easy:SetOpt_InFileSize_Large(filesize)
filesize should be used to tell
libcurl what the expected size of the input file is. This value must be passed
as a curl_off_t.
For uploading using SCP, this option or #CURLOPT_INFILESIZE is
mandatory.
To unset this value again, get it to -1.
When sending emails using SMTP, this command can be used to specify the optional SIZE parameter for the MAIL FROM command.
This option does not limit how much data libcurl will actually send, as that is controlled entirely by what the read callback returns, but telling one value and sending a different amount may lead to errors.