curl_easy_recv(3) Library Functions Manual curl_easy_recv(3)
NAME
curl_easy_recv - receives raw data on an "easy" connection
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_recv(CURL *curl, void *buffer, size_t buflen, size_t *n);
DESCRIPTION
This function receives raw data from the established connection. You may
use it together with curl_easy_send(3) to implement custom protocols us-
ing 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 your buffer memory that gets populated by the re-
ceived data. buflen is the maximum amount of data you can get in that
buffer. The variable n points to receives the number of received 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_recv(3) does not work on connections that were created without
this option.
The call returns CURLE_AGAIN if there is no data to read - the socket is
used in non-blocking mode internally. When CURLE_AGAIN is returned, use
your operating system facilities like select(2) to wait for data. The
socket may be obtained using curl_easy_getinfo(3) with CURLINFO_AC-
TIVESOCKET(3).
Wait on the socket only if curl_easy_recv(3) returns CURLE_AGAIN. The
reason for this is libcurl or the SSL library may internally cache some
data, therefore you should call curl_easy_recv(3) until all data is read
which would include any cached data.
Furthermore if you wait on the socket and it tells you there is data to
read, curl_easy_recv(3) may return CURLE_AGAIN if the only data that was
read was for internal SSL processing, and no other data is available.
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) {
char buf[256];
size_t nread;
curl_socket_t sockfd;
/* Extract the socket from the curl handle - we need it for waiting. */
res = curl_easy_getinfo(curl, CURLINFO_ACTIVESOCKET, &sockfd);
/* read data */
res = curl_easy_recv(curl, buf, sizeof(buf), &nread);
}
}
}
AVAILABILITY
Added in curl 7.18.2
RETURN VALUE
On success, returns CURLE_OK, stores the received data into buffer, and
the number of bytes it actually read into *n.
On failure, returns the appropriate error code.
The function may return CURLE_AGAIN. In this case, use your operating
system facilities to wait until data can be read, and retry.
Reading exactly 0 bytes indicates a closed connection.
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_send(3),
curl_easy_setopt(3)
libcurl 2026-07-12 curl_easy_recv(3)
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