The code explicitly switches from HEAD to GET for most redirects.
Possibly because someone misread a spec (which does require switching from
POST to GET for 303 redirects). Or possibly because the spec really is that
bad. Upstream bug: https://github.com/haskell/HTTP/issues/24
Since we absolutely don't want to download entire (large) files from
the web when checking that they exist with HEAD, I wrote my own redirect
follower, based closely on the one used by Network.Browser, but without
this misfeature.
Note that Network.Browser checks that the redirect url is a http url
and fails if not. I don't, because I want to not need to change this
code when it gets https support (related: I'm surprised to see it
doesn't support https yet..). The check does not seem security significant;
it doesn't support file:// urls for example. If a http url is redirected
to https, the Network.Browser will actually make a http connection again.
This could loop, but only up to 5 times.
If there's no Content-Length, or the key has no size, this check is not
done, but it should happen most of the time, and protect against web
content that has changed.
Can be used to specify what file the url is added to. This can be used to
override the default filename that is used when adding an url, which is
based on the url. Or, when the file already exists, the url is recorded as
another location of the file.
Under ghc 7.4, this seems to be able to handle all filename encodings
again. Including filename encodings that do not match the LANG setting.
I think this will not work with earlier versions of ghc, it uses some ghc
internals.
Turns out that ghc 7.4 has a special filesystem encoding that it uses when
reading/writing filenames (as FilePaths). This encoding is documented
to allow "arbitrary undecodable bytes to be round-tripped through it".
So, to get FilePaths from eg, git ls-files, set the Handle that is reading
from git to use this encoding. Then things basically just work.
However, I have not found a way to make Text read using this encoding.
Text really does assume unicode. So I had to switch back to using String
when reading/writing data to git. Which is a pity, because it's some
percent slower, but at least it works.
Note that stdout and stderr also have to be set to this encoding, or
printing out filenames that contain undecodable bytes causes a crash.
IMHO this is a misfeature in ghc, that the user can pass you a filename,
which you can readFile, etc, but that default, putStr of filename may
cause a crash!
Git.CheckAttr gave me special trouble, because the filenames I got back
from git, after feeding them in, had further encoding breakage.
Rather than try to deal with that, I just zip up the input filenames
with the attributes. Which must be returned in the same order queried
for this to work.
Also of note is an apparent GHC bug I worked around in Git.CheckAttr. It
used to forkProcess and feed git from the child process. Unfortunatly,
after this forkProcess, accessing the `files` variable from the parent
returns []. Not the value that was passed into the function. This screams
of a bad bug, that's clobbering a variable, but for now I just avoid
forkProcess there to work around it. That forkProcess was itself only added
because of a ghc bug, #624389. I've confirmed that the test case for that
bug doesn't reproduce it with ghc 7.4. So that's ok, except for the new ghc
bug I have not isolated and reported. Why does this simple bit of code
magnet the ghc bugs? :)
Also, the symlink touching code is currently broken, when used on utf-8
filenames in a non-utf-8 locale, or probably on any filename containing
undecodable bytes, and I temporarily commented it out.
