fix(http): raise aiohttp max_field_size for large response headers

GitHub OAuth token responses include ~9KB Content-Security-Policy
headers that exceed aiohttp's 8190 default and fail MCP token exchange
with LineTooLong. Pass a higher max_field_size/max_line_size on both
the shared proxy session and the aiohttp transport session factory.

Fixes #48468

litellm/constants.py

@@ -388,6 +388,10 @@ AIOHTTP_CONNECTOR_LIMIT: Final = get_env_int("AIOHTTP_CONNECTOR_LIMIT", 1000)
 AIOHTTP_CONNECTOR_LIMIT_PER_HOST: Final = get_env_int("AIOHTTP_CONNECTOR_LIMIT_PER_HOST", 500)
 AIOHTTP_KEEPALIVE_TIMEOUT: Final = get_env_int("AIOHTTP_KEEPALIVE_TIMEOUT", 15)
 AIOHTTP_TTL_DNS_CACHE: Final = get_env_int("AIOHTTP_TTL_DNS_CACHE", 300)
+# Raised above aiohttp's 8190 default so large response headers (e.g. GitHub CSP on OAuth
+# token exchange) parse instead of raising LineTooLong. https://github.com/BerriAI/litellm/issues/48468
+AIOHTTP_MAX_FIELD_SIZE: Final = get_env_int("AIOHTTP_MAX_FIELD_SIZE", 32768)
+AIOHTTP_MAX_LINE_SIZE: Final = get_env_int("AIOHTTP_MAX_LINE_SIZE", 32768)
 # TCP keep-alive (SO_KEEPALIVE) — opt-in. Required when running behind NAT/LBs
 # whose idle timeout is shorter than provider response timeouts (e.g. AWS NAT
 # Gateway: 350s vs OpenAI/Azure: 600s). Without this, the kernel sends nothing

litellm/llms/custom_httpx/http_handler.py

@@ -29,6 +29,8 @@ from litellm.constants import (
     AIOHTTP_CONNECTOR_LIMIT,
     AIOHTTP_CONNECTOR_LIMIT_PER_HOST,
     AIOHTTP_KEEPALIVE_TIMEOUT,
+    AIOHTTP_MAX_FIELD_SIZE,
+    AIOHTTP_MAX_LINE_SIZE,
     AIOHTTP_NEEDS_CLEANUP_CLOSED,
     AIOHTTP_SO_KEEPALIVE,
     AIOHTTP_TCP_KEEPCNT,
@@ -1351,6 +1353,8 @@ class AsyncHTTPHandler:
                 connector=TCPConnector(**transport_connector_kwargs),
                 cookie_jar=DummyCookieJar(),
                 trust_env=trust_env,
+                max_field_size=AIOHTTP_MAX_FIELD_SIZE,
+                max_line_size=AIOHTTP_MAX_LINE_SIZE,
             )
 
         # Use shared session if provided and valid

litellm/proxy/proxy_server.py

@@ -68,6 +68,8 @@ from litellm.constants import (
     AIOHTTP_CONNECTOR_LIMIT,
     AIOHTTP_CONNECTOR_LIMIT_PER_HOST,
     AIOHTTP_KEEPALIVE_TIMEOUT,
+    AIOHTTP_MAX_FIELD_SIZE,
+    AIOHTTP_MAX_LINE_SIZE,
     AIOHTTP_NEEDS_CLEANUP_CLOSED,
     AIOHTTP_TTL_DNS_CACHE,
     AUDIO_SPEECH_CHUNK_SIZE,
@@ -1398,7 +1400,12 @@ async def initialize_shared_aiohttp_session() -> "ClientSession | None":
             connector_kwargs["socket_factory"] = socket_factory
 
         connector: Final = TCPConnector(**connector_kwargs)
-        session: Final = ClientSession(connector=connector, cookie_jar=DummyCookieJar())
+        session: Final = ClientSession(
+            connector=connector,
+            cookie_jar=DummyCookieJar(),
+            max_field_size=AIOHTTP_MAX_FIELD_SIZE,
+            max_line_size=AIOHTTP_MAX_LINE_SIZE,
+        )
 
