Error: Cannot set headers after they are sent to the client when using `devMiddleware.etag` and `static`

[mjames-c]

Bug report

Error using devServer. devMiddleware.etag: "weak" with devServer.static causes webpack-dev-server to crash with the following runtime error (webpack-dev-server@5.2.1)

  Error: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (node:_http_outgoing:655:11)
    at SendStream.redirect (<omitted>/node_modules/.pnpm/serve-static@1.16.2/node_modules/serve-static/index.js:202:9)
    at SendStream.emit (node:events:518:28)
    at SendStream.emit (node:domain:489:12)
    at SendStream.redirect (<omitted>/node_modules/.pnpm/send@0.19.0/node_modules/send/index.js:475:10)
    at onstat (<omitted>/node_modules/.pnpm/send@0.19.0/node_modules/send/index.js:722:41)
    at FSReqCallback.oncomplete (node:fs:198:5) {
  code: 'ERR_HTTP_HEADERS_SENT'
}

How Do We Reproduce?

1. update your webpack config with the following:

// webpack.config.js
{
  entry: './some/dir',
  devMiddleware: {
    etag: 'weak',
  },
  static: {
    directory: "./some/dir",
  },
}

2. spin up the dev server and then load the page in your browser (you may need to refresh once)

Please paste the results of npx webpack-cli info here, and mention other relevant information

  System:
    OS: Linux 6.8 Ubuntu 22.04.5 LTS 22.04.5 LTS (Jammy Jellyfish)
    CPU: (16) x64 Intel(R) Xeon(R) Platinum 8375C CPU @ 2.90GHz
    Memory: 102.13 GB / 123.81 GB
  Packages:
    babel-loader: ^8.0.6 => 8.2.4 
    css-loader: ^5.2.4 => 5.2.6 
    ejs-loader: ^0.5.0 => 0.5.0 
    file-loader: ^5.0.2 => 5.0.2 
    html-webpack-plugin: ~5.5.0 => 5.5.3 
    loader-runner: ^4.1.0 => 4.2.0 
    loader-utils: ^1.2.3 => 1.2.3 
    postcss-loader: ^5.2.0 => 5.2.0 
    raw-loader: ^4.0.0 => 4.0.2 
    svg-url-loader: ^3.0.3 => 3.0.3 
    svgo-loader: ^3.0.0 => 3.0.0 
    swc-loader: ^0.2.6 => 0.2.6 
    terser-webpack-plugin: ^5.2.4 => 5.3.9 
    thread-loader: ^4.0.2 => 4.0.2 
    ts-loader: ^9.4.4 => 9.4.4 
    url-loader: ^4.1.1 => 4.1.1 
    webfontloader: ^1.6.28 => 1.6.28 
    webpack: 5.99.9 => 5.99.9 
    webpack-cli: ^5.1.4 => 5.1.4 
    webpack-dev-server: ^5.2.1 => 5.2.1 
    webpackbar: ^5.0.0-3 => 5.0.0-3 

[mjames-c]

I discovered that the underlying issue is with overlapping paths between generated assets and static assets. If ya'll are ok with supporting that this could easily be fixed by wrapping the express static middleware in a res.headersSent check

[alexander-akait]

PR welcome