temporary fix for unhandled AlternativeServiceAvailable event (#5898)

* temporary fix for unhandled AlternativeServiceAvailable event

* [autofix.ci] apply automated fixes

* better log message for AlternativeServiceAvailable service

* [autofix.ci] apply automated fixes

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

mitmproxy/proxy/layers/http/_http2.py

@@ -275,6 +275,10 @@ class Http2Connection(HttpConnection):
             # https://http2.github.io/http2-spec/#rfc.section.4.1
             # Implementations MUST ignore and discard any frame that has a type that is unknown.
             yield Log(f"Ignoring unknown HTTP/2 frame type: {event.frame.type}")
+        elif isinstance(event, h2.events.AlternativeServiceAvailable):
+            yield Log(
+                "Received HTTP/2 Alt-Svc frame, which will not be forwarded.", DEBUG
+            )
         else:
             raise AssertionError(f"Unexpected event: {event!r}")
         return False

test/mitmproxy/proxy/layers/http/test_http2.py

@@ -1,4 +1,5 @@
 import time
+from logging import DEBUG
 
 import h2.settings
 import hpack
@@ -1191,3 +1192,31 @@ def test_keepalive_disconnect(tctx, monkeypatch):
         >> reply(to=wakeup_command, side_effect=advance_time)
         << None
     )
+
+
+def test_alt_svc(tctx):
+    playbook, cff = start_h2_client(tctx)
+    flow = Placeholder(HTTPFlow)
+    server = Placeholder(Server)
+    initial = Placeholder(bytes)
+
+    assert (
+        playbook
+        >> DataReceived(
+            tctx.client,
+            cff.build_headers_frame(
+                example_request_headers, flags=["END_STREAM"]
+            ).serialize(),
+        )
+        << http.HttpRequestHeadersHook(flow)
+        >> reply()
+        << http.HttpRequestHook(flow)
+        >> reply()
+        << OpenConnection(server)
+        >> reply(None, side_effect=make_h2)
+        << SendData(server, initial)
+        >> DataReceived(
+            server, cff.build_alt_svc_frame(0, b"example.com", b'h3=":443"').serialize()
+        )
+        << Log("Received HTTP/2 Alt-Svc frame, which will not be forwarded.", DEBUG)
+    )