repo/core/curl/files/curl_easy_recv.3

.\" generated by cd2nroff 0.1 from curl_easy_recv.md
.TH curl_easy_recv 3 "2024-06-01" libcurl
.SH NAME
curl_easy_recv \- receives raw data on an "easy" connection
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_recv(CURL *curl, void *buffer, size_t buflen, size_t *n);
.fi
.SH DESCRIPTION
This function receives raw data from the established connection. You may use
it together with \fIcurl_easy_send(3)\fP 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.

\fBbuffer\fP is a pointer to your buffer memory that gets populated by the
received data. \fBbuflen\fP is the maximum amount of data you can get in that
buffer. The variable \fBn\fP points to receives the number of received bytes.

To establish the connection, set \fICURLOPT_CONNECT_ONLY(3)\fP option before
calling \fIcurl_easy_perform(3)\fP or \fIcurl_multi_perform(3)\fP. Note that
\fIcurl_easy_recv(3)\fP does not work on connections that were created without
this option.

The call returns \fBCURLE_AGAIN\fP if there is no data to read \- the socket is
used in non\-blocking mode internally. When \fBCURLE_AGAIN\fP is returned, use
your operating system facilities like \fIselect(2)\fP to wait for data. The
socket may be obtained using \fIcurl_easy_getinfo(3)\fP with
\fICURLINFO_ACTIVESOCKET(3)\fP.

Wait on the socket only if \fIcurl_easy_recv(3)\fP returns \fBCURLE_AGAIN\fP.
The reason for this is libcurl or the SSL library may internally cache some
data, therefore you should call \fIcurl_easy_recv(3)\fP 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,
\fIcurl_easy_recv(3)\fP may return \fBCURLE_AGAIN\fP if the only data that was
read was for internal SSL processing, and no other data is available.
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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;
      long 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);
    }
  }
}
.fi
.SH AVAILABILITY
Added in 7.18.2.
.SH RETURN VALUE
On success, returns \fBCURLE_OK\fP, stores the received data into
\fBbuffer\fP, and the number of bytes it actually read into \fB*n\fP.

On failure, returns the appropriate error code.

The function may return \fBCURLE_AGAIN\fP. 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 \fBCURLE_UNSUPPORTED_PROTOCOL\fP.
.SH SEE ALSO
.BR curl_easy_getinfo (3),
.BR curl_easy_perform (3),
.BR curl_easy_send (3),
.BR curl_easy_setopt (3)