What is the curl error 52 "empty reply from server"?

Solution 1:

This can happen if curl is asked to do plain HTTP on a server that does HTTPS.

Example:

$ curl http://google.com:443
curl: (52) Empty reply from server

Solution 2:

Curl gives this error when there is no reply from a server, since it is an error for HTTP not to respond anything to a request.

I suspect the problem you have is that there is some piece of network infrastructure, like a firewall or a proxy, between you and the host in question. Getting this to work, therefore, will require you to discuss the issue with the people responsible for that hardware.

Solution 3:

It can happen when server does not respond due to 100% CPU or Memory utilization.

I got this error when I was trying to access sonarqube API and the server was not responding due to full memory utilization

Solution 4:

In my case it was server redirection; curl -L solved my problem.

Solution 5:

Another common reason for an empty reply is timeout. Check all the hops from where the cron job is running from to your PHP/target server. There's probably a device/server/nginx/LB/proxy somewhere along the line that terminates the request earlier than you expected, resulting in an empty response.