fix: address review feedback for accept header parsing

- Normalize media types to lowercase for case-insensitive matching per RFC 7231
- Use exact match instead of startswith to prevent over-matching
- Replace headers.update with headers.pop for cleaner Accept removal in tests

Author: shivama205

src/mcp/server/streamable_http.py

@@ -399,15 +399,11 @@ def _check_accept_headers(self, request: Request) -> tuple[bool, bool]:
         - text/* matches any text/ subtype
         """
         accept_header = request.headers.get("accept", "")
-        accept_types = [media_type.strip().split(";")[0].strip() for media_type in accept_header.split(",")]
+        accept_types = [media_type.strip().split(";")[0].strip().lower() for media_type in accept_header.split(",")]
 
         has_wildcard = "*/*" in accept_types
-        has_json = has_wildcard or any(
-            media_type.startswith(CONTENT_TYPE_JSON) or media_type == "application/*" for media_type in accept_types
-        )
-        has_sse = has_wildcard or any(
-            media_type.startswith(CONTENT_TYPE_SSE) or media_type == "text/*" for media_type in accept_types
-        )
+        has_json = has_wildcard or any(t in (CONTENT_TYPE_JSON, "application/*") for t in accept_types)
+        has_sse = has_wildcard or any(t in (CONTENT_TYPE_SSE, "text/*") for t in accept_types)
 
         return has_json, has_sse
 

tests/shared/test_streamable_http.py

@@ -574,7 +574,7 @@ def test_accept_header_validation(basic_server: None, basic_server_url: str):
     """Test that Accept header is properly validated."""
     # Test without Accept header (suppress requests library default Accept: */*)
     session = requests.Session()
-    session.headers.update({"Accept": None})  # type: ignore[arg-type]
+    session.headers.pop("Accept")
     response = session.post(
         f"{basic_server_url}/mcp",
         headers={"Content-Type": "application/json"},
@@ -876,7 +876,7 @@ def test_json_response_missing_accept_header(json_response_server: None, json_se
     mcp_url = f"{json_server_url}/mcp"
     # Suppress requests library default Accept: */* header
     session = requests.Session()
-    session.headers.update({"Accept": None})  # type: ignore[arg-type]
+    session.headers.pop("Accept")
     response = session.post(
         mcp_url,
         headers={
@@ -1017,7 +1017,7 @@ def test_get_validation(basic_server: None, basic_server_url: str):
 
     # Test without Accept header (suppress requests library default Accept: */*)
     session = requests.Session()
-    session.headers.update({"Accept": None})  # type: ignore[arg-type]
+    session.headers.pop("Accept")
     response = session.get(
         mcp_url,
         headers={