• Operating System: macOS 10.15.2
• Node Version: 12.8.1
• NPM Version: 6.10.2
• webpack Version: see package.json below
• webpack-dev-server Version: see package.json below
• Browser: N/A

• This is a bug
• This is a modification request

Code

// webpack.config.js module.exports = { devServer: { port: 4000, proxy: { '/api': 'http://localhost:3000' } } }

// index.js const express = require("express"); const app = express(); app.get("*", (req, res) => { res.send("foo"); }); // error handling middleware app.use((error, req, res, next) => { res.send("my custom error page"); }); app.listen(3000);

// package.json { "dependencies": { "express": "^4.17.1", "webpack": "^4.41.5", "webpack-cli": "^3.3.10", "webpack-dev-server": "^3.10.1" } }

Expected Behavior

1. Run node index.js
2. Run webpack-dev-server
3. curl "localhost:4000/api/%"

The response should be "my custom error page", indicating that the Express error handling middleware for the API server was used.

Actual Behavior

The response is URIError: Failed to decode param …, indicating that the Express error handling middleware for the API server was not used.

I would not expect webpack-dev-server to change how errors are handled for proxied requests.

Technical notes

I played around with using http-proxy-middleware on its own to see if the root issue was inside there, but using the following code, I could not reproduce this issue:

const httpProxyMiddleware = require("http-proxy-middleware"); const express = require("express"); { const app = express(); app.get("*", (req, res) => { res.send("foo"); }); app.use((error, req, res, next) => { res.send("my custom error page"); }); app.listen(3000); } { const app = express(); app.use(httpProxyMiddleware({ target: "http://localhost:3000" })); app.listen(4000); }

For Bugs; How can we reproduce the behavior?

See above

For Features; What is the motivation and/or use-case for the feature?

N/A