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resolve: add CURLOPT_DNS_SHUFFLE_ADDRESSES
This patch adds CURLOPT_DNS_SHUFFLE_ADDRESSES to explicitly request shuffling of IP addresses returned for a hostname when there is more than one. This is useful when the application knows that a round robin approach is appropriate and is willing to accept the consequences of potentially discarding some preference order returned by the system's implementation. Closes #1694
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.\" ************************************************************************** | ||
.\" * _ _ ____ _ | ||
.\" * Project ___| | | | _ \| | | ||
.\" * / __| | | | |_) | | | ||
.\" * | (__| |_| | _ <| |___ | ||
.\" * \___|\___/|_| \_\_____| | ||
.\" * | ||
.\" * 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. | ||
.\" * | ||
.\" * 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. | ||
.\" * | ||
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY | ||
.\" * KIND, either express or implied. | ||
.\" * | ||
.\" ************************************************************************** | ||
.\" | ||
.TH CURLOPT_DNS_SHUFFLE_ADDRESSES 3 "3 March 2018" "libcurl 7.60.0" "curl_easy_setopt options" | ||
.SH NAME | ||
CURLOPT_DNS_SHUFFLE_ADDRESSES \- Shuffle addresses when a hostname returns more than one | ||
.SH SYNOPSIS | ||
.nf | ||
#include <curl/curl.h> | ||
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DNS_SHUFFLE_ADDRESSES, long onoff); | ||
.fi | ||
.SH DESCRIPTION | ||
When a name is resolved and more than one IP address is returned, shuffle the | ||
order of all returned addresses so that they will be used in a random order. | ||
This is similar to the ordering behavior of gethostbyname which is no longer | ||
used on most platforms. | ||
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Addresses will not be reshuffled if a name resolution is completed using the | ||
DNS cache. \fICURLOPT_DNS_CACHE_TIMEOUT(3)\fP can be used together with this | ||
option to reduce DNS cache timeout or disable caching entirely if frequent | ||
reshuffling is needed. | ||
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Since the addresses returned will be reordered randomly, their order will not | ||
be in accordance with RFC 3484 or any other deterministic order that may be | ||
generated by the system's name resolution implementation. This may have | ||
performance impacts and may cause IPv4 to be used before IPv6 or vice versa. | ||
.SH DEFAULT | ||
0 (disabled) | ||
.SH PROTOCOLS | ||
All | ||
.SH EXAMPLE | ||
.nf | ||
CURL *curl = curl_easy_init(); | ||
if(curl) { | ||
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com"); | ||
curl_easy_setopt(curl, CURLOPT_DNS_SHUFFLE_ADDRESSES, 1L); | ||
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curl_easy_perform(curl); | ||
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/* always cleanup */ | ||
curl_easy_cleanup(curl); | ||
} | ||
.fi | ||
.SH AVAILABILITY | ||
Added in 7.60.0 | ||
.SH RETURN VALUE | ||
CURLE_OK or an error such as CURLE_UNKNOWN_OPTION. | ||
.SH "SEE ALSO" | ||
.BR CURLOPT_DNS_CACHE_TIMEOUT "(3), " CURLOPT_IPRESOLVE "(3), " |
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<testcase> | ||
<info> | ||
<keywords> | ||
unittest | ||
curlopt_dns_shuffle_addresses | ||
</keywords> | ||
</info> | ||
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# | ||
# Client-side | ||
<client> | ||
<server> | ||
none | ||
</server> | ||
<features> | ||
unittest | ||
</features> | ||
<name> | ||
verify DNS shuffling | ||
</name> | ||
<tool> | ||
unit1608 | ||
</tool> | ||
</client> | ||
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</testcase> |
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/*************************************************************************** | ||
* _ _ ____ _ | ||
* Project ___| | | | _ \| | | ||
* / __| | | | |_) | | | ||
* | (__| |_| | _ <| |___ | ||
* \___|\___/|_| \_\_____| | ||
* | ||
* 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. | ||
* | ||
* 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. | ||
* | ||
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY | ||
* KIND, either express or implied. | ||
* | ||
***************************************************************************/ | ||
#include "curlcheck.h" | ||
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#include "hostip.h" | ||
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#define NUM_ADDRS 8 | ||
static struct Curl_addrinfo addrs[NUM_ADDRS]; | ||
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static CURLcode unit_setup(void) | ||
{ | ||
int i; | ||
for(i = 0; i < NUM_ADDRS - 1; i++) { | ||
addrs[i].ai_next = &addrs[i + 1]; | ||
} | ||
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return CURLE_OK; | ||
} | ||
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static void unit_stop(void) | ||
{ | ||
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} | ||
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UNITTEST_START | ||
{ | ||
int i; | ||
CURLcode code; | ||
struct Curl_addrinfo* addrhead = addrs; | ||
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struct Curl_easy *easy = curl_easy_init(); | ||
abort_unless(easy, "out of memory"); | ||
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code = curl_easy_setopt(easy, CURLOPT_DNS_SHUFFLE_ADDRESSES, 1L); | ||
abort_unless(code == CURLE_OK, "curl_easy_setopt failed"); | ||
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/* Shuffle repeatedly and make sure that the list changes */ | ||
for(i = 0; i < 10; i++) { | ||
if(CURLE_OK != Curl_shuffle_addr(easy, &addrhead)) | ||
break; | ||
if(addrhead != addrs) | ||
break; | ||
} | ||
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curl_easy_cleanup(easy); | ||
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abort_unless(addrhead != addrs, "addresses are not being reordered"); | ||
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return 0; | ||
} | ||
UNITTEST_STOP |