Why am I getting a \'CURL ERROR: Recv failure: Connection reset by peer\' error in my PHP Curl requests?

CURL Error: Recv Failure: Connection Reset by Peer in PHP Curl

When attempting to establish a connection to a remote server via CURL in PHP, an error message of "CURL ERROR: Recv failure: Connection reset by peer" may arise. This error typically occurs when the server has abruptly terminated the connection, resulting in a lost or incomplete data transfer.

Underlying Causes

Several factors can contribute to this error:

1. TCP/IP Issues: Network configuration problems, such as firewall settings, can prevent proper connection establishment, causing the server to reset the connection.


2. Kernel Bug: Kernel versions, particularly in older Linux distributions, may contain bugs that interfere with TCP window scaling, leading to connection disruptions.


3. PHP & CURL Bugs: Vulnerabilities in PHP or CURL versions can also cause connection issues. Upgrading to the latest versions is recommended.


4. Incorrect MTU: Modifying the Maximum Transmission Unit (MTU) size on the network can disrupt communication, triggering the "Connection reset by peer" error.


5. Firewall Interference: Firewalls can block or limit connections to specific ports, such as port 80. Verify that the firewall settings permit communication through the required port.

Troubleshooting and Resolution

To address this error, consider the following solutions:

• Update System and Components: Ensure that your operating system, PHP, and CURL are up-to-date to mitigate potential bugs or vulnerabilities.


• Adjust MTU: Reset the MTU size to the default value of 1500 bytes or consult with your network administrator for the optimal MTU setting.


• Disable SSL Verification: If the remote URL uses HTTPS, disable SSL verification in the CURL settings using:

  curl_setopt($c, CURLOPT_SSL_VERIFYPEER, false);
  curl_setopt($c, CURLOPT_SSL_VERIFYHOST, false);

• Test Connectivity: Attempt the connection from a different server or use online testing tools to verify the network and remote server connectivity.


• Verify Firewall Settings: Ensure that the firewall does not block communication with the remote server on the required port.


• Resolve Kernel Bugs: Upgrade to a kernel version that has resolved any known bugs affecting TCP window scaling.

By addressing these potential causes and implementing appropriate troubleshooting steps, you can resolve the "CURL ERROR: Recv failure: Connection reset by peer" issue and establish a stable connection to the remote server.

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