Fix initializing Headers from Headers.

It didn't work when a header had multiple values.

src/websockets/datastructures.py

@@ -74,10 +74,10 @@ class Headers(MutableMapping[str, str]):
 
     __slots__ = ["_dict", "_list"]
 
-    def __init__(self, *args: Any, **kwargs: str) -> None:
+    # Like dict, Headers accepts an optional "mapping or iterable" argument.
+    def __init__(self, *args: HeadersLike, **kwargs: str) -> None:
         self._dict: Dict[str, List[str]] = {}
         self._list: List[Tuple[str, str]] = []
-        # MutableMapping.update calls __setitem__ for each (name, value) pair.
         self.update(*args, **kwargs)
 
     def __str__(self) -> str:
@@ -86,7 +86,7 @@ def __str__(self) -> str:
     def __repr__(self) -> str:
         return f"{self.__class__.__name__}({self._list!r})"
 
-    def copy(self) -> "Headers":
+    def copy(self) -> Headers:
         copy = self.__class__()
         copy._dict = self._dict.copy()
         copy._list = self._list.copy()
@@ -139,6 +139,16 @@ def clear(self) -> None:
         self._dict = {}
         self._list = []
 
+    def update(self, *args: HeadersLike, **kwargs: str) -> None:
+        """
+        Update from a Headers instance and/or keyword arguments.
+
+        """
+        args = tuple(
+            arg.raw_items() if isinstance(arg, Headers) else arg for arg in args
+        )
+        super().update(*args, **kwargs)
+
     # Methods for handling multiple values
 
     def get_all(self, key: str) -> List[str]:

tests/test_datastructures.py

@@ -3,10 +3,68 @@
 from websockets.datastructures import *
 
 
+class MultipleValuesErrorTests(unittest.TestCase):
+    def test_multiple_values_error_str(self):
+        self.assertEqual(str(MultipleValuesError("Connection")), "'Connection'")
+        self.assertEqual(str(MultipleValuesError()), "")
+
+
 class HeadersTests(unittest.TestCase):
     def setUp(self):
         self.headers = Headers([("Connection", "Upgrade"), ("Server", "websockets")])
 
+    def test_init(self):
+        self.assertEqual(
+            Headers(),
+            Headers(),
+        )
+
+    def test_init_from_kwargs(self):
+        self.assertEqual(
+            Headers(connection="Upgrade", server="websockets"),
+            self.headers,
+        )
+
+    def test_init_from_headers(self):
+        self.assertEqual(
+            Headers(self.headers),
+            self.headers,
+        )
+
+    def test_init_from_headers_and_kwargs(self):
+        self.assertEqual(
+            Headers(Headers(connection="Upgrade"), server="websockets"),
+            self.headers,
+        )
+
+    def test_init_from_mapping(self):
+        self.assertEqual(
+            Headers({"Connection": "Upgrade", "Server": "websockets"}),
+            self.headers,
+        )
+
+    def test_init_from_mapping_and_kwargs(self):
+        self.assertEqual(
+            Headers({"Connection": "Upgrade"}, server="websockets"),
+            self.headers,
+        )
+
+    def test_init_from_iterable(self):
+        self.assertEqual(
+            Headers([("Connection", "Upgrade"), ("Server", "websockets")]),
+            self.headers,
+        )
+
+    def test_init_from_iterable_and_kwargs(self):
+        self.assertEqual(
+            Headers([("Connection", "Upgrade")], server="websockets"),
+            self.headers,
+        )
+
+    def test_init_multiple_positional_arguments(self):
+        with self.assertRaises(TypeError):
+            Headers(Headers(connection="Upgrade"), Headers(server="websockets"))
+
     def test_str(self):
         self.assertEqual(
             str(self.headers), "Connection: Upgrade\r\nServer: websockets\r\n\r\n"
@@ -27,10 +85,6 @@ def test_serialize(self):
             b"Connection: Upgrade\r\nServer: websockets\r\n\r\n",
         )
 
-    def test_multiple_values_error_str(self):
-        self.assertEqual(str(MultipleValuesError("Connection")), "'Connection'")
-        self.assertEqual(str(MultipleValuesError()), "")
-
     def test_contains(self):
         self.assertIn("Server", self.headers)
 
