WIP: bpo-36021: WindowsDefault does not execute os.startfile() for a local file

Lib/test/test_webbrowser.py

@@ -328,5 +328,25 @@ def test_environment_preferred(self):
             self.assertEqual(webbrowser.get().name, sys.executable)
 
 
+@unittest.skipIf(sys.platform[:3] != 'win', 'requires Windows')
+class TestWindowsDefault(unittest.TestCase):
+    @mock.patch('os.startfile')
+    @mock.patch('os.access', return_value=False)
+    @mock.patch('os.path.isfile', return_value=True)
+    def test_do_run_startfile_for_local(self, mock_isfile, mock_access, mock_startfile):
+        webbrowser.WindowsDefault().open('file:///tmp/test.html')
+        mock_startfile.assert_called()
+
+    @mock.patch('os.startfile')
+    def test_do_not_run_startfile_for_local_calc(self, mock_startfile):
+        webbrowser.WindowsDefault().open(sys.executable)
+        mock_startfile.assert_not_called()
+
+    @mock.patch('os.startfile')
+    def test_do_run_startfile_with_external_resource(self, mock_startfile):
+        webbrowser.WindowsDefault().open('https://pythontest.net')
+        mock_startfile.assert_called()
+
+
 if __name__=='__main__':
     unittest.main()

Lib/webbrowser.py

@@ -8,6 +8,7 @@
 import sys
 import subprocess
 import threading
+import urllib.parse
 
 __all__ = ["Error", "open", "open_new", "open_new_tab", "get", "register"]
 
@@ -576,9 +577,29 @@ def register_standard_browsers():
 
 if sys.platform[:3] == "win":
     class WindowsDefault(BaseBrowser):
+        def _is_html(self, path):
+            HTML_EXTENSIONS = (
+                '.html', '.htm', '.mht', '.mhtml', '.shtml',
+                '.xht', '.xhtml'
+            )
+            return os.path.splitext(path)[-1] in HTML_EXTENSIONS
+
         def open(self, url, new=0, autoraise=True):
             try:
-                os.startfile(url)
+                allowed_schemes = set(
+                    urllib.parse.uses_relative +
+                    urllib.parse.uses_netloc +
+                    urllib.parse.uses_params) - set(['file', ''])
+
+                parsed_url = urllib.parse.urlparse(url)
+                if parsed_url.scheme not in allowed_schemes:
+                    path = parsed_url.path if parsed_url.scheme == 'file' else url
+
+                    if self._is_html(path):
+                        os.startfile(url)
+                else:
+                    os.startfile(url)
+
             except OSError:
                 # [Error 22] No application is associated with the specified
                 # file for this operation: '<URL>'

Misc/NEWS.d/next/Library/2019-02-19-10-50-22.bpo-36021.T83KHF.rst

@@ -0,0 +1,2 @@
+WindowsDefault does not use os.startfile() when the location of the resource is
+local file. Contributed by Stéphane Wirtel