CURLOPT_CONNECT_ONLY(3)

hey bestie 💖 welcome to CURLOPT_CONNECT_ONLY from curl’s Library Functions Manual, section 3. this is the “stop when connected to target server” page, and it’s lowkey iconic for connection setup vibes ✨

🌸 NAME 🌸

CURLOPT_CONNECT_ONLY — stop when connected to target server.

✨ SYNOPSIS ✨

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_ONLY, long only);

💖 DESCRIPTION 💖

okay so the move is: 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. periodt.

• CURLOPT_CONNECT_ONLY — pass a long; 1 means do the proxy auth + connection setup, skip the data transfer, and return.

the option can be used to simply test a connection to a server, but it’s 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. iykyk 🫶

since 7.86.0, this option can be set to '2', and if WebSocket is used, libcurl performs the request and reads all response headers before handing over control to the application. for other protocols, the behavior of '2' is undefined.

⚠️ heads up bestie: for non-WebSocket protocols, the behavior of '2' is undefined — do not rely on that vibe.

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. literally no cap 🧚

🎀 DEFAULT 🎀

0

🦋 PROTOCOLS 🦋

this functionality affects all supported protocols 🌈

💅 EXAMPLE 💅

here’s the whole little program, copy-paste ready bestie:

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

🌈 HISTORY 🌈

WS and WSS support added in 7.86.0. that’s the lore 💜

⭐ AVAILABILITY ⭐

added in curl 7.15.2 — she’s been around 👑

🔥 RETURN VALUE 🔥

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

🍓 SEE ALSO 🍓

• CURLOPT_HTTPPROXYTUNNEL(3)
• CURLOPT_VERBOSE(3)
• curl_easy_recv(3)
• curl_easy_send(3)

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okay that’s the whole page, bestie — source: libcurl, dated 2026-10-12 🫶💅 go slay your connection setup ✨