Bug (fixes #7510)

res.send detects DataView via ArrayBuffer.isView() and sets the binary Content-Type, but the chunk then falls through to Buffer.from(chunk, encoding). Buffer.from(dataView) returns an empty Buffer, so a DataView-bodied response went out as 200 with Content-Length: 0 and no payload.

Repro:

app.get('/', (req, res) => {
  const bytes = new Uint8Array([0, 1, 2, 3, 0])
  res.send(new DataView(bytes.buffer, 1, 3))
})
// GET / returned empty instead of the three bytes 01 02 03

Fix

Convert a DataView to a Buffer over its exact byte range right after the Content-Type decision, using Buffer.from(buffer, byteOffset, byteLength). Typed arrays (Uint8Array, Uint16Array, …) continue through the existing fast path untouched, so the Uint16Array compat raised on #7433 is preserved.

if (chunk instanceof DataView) {
  chunk = Buffer.from(chunk.buffer, chunk.byteOffset, chunk.byteLength);
  encoding = undefined;
}

Tests

Two regression tests added to test/res.send.js:

1. DataView over the whole buffer — asserts Content-Length: 3 and body "hey".
2. DataView with offset and length — [0xff, 0x68, 0x65, 0x79, 0xff] with new DataView(buf, 1, 3) — asserts the surrounding 0xff bytes don't leak into the response.

All 1263 existing tests still pass. npm run lint is clean.