fix(frontend): proxy LangGraph SSE without buffering#2797
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fix(frontend): proxy LangGraph SSE without buffering#2797LittleChenLiya wants to merge 6 commits into
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Pull request overview
This PR changes how the frontend proxies LangGraph-compatible gateway endpoints by replacing Next.js rewrites with an App Router Route Handler, aiming to preserve SSE streaming behavior (avoid response buffering) on /api/langgraph/*.
Changes:
- Add
/api/langgraph/[[...path]]Route Handler that proxies to the gateway while streaming the upstream response body and normalizing headers to discourage buffering/transforms. - Add unit tests to validate URL construction, header forwarding/stripping, and streaming response behavior.
- Replace the previous
/api/:path*catch-all gateway rewrite with an explicit allowlist to prevent it from intercepting/api/langgraph/*.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| frontend/src/app/api/langgraph/[[...path]]/route.ts | Introduces a Node.js runtime Route Handler proxy for LangGraph paths with streaming response passthrough and header normalization. |
| frontend/tests/unit/app/api/langgraph-route.test.ts | Adds unit coverage for URL encoding, header filtering, request body streaming, and response header normalization. |
| frontend/next.config.js | Removes /api/langgraph rewrites and replaces the gateway catch-all rewrite with an explicit set of gateway route rewrites. |
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修复 #2785
问题
Windows 本地开发环境中，LangGraph SSE 通过 Next rewrites 转发到 gateway 时会被前端代理路径缓冲。表现为模型已经开始输出，但浏览器端要等较久后才一次性收到内容。
对比验证：
http://127.0.0.1:8001/api/threads/.../runs/stream可以增量收到 SSE event。http://localhost:3000/api/langgraph/.../stream会出现 event 延迟集中到达。这说明后端和模型本身可以流式输出，问题主要在前端 dev proxy 的 rewrite 路径上；不是单纯缺少
messages-tuplestream mode。修改
/api/langgraph/runs/stream/api/langgraph/threads/[threadId]/runs/stream/api/langgraph/threads/[threadId]/runs/[runId]/stream/api/.../stream，并直接返回 upstream response body，避免 SSE 被中间层缓冲。/api/langgraph/*不接管，继续通过 fallback rewrite 代理到 gateway，降低非流式 API 的副作用。accept-encoding: identity。Connection指名 header、host和不可靠的content-length。NEXT_PUBLIC_LANGGRAPH_BASE_URL时，不暴露同源 stream proxy 到内部 gateway。测试
新增/更新单测覆盖：
Cache-Control保持 upstream 原值；upstream 没有时代理不自行生成。Connection指名的 hop-by-hop headers 会在请求和响应两侧被剥离。HEAD/OPTIONS不附带 body 或duplex。DEER_FLOW_INTERNAL_GATEWAY_BASE_URL回退到默认 gateway URL。NEXT_PUBLIC_LANGGRAPH_BASE_URL配置后，同源 stream proxy 不继续映射到内部 gateway。next.config.js使用 fallback rewrites，让 stream App Route 优先命中，同时普通/api/langgraph/*仍回落到 gateway。本地已执行：
pnpm.cmd formatpnpm.cmd lint，仅有既有 hook dependency warnings，无 errorpnpm.cmd typecheckpnpm.cmd testBETTER_AUTH_SECRET=local-dev-secret pnpm.cmd build额外验证：
OPTIONS响应命中 Route Handler，并带有X-Accel-Buffering。/api/langgraph/threads不带X-Accel-Buffering，确认仍走 fallback rewrite。