Added initial support for null device

- added special file and file buffer for null device
- fixes #418

Author: mrbean-bremen

Diff for: CHANGES.md

@@ -4,6 +4,7 @@ The release versions are PyPi releases.
 ## Version 3.5 (as yet unreleased)
 
 #### New Features
+  * added support for null device ([#418](../../issues/418))
 
 #### Infrastructure
 

Diff for: pyfakefs/fake_filesystem.py

@@ -107,7 +107,7 @@
 
 from pyfakefs.deprecator import Deprecator
 from pyfakefs.fake_scandir import scandir, walk
-from pyfakefs.helpers import FakeStatResult, FileBufferIO, IS_PY2
+from pyfakefs.helpers import FakeStatResult, FileBufferIO, IS_PY2, NullFileBufferIO
 from pyfakefs.helpers import is_int_type, is_byte_string, is_unicode_string
 from pyfakefs.helpers import make_string_path
 
@@ -498,6 +498,19 @@ def SetIno(self, st_ino):
         self.st_ino = st_ino
 
 
+class FakeNullFile(FakeFile):
+    def __init__(self, filesystem):
+        devnull = '/dev/nul' if filesystem.is_windows_fs else '/dev/nul'
+        super(FakeNullFile, self).__init__(devnull, filesystem=filesystem, contents=b'')
+
+    @property
+    def byte_contents(self):
+        return b''
+
+    def _set_initial_contents(self, contents):
+        pass
+
+
 Deprecator.add(FakeFile, FakeFile.set_large_file_size, 'SetLargeFileSize')
 Deprecator.add(FakeFile, FakeFile.set_contents, 'SetContents')
 Deprecator.add(FakeFile, FakeFile.is_large_file, 'IsLargeFile')
@@ -825,6 +838,7 @@ def __init__(self, path_separator=os.path.sep, total_size=None):
         self.mount_points = {}
         self.add_mount_point(self.root.name, total_size)
         self._add_standard_streams()
+        self.dev_null = FakeNullFile(self)
 
     def reset(self, total_size=None):
         """Remove all file system contents and reset the root."""
@@ -1663,6 +1677,8 @@ def exists(self, file_path, check_link=False):
             raise TypeError
         if not file_path:
             return False
+        if file_path == self.dev_null.name:
+            return not self.is_windows_fs
         try:
             if self.is_filepath_ending_with_separator(file_path):
                 return False
@@ -1740,7 +1756,8 @@ def resolve_path(self, file_path, allow_fd=False, raw_io=True):
         file_path = self.absnormpath(self._original_path(file_path))
         if self._is_root_path(file_path):
             return file_path
-
+        if file_path == self.dev_null.name:
+            return file_path
         path_components = self._path_components(file_path)
         resolved_components = self._resolve_components(path_components, raw_io)
         return self._components_to_path(resolved_components)
@@ -1861,6 +1878,8 @@ def get_object_from_normpath(self, file_path):
         file_path = make_string_path(file_path)
         if file_path == self.root.name:
             return self.root
+        if file_path == self.dev_null.name:
+            return self.dev_null
 
         file_path = self._original_path(file_path)
         path_components = self._path_components(file_path)
@@ -3360,6 +3379,8 @@ class FakeOsModule(object):
     my_os_module = fake_filesystem.FakeOsModule(filesystem)
     """
 
+    devnull = None
+
     def __init__(self, filesystem, os_path_module=None):
         """Also exposes self.path (to fake os.path).
 
@@ -3382,6 +3403,8 @@ def __init__(self, filesystem, os_path_module=None):
             self.fdopen = self._fdopen_ver2
         else:
             self.fdopen = self._fdopen
+        self.__class__.devnull = ('/dev/nul' if filesystem.is_windows_fs
+                                  else '/dev/nul')
 
     def _fdopen(self, *args, **kwargs):
         """Redirector to open() builtin function.
@@ -3506,7 +3529,8 @@ def open(self, file_path, flags, mode=None, dir_fd=None):
         fake_file = FakeFileOpen(
             self.filesystem, delete_on_close=delete_on_close, raw_io=True)(
             file_path, str_flags, open_modes=open_modes)
-        self.chmod(file_path, mode)
+        if fake_file.file_object != self.filesystem.dev_null:
+            self.chmod(file_path, mode)
         return fake_file.fileno()
 
