WebSocket using callback

This example sets up a WebSocket download and handles all the incoming data in the standard write callback.

If your WebSocket need is more of a back-and-forth communication, you might want to rather use the dedicated send and receive functions shown in the simple WebSocket example.

#include <stdio.h>
#include <curl/curl.h>

static size_t write_cb(char *b, size_t size, size_t nitems, void *p)
{
  CURL *curl = p;
  size_t i;
  const struct curl_ws_frame *frame = curl_ws_meta(curl);
  fprintf(stderr, "Type: %s\n",
          frame->flags & CURLWS_BINARY ? "binary" : "text");
  fprintf(stderr, "Bytes: %u", (unsigned int)(nitems * size));
  for(i = 0; i < nitems; i++)
    fprintf(stderr, "%02x ", (unsigned char)b[i]);
  return nitems;
}

int main(void)
{
  CURL *curl;

  CURLcode result = curl_global_init(CURL_GLOBAL_ALL);
  if(result != CURLE_OK)
    return (int)result;

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "wss://example.com");

    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_cb);
    /* pass the easy handle to the callback */
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, curl);

    /* Perform the request, result gets the return code */
    result = curl_easy_perform(curl);
    /* Check for errors */
    if(result != CURLE_OK)
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(result));

    /* always cleanup */
    curl_easy_cleanup(curl);
  }
  curl_global_cleanup();
  return (int)result;
}