Sending trailers

"Trailers" is an HTTP/1 feature where headers can be passed onat the end ofa transfer. This callback is used for when you want to send trailers withcurl after an upload has been performed. An upload in the form of a chunkedencoded POST.

The callback set withCURLOPT_TRAILERFUNCTION is called and the function canthen append headers to a list. One or many. When done, libcurl sends off thoseas trailers to the server.