Support slicing header sequences

h11/_headers.py

@@ -116,7 +116,19 @@ def __len__(self) -> int:
     def __repr__(self) -> str:
         return "<Headers(%s)>" % repr(list(self))
 
-    def __getitem__(self, idx: int) -> Tuple[bytes, bytes]:  # type: ignore[override]
+    @overload
+    def __getitem__(self, idx: int) -> Tuple[bytes, bytes]:
+        ...
+
+    @overload
+    def __getitem__(self, idx: slice) -> "Headers":
+        ...
+
+    def __getitem__(
+        self, idx: Union[int, slice]
+    ) -> Union[Tuple[bytes, bytes], "Headers"]:
+        if isinstance(idx, slice):
+            return Headers(self._full_items[idx])
         _, name, value = self._full_items[idx]
         return (name, value)
 

h11/tests/test_headers.py

@@ -11,6 +11,34 @@
 from .._util import LocalProtocolError
 
 
+@pytest.mark.parametrize(
+    "index",
+    [
+        slice(None, 1),
+        slice(None, 3),
+        slice(1, 1),
+        slice(None, None, -1),
+        slice(None, None, 2),
+    ],
+)
+def test_headers_slicing(index: slice) -> None:
+    headers = Request(
+        method="GET",
+        target="/",
+        headers=[("Host", "example.org"), ("X-First", "one"), ("X-Second", "two")],
+    ).headers
+    items = list(headers)
+    raw_items = headers.raw_items()
+
+    sliced = headers[index]
+
+    assert isinstance(sliced, Headers)
+    assert list(sliced) == items[index]
+    assert sliced.raw_items() == raw_items[index]
+    assert list(headers) == items
+    assert headers.raw_items() == raw_items
+
+
 def test_normalize_and_validate() -> None:
     assert normalize_and_validate([("foo", "bar")]) == [(b"foo", b"bar")]
     assert normalize_and_validate([(b"foo", b"bar")]) == [(b"foo", b"bar")]

newsfragments/209.bugfix.rst

@@ -0,0 +1 @@
+Support slicing the header sequence exposed by events, retaining normalized header pairs and original header-name casing.