decolua/9router · error

[antigravity]

Error message

[antigravity] ${error.message}

What it means

The antigravity MITM handler intercepts requests, remaps the model, forwards the body to the local router's /v1/chat/completions, and pipes the SSE response back. Any failure in that pipeline (body parse, model mapping, router fetch, SSE piping) is logged as '[antigravity] <message>'; for stream requests it emits an SSE error chunk so the SDK does not hang, otherwise a JSON error response.

Solutions

  1. Verify the 9Router gateway is running on the port the MITM proxy forwards to (default 20128).
  2. Check the error message in the dump file / logs — JSON parse errors mean the tool sent a non-JSON body; router errors mean check the router's own logs.
  3. Confirm the requested model has a mapping in the model-map config for antigravity.
  4. Retry the request; transient SSE disconnects are surfaced here but are often upstream-side.

Example fix

// before: router not running
fetch http://127.0.0.1:20128/v1/chat/completions -> ECONNREFUSED
// after: start the gateway first
PORT=20128 npm run start  # then retry the tool request
Defensive patterns

Strategy: try-catch

Validate before calling

// before routing, verify the gateway is up
const health = await fetch('http://127.0.0.1:20128/dashboard').then(r => r.ok).catch(() => false);
if (!health) throw new Error('Router gateway not running on :20128');
JSON.parse(bodyBuffer.toString()); // fail fast on malformed body

Try / catch

try {
  const routerRes = await fetchRouter(body, '/v1/chat/completions', req.headers);
  await pipeSSE(routerRes, res, dumper);
} catch (error) {
  err(`[antigravity] ${error.message}`);
  if (isStream && !res.headersSent) {
    res.writeHead(200, { 'Content-Type': 'text/event-stream' });
    res.end(`data: ${JSON.stringify({ error: { message: error.message } })}\r\n\r\n`);
  }
}

Prevention

When it happens

Trigger: intercept() called with malformed JSON body (JSON.parse throws), router not running on the local port (fetchRouter fails), model name with no mapping, or the SSE stream from the router aborts mid-pipe.

Common situations: Tool configured to point at the MITM proxy before `9router` server is started; antigravity CLI updated to a model id the mapper doesn't know; request body format changed upstream.

Related errors

AI-assisted analysis of decolua/9router@90b52e06ff (2026-08-30). Data as JSON: /api/errors/8775c0854e2d0458. Report an issue: GitHub.

Appendix: source

Thrown at src/mitm/handlers/antigravity.js:20

const { IS_DEV } = require("../config");
const { fetchRouter, pipeSSE } = require("./base");

/**
 * Intercept Antigravity request — forward Gemini body as-is to /v1/chat/completions.
 * Router auto-detects format via body.userAgent==="antigravity" + body.request.contents,
 * runs antigravity→openai→provider→openai→antigravity translators internally.
 */
async function intercept(req, res, bodyBuffer, mappedModel) {
  const dumper = IS_DEV ? createResponseDumper(req, "intercept-antigravity") : null;
  const isStream = req.url.includes(":streamGenerateContent");
  try {
    const body = JSON.parse(bodyBuffer.toString());
    if (body.model) body.model = mappedModel;

    const routerRes = await fetchRouter(body, "/v1/chat/completions", req.headers);
    await pipeSSE(routerRes, res, dumper);
  } catch (error) {
    err(`[antigravity] ${error.message}`);
    if (dumper) { dumper.writeChunk(`\n[ERROR] ${error.message}\n`); dumper.end(); }
    // For stream endpoint, send SSE error chunk so SDK doesn't hang waiting
    if (isStream) {
      if (!res.headersSent) res.writeHead(200, { "Content-Type": "text/event-stream" });
      res.end(`data: ${JSON.stringify({ error: { message: error.message } })}\r\n\r\n`);
    } else {
      if (!res.headersSent) res.writeHead(500, { "Content-Type": "application/json" });
      res.end(JSON.stringify({ error: { message: error.message, type: "mitm_error" } }));
    }
  }
}

module.exports = { intercept };

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