curl / libcurl / API / curl_easy_init

curl_ws_send - send websocket data


curl_ws_send - send WebSocket data


#include <curl/curl.h>
CURLcode curl_ws_send(CURL *curl, const void *buffer, size_t buflen,
                      size_t *sent, curl_off_t fragsize,
                      unsigned int flags);


This function call is EXPERIMENTAL.

Send the specific message fragment over an established WebSocket connection. The buffer holds the data to send and it is buflen number of payload bytes in that memory area.

sent is returned as the number of payload bytes actually sent.

To send a (huge) fragment using multiple calls with partial content per invoke, set the CURLWS_OFFSET bit and the fragsize argument as the total expected size for the first part, then set the CURLWS_OFFSET with a zero fragsize for the following parts.

If not sending a partial fragment or if this is raw mode, fragsize should be set to zero.

If CURLWS_RAW_MODE is enabled in CURLOPT_WS_OPTIONS, the flags argument should be set to 0.

To send a message consisting of multiple frames, set the CURLWS_CONT bit in all frames except the final one.



The buffer contains text data. Note that this makes a difference to WebSocket but libcurl itself does not make any verification of the content or precautions that you actually send valid UTF-8 content.


This is binary data.


This is not the final fragment of the message, which implies that there is another fragment coming as part of the same message where this bit is not set.


Close this transfer.


This is a ping.


This is a pong.


The provided data is only a partial fragment and there is more coming in a following call to curl_ws_send(). When sending only a piece of the fragment like this, the fragsize must be provided with the total expected fragment size in the first call and it needs to be zero in subsequent calls.


This functionality affects ws only


#include <string.h> /* for strlen */
const char *send_payload = "magic";
int main(void)
  size_t sent;
  CURLcode res;
  CURL *curl = curl_easy_init();
  curl_easy_setopt(curl, CURLOPT_URL, "wss://");
  curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 2L);
  res = curl_ws_send(curl, send_payload, strlen(send_payload), &sent, 0,
  return (int)res;


Added in curl 7.86.0

Return value

CURLE_OK (zero) means that the data was sent properly, non-zero means an error occurred as <curl/curl.h> defines. See the libcurl-errors man page for the full list with descriptions.

See also

curl_easy_getinfo(3), curl_easy_perform(3), curl_easy_setopt(3), curl_ws_recv(3), libcurl-ws(3)

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