[HPM] Error occurred while proxying request [ECONNRESET]

Web development Jul 14, 2023

Here is the full error thrown from http-proxy-middleware

[HPM] Error occurred while proxying request localhost:3000/foo to http://localhost:3009/ [ECONNRESET](https://nodejs.org/api/errors.html#errors_common_system_errors)

Causes

TLDR;

When sending client --> proxy --> API server

Proxy transform body to JS object and it try to proxy that JS object so it fails.

HTTP is plain text protocol it accept ‘string’ as a body.

Solution

Transform that parsed JS object back to JSON string i.e.

[Client]        [Proxy in]    [Proxy out]     [API server]
JSON string --> JS Object --> JSON String --> JS Object

You can do that by adding a hook supported by http-proxy-middleware lib.

options.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);
  };
// ADD SUPPORT FOR
// contentType: 'application/json; charset:utf-8'
if (contentType.includes('application/json')) {
    writeBody(JSON.stringify(req.body));
  }
if (contentType === 'application/x-www-form-urlencoded') {
    writeBody(querystring.stringify(req.body));
  }
}