curl_easy_send(3) Library Functions Manual curl_easy_send(3)
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
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.
buffer is a pointer to the data of length buflen that you want sent. The
variable n points to receives the number of sent bytes.
To establish the connection, set 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.
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 se-
lect(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.
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
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);
res = curl_easy_perform(curl);
if(res == CURLE_OK) {
curl_socket_t sockfd;
size_t sent;
/* Extract the socket from the curl handle - we need it for waiting. */
res = curl_easy_getinfo(curl, CURLINFO_ACTIVESOCKET, &sockfd);
/* send data */
res = 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.
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)
libcurl 2026-07-12 curl_easy_send(3)
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