Check flow.killable before killing prior knowledge h2 connections. (#7514)

* check for killable flow

* [autofix.ci] apply automated fixes

* add test

* changelog

* restructure test

* [autofix.ci] apply automated fixes

---------

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

CHANGELOG.md

@@ -17,6 +17,8 @@
   ([#7497](https://github.com/mitmproxy/mitmproxy/pull/7497), @sujaldev)
 - Add mitmweb tutorial to docs.
   ([#7509](https://github.com/mitmproxy/mitmproxy/pull/7509), @EstherRoeth)
+- Fixed a bug that caused mitmproxy to crash when loading prior knowledge h2 flows.
+  ([#7514](https://github.com/mitmproxy/mitmproxy/pull/7514), @sujaldev)
 
 ## 12 January 2025: mitmproxy 11.1.0
 

mitmproxy/addons/disable_h2c.py

@@ -30,7 +30,8 @@ class DisableH2C:
             and f.request.http_version == "HTTP/2.0"
         )
         if is_connection_preface:
-            f.kill()
+            if f.killable:
+                f.kill()
             logging.warning(
                 "Initiating HTTP/2 connections with prior knowledge are currently not supported."
             )

test/mitmproxy/addons/test_disable_h2c.py

@@ -37,3 +37,18 @@ class TestDisableH2CleartextUpgrade:
             a.request(f)
             assert not f.killable
             assert f.error.msg == flow.Error.KILLED_MESSAGE
+
+    def test_non_killable_flows(self):
+        with taddons.context() as tctx:
+            a = disable_h2c.DisableH2C()
+            tctx.configure(a)
+
+            f = tflow.tflow()
+            f.request = tutils.treq(
+                method=b"PRI",
+                path=b"*",
+                http_version=b"HTTP/2.0",
+            )
+            f.kill()
+
+            a.request(f)