res.send(DataView) silently drops the view’s bytes #7510

res.send() recognizes DataView as binary via ArrayBuffer.isView(), but later calls Buffer.from(dataView), which produces an empty Buffer. A non-empty view therefore returns HTTP 200 with Content-Length: 0.

Reproduced with Express 5.2.1, current master (9efc29e), Node 24.14.1, Linux:

const express = require('express')
const app = express()
app.get('/', (req, res) => {
  const bytes = new Uint8Array([0, 1, 2, 3, 0])
  res.send(new DataView(bytes.buffer, 1, 3))
})
app.listen(3000)
// GET / returns an empty response instead of the bytes 01 02 03.

Expected: send exactly the DataView's byte range, with the correct Content-Length and ETag. The bug also occurs with ETags disabled and with cross-realm views.

This revisits the DataView-specific problem from #7433, which its author closed without merging. It is separate from bare ArrayBuffer support in #7362.

A focused patch is ready: detect DataViews with node:util.types.isDataView, then convert only their backing byte range. Buffer and other typed-array behavior remain unchanged, including the Uint16Array compatibility concern raised in #7433.

The patch adds 11 regression cases (eight fail before the fix); all 1,272 tests pass with npm run test-ci, and npm run lint passes. No dependency changes.

AI assistance was used for investigation, implementation, and local validation.