Antigravity to JEB 5.37 Decompiler MCP Server Bridge

jeb-antigravity-mcp-bridge.js

/*
    - Bridges JEB's legacy HTTP+SSE MCP to Antigravity's Streamable HTTP MCP.
    - Fixes JEB's incorrect MCP protocol implementation (lines 31-33)
    
    - Run with:
    node jeb-antigravity-mcp-bridge.js

    - Example config for Antigravity's mcp_config.json (you point AG to the proxy):
        {
          "mcpServers": {
            "jeb-proxy": {
              "command": "npx",
              "args": [
                "-y",
                "mcp-remote",
                "http://localhost:8426/mcp"
              ]
            }
          }
        }
*/

const http = require('http');

const JEB_PORT = 8425;
const PROXY_PORT = 8426;

http.createServer((req, res) => {
    let targetPath = req.url;

    if (req.method === 'POST' && req.url.includes('sessionId=')) {
        targetPath = req.url.replace('/mcp?', '/?');
    }

    console.log(`\n[Antigravity -> Proxy] ${req.method} ${req.url}`);
    console.log(`[Proxy -> JEB] Forwarding to: ${targetPath}`);

    const doProxy = (headers, bodyBuffer) => {
        const proxyReq = http.request({
            hostname: 'localhost',
            port: JEB_PORT,
            path: targetPath,
            method: req.method,
            headers: headers
        }, (proxyRes) => {
            res.writeHead(proxyRes.statusCode, proxyRes.headers);
            console.log(`[JEB -> Proxy] Response Status: ${proxyRes.statusCode}`);

            proxyRes.on('data', (chunk) => {
                let data = chunk.toString();
                // Fix the SSE endpoint URL
                if (data.includes('endpoint') && data.includes('sessionId=')) {
                    data = data.replace(/http:\/\/[a-zA-Z0-9\.:]+\/\?sessionId=/g, '?sessionId=');
                }
                res.write(data);
            });

            proxyRes.on('end', () => res.end());
        });

        proxyReq.on('error', (e) => {
            console.error('[Proxy Error]', e.message);
            res.writeHead(502).end();
        });

        if (bodyBuffer) proxyReq.write(bodyBuffer);
        proxyReq.end();
    };

    // If it's a POST request, intercept the body to clean the JSON
    if (req.method === 'POST') {
        let bodyChunks = [];
        req.on('data', chunk => bodyChunks.push(chunk));
        req.on('end', () => {
            let buffer = Buffer.concat(bodyChunks);
            try {
                let json = JSON.parse(buffer.toString('utf8'));
                
                // If this is the initialize request, strip the incompatible capabilities
                if (json.method === 'initialize' && json.params?.capabilities?.elicitation) {
                    console.log(`[Proxy] *** Intercepted 'initialize' payload! Stripping incompatible 'elicitation' capability... ***`);
                    delete json.params.capabilities.elicitation; // Remove the field JEB crashes on
                    
                    // Repackage the payload and update the Content-Length header
                    buffer = Buffer.from(JSON.stringify(json), 'utf8');
                    req.headers['content-length'] = buffer.length; 
                }
            } catch (e) {
                // Ignore parse errors, just pass data through
            }
            doProxy(req.headers, buffer);
        });
    } else {
        // GET requests (like SSE streams) have no body, just pass through
        doProxy(req.headers, null);
    }

}).listen(PROXY_PORT, () => {
    console.log(`Proxy running! Point Antigravity to: http://localhost:${PROXY_PORT}/mcp`);
});