Solve curl 52 empty reply from server

In a situation whereby the libcurl does not get any response from the server after a service request, a curl (52) empty reply from server will be triggered.

Our Linux Server Experts have helped numerous clients to solve curl related issues as part of our Server Support Services.

In this context, we shall look into what triggers this error and how to resolve it.

Why does curl (52) empty reply from server occurs?

We will see different scenarios of this error and how to resolve.

i. Origin: When an unsupported old version of libcurl is being used by  Curl.
Solution: Doing an upgrade of libcurl to a newer version will help resolve it.
ii. Origin: Some conflicting factors such as insufficient permissions in files or firewall could be behind this curl issue.
Solution: First, we have to troubleshoot the system to see if there are conflicting permission issues as well as the firewall rules to ensure that vital ports such as HTTP and HTTPS are active.
iii. Origin: In a case where a loopback request fails in WordPress, the website crashes.
Solution: To fix this, modify the "wp-config.php" file with the following attribute to set a cron job to maintain the Loopback request;

define(‘ALTERNATE_WP_CRON’, true);

iv. Origin: curl used with a port assigned to the url.
Solution: Resolve by assigning a different port.
v. Origin: When http is used instead of HTTPS.
Solution: It is best to use the HTTPS protocol.

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Curl is the command line tool which is responsible for running curl through a Server shell. curl runs under the libcurl library which relays response from the server whenever a request is called.

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