xref: /third_party/curl/docs/libcurl/curl_easy_recv.md

---
c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
SPDX-License-Identifier: curl
Title: curl_easy_recv
Section: 3
Source: libcurl
See-also:
  - curl_easy_getinfo (3)
  - curl_easy_perform (3)
  - curl_easy_send (3)
  - curl_easy_setopt (3)
---

# NAME

curl_easy_recv - receives raw data on an "easy" connection

# SYNOPSIS

~~~c
#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 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 your buffer memory that gets populated by the
received 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_ACTIVESOCKET(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.

# EXAMPLE

~~~c
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);
    }
  }
}
~~~

# AVAILABILITY

Added in 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**.