require config.yml use UTF-8 as encoding

config.yml requires ASCII or UTF-8 encoding because this code does not
auto-detect the file's encoding.  That is left up to the YAML library.
YAML allows ASCII, UTF-8, UTF-16, and UTF-32 encodings.  Since it is a
good idea to manage config.yml (WITHOUT PASSWORDS!) in git, it makes
sense to use a globally standard encoding.

fdroidserver/common.py

@@ -336,6 +336,12 @@ def read_config(opts=None):
     reading it.  config.py is deprecated and supported for backwards
     compatibility.
 
+    config.yml requires ASCII or UTF-8 encoding because this code does
+    not auto-detect the file's encoding.  That is left up to the YAML
+    library.  YAML allows ASCII, UTF-8, UTF-16, and UTF-32 encodings.
+    Since it is a good idea to manage config.yml (WITHOUT PASSWORDS!)
+    in git, it makes sense to use a globally standard encoding.
+
     """
     global config, options
 
@@ -354,7 +360,7 @@ def read_config(opts=None):
 
     if os.path.exists(config_file):
         logging.debug(_("Reading '{config_file}'").format(config_file=config_file))
-        with open(config_file) as fp:
+        with open(config_file, encoding='utf-8') as fp:
             config = yaml.safe_load(fp)
     elif os.path.exists(old_config_file):
         logging.warning(_("""{oldfile} is deprecated, use {newfile}""")

tests/common.TestCase

@@ -1687,6 +1687,34 @@ class CommonTest(unittest.TestCase):
         config = fdroidserver.common.read_config(fdroidserver.common.options)
         self.assertEqual('yml', config.get('apksigner'))
 
+    def test_with_config_yml_utf8(self):
+        """Make sure it is possible to use config.yml in UTF-8 encoding."""
+        testdir = tempfile.mkdtemp(
+            prefix=inspect.currentframe().f_code.co_name, dir=self.tmpdir
+        )
+        os.chdir(testdir)
+        teststr = '/πÇÇ现代通用字-български-عربي1/ö/yml'
+        with open('config.yml', 'w', encoding='utf-8') as fp:
+            fp.write('apksigner: ' + teststr)
+        self.assertTrue(os.path.exists('config.yml'))
+        self.assertFalse(os.path.exists('config.py'))
+        config = fdroidserver.common.read_config(fdroidserver.common.options)
+        self.assertEqual(teststr, config.get('apksigner'))
+
+    def test_with_config_yml_utf8_as_ascii(self):
+        """Make sure it is possible to use config.yml Unicode encoded as ASCII."""
+        testdir = tempfile.mkdtemp(
+            prefix=inspect.currentframe().f_code.co_name, dir=self.tmpdir
+        )
+        os.chdir(testdir)
+        teststr = '/πÇÇ现代通用字-български-عربي1/ö/yml'
+        with open('config.yml', 'w') as fp:
+            yaml.dump({'apksigner': teststr}, fp)
+        self.assertTrue(os.path.exists('config.yml'))
+        self.assertFalse(os.path.exists('config.py'))
+        config = fdroidserver.common.read_config(fdroidserver.common.options)
+        self.assertEqual(teststr, config.get('apksigner'))
+
     def test_with_config_yml_with_env_var(self):
         """Make sure it is possible to use config.yml alone."""
         testdir = tempfile.mkdtemp(