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e3fe020089
Remove the PROTOCOLS section from the source files completely and instead generate them based on the header data in the curldown files. It also generates TLS backend information for options marked for TLS as protocol. Closes #13175
87 lines
2.3 KiB
Markdown
87 lines
2.3 KiB
Markdown
---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.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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Protocol:
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- All
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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 hostnames are used within that timeout 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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# 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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