Where is the auto-decompression behavior documented? #1819

It is in the Fetch Standard: HTTP-network fetch invokes handling content codings on the received bytes. For node-fetch, the README also documents compress: true as the default and compress: false as its extension to disable decoding. You can inspect the actual bytes with:

import fetch from 'node-fetch';

async function readBothWays(url) {
  const decoded = await fetch(url);
  const plainBytes = Buffer.from(await decoded.arrayBuffer());

  const encoded = await fetch(url, { compress: false });
  const wireBytes = Buffer.from(await encoded.arrayBuffer());
  return { plainBytes, wireBytes };
}

With node-fetch 3.3.2 and a local server that deliberately sent compressed bodies, I verified decoding for gzip, deflate, and Brotli. The second request retained the compressed bytes for each. compress: false also stops node-fetch adding its automatic Accept-Encoding header; what the server sends still determines whether those bytes are compressed. Calling text() on compressed bytes can obscure this distinction, so compare buffers. node-fetch options.