How to Implement Persistent HTTP Connections with cURL in PHP?

When using the cURL library in PHP for HTTP requests, high interrupt rates can occur on network interfaces due to excessive connection openings. This is especially evident when making numerous requests to an external API or database server.

To address this issue, it is crucial to understand if cURL supports persistent connections and how to utilize them. Let's delve into the questions and answers provided:

1. Can cURL be made to open a keepalive session?

Yes, cURL supports persistent HTTP connections by default. By reusing the same cURL handle, connections can remain open and reused, eliminating the need for repeated connection setup and teardown.

2. What does it take to reuse a connection? -- is it as simple as reusing the cURL handle resource?

Reusing cURL connections is as simple as reusing the cURL handle resource. By maintaining the same handle throughout the script's execution, cURL will automatically manage connection persistence.

3. Do I need to set any special cURL options? (e.g. force HTTP 1.1?)

In most cases, no special cURL options need to be set for persistent connections. Default settings allow for HTTP/1.1 connections and connection reuse. However, if specific HTTP headers or settings are required, they can be configured using the CURLOPT_HTTPHEADER option.

4. Are there any gotchas with cURL keepalive connections? This script runs for hours at a time; will I be able to use a single connection, or will I need to periodically reconnect?

cURL handles keep-alive connections automatically. However, the server may impose limits (e.g., keep-alive timeouts or maximum requests). If the connection limit is exceeded, cURL will automatically open a new connection.