dnsproxy2 --Android系统DNS修改工具优化版

/* * Copyright (C) 2008 The Android Open Source Project * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include "resolv_cache.h" #include <resolv.h> #include <stdlib.h> #include <string.h> #include <time.h> #include "pthread.h" #include <errno.h> #include "arpa_nameser.h" #include <sys/system_properties.h> #include <net/if.h> #include <netdb.h> #include <linux/if.h> #include <arpa/inet.h rel='nofollow' onclick='return false;'> #include "resolv_private.h" #include "resolv_iface.h" #include "res_private.h" /* This code implements a small and *simple* DNS resolver cache. * * It is only used to cache DNS answers for a time defined by the smallest TTL * among the answer records in order to reduce DNS traffic. It is not supposed * to be a full DNS cache, since we plan to implement that in the future in a * dedicated process running on the system. * * Note that its design is kept simple very intentionally, i.e.: * * - it takes raw DNS query packet data as input, and returns raw DNS * answer packet data as output * * (this means that two similar queries that encode the DNS name * differently will be treated distinctly). * * the smallest TTL value among the answer records are used as the time * to keep an answer in the cache. * * this is bad, but we absolutely want to avoid parsing the answer packets * (and should be solved by the later full DNS cache process). * * - the implementation is just a (query-data) => (answer-data) hash table * with a trivial least-recently-used expiration policy. * * Doing this keeps the code simple and avoids to deal with a lot of things * that a full DNS cache is expected to do. * * The API is also very simple: * * - the client calls _resolv_cache_get() to obtain a handle to the cache. * this will initialize the cache on first usage. the result can be NULL * if the cache is disabled. * * - the client calls _resolv_cache_lookup() before performing a query * * if the function returns RESOLV_CACHE_FOUND, a copy of the answer data * has been copied into the client-provided answer buffer. * * if the function returns RESOLV_CACHE_NOTFOUND, the client should perform * a request normally, *then* call _resolv_cache_add() to add the received * answer to the cache. * * if the function returns RESOLV_CACHE_UNSUPPORTED, the client should * perform a request normally, and *not* call _resolv_cache_add() * * note that RESOLV_CACHE_UNSUPPORTED is also returned if the answer buffer * is too short to accomodate the cached result. * * - when network settings change, the cache must be flushed since the list * of DNS servers probably changed. this is done by calling * _resolv_cache_reset() * * the parameter to this function must be an ever-increasing generation * number corresponding to the current network settings state. * * This is done because several threads could detect the same network * settings change (but at different times) and will all end up calling the * same function. Comparing with the last used generation number ensures * that the cache is only flushed once per network change. */ /* the name of an environment variable that will be checked the first time * this code is called if its value is "0", then the resolver cache is * disabled. */ #define CONFIG_ENV "BIONIC_DNSCACHE" /* entries older than CONFIG_SECONDS seconds are always discarded. */ #define CONFIG_SECONDS (60*10) /* 10 minutes */ /* default number of entries kept in the cache. This value has been * determined by browsing through various sites and counting the number * of corresponding requests. Keep in mind that our framework is currently * performing two requests per name lookup (one for IPv4, the other for IPv6) * * www.google.com 4 * www.ysearch.com 6 * www.amazon.com 8 * www.nytimes.com 22 * www.espn.com 28 * www.msn.com 28 * www.lemonde.fr 35 * * (determined in 2009-2-17 from Paris, France, results may vary depending * on location) * * most high-level websites use lots of media/ad servers with different names * but these are generally reused when browsing through the site. * * As such, a value of 64 should be relatively comfortable at the moment. * * The system property ro.net.dns_cache_size can be used to override the default * value with a custom value * * * ****************************************** * * NOTE - this has changed. * * 1) we've added IPv6 support so each dns query results in 2 responses * * 2) we've made this a system-wide cache, so the cost is less (it's not * * duplicated in each process) and the need is greater (more processes * * making different requests). * * Upping by 2x for IPv6 * * Upping by another 5x for the centralized nature * ***************************************** */ #define CONFIG_MAX_ENTRIES 64 * 2 * 5 /* name of the system property that can be used to set the cache size */ #define DNS_CACHE_SIZE_PROP_NAME "ro.net.dns_cache_size" /****************************************************************************/ /****************************************************************************/ /***** *****/ /***** *****/ /***** *****/ /****************************************************************************/ /****************************************************************************/ /* set to 1 to debug cache operations */ #define DEBUG 0 /* set to 1 to debug query data */ #define DEBUG_DATA 0 #undef XLOG #if DEBUG # include "libc_logging.h" # define XLOG(...) __libc_format_log(ANDROID_LOG_DEBUG,"libc",__VA_ARGS__) #include <stdio.h> #include <stdarg.h> /** BOUNDED BUFFER FORMATTING **/ /* technical note: * * the following debugging routines are used to append data to a bounded * buffer they take two parameters that are: * * - p : a pointer to the current cursor position in the buffer * this value is initially set to the buffer's address. * * - end : the address of the buffer's limit, i.e. of the first byte * after the buffer. this address should never be touched. * * IMPORTANT: it is assumed that end > buffer_address, i.e. * that the buffer is at least one byte. * * the _bprint_() functions return the new value of 'p' after the data * has been appended, and also ensure the following: * * - the returned value will never be strictly great