Tribblix: manual page: curl_ws

curl_ws_send(3) Introduction to Library Functions curl_ws_send(3)

NAME

curl_ws_send - send WebSocket data

SYNOPSIS

#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 chunk over an established WebSocket
connection. buffer must point to a valid memory location containing
(at least) buflen bytes of payload memory.

sent is set to the number of payload bytes actually sent. If the
return value is CURLE_OK but sent is less than the given buflen,
libcurl was unable to consume the complete payload in a single call.
In this case the application must call this function again until all
payload is processed. buffer and buflen must be updated on every
following invocation to only point to the remaining piece of the
payload.

fragsize should always be set to zero unless a (huge) frame shall be
sent using multiple calls with partial content per call explicitly.
In that case you must set the CURLWS_OFFSET bit and set the fragsize
as documented in the section on CURLWS_OFFSET below.

flags must contain at least one flag indicating the type of the
message. To send a fragmented message consisting of multiple frames,
additionally set the CURLWS_CONT bit in all frames except the final
one.

For more details on the supported flags see below and in
curl_ws_meta(3).

If CURLWS_RAW_MODE is enabled in CURLOPT_WS_OPTIONS(3), the flags
argument should be set to 0.

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

Supports all flags documented in curl_ws_meta(3) and additionally the
following flags.

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

PROTOCOLS

This functionality affects ws only

EXAMPLE

#include <string.h> /* for strlen */

int main(void)
{
const char *buffer = "PAYLOAD";
size_t offset = 0;
CURLcode res = CURLE_OK;
CURL *curl = curl_easy_init();

curl_easy_setopt(curl, CURLOPT_URL, "wss://example.com/");
curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 2L);
/* start HTTPS connection and upgrade to WSS, then return control */
curl_easy_perform(curl);

while(!res) {
size_t sent;
res = curl_ws_send(curl, buffer + offset, strlen(buffer) - offset, &sent,
0, CURLWS_TEXT);
offset += sent;

if(res == CURLE_OK) {
if(offset == strlen(buffer))
break; /* finished sending */
}

if(res == CURLE_AGAIN)
/* in real application: wait for socket here, e.g. using select() */
res = CURLE_OK;
}

curl_easy_cleanup(curl);
return (int)res;
}

AVAILABILITY

Added in curl 7.86.0

RETURN VALUE

This function returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3). If CURLOPT_ERRORBUFFER(3) was set
with curl_easy_setopt(3) there can be an error message stored in the
error buffer when non-zero is returned.

Instead of blocking, the function returns CURLE_AGAIN. The correct
behavior is then to wait for the socket to signal readability before
calling this function again.

Any other non-zero return value indicates an error. See the
libcurl-errors(3) man page for the full list with descriptions.