long chunk_bgn_callback(const void *transfer_info, void *ptr,
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CHUNK_BGN_FUNCTION,
DESCRIPTIONPass a pointer to your callback function, which should match the prototype shown above.
This callback function gets called by libcurl before a part of the stream is going to be transferred (if the transfer supports chunks).
The transfer_info pointer will point to a struct curl_fileinfo with details about the file that is about to get transferred.
This callback makes sense only when using the CURLOPT_WILDCARDMATCH(3) option for now.
The target of transfer_info parameter is a "feature depended" structure. For the FTP wildcard download, the target is curl_fileinfo structure (see curl/curl.h). The parameter ptr is a pointer given by CURLOPT_CHUNK_DATA(3). The parameter remains contains number of chunks remaining per the transfer. If the feature is not available, the parameter has zero value.
Return CURL_CHUNK_BGN_FUNC_OK if everything is fine, CURL_CHUNK_BGN_FUNC_SKIP if you want to skip the concrete chunk or CURL_CHUNK_BGN_FUNC_FAIL to tell libcurl to stop if some error occurred.