dokan: make the module importable even if dokan is not installed.

This is useful for programs that bundle the dokan libraries and want to install
them if not available.  Check the "is_available" attribute to see if dokan is
actually available on the system.

fs/expose/dokan/__init__.py

@@ -72,15 +72,14 @@ from fs.functools import wraps
 
 try:
     import libdokan
-except EnvironmentError:
-    raise ImportError("Dokan not found")
-except NotImplementedError:
-    raise ImportError("Dokan found but not usable")
+except (NotImplementedError,EnvironmentError,ImportError):
+    is_available = False
+    sys.modules.pop("fs.expose.dokan.libdokan",None)
+    libdokan = None
+else:
+    is_available = True
 
 
-DokanMain = libdokan.DokanMain
-DokanOperations = libdokan.DokanOperations
-
 #  Options controlling the behaiour of the Dokan filesystem
 DOKAN_OPTION_DEBUG = 1
 DOKAN_OPTION_STDERR = 2
@@ -172,11 +171,12 @@ def handle_fs_errors(func):
 
 MIN_FH = 100
 
-class FSOperations(DokanOperations):
-    """DokanOperations interface delegating all activities to an FS object."""
+class FSOperations:
+    """Object delegating all DOKAN_OPERTAIONS pointers to an FS object."""
 
     def __init__(self, fs, fsname="Dokan FS", volname="Dokan Volume"):
-        super(FSOperations,self).__init__()
+        if libdokan is None:
+            raise OSError("dokan library is not available")
         self.fs = fs
         self.fsname = fsname
         self.volname = volname
@@ -190,6 +190,17 @@ class FSOperations(DokanOperations):
         #  We explicitly keep track of the size FUSE expects a file to be.
         #  This dict is indexed by path, then file handle.
         self._files_size_written = {}
+        
+    def get_ops_struct(self):
+        """Get a DOKAN_OPERATIONS struct mapping to our methods."""
+        struct = libdokan.DOKAN_OPERATIONS()
+        for (nm,typ) in libdokan.DOKAN_OPERATIONS._fields_:
+            try:
+                setattr(struct,nm,typ(getattr(self,nm)))
+            except AttributeError:
+                #  This bizarre syntax creates a NULL function pointer.
+                setattr(struct,nm,typ())
+        return struct
 
     def _get_file(self, fh):
         try:
@@ -591,13 +602,6 @@ def _datetime2filetime(dtime):
     return _timestamp2filetime(_datetime2timestamp(dtime))
 
 
-d = datetime.datetime.now()
-t = _datetime2timestamp(d)
-f = _datetime2filetime(d)
-assert d == _timestamp2datetime(t)
-assert t == _filetime2timestamp(_timestamp2filetime(t))
-assert d == _filetime2datetime(f)
-
 ERROR_FILE_EXISTS = 80
 ERROR_DIR_NOT_EMPTY = 145
 ERROR_NOT_SUPPORTED = 50
@@ -651,6 +655,8 @@ def mount(fs, drive, foreground=False, ready_callback=None, unmount_callback=Non
         * FSOperationsClass:  custom FSOperations subclass to use
 
     """
+    if libdokan is None:
+        raise OSError("the dokan library is not available")
     drive = _normalise_drive_string(drive)
     #  This function captures the logic of checking whether the Dokan mount
     #  is up and running.  Unfortunately I can't find a way to get this
@@ -689,7 +695,8 @@ def mount(fs, drive, foreground=False, ready_callback=None, unmount_callback=Non
             check_thread = threading.Thread(target=check_ready)
             check_thread.daemon = True
             check_thread.start()
-        res = DokanMain(ctypes.byref(opts),ctypes.byref(ops.buffer))
+        opstruct = ops.get_ops_struct()
+        res = libdokan.DokanMain(ctypes.byref(opts),ctypes.byref(opstruct))
         if res != DOKAN_SUCCESS:
             raise OSError("Dokan failed with error: %d" % (res,))
         if unmount_callback:
@@ -745,6 +752,8 @@ class MountProcess(subprocess.Popen):
     unmount_timeout = 5
 
     def __init__(self, fs, drive, dokan_opts={}, nowait=False, **kwds):
+        if libdokan is None:
+            raise OSError("the dokan library is not available")
         self.drive = _normalise_drive_string(drive)
         self.path = self.drive + ":\\"
         cmd = 'from fs.expose.dokan import MountProcess; '

fs/expose/dokan/libdokan.py

@@ -209,23 +209,6 @@ class DOKAN_OPERATIONS(Structure):
 
 
 
-class DokanOperations(object):
-    """Object interface to defining a DOKAN_OPERATIONS structure."""
-
-    def __init__(self):
-        self.buffer = DOKAN_OPERATIONS()
-        for (nm,typ) in DOKAN_OPERATIONS._fields_:
-            try:
-                setattr(self.buffer,nm,typ(getattr(self,nm)))
-            except AttributeError:
-                #  This bizarre syntax creates a NULL function pointer.
-                setattr(self.buffer,nm,typ())
-
-    def _noop(self,*args):
-        return -1
-
-
-
 DokanMain.restype = c_int
 DokanMain.argtypes = (
     POINTER(DOKAN_OPTIONS),

fs/tests/test_expose.py

@@ -133,11 +133,8 @@ else:
             return self.mounted_fs.exists(p)
 
 
-try:
-    from fs.expose import dokan
-except ImportError:
-    pass
-else:
+from fs.expose import dokan
+if dokan.is_available:
     from fs.osfs import OSFS
     class DokanTestCases(FSTestCases):
         """Specialised testcases for filesystems exposed via Dokan.