| 35 | * before the multi-second tool result. |
| 36 | */ |
| 37 | const startSeverableRelay = ( |
| 38 | originUrl: string, |
| 39 | ): Promise<{ |
| 40 | readonly url: (path: string) => string; |
| 41 | readonly severPostMidCall: () => Promise<void>; |
| 42 | readonly close: () => void; |
| 43 | }> => { |
| 44 | const origin = new URL(originUrl); |
| 45 | // The tools/call POST hop, captured the moment its response headers arrive |
| 46 | // (before any body: this is independent of whether the server emits a priming |
| 47 | // event, so the trigger is identical on fixed and unfixed servers). The sever |
| 48 | // must land AFTER the stream opened but BEFORE the tool result, so it fires a |
| 49 | // bounded grace after the headers — long enough for a priming event to have |
| 50 | // flushed and been read by the SDK, far short of the multi-second tool call. |
| 51 | const SEVER_GRACE_MS = 2_000; |
| 52 | let toolCallHop: { readonly upstream: ClientRequest; readonly res: ServerResponse } | null = null; |
| 53 | let onToolCallOpen: (() => void) | null = null; |
| 54 | const toolCallOpened = new Promise<void>((resolve) => { |
| 55 | onToolCallOpen = resolve; |
| 56 | }); |
| 57 | |
| 58 | const server = createServer((req, res) => { |
| 59 | // Detect the tools/call POST by its request body (initialize also returns |
| 60 | // SSE, so a plain content-type check would arm on the wrong stream). |
| 61 | const bodyChunks: Buffer[] = []; |
| 62 | let isToolCall = false; |
| 63 | req.on("data", (chunk: Buffer) => { |
| 64 | bodyChunks.push(chunk); |
| 65 | if (!isToolCall && Buffer.concat(bodyChunks).toString("utf8").includes('"tools/call"')) { |
| 66 | isToolCall = true; |
| 67 | } |
| 68 | }); |
| 69 | const upstream = httpRequest( |
| 70 | { |
| 71 | host: origin.hostname, |
| 72 | port: Number(origin.port), |
| 73 | path: req.url, |
| 74 | method: req.method, |
| 75 | headers: { ...req.headers, host: origin.host }, |
| 76 | }, |
| 77 | (upstreamRes) => { |
| 78 | res.writeHead(upstreamRes.statusCode ?? 502, upstreamRes.headers); |
| 79 | if ( |
| 80 | isToolCall && |
| 81 | (upstreamRes.headers["content-type"] ?? "").includes("text/event-stream") |
| 82 | ) { |
| 83 | toolCallHop = { upstream, res }; |
| 84 | onToolCallOpen?.(); |
| 85 | } |
| 86 | upstreamRes.pipe(res); |
| 87 | }, |
| 88 | ); |
| 89 | upstream.on("error", () => { |
| 90 | try { |
| 91 | res.destroy(); |
| 92 | } catch { |
| 93 | /* already torn down */ |
| 94 | } |