fix: forward error requests to the proxy (#2425)

Author: OliverJAsh

lib/Server.js

@@ -288,7 +288,7 @@ class Server {
  this.websocketProxies.push(proxyMiddleware);
  }
 
- this.app.use((req, res, next) => {
+ const handle = (req, res, next) => {
  if (typeof proxyConfigOrCallback === 'function') {
  const newProxyConfig = proxyConfigOrCallback();
 
@@ -319,7 +319,11 @@ class Server {
  } else {
  next();
  }
- });
+ };
+
+ this.app.use(handle);
+ // Also forward error requests to the proxy so it can handle them.
+ this.app.use((error, req, res, next) => handle(req, res, next));
  });
  }
 

test/server/proxy-option.test.js

@@ -326,6 +326,19 @@ describe('proxy option', () => {
  // Parse application/json
  proxy.use(bodyParser.json());
 
+ // This forces Express to try to decode URLs, which is needed for the test
+ // associated with the middleware below.
+ proxy.all('*', (_req, res, next) => {
+ next();
+ });
+ // We must define all 4 params in order for this to be detected as an
+ // error handling middleware.
+ // eslint-disable-next-line no-unused-vars
+ proxy.use((error, proxyReq, res, next) => {
+ res.status(500);
+ res.send('error from proxy');
+ });
+
  proxy.get('/get', (proxyReq, res) => {
  res.send('GET method from proxy');
  });
@@ -372,6 +385,10 @@ describe('proxy option', () => {
  });
  });
 
+ it('errors', (done) => {
+ req.get('/%').expect(500, 'error from proxy', done);
+ });
+
  it('GET method', (done) => {
  req.get('/get').expect(200, 'GET method from proxy', done);
  });