         verbose_proxy_logger.info(
             "SESSION REUSE: Created shared aiohttp session for connection pooling (ID: %s, limit=%s, limit_per_host=%s)",

tests/unit/llms/custom_httpx/test_aiohttp_cleanup_closed.py

@@ -37,3 +37,24 @@ def test_create_aiohttp_transport_omits_enable_cleanup_closed_when_not_needed(
             transport.get_valid_client_session()
 
     assert "enable_cleanup_closed" not in mock_tcp_connector.call_args.kwargs
+
+
+def test_create_aiohttp_transport_raises_header_size_limits():
+    from litellm.constants import AIOHTTP_MAX_FIELD_SIZE, AIOHTTP_MAX_LINE_SIZE
+    from litellm.llms.custom_httpx import http_handler as http_handler_module
+
+    connector_mock = MagicMock(name="connector")
+    session_mock = MagicMock(name="session")
+
+    with patch.object(http_handler_module, "TCPConnector", return_value=connector_mock):
+        with (
+            patch.object(http_handler_module, "ClientSession", return_value=session_mock) as mock_session,
+            patch.object(http_handler_module, "DummyCookieJar", return_value=MagicMock(name="cookie_jar")),
+        ):
+            transport = http_handler_module.AsyncHTTPHandler.create_aiohttp_transport(shared_session=None)
+            transport.get_valid_client_session()
+
+    assert mock_session.call_args.kwargs["max_field_size"] == AIOHTTP_MAX_FIELD_SIZE
+    assert mock_session.call_args.kwargs["max_line_size"] == AIOHTTP_MAX_LINE_SIZE
+    assert AIOHTTP_MAX_FIELD_SIZE > 8190
+    assert AIOHTTP_MAX_LINE_SIZE > 8190

tests/unit/proxy/test_aiohttp_cleanup_closed.py

@@ -11,9 +11,7 @@ def test_initialize_shared_aiohttp_session_sets_enable_cleanup_closed_when_neede
     session_mock = MagicMock(name="session")
     monkeypatch.setattr(proxy_server_module, "AIOHTTP_NEEDS_CLEANUP_CLOSED", True)
 
-    with patch(
-        "aiohttp.TCPConnector", return_value=connector_mock
-    ) as mock_tcp_connector:
+    with patch("aiohttp.TCPConnector", return_value=connector_mock) as mock_tcp_connector:
         with patch("aiohttp.ClientSession", return_value=session_mock):
             asyncio.run(proxy_server_module._initialize_shared_aiohttp_session())
 
@@ -29,10 +27,24 @@ def test_initialize_shared_aiohttp_session_omits_enable_cleanup_closed_when_not_
     session_mock = MagicMock(name="session")
     monkeypatch.setattr(proxy_server_module, "AIOHTTP_NEEDS_CLEANUP_CLOSED", False)
 
-    with patch(
-        "aiohttp.TCPConnector", return_value=connector_mock
-    ) as mock_tcp_connector:
+    with patch("aiohttp.TCPConnector", return_value=connector_mock) as mock_tcp_connector:
         with patch("aiohttp.ClientSession", return_value=session_mock):
             asyncio.run(proxy_server_module._initialize_shared_aiohttp_session())
 
     assert "enable_cleanup_closed" not in mock_tcp_connector.call_args.kwargs
+
+
+def test_initialize_shared_aiohttp_session_raises_header_size_limits():
+    from litellm.constants import AIOHTTP_MAX_FIELD_SIZE, AIOHTTP_MAX_LINE_SIZE
+    from litellm.proxy import proxy_server as proxy_server_module
+
+    connector_mock = MagicMock(name="connector")
+    session_mock = MagicMock(name="session")
+
+    with patch("aiohttp.TCPConnector", return_value=connector_mock):
+        with patch("aiohttp.ClientSession", return_value=session_mock) as mock_session:
+            asyncio.run(proxy_server_module._initialize_shared_aiohttp_session())
+
+    assert mock_session.call_args.kwargs["max_field_size"] == AIOHTTP_MAX_FIELD_SIZE
+    assert mock_session.call_args.kwargs["max_line_size"] == AIOHTTP_MAX_LINE_SIZE
+    assert AIOHTTP_MAX_FIELD_SIZE > 8190