Persistent HTTP Connections with PHP Curl

When using the Curl library for HTTP requests, maintaining persistent connections can significantly improve performance by reducing connection overhead. This article explores how to establish and manage keepalive connections using Curl.

Reusing Curl Handles for Persistent Connections

By default, Curl reuses connections for subsequent requests when the same Curl handle is used. This means that you can reuse the handle for multiple requests without needing to re-establish the connection each time.

Setting Keepalive Options

Curl does not require any special options to enable keepalive connections. However, if you need to customize the keepalive parameters, you can use the following options:

• CURLOPT_FORBID_REUSE: Set to TRUE to prevent connection reuse.
• CURLOPT_HTTPHEADER: Allows you to specify additional headers, including the Connection: keep-alive header to explicitly request keepalive.

Gotchas

While Curl manages keepalive connections automatically, there are a few potential pitfalls:

• Server Keepalive Timeout: Servers may set keepalive timeouts, which will close the connection after a period of inactivity or a certain number of requests. Curl will automatically reopen the connection when this happens.
• Curl Version: Older versions of Curl may not fully support HTTP 1.1 keepalive properly. Ensure you are using an up-to-date Curl version.

Conclusion

By reusing Curl handles and considering the options mentioned above, you can establish and maintain keepalive connections with your HTTP requests. This can significantly reduce overhead and improve performance, especially when working with high-frequency requests.