CURLOPT_READFUNCTION

CURLOPT_READFUNCTION is one of the accepted parameters for curl_setopt parameter #2.

CURLOPT_READFUNCTION — A callable with the following signature:

 The callback should return a `string`
 with a length equal or smaller than the amount of data requested,
 typically by reading it from the passed stream `resource`. It should
 return an empty `string` to signal `EOF`.
 Available as of cURL 7.1.0.

CURLOPT_READFUNCTION = 20012;