protocol attribute for h2 responses

docs/topics/request-response.rst

@@ -694,7 +694,7 @@ Response objects
     :type ip_address: :class:`ipaddress.IPv4Address` or :class:`ipaddress.IPv6Address`
 
     :param protocol: The protocol that was used to download the response.
-        For instance: "HTTP/1.0", "HTTP/1.1"
+        For instance: "HTTP/1.0", "HTTP/1.1", "h2"
     :type protocol: :class:`str`
 
     .. versionadded:: 2.0.0

scrapy/core/http2/stream.py

@@ -15,6 +15,7 @@ from twisted.web.client import ResponseFailed
 from scrapy.http import Request
 from scrapy.http.headers import Headers
 from scrapy.responsetypes import responsetypes
+from scrapy.utils.python import to_unicode
 
 if TYPE_CHECKING:
     from scrapy.core.http2.protocol import H2ClientProtocol
@@ -458,6 +459,7 @@ class Stream:
             request=self._request,
             certificate=self._protocol.metadata['certificate'],
             ip_address=self._protocol.metadata['ip_address'],
+            protocol=to_unicode(self._protocol.transport.negotiatedProtocol),
         )
 
         self._deferred_response.callback(response)

tests/test_downloader_handlers_http2.py

@@ -22,6 +22,13 @@ class Https2TestCase(Https11TestCase):
     download_handler_cls = H2DownloadHandler
     HTTP2_DATALOSS_SKIP_REASON = "Content-Length mismatch raises InvalidBodyLengthError"
 
+    def test_protocol(self):
+        request = Request(self.getURL("host"), method="GET")
+        d = self.download_request(request, Spider("foo"))
+        d.addCallback(lambda r: r.protocol)
+        d.addCallback(self.assertEqual, "h2")
+        return d
+
     @defer.inlineCallbacks
     def test_download_with_maxsize_very_large_file(self):
         with mock.patch('scrapy.core.http2.stream.logger') as logger: