How to Debug HTTPS Connectivity Issues with cURL When Only Headers Are Returned?

Debugging HTTPS Connectivity Issues with cURL

CURL's failure to retrieve content from an HTTPS site can be frustrating, especially when only headers are returned with a zero-length payload. To effectively address this issue, it's crucial to understand the potential causes and available solutions.

One common culprit is an outdated CA certificate bundle. CURL relies on this bundle for validating SSL certificates. To resolve this, download the latest CA certificate bundle from the official CURL website and specify its path using CURLOPT_CAINFO. This will ensure that CURL uses the most up-to-date certificate authority certificates.

Another potential issue is incorrect or outdated TLS protocols. Ensure that CURL is using the latest TLS protocols by setting CURLOPT_SSLVERSION to CURL_SSLVERSION_TLSv1_2 or higher. Additionally, verify that the web server you're connecting to supports the specified TLS protocol.

Firewall restrictions can also interfere with HTTPS connections. Temporarily disable any firewalls or proxies to isolate the issue. If disabling these resolves the problem, investigate firewall or proxy settings that may need to be adjusted.

If the above recommendations prove ineffective, consider updating the underlying cURL library to the latest version. Outdated versions may have known bugs or vulnerabilities that can hinder HTTPS connectivity.

Remember, disabling certificate verification or host validation (CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST) is a security risk and should be avoided. It's essential to prioritize security while troubleshooting connectivity issues.

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