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Relax Accept header requirement for JSON-only responses (#1500)

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adam jones 2025-10-27 17:46:04 +00:00 • committed by GitHub
commit 31ae5f4dc4
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1 changed files with 69 additions and 8 deletions
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32
src/mcp/server/streamable_http.py
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@ -306,20 +306,36 @@ class StreamableHTTPServerTransport:
return any(part == CONTENT_TYPE_JSON for part in content_type_parts)
async def _validate_accept_header(self, request: Request, scope: Scope, send: Send) -> bool:
"""Validate Accept header based on response mode. Returns True if valid."""
has_json, has_sse = self._check_accept_headers(request)
if self.is_json_response_enabled:
# For JSON-only responses, only require application/json
if not has_json:
response = self._create_error_response(
"Not Acceptable: Client must accept application/json",
HTTPStatus.NOT_ACCEPTABLE,
)
await response(scope, request.receive, send)
return False
# For SSE responses, require both content types
elif not (has_json and has_sse):
response = self._create_error_response(
"Not Acceptable: Client must accept both application/json and text/event-stream",
HTTPStatus.NOT_ACCEPTABLE,
)
await response(scope, request.receive, send)
return False
return True
async def _handle_post_request(self, scope: Scope, request: Request, receive: Receive, send: Send) -> None:
"""Handle POST requests containing JSON-RPC messages."""
writer = self._read_stream_writer
if writer is None:
raise ValueError("No read stream writer available. Ensure connect() is called first.")
try:
# Check Accept headers
has_json, has_sse = self._check_accept_headers(request)
if not (has_json and has_sse):
response = self._create_error_response(
("Not Acceptable: Client must accept both application/json and text/event-stream"),
HTTPStatus.NOT_ACCEPTABLE,
)
await response(scope, receive, send)
# Validate Accept header
if not await self._validate_accept_header(request, scope, send):
return
# Validate Content-Type