How to Properly Format CURLOPT_POSTFIELDS in cURL POST Requests?

CURLOPT_POSTFIELDS in Curl for POST Requests

When using curl to perform a POST request and specifying the CURLOPT_POSTFIELDS option, it is crucial to consider the appropriate format. For instance, consider posting two fields, "first" and "last":

"first=John&last=Smith"

String Formatting

If sending a string as the POST data, it should be URL-encoded to ensure proper character encoding. The following code demonstrates this:

$data = urlencode("first=John&last=Smith");

Array Formatting

However, if the POST data is an array, it must follow the "key => value" format:

$data = [
    'first' => 'John',
    'last' => 'Smith'
];

In this case, curl will automatically set the Content-Type header to "multipart/form-data".

Content-Type Header

Setting the Content-Type header explicitly is recommended for better compatibility. For example, to set it to "application/json":

curl_setopt($ch, CURLOPT_HTTPHEADER, ['Content-Type: application/json']);

Using http_build_query()

Alternatively, instead of manually building the query string, PHP's http_build_query() function can be used:

$query = http_build_query($data, '', '&');
curl_setopt($ch, CURLOPT_POSTFIELDS, $query);

This function handles the URL-encoding and proper key=value formatting seamlessly.

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