Version: Deno 2.1.5

TLDR: when http.request's opinions include proxy settings and options.path is a full URL (e.g., http://httpbin.org/200), the website that proxy server accesses should be http://httpbin.org/200, but in Deno it is http://httpbin.org/http://httpbin.org/200.

POC:

import axios from "axios";
const instance = axios.create({
  baseURL: "http://httpbin.org/",
  proxy: {
    protocol: "http",
    host: "127.0.0.1",
    port: 8892,
  },
});
try {
  const resp = await instance.get("/get");
  console.log("success", resp.config);
} catch (e) {
  console.log(e);
}

For convenience, I use Axios as demo, and related code is here. When I add a patch options.path = new URL(options.path).pathname;, it becomes correct.
This demo requires a http proxy running at port 8892 (such as Fiddler or mitmproxy).

In Node.JS, it can get http://httpbin.org/get correctly. In Deno, it gets a 404, while Fiddler shows it is requesting http://httpbin.org/http://httpbin.org/get