关于 express.json() (body-parser) breaks http-proxy-middleware POST request

如果在express项目中同时使用了 express.json() 和 http-proxy-middleware 这两个中间件，那么带有payload的post请求就会报504 gateway timeout的error。

解决办法：

在 option onProxyReq 中加入对payload的处理

onProxyReq = (proxyReq, req: Request, res) => {
  if (!req.body || !Object.keys(req.body).length) {
    return;
  }

  const contentType = proxyReq.getHeader('Content-Type');
  const writeBody = (bodyData: string) => {
    proxyReq.setHeader('Content-Length', Buffer.byteLength(bodyData));
    proxyReq.write(bodyData);
  };

  if (contentType.toString().includes('application/json')) {
    writeBody(JSON.stringify(req.body));
  }

  if (contentType.toString().includes('application/x-www-form-urlencoded')) {
    writeBody(querystring.stringify(req.body));
  }
}