Please describe the problem.

If a filename has a single space (and only one space), git annex add will fail out with the following message:

add one two git-annex: unknown response from git cat-file ("HEAD:./one two missing",Ref "HEAD:./one two")
CallStack (from HasCallStack):
  error, called at ./Git/CatFile.hs:102:28 in main:Git.CatFile

What steps will reproduce the problem?

Run the following:

git init .
git annex init
touch "one two"
# this will cause error
git annex add "one two"
touch "one two three"
# this is fine
git annex add "one two three"

What version of git-annex are you using? On what operating system?

Output of git annex version

git-annex version: 6.20161027
build flags: Assistant Webapp Pairing Testsuite S3(multipartupload)(storageclasses) WebDAV Inotify DBus DesktopNotify XMPP ConcurrentOutput TorrentParser MagicMime Feeds Quvi
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 SHA1E SHA1 MD5E MD5 WORM URL
remote types: git gcrypt S3 bup directory rsync web bittorrent webdav tahoe glacier ddar hook external
local repository version: 5
supported repository versions: 3 5 6
upgrade supported from repository versions: 0 1 2 3 4 5
operating system: linux x86_64

Operating System: Linux (NixOS 16.09.909.238c7e0 (Flounder))

Please provide any additional information below.

Maybe related to https://git-annex.branchable.com/forum/unknown_response_from_git_cat-file/ or https://git-annex.branchable.com/bugs/git_annex_import_fails_on_filenames_with_newlines_in_them/?

EDIT: Somewhat surprisingly, if I build from source using cabal, everything works fine.

.cabal-sandbox/bin/git-annex version
git-annex version: 6.20161113-g1e88c12
build flags: Assistant Webapp Pairing Testsuite WebDAV Inotify ConcurrentOutput TorrentParser MagicMime Feeds Quvi
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 SHA1E SHA1 MD5E MD5 WORM URL
remote types: git gcrypt bup directory rsync web bittorrent webdav tahoe glacier ddar hook external

Not sure whether this means that this bug is actually fixed or whether it's an artifact of how things are built in Nix.

Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Just starting out with it as a way of archiving some of my media seems to work great apart from this. Thanks a bunch!

This bug was already fixed in git-annex 6.20161031. I told the Debian maintainer about the bug fix at the time; package has not been updated yet. done on git-annex side. --Joey