Add low-level line ending conversion functions with its test file

They will be put in use in next changesets.

dulwich/line_ending.py

@@ -0,0 +1,45 @@
+# line_ending.py -- Line ending conversion functions
+# Copyright (C) 2018-2018 Boris Feld <boris.feld@comet.ml>
+#
+# Dulwich is dual-licensed under the Apache License, Version 2.0 and the GNU
+# General Public License as public by the Free Software Foundation; version 2.0
+# or (at your option) any later version. You can redistribute it and/or
+# modify it under the terms of either of these two licenses.
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# You should have received a copy of the licenses; if not, see
+# <http://www.gnu.org/licenses/> for a copy of the GNU General Public License
+# and <http://www.apache.org/licenses/LICENSE-2.0> for a copy of the Apache
+# License, Version 2.0.
+#
+
+""" All line-ending related functions, from conversions to config processing
+"""
+
+CRLF = b"\r\n"
+LF = b"\n"
+
+
+def convert_crlf_to_lf(text_hunk):
+    """Convert CRLF in text hunk into LF
+
+    :param text_hunk: A bytes string representing a text hunk
+    :return: The text hunk with the same type, with CRLF replaced into LF
+    """
+    return text_hunk.replace(CRLF, LF)
+
+
+def convert_lf_to_crlf(text_hunk):
+    """Convert LF in text hunk into CRLF
+
+    :param text_hunk: A bytes string representing a text hunk
+    :return: The text hunk with the same type, with LF replaced into CRLF
+    """
+    # TODO find a more efficient way of doing it
+    intermediary = text_hunk.replace(CRLF, LF)
+    return intermediary.replace(LF, CRLF)

dulwich/tests/__init__.py

@@ -110,6 +110,7 @@ def self_test_suite():
         'hooks',
         'ignore',
         'index',
+        'line_ending',
         'lru_cache',
         'mailmap',
         'objects',

dulwich/tests/test_line_ending.py

@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+# test_line_ending.py -- Tests for the line ending functions
+# encoding: utf-8
+# Copyright (C) 2018-2019 Boris Feld <boris.feld@comet.ml>
+#
+# Dulwich is dual-licensed under the Apache License, Version 2.0 and the GNU
+# General Public License as public by the Free Software Foundation; version 2.0
+# or (at your option) any later version. You can redistribute it and/or
+# modify it under the terms of either of these two licenses.
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# You should have received a copy of the licenses; if not, see
+# <http://www.gnu.org/licenses/> for a copy of the GNU General Public License
+# and <http://www.apache.org/licenses/LICENSE-2.0> for a copy of the Apache
+# License, Version 2.0.
+#
+
+"""Tests for the line ending conversion."""
+
+from dulwich.line_ending import convert_crlf_to_lf, convert_lf_to_crlf
+
+from dulwich.tests import TestCase
+
+
+class LineEndingConversion(TestCase):
+    """Test the line ending conversion functions in various cases"""
+
+    def test_convert_crlf_to_lf_no_op(self):
+        self.assertEqual(convert_crlf_to_lf(b"foobar"), b"foobar")
+
+    def test_convert_crlf_to_lf(self):
+        self.assertEqual(
+            convert_crlf_to_lf(b"line1\r\nline2"), b"line1\nline2"
+        )
+
+    def test_convert_crlf_to_lf_mixed(self):
+        self.assertEqual(
+            convert_crlf_to_lf(b"line1\r\n\nline2"), b"line1\n\nline2"
+        )
+
+    def test_convert_lf_to_crlf_no_op(self):
+        self.assertEqual(convert_lf_to_crlf(b"foobar"), b"foobar")
+
+    def test_convert_lf_to_crlf(self):
+        self.assertEqual(
+            convert_lf_to_crlf(b"line1\nline2"), b"line1\r\nline2"
+        )
+
+    def test_convert_lf_to_crlf_mixed(self):
+        self.assertEqual(
+            convert_lf_to_crlf(b"line1\r\n\nline2"), b"line1\r\n\r\nline2"
+        )