Do Not Proxy Request When Custom Router Throws Error

[bforbis]

I am trying to take complete control of the target routing. I would like the proxied request to be aborted before the client socket is opened if my router was unable to determine a target host. Is this possible to do?

createProxyMiddleware({
  // target is a required parameter
  target: 'do-not-use', 
  router: (req) => {
    try {
      ...
      return target;
    }
    catch (err) {
      req.res.sendStatus(500);
    }
  },
});

The current http-proxy code will still use the original target "do-not-use". I would rather the proxy just abort the request entirely if the router function does not return a target.

[chimurai]

Currently it is not possible.

How do you use the http-proxy-middleware?

Via webpack-dev-server (create-react-app, angular-cli, vue-cli...)? Or do you mount it in your own express or express-like server?

[bforbis]

This is in an express server. Looking through the code in prepareProxyRequest, it seems like there should be some error handling there to catch errors.

The two error return types I can think of for a custom router causes two separate issues.

1. Return empty string from router: This causes the proxy to use the default target "do-not-use", which will throw a socket connection error
2. Throw an error in the router: This causes an uncaught promise rejection error at the NodeJS level, since there is no error handling in the proxy-middleware code.

[chimurai]

You could use express's error handling: https://expressjs.com/en/guide/error-handling.html

Basically throw an error in the router and use a default middleware error handler to handle all sorts of errors from middlewares.

import * as express from 'express';
import { createProxyMiddleware } from 'http-proxy-middleware';

const app = express();

const proxy = createProxyMiddleware({
  // target is a required parameter
  target: 'do-not-use', 
  router: (req) => {
    try {
      ...
      return target;
    }
    catch (err) {
      throw err;
    }
  },
});

app.use(proxy);
app.use((err, req, res, next) => {
  res.send(500, 'oops some routing went wrong')
});

[bforbis]

I tried this out, but I am still getting UnhandledPromiseRejection errors logged to the console. Should the code that calls prepareProxyRequest catch the error and then pass it to the next() function?

try {
  const activeProxyOptions = await this.prepareProxyRequest(req);
  this.proxy.web(req, res, activeProxyOptions);
}
catch(err) {
  next(err);
}

[chimurai]

Was hoping that UnhandledPromiseRejection wouldn't happen.

Your suggestion to solve it makes sense than.

Do you mind creating PR with your suggestion to fix this issue?