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Add X-Accel-Buffering: no header to SSE responses - #848
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Proxy servers like Nginx buffer responses by default, which causes SSE streams to be delayed. Adding the X-Accel-Buffering: no header instructs reverse proxies to disable response buffering for SSE endpoints, ensuring real-time streaming delivery. Applied to all three SSE response locations: - HttpServletSseServerTransportProvider (SSE endpoint) - HttpServletStreamableServerTransportProvider (GET and POST SSE) Fixes modelcontextprotocol#293 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Adds the X-Accel-Buffering: no header to all SSE response endpoints to prevent reverse proxy buffering.
Problem
Proxy servers like Nginx buffer HTTP responses by default. For SSE (Server-Sent Events) endpoints, this causes events to be held in the buffer and delivered in batches instead of being streamed in real-time. This is particularly problematic for MCP transports that rely on SSE for real-time communication.
Fix
Added response.setHeader("X-Accel-Buffering", "no") to all three SSE response locations:
This header is a de facto standard supported by Nginx, AWS ALB, and other common proxies. It has no effect when no proxy is present.
Testing
All 680 existing tests pass (1 pre-existing Docker container startup failure unrelated to this change).
Fixes #293