---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: curl_ws_send
Section: 3
Source: libcurl
See-also:
  - curl_easy_getinfo (3)
  - curl_easy_perform (3)
  - curl_easy_setopt (3)
  - curl_ws_recv (3)
  - libcurl-ws (3)
Protocol:
  - WS
Added-in: 7.86.0
---

# NAME

curl_ws_send - send WebSocket data

# SYNOPSIS

~~~c
#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);
~~~

# DESCRIPTION

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(3), 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.

Warning: while it is possible to invoke this function from a callback,
such a call is blocking in this situation, e.g. only returns after all data
has been sent or an error is encountered.

# FLAGS

## CURLWS_TEXT

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.

## CURLWS_BINARY

This is binary data.

## CURLWS_CONT

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.

## CURLWS_CLOSE

Close this transfer.

## CURLWS_PING

This is a ping.

## CURLWS_PONG

This is a pong.

## CURLWS_OFFSET

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.

# %PROTOCOLS%

# EXAMPLE

~~~c
#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://example.com/");
  curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 2L);
  curl_easy_perform(curl);
  res = curl_ws_send(curl, send_payload, strlen(send_payload), &sent, 0,
                     CURLWS_PING);
  curl_easy_cleanup(curl);
  return (int)res;
}
~~~

# %AVAILABILITY%

# 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(3) man
page for the full list with descriptions.