curl: (52) Empty reply from server

curl: (52) Empty reply from server means the TCP connection was established, curl sent its request, and the server closed the connection without sending any HTTP response, not even a status line. curl exits with code 52 (CURLE_GOT_NOTHING). The problem is on the server side or in something in between: look at the server's and the proxy's logs, and check that you are talking HTTP to an HTTP port and HTTPS to an HTTPS port.

Reproduce the error

A TCP server on port 4880 that reads the request and closes the socket without answering:

node -e 'require("net").createServer((s) => s.once("data", () => s.end())).listen(4880, "127.0.0.1"); setTimeout(() => process.exit(0), 4000)' &
sleep 1
curl -sS http://127.0.0.1:4880/
echo "exit status: $?"
wait

curl: (52) Empty reply from server
exit status: 52

Compare with similar errors

Find out where it breaks

curl -v http://HOST:PORT/path

In the verbose output, Connected to shows that TCP worked; for HTTPS, the SSL connection using line shows the TLS handshake finished. If the last line before the error is the request you sent (> GET /path HTTP/1.1), the server or a proxy closed the connection after reading it.

Common checks:

• Scheme and port: curl http://host:443/ sends plain HTTP to a TLS port. Use https://.
• Server logs: an application that crashes on a specific request (large header, unexpected body) produces exactly this error.
• Proxies: unset http_proxy/https_proxy or use --noproxy '*' to rule out a proxy that drops the request.
• Containers: a server bound to 127.0.0.1 inside a container is unreachable through the published port; bind to 0.0.0.0.