Throughput of proxying compressed data with fetch and Deno.serve has deteriorated

[magurotuna]

Description

Let's take a look at the following simple script:

Deno.serve({ port: PORT }, async (_req) => {
  const url = `http://localhost:${UPSTREAM_PORT}`;
  const resp = await fetch(url);
  return new Response(resp.body, { headers: resp.headers });
});

This script fetches the data from the upstream server and just forwards it to the end client.

The problem is that only when the upstream server serves data in a compressed format (e.g. brotli), the throughput becomes significantly worse. This increased throughput can be observed in v1.45.3 and later.

If the upstream server serves uncompressed data, the throughput hasn't decreased.

Reproducer

I have created a repository which contains several components to measure the throughput in this specific setting.

https://github.com/magurotuna/deno_fetch_decompression_throughput

Additional info

Version: Deno 1.45.3 and later