     def close(self, file_des):
@@ -4294,7 +4318,9 @@ def __init__(self, file_object, file_path, update=False, read=False,
         contents = file_object.byte_contents
         self._encoding = encoding or locale.getpreferredencoding(False)
         errors = errors or 'strict'
-        self._io = FileBufferIO(contents, linesep=filesystem.line_separator(),
+        buffer_class = (NullFileBufferIO if file_object == filesystem.dev_null
+                        else FileBufferIO)
+        self._io = buffer_class(contents, linesep=filesystem.line_separator(),
                                 binary=binary, encoding=encoding,
                                 newline=newline, errors=errors)
 
@@ -4868,11 +4894,15 @@ def _handle_file_arg(self, file_):
             # open a file file by path
             filedes = None
             file_path = file_
-            real_path = self.filesystem.resolve_path(
-                file_path, raw_io=self.raw_io)
-            if self.filesystem.exists(file_path):
-                file_object = self.filesystem.get_object_from_normpath(
-                    real_path)
+            if file_path == self.filesystem.dev_null.name:
+                file_object = self.filesystem.dev_null
+                real_path = file_path
+            else:
+                real_path = self.filesystem.resolve_path(
+                    file_path, raw_io=self.raw_io)
+                if self.filesystem.exists(file_path):
+                    file_object = self.filesystem.get_object_from_normpath(
+                        real_path)
         return file_object, file_path, filedes, real_path
 
     def _handle_file_mode(self, mode, newline, open_modes):

Diff for: pyfakefs/helpers.py

@@ -260,7 +260,7 @@ def __init__(self, contents=None, linesep='\n', binary=False,
         self.binary = binary
         self._bytestream = io.BytesIO()
         if contents is not None:
-            self._bytestream.write(self.encoded_string(contents))
+            self.putvalue(contents)
             self._bytestream.seek(0)
 
     def encoding(self):
@@ -377,7 +377,7 @@ def write(self, s):
             raise TypeError('Incorrect type for writing')
         contents = self.convert_newlines_for_writing(s)
         length = len(contents)
-        self._bytestream.write(self.encoded_string(contents))
+        self.putvalue(contents)
         return length
 
     def writelines(self, lines):
@@ -399,3 +399,9 @@ def next(self):
 
     def __getattr__(self, name):
         return getattr(self._bytestream, name)
+
+
+class NullFileBufferIO(FileBufferIO):
+    """Special stream for null device. Does nothing on writing."""
+    def putvalue(self, s):
+        pass

Diff for: pyfakefs/tests/fake_open_test.py

@@ -971,6 +971,13 @@ def test_unicode_filename(self):
         with self.open(file_path, 'rb') as f:
             self.assertEqual(b'test', f.read())
 
+    def test_write_devnull(self):
+        for mode in ('r+', 'w', 'w+', 'a', 'a+'):
+            with self.open(self.os.devnull, mode) as f:
+                f.write('test')
+            with self.open(self.os.devnull) as f:
+                self.assertEqual('', f.read())
+
 
 class RealFileOpenTest(FakeFileOpenTest):
     def use_real_fs(self):

Diff for: pyfakefs/tests/fake_os_test.py

@@ -4156,6 +4156,23 @@ def test_writing_behind_end_of_file(self):
         self.os.close(fd2)
         self.os.close(fd3)
 
+    def test_devnull_posix(self):
+        self.check_posix_only()
+        self.assertTrue(self.os.path.exists(self.os.devnull))
+
+    def test_devnull_windows(self):
+        self.check_windows_only()
+        self.assertFalse(self.os.path.exists(self.os.devnull))
+
+    def test_write_devnull(self):
+        fd = self.os.open(self.os.devnull, os.O_RDWR)
+        self.assertEqual(4, self.os.write(fd, b'test'))
+        self.assertEqual(b'', self.os.read(fd, 4))
+        self.os.close(fd)
+        fd = self.os.open(self.os.devnull, os.O_RDONLY)
+        self.assertEqual(b'', self.os.read(fd, 4))
+        self.os.close(fd)
+
 
 class RealOsModuleLowLevelFileOpTest(FakeOsModuleLowLevelFileOpTest):
     def use_real_fs(self):