fix: csv output under Windows with correct newlines (#4557) (#4558)

* fixes #4557

cve_bin_tool/output_engine/__init__.py

@@ -882,7 +882,10 @@ def output_file(self, output_type="console"):
             with open(self.filename, "wb") as f:
                 self.output_cves(f, output_type)
         else:
-            with open(self.filename, "w", encoding="utf8") as f:
+            # if type is csv, file should be opened with newline=''
+            # see https://docs.python.org/3/library/csv.html#csv.writer
+            newline = "" if output_type == "csv" else None
+            with open(self.filename, mode="w", newline=newline, encoding="utf8") as f:
                 self.output_cves(f, output_type)
 
     def check_file_path(self, filepath: str, output_type: str, prefix: str = "output"):

test/test_output_engine.py

@@ -1270,6 +1270,16 @@ def test_output_file(self):
         self.assertEqual(contains_filename, True)
         self.assertEqual(contains_msg, True)
 
+    def test_csv_output_file(self):
+        self.output_engine.output_file(output_type="csv")
+        filename = Path(self.output_engine.filename)
+        n_cves = sum(len(c["cves"]) for c in self.MOCK_OUTPUT.values())
+        with filename.open(newline="", mode="r") as f:
+            n_lines = len(f.read().splitlines())
+            # cvs file should have one line per cve plus a header line
+            assert n_lines == n_cves + 1
+        filename.unlink()
+
     def test_output_file_wrapper(self):
         """Test file generation logic in output_file_wrapper"""
         logger = logging.getLogger()