CURLOPT_CONNECT_ONLY(3) Library Functions Manual CURLOPT_CONNECT_ONLY(3)

CURLOPT_CONNECT_ONLY - stop when connected to target server

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_ONLY, long only);

Pass a long. If the parameter equals 1, it tells the library to perform all the required proxy authentication and connection setup, but no data transfer, and then return.

The option can be used to simply test a connection to a server, but is more useful when used with the CURLINFO_ACTIVESOCKET(3) option to curl_easy_getinfo(3) as the library can set up the connection and then the application can obtain the most recently used socket for special data transfers.

Since 7.86.0, this option can be set to '2' and if HTTP or WebSocket are used, libcurl performs the request and reads all response headers before handing over control to the application.

Transfers marked connect only do not reuse any existing connections and connections marked connect only are not allowed to get reused.

If the connect only transfer is done using the multi interface, the particular easy handle must remain added to the multi handle for as long as the application wants to use it. Once it has been removed with curl_multi_remove_handle(3), curl_easy_send(3) and curl_easy_recv(3) do not function.

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int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode ret;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
    ret = curl_easy_perform(curl);
    if(ret == CURLE_OK) {
      /* only connected! */
    }
  }
}

Added in 7.15.2. WS and WSS support added in 7.86.0.

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

CURLOPT_HTTPPROXYTUNNEL(3), CURLOPT_VERBOSE(3), curl_easy_recv(3), curl_easy_send(3)

2024-05-22 libcurl