**************************************************************************
* _ _ ____ _
* Project ___| | | | _ \| |
* / __| | | | |_) | |
* | (__| |_| | _ <| |___
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*
* Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
*
* This software is licensed as described in the file COPYING, which
* you should have received as part of this distribution. The terms
* are also available at https://curl.haxx.se/docs/copyright.html.
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* You may opt to use, copy, modify, merge, publish, distribute and/or sell
* copies of the Software, and permit persons to whom the Software is
* furnished to do so, under the terms of the COPYING file.
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
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**************************************************************************

curl_easy_upkeep - Perform any connection upkeep checks. #include <curl/curl.h> "CURLcode curl_easy_upkeep(CURL *" handle ");" Some protocols have "connection upkeep" mechanisms. These mechanisms usually send some traffic on existing connections in order to keep them alive; this can prevent connections from being closed due to overzealous firewalls, for example. Currently the only protocol with a connection upkeep mechanism is HTTP/2: when the connection upkeep interval is exceeded and curl_easy_upkeep(3) is called, an HTTP/2 PING frame is sent on the connection. This function must be explicitly called in order to perform the upkeep work. The connection upkeep interval is set with CURLOPT_UPKEEP_INTERVAL_MS(3). Added in 7.62.0. On success, returns CURLE_OK. On failure, returns the appropriate error code.

CURL *curl = curl_easy_init();
if(curl) {
 /* Make a connection to an HTTP/2 server. */
 curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

 /* Set the interval to 30000ms / 30s */
 curl_easy_setopt(curl, CURLOPT_UPKEEP_INTERVAL_MS, 30000L);

 curl_easy_perform(curl);

 /* Perform more work here. */

 /* While the connection is being held open, curl_easy_upkeep() can be
 called. If curl_easy_upkeep() is called and the time since the last
 upkeep exceeds the interval, then an HTTP/2 PING is sent. */
 curl_easy_upkeep(curl);

 /* Perform more work here. */

 /* always cleanup */
 curl_easy_cleanup(curl);
}