Sends raw data over an "easy" connection
#include <curl/easy.h>
CURLcode curl_easy_send( CURL *curl, const void *buffer, size_t buflen, size_t *n);
This function sends arbitrary data over the established connection. You may use it together with curl_easy_recv(3) to implement custom protocols using libcurl. This functionality can be particularly useful if you use proxies and/or SSL encryption: libcurl will take care of proxy negotiation and connection set-up.
buffer is a pointer to the data of length buflen that you want sent. The variable n points to will receive the number of sent bytes.
To establish the connection, set CURLOPT_CONNECT_ONLY(3) option before calling curl_easy_perform(3). Note that curl_easy_send(3) will not work on connections that were created without this option.
You must ensure that the socket is writable before calling curl_easy_send(3), otherwise the call will return CURLE_AGAIN - the socket is used in non-blocking mode internally. Use curl_easy_getinfo(3) with CURLINFO_LASTSOCKET to obtain the socket; use your operating system facilities like select(2) to check if it can be written to.
Added in 7.18.2.
On success, returns CURLE_OK and stores the number of bytes actually sent into *n. Note that this may very well be less than the amount you wanted to send.
On failure, returns the appropriate error code.
If there's no socket available to use from the previous transfer, this function returns CURLE_UNSUPPORTED_PROTOCOL.
See sendrecv.c in docs/examples directory for usage example.