Message is not upgraded if Upgrade header is missing (#7895)

CHANGES/7895.bugfix

@@ -0,0 +1 @@
+Fixed messages being reported as upgraded without an Upgrade header in Python parser. -- by :user:`Dreamsorcerer`

aiohttp/http_parser.py

@@ -503,7 +503,8 @@ def parse_headers(
                 close_conn = True
             elif v == "keep-alive":
                 close_conn = False
-            elif v == "upgrade":
+            # https://www.rfc-editor.org/rfc/rfc9110.html#name-101-switching-protocols
+            elif v == "upgrade" and headers.get(hdrs.UPGRADE):
                 upgrade = True
 
         # encoding

tests/test_http_parser.py

@@ -473,6 +473,15 @@ def test_conn_upgrade(parser: Any) -> None:
     assert upgrade
 
 
+def test_bad_upgrade(parser: Any) -> None:
+    """Test not upgraded if missing Upgrade header."""
+    text = b"GET /test HTTP/1.1\r\nconnection: upgrade\r\n\r\n"
+    messages, upgrade, tail = parser.feed_data(text)
+    msg = messages[0][0]
+    assert not msg.upgrade
+    assert not upgrade
+
+
 def test_compression_empty(parser: Any) -> None:
     text = b"GET /test HTTP/1.1\r\n" b"content-encoding: \r\n\r\n"
     messages, upgrade, tail = parser.feed_data(text)