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POAre there any problems with this symlink traversal code for Windows?
 

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  1. POAre there any problems with this symlink traversal code for Windows?
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    <p>In my efforts to resolve <a href="http://bugs.python.org/issue1578269" rel="nofollow noreferrer">Python issue 1578269</a>, I've been working on trying to resolve the target of a symlink in a robust way. I started by using GetFinalPathNameByHandle as recommended <a href="https://stackoverflow.com/questions/221417/how-do-i-programmatically-access-the-target-path-of-a-windows-symbolic-link">here on stackoverflow</a> and by <a href="http://msdn.microsoft.com/en-us/library/aa364962%28VS.85%29.aspx" rel="nofollow noreferrer">Microsoft</a>, but it turns out that technique fails when the target is in use (such as with pagefile.sys).</p> <p>So, I've written a new routine to accomplish this using CreateFile and DeviceIoControl (as it appears this is what Explorer does). The relevant code from <a href="https://svn.jaraco.com/jaraco/python/jaraco.windows/jaraco/windows/filesystem.py" rel="nofollow noreferrer">jaraco.windows.filesystem</a> is included below.</p> <p>The question is, is there a better technique for reliably resolving symlinks in Windows? Can you identify any issues with this implementation?</p> <pre><code> def relpath(path, start=os.path.curdir): """ Like os.path.relpath, but actually honors the start path if supplied. See http://bugs.python.org/issue7195 """ return os.path.normpath(os.path.join(start, path)) def trace_symlink_target(link): """ Given a file that is known to be a symlink, trace it to its ultimate target. Raises TargetNotPresent when the target cannot be determined. Raises ValueError when the specified link is not a symlink. """ if not is_symlink(link): raise ValueError("link must point to a symlink on the system") while is_symlink(link): orig = os.path.dirname(link) link = _trace_symlink_immediate_target(link) link = relpath(link, orig) return link def _trace_symlink_immediate_target(link): handle = CreateFile( link, 0, FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE, None, OPEN_EXISTING, FILE_FLAG_OPEN_REPARSE_POINT|FILE_FLAG_BACKUP_SEMANTICS, None, ) res = DeviceIoControl(handle, FSCTL_GET_REPARSE_POINT, None, 10240) bytes = create_string_buffer(res) p_rdb = cast(bytes, POINTER(REPARSE_DATA_BUFFER)) rdb = p_rdb.contents if not rdb.tag == IO_REPARSE_TAG_SYMLINK: raise RuntimeError("Expected IO_REPARSE_TAG_SYMLINK, but got %d" % rdb.tag) return rdb.get_print_name() </code></pre>
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    1. USJason R. Coombs
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