Better handling of unknown frame types

(cherry picked from commit 563e5c6)

Author: Lukasa

h2/connection.py

@@ -28,8 +28,7 @@
 from .exceptions import (
     ProtocolError, NoSuchStreamError, FlowControlError, FrameTooLargeError,
     TooManyStreamsError, StreamClosedError, StreamIDTooLowError,
-    NoAvailableStreamIDError, UnsupportedFrameError, RFC1122Error,
-    DenialOfServiceError
+    NoAvailableStreamIDError, RFC1122Error, DenialOfServiceError
 )
 from .frame_buffer import FrameBuffer
 from .settings import (
@@ -49,6 +48,15 @@ class OversizedHeaderListError(Exception):
         pass
 
 
+try:
+    from hyperframe.frame import ExtensionFrame
+except ImportError:  # Platform-specific: Hyperframe < 5.0.0
+    # If the frame doesn't exist, that's just fine: we'll define it ourselves
+    # and the method will just never be called.
+    class ExtensionFrame(object):
+        pass
+
+
 class ConnectionState(Enum):
     IDLE = 0
     CLIENT_OPEN = 1
@@ -403,6 +411,7 @@ def __init__(self, client_side=True, header_encoding='utf-8', config=None):
             GoAwayFrame: self._receive_goaway_frame,
             ContinuationFrame: self._receive_naked_continuation,
             AltSvcFrame: self._receive_alt_svc_frame,
+            ExtensionFrame: self._receive_unknown_frame
         }
 
     def _prepare_for_sending(self, frames):
@@ -1491,10 +1500,6 @@ def _receive_frame(self, frame):
             if frame.stream_id not in self._reset_streams:
                 raise
             events = []
-        except KeyError as e:  # pragma: no cover
-            # We don't have a function for handling this frame. Let's call this
-            # a PROTOCOL_ERROR and exit.
-            raise UnsupportedFrameError("Unexpected frame: %s" % frame)
         else:
             self._prepare_for_sending(frames)
 
@@ -1829,6 +1834,18 @@ def _receive_alt_svc_frame(self, frame):
 
         return frames, events
 
+    def _receive_unknown_frame(self, frame):
+        """
+        We have received a frame that we do not understand. This is almost
+        certainly an extension frame, though it's impossible to be entirely
+        sure.
+
+        RFC 7540 § 5.5 says that we MUST ignore unknown frame types: so we
+        do.
+        """
+        # We don't do anything here.
+        return [], []
+
     def _local_settings_acked(self):
         """
         Handle the local settings being ACKed, update internal state.

h2/frame_buffer.py

@@ -65,11 +65,13 @@ def _parse_frame_header(self, data):
         """
         try:
             frame, length = Frame.parse_frame_header(data[:9])
-        except UnknownFrameError as e:
+        except UnknownFrameError as e:  # Platform-specific: Hyperframe < 5.0
             # Here we do something a bit odd. We want to consume the frame data
             # as consistently as possible, but we also don't ever want to yield
             # None. Instead, we make sure that, if there is no frame, we
             # recurse into ourselves.
+            # This can only happen now on older versions of hyperframe.
+            # TODO: Remove in 3.0
             length = e.length
             frame = None
         except ValueError as e: