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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
This commit is contained in:
Rick Deist 2018-03-17 20:10:04 +01:00 committed by Daniel Stenberg
parent fb4f568b1e
commit d95f3dc0b1
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GPG Key ID: 5CC908FDB71E12C2
14 changed files with 270 additions and 3 deletions
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2
docs/libcurl/curl_easy_setopt.3
View File

@ -468,6 +468,8 @@ Bind name resolves to this IP4 address. See \fICURLOPT_DNS_LOCAL_IP4(3)\fP
Bind name resolves to this IP6 address. See \fICURLOPT_DNS_LOCAL_IP6(3)\fP
.IP CURLOPT_DNS_SERVERS
Preferred DNS servers. See \fICURLOPT_DNS_SERVERS(3)\fP
.IP CURLOPT_DNS_SHUFFLE_ADDRESSES
Shuffle addresses before use. See \fICURLOPT_DNS_SHUFFLE_ADDRESSES(3)\fP
.IP CURLOPT_ACCEPTTIMEOUT_MS
Timeout for waiting for the server's connect back to be accepted. See \fICURLOPT_ACCEPTTIMEOUT_MS(3)\fP
.IP CURLOPT_HAPPY_EYEBALLS_TIMEOUT_MS

69
docs/libcurl/opts/CURLOPT_DNS_SHUFFLE_ADDRESSES.3 Normal file
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@ -0,0 +1,69 @@
.\" **************************************************************************
.\" * _ _ ____ _
.\" * 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>
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.
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.
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);
curl_easy_perform(curl);
/* 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), "

1
docs/libcurl/opts/Makefile.inc
View File

@ -112,6 +112,7 @@ man_MANS = \
CURLOPT_DNS_LOCAL_IP4.3 \
CURLOPT_DNS_LOCAL_IP6.3 \
CURLOPT_DNS_SERVERS.3 \
CURLOPT_DNS_SHUFFLE_ADDRESSES.3 \
CURLOPT_DNS_USE_GLOBAL_CACHE.3 \
CURLOPT_EGDSOCKET.3 \
CURLOPT_ERRORBUFFER.3 \

1
docs/libcurl/symbols-in-versions
View File

@ -373,6 +373,7 @@ CURLOPT_DNS_INTERFACE 7.33.0
CURLOPT_DNS_LOCAL_IP4 7.33.0
CURLOPT_DNS_LOCAL_IP6 7.33.0
CURLOPT_DNS_SERVERS 7.24.0
CURLOPT_DNS_SHUFFLE_ADDRESSES 7.60.0
CURLOPT_DNS_USE_GLOBAL_CACHE 7.9.3 7.11.1
CURLOPT_EGDSOCKET 7.7
CURLOPT_ENCODING 7.10

3
include/curl/curl.h
View File

@ -1844,6 +1844,9 @@ typedef enum {
/* send HAProxy PROXY protocol header? */
CINIT(HAPROXYPROTOCOL, LONG, 274),
/* shuffle addresses before use when DNS returns multiple */
CINIT(DNS_SHUFFLE_ADDRESSES, LONG, 275),
CURLOPT_LASTENTRY /* the last unused */
} CURLoption;

74
lib/hostip.c
View File

@ -5,7 +5,7 @@
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
* 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
@ -54,6 +54,7 @@
#include "sendf.h"
#include "hostip.h"
#include "hash.h"
#include "rand.h"
#include "share.h"
#include "strerror.h"
#include "url.h"
@ -366,6 +367,70 @@ Curl_fetch_addr(struct connectdata *conn,
return dns;
}
/*
* Curl_shuffle_addr() shuffles the order of addresses in a 'Curl_addrinfo'
* struct by re-linking its linked list.
*
* The addr argument should be the address of a pointer to the head node of a
* `Curl_addrinfo` list and it will be modified to point to the new head after
* shuffling.
*
* Not declared static only to make it easy to use in a unit test!
*
* @unittest: 1608
*/
CURLcode Curl_shuffle_addr(struct Curl_easy *data, Curl_addrinfo **addr)
{
CURLcode result = CURLE_OK;
const int num_addrs = Curl_num_addresses(*addr);
if(num_addrs > 1) {
Curl_addrinfo **nodes;
infof(data, "Shuffling %i addresses", num_addrs);
nodes = malloc(num_addrs*sizeof(*nodes));
if(nodes) {
int i;
unsigned int *rnd;
const size_t rnd_size = num_addrs * sizeof(*rnd);
/* build a plain array of Curl_addrinfo pointers */
nodes[0] = *addr;
for(i = 1; i < num_addrs; i++) {
nodes[i] = nodes[i-1]->ai_next;
}
rnd = malloc(rnd_size);
if(rnd) {
/* Fisher-Yates shuffle */
if(Curl_rand(data, (unsigned char *)rnd, rnd_size) == CURLE_OK) {
Curl_addrinfo *swap_tmp;
for(i = num_addrs - 1; i > 0; i--) {
swap_tmp = nodes[rnd[i] % (i + 1)];
nodes[rnd[i] % (i + 1)] = nodes[i];
nodes[i] = swap_tmp;
}
/* relink list in the new order */
for(i = 1; i < num_addrs; i++) {
nodes[i-1]->ai_next = nodes[i];
}
nodes[num_addrs-1]->ai_next = NULL;
*addr = nodes[0];
}
free(rnd);
}
else
result = CURLE_OUT_OF_MEMORY;
free(nodes);
}
else
result = CURLE_OUT_OF_MEMORY;
}
return result;
}
/*
* Curl_cache_addr() stores a 'Curl_addrinfo' struct in the DNS cache.
*
@ -386,6 +451,13 @@ Curl_cache_addr(struct Curl_easy *data,
struct Curl_dns_entry *dns;
struct Curl_dns_entry *dns2;
/* shuffle addresses if requested */
if(data->set.dns_shuffle_addresses) {
CURLcode result = Curl_shuffle_addr(data, &addr);
if(!result)
return NULL;
}
/* Create an entry id, based upon the hostname and port */
entry_id = create_hostcache_id(hostname, port);
/* If we can't create the entry id, fail */

13
lib/hostip.h
View File

@ -7,7 +7,7 @@
* | (__| |_| | _ <| |___
* \___|\___/|_| \_\_____|
*
* Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
* 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
@ -182,6 +182,17 @@ struct Curl_dns_entry *
Curl_fetch_addr(struct connectdata *conn,
const char *hostname,
int port);
/*
* Curl_shuffle_addr() shuffles the order of addresses in a 'Curl_addrinfo'
* struct by re-linking its linked list.
*
* The addr argument should be the address of a pointer to the head node of a
* `Curl_addrinfo` list and it will be modified to point to the new head after
* shuffling.
*/
CURLcode Curl_shuffle_addr(struct Curl_easy *data, Curl_addrinfo **addr);
/*
* Curl_cache_addr() stores a 'Curl_addrinfo' struct in the DNS cache.
*

3
lib/setopt.c
View File

@ -2561,6 +2561,9 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option,
return CURLE_BAD_FUNCTION_ARGUMENT;
data->set.happy_eyeballs_timeout = arg;
break;
case CURLOPT_DNS_SHUFFLE_ADDRESSES:
data->set.dns_shuffle_addresses = (0 != va_arg(param, long)) ? TRUE:FALSE;
break;
default:
/* unknown tag and its companion, just ignore: */
result = CURLE_UNKNOWN_OPTION;

2
lib/urldata.h
View File

@ -1674,6 +1674,8 @@ struct UserDefined {
bool suppress_connect_headers; /* suppress proxy CONNECT response headers
from user callbacks */
bool dns_shuffle_addresses; /* whether to shuffle addresses before use */
struct Curl_easy *stream_depends_on;
bool stream_depends_e; /* set or don't set the Exclusive bit */
int stream_weight;

2
packages/OS400/curl.inc.in
View File

@ -1330,6 +1330,8 @@
d c 20272
d CURLOPT_RESOLVER_START_DATA...
d c 10273
d CURLOPT_DNS_SHUFFLE_ADDRESSES...
d c 00274
*
/if not defined(CURL_NO_OLDIES)
d CURLOPT_FILE c 10001

1
tests/data/Makefile.inc
View File

@ -177,6 +177,7 @@ test1533 test1534 test1535 test1536 test1537 test1538 \
test1540 \
test1550 test1551 test1552 test1553 test1554 test1555 test1556 \
test1600 test1601 test1602 test1603 test1604 test1605 test1606 test1607 \
test1608 \
\
test1700 test1701 test1702 \
\

26
tests/data/test1608 Normal file
View File

@ -0,0 +1,26 @@
<testcase>
<info>
<keywords>
unittest
curlopt_dns_shuffle_addresses
</keywords>
</info>
#
# Client-side
<client>
<server>
none
</server>
<features>
unittest
</features>
<name>
verify DNS shuffling
</name>
<tool>
unit1608
</tool>
</client>
</testcase>

6
tests/unit/Makefile.inc
View File

@ -9,7 +9,8 @@ UNITPROGS = unit1300 unit1301 unit1302 unit1303 unit1304 unit1305 unit1307 \
unit1308 unit1309 unit1323 \
unit1330 unit1394 unit1395 unit1396 unit1397 unit1398 \
unit1399 \
unit1600 unit1601 unit1602 unit1603 unit1604 unit1605 unit1606 unit1607
unit1600 unit1601 unit1602 unit1603 unit1604 unit1605 unit1606 unit1607 \
unit1608
unit1300_SOURCES = unit1300.c $(UNITFILES)
unit1300_CPPFLAGS = $(AM_CPPFLAGS)
@ -88,3 +89,6 @@ unit1606_CPPFLAGS = $(AM_CPPFLAGS)
unit1607_SOURCES = unit1607.c $(UNITFILES)
unit1607_CPPFLAGS = $(AM_CPPFLAGS)
unit1608_SOURCES = unit1608.c $(UNITFILES)
unit1608_CPPFLAGS = $(AM_CPPFLAGS)

70
tests/unit/unit1608.c Normal file
View File

@ -0,0 +1,70 @@
/***************************************************************************
* _ _ ____ _
* 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"
#include "hostip.h"
#define NUM_ADDRS 8
static struct Curl_addrinfo addrs[NUM_ADDRS];
static CURLcode unit_setup(void)
{
int i;
for(i = 0; i < NUM_ADDRS - 1; i++) {
addrs[i].ai_next = &addrs[i + 1];
}
return CURLE_OK;
}
static void unit_stop(void)
{
}
UNITTEST_START
{
int i;
CURLcode code;
struct Curl_addrinfo* addrhead = addrs;
struct Curl_easy *easy = curl_easy_init();
abort_unless(easy, "out of memory");
code = curl_easy_setopt(easy, CURLOPT_DNS_SHUFFLE_ADDRESSES, 1L);
abort_unless(code == CURLE_OK, "curl_easy_setopt failed");
/* 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;
}
curl_easy_cleanup(easy);
abort_unless(addrhead != addrs, "addresses are not being reordered");
return 0;
}
UNITTEST_STOP