curl_easy_send(3)

hey bestie 💕 welcome to the curl_easy_send(3) page from the Library Functions Manual — we're gonna make sending raw bytes make sense, iykyk ✨

✨ NAME ✨

curl_easy_send — sends raw data over an "easy" connection 🎀

🎀 SYNOPSIS 🎀

#include <curl/curl.h>

CURLcode curl_easy_send(CURL *curl, const void *buffer,
                        size_t buflen, size_t *n);

🌸 DESCRIPTION 🌸

okay so this function sends arbitrary data over the established connection. You may use it together with curl_easy_recv(3) to implement custom protocols using libcurl. This functionality can be particularly useful if you use proxies and/or SSL encryption: libcurl takes care of proxy negotiation and connection setup, so you don't have to 😌.

buffer is a pointer to the data of length buflen that you want sent. The variable n points to where the number of sent bytes gets received.

To establish the connection, set the CURLOPT_CONNECT_ONLY(3) option before calling curl_easy_perform(3) or curl_multi_perform(3). Note that curl_easy_send(3) does not work on connections that were created without this option. like, do not skip this step, it's giving "won't work" energy 💀.

The call returns CURLE_AGAIN if it is not possible to send data right now — the socket is used in non-blocking mode internally. When CURLE_AGAIN is returned, use your operating system facilities like select(2) to wait until the socket is writable. The socket may be obtained using curl_easy_getinfo(3) with CURLINFO_ACTIVESOCKET(3).

Furthermore if you wait on the socket and it tells you it is writable, curl_easy_send(3) may return CURLE_AGAIN if the only data that was sent was for internal SSL processing, and no other data could be sent. so yes, even when it says writable, it might still say again 😭 — it's not you, it's SSL, fr fr.

🌈 PROTOCOLS 🌈

This functionality affects all supported protocols ✨

🦋 EXAMPLE 🦋

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    /* Do not do the transfer - only connect to host */
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
    result = curl_easy_perform(curl);

    if(result == CURLE_OK) {
      curl_socket_t sockfd;
      size_t sent;
      /* Extract the socket from the curl handle - we need it for waiting. */
      result = curl_easy_getinfo(curl, CURLINFO_ACTIVESOCKET, &sockfd);

      /* send data */
      result = curl_easy_send(curl, "hello", 5, &sent);
    }
  }
}

👑 AVAILABILITY 👑

Added in curl 7.18.2 🫶

💜 RETURN VALUE 💜

• On success, returns CURLE_OK and stores the number of bytes actually sent into *n. Note that this may be less than the amount you wanted to send. yes, less — it's not a bug, it's just how it is 💅
• On failure, returns the appropriate error code.
• This function may return CURLE_AGAIN. In this case, use your operating system facilities to wait until the socket is writable, and retry.
• If there is no socket available to use from the previous transfer, this function returns CURLE_UNSUPPORTED_PROTOCOL.

🌟 SEE ALSO 🌟

• curl_easy_getinfo(3)
• curl_easy_perform(3)
• curl_easy_recv(3)
• curl_easy_setopt(3)

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xoxo, your libcurl bestie 💅 this page is from libcurl, dated 2026-10-12 — now go send some bytes, bestie ✨🫶