@@ -59,11 +113,6 @@ def test_getitem_key_error(self):
         with self.assertRaises(KeyError):
             self.headers["Upgrade"]
 
-    def test_getitem_multiple_values_error(self):
-        self.headers["Server"] = "2"
-        with self.assertRaises(MultipleValuesError):
-            self.headers["Server"]
-
     def test_setitem(self):
         self.headers["Upgrade"] = "websocket"
         self.assertEqual(self.headers["Upgrade"], "websocket")
@@ -72,11 +121,6 @@ def test_setitem_case_insensitive(self):
         self.headers["upgrade"] = "websocket"
         self.assertEqual(self.headers["Upgrade"], "websocket")
 
-    def test_setitem_multiple_values(self):
-        self.headers["Connection"] = "close"
-        with self.assertRaises(MultipleValuesError):
-            self.headers["Connection"]
-
     def test_delitem(self):
         del self.headers["Connection"]
         with self.assertRaises(KeyError):
@@ -87,12 +131,6 @@ def test_delitem_case_insensitive(self):
         with self.assertRaises(KeyError):
             self.headers["Connection"]
 
-    def test_delitem_multiple_values(self):
-        self.headers["Connection"] = "close"
-        del self.headers["Connection"]
-        with self.assertRaises(KeyError):
-            self.headers["Connection"]
-
     def test_eq(self):
         other_headers = Headers([("Connection", "Upgrade"), ("Server", "websockets")])
         self.assertEqual(self.headers, other_headers)
@@ -124,12 +162,75 @@ def test_get_all_case_insensitive(self):
     def test_get_all_no_values(self):
         self.assertEqual(self.headers.get_all("Upgrade"), [])
 
-    def test_get_all_multiple_values(self):
-        self.headers["Connection"] = "close"
-        self.assertEqual(self.headers.get_all("Connection"), ["Upgrade", "close"])
-
     def test_raw_items(self):
         self.assertEqual(
             list(self.headers.raw_items()),
             [("Connection", "Upgrade"), ("Server", "websockets")],
         )
+
+
+class MultiValueHeadersTests(unittest.TestCase):
+    def setUp(self):
+        self.headers = Headers([("Server", "Python"), ("Server", "websockets")])
+
+    def test_init_from_headers(self):
+        self.assertEqual(
+            Headers(self.headers),
+            self.headers,
+        )
+
+    def test_init_from_headers_and_kwargs(self):
+        self.assertEqual(
+            Headers(Headers(server="Python"), server="websockets"),
+            self.headers,
+        )
+
+    def test_str(self):
+        self.assertEqual(
+            str(self.headers), "Server: Python\r\nServer: websockets\r\n\r\n"
+        )
+
+    def test_repr(self):
+        self.assertEqual(
+            repr(self.headers),
+            "Headers([('Server', 'Python'), ('Server', 'websockets')])",
+        )
+
+    def test_copy(self):
+        self.assertEqual(repr(self.headers.copy()), repr(self.headers))
+
+    def test_serialize(self):
+        self.assertEqual(
+            self.headers.serialize(),
+            b"Server: Python\r\nServer: websockets\r\n\r\n",
+        )
+
+    def test_iter(self):
+        self.assertEqual(set(iter(self.headers)), {"server"})
+
+    def test_len(self):
+        self.assertEqual(len(self.headers), 1)
+
+    def test_getitem_multiple_values_error(self):
+        with self.assertRaises(MultipleValuesError):
+            self.headers["Server"]
+
+    def test_setitem(self):
+        self.headers["Server"] = "redux"
+        self.assertEqual(
+            self.headers.get_all("Server"), ["Python", "websockets", "redux"]
+        )
+
+    def test_delitem(self):
+        del self.headers["Server"]
+        with self.assertRaises(KeyError):
+            self.headers["Server"]
+
+    def test_get_all(self):
+        self.assertEqual(self.headers.get_all("Server"), ["Python", "websockets"])
+
+    def test_raw_items(self):
+        self.assertEqual(
+            list(self.headers.raw_items()),
+            [("Server", "Python"), ("Server", "websockets")],
+        )