Thanks for looking at this. Perhaps you weren’t pasting the HTTP response into “socat”. After the six request lines are printed out, I enter the five lines between <HTTP response start> and <HTTP response end>; I didn’t really make this obvious. Otherwise, urlopen() hangs waiting for the response and read() never even gets called.

Here’s a Python-only HTTP server to demonstrate without needing “socat”. Run this in one terminal:

from http.server import HTTPServer, BaseHTTPRequestHandler
class Handler(BaseHTTPRequestHandler):
    protocol_version = "HTTP/1.1"
    def do_GET(self):
        self.send_response(200)
        self.send_header("Transfer-Encoding", "chunked")
        self.end_headers()
        self.wfile.write(b"0\r\n\r\n")
HTTPServer(("", 8000), Handler).serve_forever()

. . . and in another terminal:

from urllib.request import urlopen
with urlopen("http://localhost:8000") as response:
    response.read()
import gc; gc.collect()