[Boost-bugs] [Boost C++ Libraries] #9824: boost::filesystem::is_empty() doesn't work with symlinks on Windows

Subject: [Boost-bugs] [Boost C++ Libraries] #9824: boost::filesystem::is_empty() doesn't work with symlinks on Windows
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-04-01 09:17:13

#9824: boost::filesystem::is_empty() doesn't work with symlinks on Windows
------------------------------+------------------------
 Reporter:  michael.burr@…    |      Owner:  bemandawes
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  filesystem
  Version:  Boost 1.56.0      |   Severity:  Regression
 Keywords:                    |
------------------------------+------------------------
 See the original information on this problem in this Stackoverflow
 question:

     hxxp://stackoverflow.com/questions/22668337/boostfilesystemis-empty-
 returns-false-for-symlinks

 The person who reported that problem/asked the question on Stackoverflow
 also set up a github project that demonstrates the problem:

     hxxps://github.com/monsdar/BoostSymLinkError

 Basically, the `filesystem::is_empty()` function doesn't follow a symlink,
 so it will return false even if the target of the symlink has a length
 greater than 0.

 The V2 filesystem library worked for this situation.  The difference is
 that V2 used the `stat()` function in the VC++ library, while the V3
 filesystem library uses the Win32 `GetFileAttributesExW()` API.  The
 latter does not follow symlinks and returns a file size of 0 regardless of
 the size of the symlink target.

 Attached is a diff for libs/filesystem/src/operations.cpp which uses the
 `stat()` technique very similar to what was used in filesystem V2.  A few
 differences:

   - `_wstat()` is used instead of `stat()` to accommodate UNICODE
 filenames
   - a bit test using `_S_IFDIR` is used to determine if the path is a
 directory instead of `S_ISDIR()` because the VC++ library doesn't include
 a `S_ISDIR()` or `_S_ISDIR()` macro.

 This patch is only lightly tested (MSVC++ 12.0, 32-bit, on Win7 x64,
 filenames with ASCII characters only).  I'm not sure what the motivations
 for changing to the `GetFileAttributesExW()` API in filesystem V3 were, so
 I'm not sure if there's a fundamental flaw in using `_wstat()` that would
 prevent using it in V3.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9824>
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