quickjs-tart

quickjs-based runtime for wallet-core logic
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curl_easy_upkeep.md (2368B)

      1 ---
      2 c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
      3 SPDX-License-Identifier: curl
      4 Title: curl_easy_upkeep
      5 Section: 3
      6 Source: libcurl
      7 See-also:
      8   - CURLOPT_TCP_KEEPALIVE (3)
      9   - CURLOPT_TCP_KEEPIDLE (3)
     10 Protocol:
     11   - All
     12 Added-in: 7.62.0
     13 ---
     14 
     15 # NAME
     16 
     17 curl_easy_upkeep - keep existing connections alive
     18 
     19 # SYNOPSIS
     20 
     21 ~~~c
     22 #include <curl/curl.h>
     23 
     24 CURLcode curl_easy_upkeep(CURL *handle);
     25 ~~~
     26 
     27 # DESCRIPTION
     28 
     29 Some protocols have "connection upkeep" mechanisms. These mechanisms usually
     30 send some traffic on existing connections in order to keep them alive; this
     31 can prevent connections from being closed due to overzealous firewalls, for
     32 example.
     33 
     34 For HTTP/2 we have an upkeep mechanism: when
     35 the connection upkeep interval is exceeded and curl_easy_upkeep(3)
     36 is called, an HTTP/2 PING frame is sent on the connection.
     37 
     38 For MQTT the upkeep interval defines when to send ping requests to prevent the
     39 server from disconnecting.
     40 
     41 This function must be explicitly called in order to perform the upkeep work.
     42 The connection upkeep interval is set with
     43 CURLOPT_UPKEEP_INTERVAL_MS(3).
     44 
     45 If you call this function on an easy handle that uses a shared connection cache
     46 then upkeep is performed on the connections in that cache, even if those
     47 connections were never used by the easy handle. (Added in 8.10.0)
     48 
     49 # %PROTOCOLS%
     50 
     51 # EXAMPLE
     52 
     53 ~~~c
     54 int main(void)
     55 {
     56   CURL *curl = curl_easy_init();
     57   if(curl) {
     58     /* Make a connection to an HTTP/2 server. */
     59     curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
     60 
     61     /* Set the interval to 30000ms / 30s */
     62     curl_easy_setopt(curl, CURLOPT_UPKEEP_INTERVAL_MS, 30000L);
     63 
     64     curl_easy_perform(curl);
     65 
     66     /* Perform more work here. */
     67 
     68     /* While the connection is being held open, curl_easy_upkeep() can be
     69        called. If curl_easy_upkeep() is called and the time since the last
     70        upkeep exceeds the interval, then an HTTP/2 PING is sent. */
     71     curl_easy_upkeep(curl);
     72 
     73     /* Perform more work here. */
     74 
     75     /* always cleanup */
     76     curl_easy_cleanup(curl);
     77   }
     78 }
     79 ~~~
     80 
     81 # %AVAILABILITY%
     82 
     83 # RETURN VALUE
     84 
     85 This function returns a CURLcode indicating success or error.
     86 
     87 CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
     88 libcurl-errors(3). If CURLOPT_ERRORBUFFER(3) was set with curl_easy_setopt(3)
     89 there can be an error message stored in the error buffer when non-zero is
     90 returned.