Retrieving HTTP Response Headers and Body with PHP cURL

When working with web services or APIs, it’s often necessary to retrieve both the headers and body of an HTTP response. In PHP, the cURL library provides a powerful way to make HTTP requests and retrieve responses. However, retrieving both headers and body in a single request can be challenging.

In this tutorial, we’ll explore how to use PHP cURL to retrieve both HTTP response headers and body in a single request.

Understanding cURL Options

To achieve our goal, we need to understand the following cURL options:

• CURLOPT_RETURNTRANSFER: This option allows us to return the transfer as a string instead of outputting it directly.
• CURLOPT_HEADERFUNCTION: This option sets a callback function that will be called for each header line received.

Using CURLOPT_HEADERFUNCTION

The most reliable way to retrieve both headers and body is by using the CURLOPT_HEADERFUNCTION option. This option allows us to set a callback function that will be called for each header line received.

Here’s an example code snippet:

$ch = curl_init();
$headers = [];
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

// Set the callback function for headers
curl_setopt($ch, CURLOPT_HEADERFUNCTION,
  function($curl, $header) use (&$headers)
  {
    $len = strlen($header);
    $header = explode(':', $header, 2);
    if (count($header) < 2) // ignore invalid headers
      return $len;

    $headers[strtolower(trim($header[0]))][] = trim($header[1]);
    
    return $len;
  }
);

$data = curl_exec($ch);
print_r($headers);

In this example, the callback function is defined as an anonymous function that takes two arguments: $curl and $header. The function explodes the header line into a key-value pair and stores it in the $headers array.

Retrieving the Body

After executing the cURL request using curl_exec(), we can retrieve the body of the response as a string. Note that the body will not include the headers, which are handled separately by the callback function.

$body = curl_exec($ch);

In this example, $body contains the response body as a string.

Best Practices

When working with cURL and HTTP responses, it’s essential to follow best practices:

• Always set CURLOPT_RETURNTRANSFER to ensure that the transfer is returned as a string.
• Use CURLOPT_HEADERFUNCTION to handle headers separately from the body.
• Avoid using CURLOPT_HEADER option, as it can lead to parsing issues and security vulnerabilities.

By following these guidelines and using the CURLOPT_HEADERFUNCTION option, you can reliably retrieve both HTTP response headers and body in a single request with PHP cURL.