Have libcurl copy data to post
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_COPYPOSTFIELDS, char *data);
Pass a char * as parameter, which should be the full data to post in a HTTP POST operation. It behaves as the CURLOPT_POSTFIELDS(3) option, but the original data is instead copied by the library, allowing the application to overwrite the original data after setting this option.
Because data are copied, care must be taken when using this option in conjunction with CURLOPT_POSTFIELDSIZE(3) or CURLOPT_POSTFIELDSIZE_LARGE(3): If the size has not been set prior to CURLOPT_COPYPOSTFIELDS(3), the data is assumed to be a zero terminated string; else the stored size informs the library about the byte count to copy. In any case, the size must not be changed after CURLOPT_COPYPOSTFIELDS(3), unless another CURLOPT_POSTFIELDS(3) or CURLOPT_COPYPOSTFIELDS(3) option is issued.
Added in 7.17.1
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.