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fix(web): break /mcp trailing-slash redirect loop that made the MCP endpoint unreachable #353

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Merged
arozumenko merged 1 commit into from
Jul 7, 2026
Merged

fix(web): break /mcp trailing-slash redirect loop that made the MCP endpoint unreachable #353

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11 changes: 9 additions & 2 deletions web/src/middleware.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -29,8 +29,15 @@ export async function middleware(request: NextRequest) {
const url = new URL(pathname + request.nextUrl.search, BACKEND_URL);
return NextResponse.rewrite(url);
}
if (pathname.startsWith('/mcp')) {
const url = new URL(pathname + request.nextUrl.search, BACKEND_URL);
if (pathname === '/mcp' || pathname.startsWith('/mcp/')) {
// FastMCP's streamable app is mounted at /mcp with its route at "/", so the
// backend expects the trailing-slash form "/mcp/". Proxy the bare "/mcp" to
// "/mcp/" here — otherwise the Starlette Mount 307-redirects to
// http://backend:8000/mcp/, leaking the internal upstream host to the client
// (which then can't resolve it → ConnectionRefused). rewrite() keeps the
// client-facing URL as /mcp, so there's no client-visible redirect or loop.
const path = pathname === '/mcp' ? '/mcp/' : pathname;
const url = new URL(path + request.nextUrl.search, BACKEND_URL);
return NextResponse.rewrite(url);
}
if (pathname === '/health') {
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