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 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.

PROTOCOLS
       All

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;
             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.

SEE ALSO
       curl_easy_getinfo(3), curl_easy_perform(3), curl_easy_send(3),
       curl_easy_setopt(3)

libcurl                          April 26 2024               curl_easy_recv(3)