From d0d260055f7d58d460dd59969cfdb37feac3b7ca Mon Sep 17 00:00:00 2001
From: Mark Larah <mark@larah.me>
Date: Mon, 29 Jun 2026 16:55:23 -0500
Subject: [PATCH] Skip multipart parts with empty Content-Type instead of
 raising

Some GraphQL servers send multipart parts without a Content-Type
header as heartbeats or keep-alive padding. Previously this raised
a TransportProtocolError, crashing the subscription stream.

Co-Authored-By: Claude <noreply@anthropic.com>
---
 gql/transport/aiohttp.py        |  3 +++
 tests/test_aiohttp_multipart.py | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/gql/transport/aiohttp.py b/gql/transport/aiohttp.py
index e7eff55f..0385d4f3 100644
--- a/gql/transport/aiohttp.py
+++ b/gql/transport/aiohttp.py
@@ -542,6 +542,9 @@ async def _parse_multipart_part(
         """
         # Verify the part has the correct content type
         content_type = part.headers.get(aiohttp.hdrs.CONTENT_TYPE, "")
+        if not content_type:
+            log.debug("Skipping part with no content-type (likely heartbeat)")
+            return None
         if not content_type.startswith("application/json"):
             raise TransportProtocolError(
                 f"Unexpected part content-type: {content_type}. "
diff --git a/tests/test_aiohttp_multipart.py b/tests/test_aiohttp_multipart.py
index d71814a4..1a5bbee5 100644
--- a/tests/test_aiohttp_multipart.py
+++ b/tests/test_aiohttp_multipart.py
@@ -480,6 +480,38 @@ async def test_aiohttp_multipart_wrong_part_content_type(multipart_server):
         assert "text/html" in str(exc_info.value)
 
 
+@pytest.mark.asyncio
+async def test_aiohttp_multipart_empty_content_type_skipped(multipart_server):
+    """Test that parts with empty/missing content-type are skipped as heartbeats."""
+    from gql.transport.aiohttp import AIOHTTPTransport
+
+    book1_payload = json.dumps({"payload": {"data": {"book": book1}}})
+
+    parts = [
+        ("--graphql\r\n" "\r\n" "\r\n"),
+        (
+            "--graphql\r\n"
+            "Content-Type: application/json\r\n"
+            "\r\n"
+            f"{book1_payload}\r\n"
+        ),
+        "--graphql--\r\n",
+    ]
+
+    server = await multipart_server(parts)
+    url = server.make_url("/")
+    transport = AIOHTTPTransport(url=url)
+
+    async with Client(transport=transport) as session:
+        query = gql(subscription_str)
+        results = []
+        async for result in session.subscribe(query):
+            results.append(result)
+
+        assert len(results) == 1
+        assert results[0]["book"]["title"] == "Book 1"
+
+
 @pytest.mark.asyncio
 async def test_aiohttp_multipart_response_headers(multipart_server):
     """Test that response headers are captured in the transport."""