91 lines
2.3 KiB
Markdown
91 lines
2.3 KiB
Markdown
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---
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c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_DNS_CACHE_TIMEOUT
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_CONNECTTIMEOUT_MS (3)
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- CURLOPT_DNS_SERVERS (3)
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- CURLOPT_DNS_USE_GLOBAL_CACHE (3)
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- CURLOPT_MAXAGE_CONN (3)
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- CURLOPT_RESOLVE (3)
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---
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# NAME
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CURLOPT_DNS_CACHE_TIMEOUT - life-time for DNS cache entries
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_CACHE_TIMEOUT, long age);
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~~~
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# DESCRIPTION
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Pass a long, this sets the timeout in seconds. Name resolve results are kept
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in memory and used for this number of seconds. Set to zero to completely
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disable caching, or set to -1 to make the cached entries remain forever. By
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default, libcurl caches this info for 60 seconds.
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We recommend users not to tamper with this option unless strictly necessary.
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If you do, be careful of using large values that can make the cache size grow
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significantly if many different host names are used within that timeout
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period.
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The name resolve functions of various libc implementations do not re-read name
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server information unless explicitly told so (for example, by calling
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*res_init(3)*). This may cause libcurl to keep using the older server even
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if DHCP has updated the server info, and this may look like a DNS cache issue
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to the casual libcurl-app user.
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DNS entries have a "TTL" property but libcurl does not use that. This DNS
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cache timeout is entirely speculative that a name resolves to the same address
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for a small amount of time into the future.
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Since version 8.1.0, libcurl prunes entries from the DNS cache if it exceeds
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30,000 entries no matter which timeout value is used.
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# DEFAULT
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60
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# PROTOCOLS
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All
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# EXAMPLE
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~~~c
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int main(void)
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{
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CURL *curl = curl_easy_init();
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if(curl) {
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CURLcode res;
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curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
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/* only reuse addresses for a short time */
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curl_easy_setopt(curl, CURLOPT_DNS_CACHE_TIMEOUT, 2L);
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res = curl_easy_perform(curl);
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/* in this second request, the cache is not be used if more than
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two seconds have passed since the previous name resolve */
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res = curl_easy_perform(curl);
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curl_easy_cleanup(curl);
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}
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}
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~~~
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# AVAILABILITY
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Always
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# RETURN VALUE
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Returns CURLE_OK
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