fix: No more BytesWarnings

Fixes python-hyper#1236.

This patch makes all header operations operate on `bytes` and converts all headers and values to bytes before operation. With a follow up patch to `hpack` it should also increase efficiency as currently, `hpack` casts everything to a `str` first before converting back to bytes: https://github.com/python-hyper/hpack/blob/02afcab28ca56eb5259904fd414baa89e9f50266/src/hpack/hpack.py#L150-L151

src/h2/connection.py

@@ -33,7 +33,7 @@
 from .frame_buffer import FrameBuffer
 from .settings import Settings, SettingCodes
 from .stream import H2Stream, StreamClosedBy
-from .utilities import SizeLimitDict, guard_increment_window
+from .utilities import SizeLimitDict, guard_increment_window, utf8_encode_headers
 from .windows import WindowManager
 
 
@@ -975,6 +975,7 @@ def push_stream(self, stream_id, promised_stream_id, request_headers):
         )
         self.streams[promised_stream_id] = new_stream
 
+        request_headers = utf8_encode_headers(request_headers)
         frames = stream.push_stream_in_band(
             promised_stream_id, request_headers, self.encoder
         )

src/h2/stream.py

@@ -25,7 +25,8 @@
 from .utilities import (
     guard_increment_window, is_informational_response, authority_from_headers,
     validate_headers, validate_outbound_headers, normalize_outbound_headers,
-    HeaderValidationFlags, extract_method_header, normalize_inbound_headers
+    HeaderValidationFlags, extract_method_header, normalize_inbound_headers,
+    utf8_encode_headers
 )
 from .windows import WindowManager
 
@@ -851,6 +852,8 @@ def send_headers(self, headers, encoder, end_stream=False):
         # we need to scan the header block to see if this is an informational
         # response.
         input_ = StreamInputs.SEND_HEADERS
+
+        headers = utf8_encode_headers(headers)
         if ((not self.state_machine.client) and
                 is_informational_response(headers)):
             if end_stream:
@@ -1319,7 +1322,7 @@ def _initialize_content_length(self, headers):
                     self._expected_content_length = int(v, 10)
                 except ValueError:
                     raise ProtocolError(
-                        "Invalid content-length header: %s" % v
+                        f"Invalid content-length header: {repr(v)}"
                     )
 
                 return