Preserve 100-continue wait through 102 and 103 responses

docs/source/api.rst

@@ -431,9 +431,10 @@ The Connection object
 
       True if the client sent a request with the ``Expect:
       100-continue`` header, and is still waiting for a response
-      (i.e., the server has not sent a 100 Continue or any other kind
-      of response, and the client has not gone ahead and started
-      sending the body anyway).
+      (i.e., the server has not sent a 100 Continue, switched protocols,
+      or sent a final response, and the client has not gone ahead and
+      started sending the body anyway). Other informational responses,
+      such as 103 Early Hints, do not clear this flag.
 
       See `RFC 7231 section 5.1.1
       <https://tools.ietf.org/html/rfc7231#section-5.1.1>`_ for details.
@@ -695,12 +696,13 @@ have to be prepared to handle :class:`Request`\s that have an
 ``Expect: 100-continue`` header. You can `read the spec
 <https://tools.ietf.org/html/rfc7231#section-5.1.1>`_ for the full
 details, but basically what this header means is that after sending
-the :class:`Request`, the client plans to pause and wait until they
-see some response from the server before they send that request's
-:class:`Data`. The server's response would normally be an
-:class:`InformationalResponse` with status ``100 Continue``, but it
-could be anything really (e.g. a full :class:`Response` with a 4xx
-status code). The crucial thing as a server, though, is that you
+the :class:`Request`, the client plans to pause and wait for a
+``100 Continue`` or a final response before they send that request's
+:class:`Data`. The server can send an :class:`InformationalResponse`
+with status ``100 Continue`` to request the body, or a final
+:class:`Response` (e.g. with a 4xx status code). Other informational
+responses, such as ``103 Early Hints``, leave the client waiting for
+``100 Continue``. The crucial thing as a server, though, is that you
 should never block trying to read a request body if the client is
 blocked waiting for you to tell them to send the request body.
 

h11/_connection.py

@@ -310,7 +310,11 @@ def _process_event(self, role: Type[Sentinel], event: Event) -> None:
         # 100-continue
         if type(event) is Request and has_expect_100_continue(event):
             self.client_is_waiting_for_100_continue = True
-        if type(event) in (InformationalResponse, Response):
+        # Other informational responses, such as 103 Early Hints, do not
+        # tell the client to send its request body.
+        if type(event) is Response or (
+            type(event) is InformationalResponse and event.status_code in (100, 101)
+        ):
             self.client_is_waiting_for_100_continue = False
         if role is CLIENT and type(event) in (Data, EndOfMessage):
             self.client_is_waiting_for_100_continue = False

h11/tests/test_connection.py

@@ -365,7 +365,8 @@ def test_automagic_connection_close_handling() -> None:
         assert conn.states == {CLIENT: MUST_CLOSE, SERVER: MUST_CLOSE}
 
 
-def test_100_continue() -> None:
+@pytest.mark.parametrize("informational_status", [None, 102, 103])
+def test_100_continue(informational_status: Optional[int]) -> None:
     def setup() -> ConnectionPair:
         p = ConnectionPair()
         p.send(
@@ -382,6 +383,14 @@ def setup() -> ConnectionPair:
         )
         for conn in p.conns:
             assert conn.client_is_waiting_for_100_continue
+        if informational_status is not None:
+            for _ in range(2):
+                p.send(
+                    SERVER,
+                    InformationalResponse(status_code=informational_status, headers=[]),
+                )
+                for conn in p.conns:
+                    assert conn.client_is_waiting_for_100_continue
         assert not p.conn[CLIENT].they_are_waiting_for_100_continue
         assert p.conn[SERVER].they_are_waiting_for_100_continue
         return p

newsfragments/211.bugfix.rst

@@ -0,0 +1,3 @@
+Preserve the waiting-for-100-continue state after informational responses
+such as 103 Early Hints, so servers still send 100 Continue before waiting
+for the request body.