return a new ETag in PUT requests.
In my WebDAV service (WsgiDAV) - ETag is only served from a HEAD
request.
So if no ETag is found with PUT - we request one with HEAD.
This patch fixes error handling and should also work with servers that
provide ETag directly upon PUT.
* Add tweak from PMario
Remove URI encoding from PUT saver and let the browser handle it as necessary. This seems to be the normal way of doing things. We have confirmed that several WebDAV servers do not expect the file names to be double-encoded.
* putSaver: detect edit conflicts to prevent clobbering, if possible
if the server supplies an ETag, we send it back when saving, allowing
the server to detect edit conflicts and respond with 412 (cf.
https://www.w3.org/1999/04/Editing/)
caveats:
* this only kicks in after the first save, as we don't have access to
the ETag when first loading the document
* there's no recovery mechanism (e.g. resetting `this.etag` in order to
force clobbering), other than manually reloading the document
* putSaver: retrieve ETag upon initialization for clobbering protection
this addresses one of the caveats from the previous commit
(2d75cb83af) - while theoretically prone
to a race condition, it seems unlikely that saving will be triggered
before the server responds
* putSaver: simplify URI extraction
this simplifies the approach introduced in
f51f6bf774, with the purpose of removing
the fragment identifier
* putSaver: localize error message
* putSaver: switch to built-in HTTP helper
in the process, fixed ETag assignment in `#save` method (was
`this.etag`, now `self.etag`) as well as a syntax error due to a missing
closing brace
* putSaver: consolidate URI handling
