curl / libcurl / API / curl_easy_send

curl_easy_send - sends raw data over a connection


curl_easy_send - sends raw data over an "easy" connection


#include <curl/curl.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 to implement custom protocols using libcurl. This functionality can be particularly useful if you use proxies and/or SSL encryption: libcurl takes care of proxy negotiation and connection setup.

buffer is a pointer to the data of length buflen that you want sent. The variable n points to receives the number of sent bytes.

To establish the connection, set CURLOPT_CONNECT_ONLY option before calling curl_easy_perform or curl_multi_perform. Note that curl_easy_send does not work on connections that were created without this option.

The call returns CURLE_AGAIN if it is not possible to send data right now - the socket is used in non-blocking mode internally. When CURLE_AGAIN is returned, use your operating system facilities like select(2) to wait until the socket is writable. The socket may be obtained using curl_easy_getinfo with CURLINFO_ACTIVESOCKET.

Furthermore if you wait on the socket and it tells you it is writable, curl_easy_send may return CURLE_AGAIN if the only data that was sent was for internal SSL processing, and no other data could be sent.


This functionality affects all supported protocols


int main(void)
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "");
    /* Do not do the transfer - only connect to host */
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
    res = curl_easy_perform(curl);
    if(res == CURLE_OK) {
      long sockfd;
      size_t sent;
      /* Extract the socket from the curl handle - we need it for waiting. */
      res = curl_easy_getinfo(curl, CURLINFO_ACTIVESOCKET, &sockfd);
      /* send data */
      res = curl_easy_send(curl, "hello", 5, &sent);


Added in curl 7.18.2

Return value

On success, returns CURLE_OK and stores the number of bytes actually sent into *n. Note that this may be less than the amount you wanted to send.

On failure, returns the appropriate error code.

This function may return CURLE_AGAIN. In this case, use your operating system facilities to wait until the socket is writable, and retry.

If there is no socket available to use from the previous transfer, this function returns CURLE_UNSUPPORTED_PROTOCOL.

See also

curl_easy_getinfo(3), curl_easy_perform(3), curl_easy_recv(3), curl_easy_setopt(3)

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