/*
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* Copyright (C) 2018 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#define LOG_TAG "Dns64Configuration"
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#define DBG 0
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#include "Dns64Configuration.h"
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#include <log/log.h>
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#include <netdb.h>
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#include <thread>
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#include <utility>
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#include <arpa/inet.h>
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#include "DnsResolver.h"
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#include "NetdConstants.h" // ScopedAddrinfo
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#include "getaddrinfo.h"
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#include "netd_resolv/resolv.h"
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#include "netdutils/BackoffSequence.h"
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#include "netdutils/DumpWriter.h"
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#include "netid_client.h"
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namespace android {
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using netdutils::DumpWriter;
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using netdutils::IPAddress;
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using netdutils::IPPrefix;
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namespace net {
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const char Dns64Configuration::kIPv4OnlyHost[] = "ipv4only.arpa.";
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const char Dns64Configuration::kIPv4Literal1[] = "192.0.0.170";
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const char Dns64Configuration::kIPv4Literal2[] = "192.0.0.171";
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void Dns64Configuration::startPrefixDiscovery(unsigned netId) {
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std::lock_guard guard(mMutex);
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// TODO: Keep previous prefix for a while
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// Currently, we remove current prefix, if any, before starting a prefix discovery.
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// This causes that Netd and framework temporarily forgets DNS64 prefix even the prefix may be
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// discovered in a short time.
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removeDns64Config(netId);
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Dns64Config cfg(getNextId(), netId);
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// Emplace a copy of |cfg| in the map.
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mDns64Configs.emplace(std::make_pair(netId, cfg));
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// Note that capturing |cfg| in this lambda creates a copy.
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std::thread discovery_thread([this, cfg] {
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// Make a mutable copy rather than mark the whole lambda mutable.
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// No particular reason.
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Dns64Config evalCfg(cfg);
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auto backoff = netdutils::BackoffSequence<>::Builder()
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.withInitialRetransmissionTime(std::chrono::seconds(1))
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.withMaximumRetransmissionTime(std::chrono::seconds(3600))
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.build();
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while (true) {
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if (!this->shouldContinueDiscovery(evalCfg)) break;
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android_net_context netcontext{};
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mGetNetworkContextCallback(evalCfg.netId, 0, &netcontext);
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// Prefix discovery must bypass private DNS because in strict mode
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// the server generally won't know the NAT64 prefix.
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netcontext.flags |= NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
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if (doRfc7050PrefixDiscovery(netcontext, &evalCfg)) {
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this->recordDns64Config(evalCfg);
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break;
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}
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if (!this->shouldContinueDiscovery(evalCfg)) break;
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if (!backoff.hasNextTimeout()) break;
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{
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std::unique_lock<std::mutex> cvGuard(mMutex);
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// TODO: Consider some chrono math, combined with wait_until()
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// perhaps, to prevent early re-resolves from the removal of
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// other netids with IPv6-only nameservers.
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mCv.wait_for(cvGuard, backoff.getNextTimeout());
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}
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}
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});
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discovery_thread.detach();
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}
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void Dns64Configuration::stopPrefixDiscovery(unsigned netId) {
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std::lock_guard guard(mMutex);
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removeDns64Config(netId);
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mCv.notify_all();
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}
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IPPrefix Dns64Configuration::getPrefix64Locked(unsigned netId) const REQUIRES(mMutex) {
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const auto& iter = mDns64Configs.find(netId);
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if (iter != mDns64Configs.end()) return iter->second.prefix64;
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return IPPrefix{};
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}
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IPPrefix Dns64Configuration::getPrefix64(unsigned netId) const {
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std::lock_guard guard(mMutex);
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return getPrefix64Locked(netId);
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}
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void Dns64Configuration::dump(DumpWriter& dw, unsigned netId) {
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static const char kLabel[] = "DNS64 config";
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std::lock_guard guard(mMutex);
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const auto& iter = mDns64Configs.find(netId);
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if (iter == mDns64Configs.end()) {
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dw.println("%s: none", kLabel);
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return;
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}
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const Dns64Config& cfg = iter->second;
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if (cfg.prefix64.length() == 0) {
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dw.println("%s: no prefix yet discovered", kLabel);
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} else {
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dw.println("%s: discovered prefix %s", kLabel, cfg.prefix64.toString().c_str());
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}
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}
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// NOTE: The full RFC 7050 DNS64 discovery process is not implemented here.
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// Instead, and more simplistic version of the same thing is done, and it
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// currently assumes the DNS64 prefix is a /96.
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bool Dns64Configuration::doRfc7050PrefixDiscovery(const android_net_context& netcontext,
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Dns64Config* cfg) {
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ALOGW("(%u, %u) Detecting NAT64 prefix from DNS...", cfg->netId, cfg->discoveryId);
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const struct addrinfo hints = {
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.ai_family = AF_INET6,
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};
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// TODO: Refactor so that netd can get all the regular getaddrinfo handling
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// that regular apps get. We bypass the UNIX socket connection back to
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// ourselves, which means we also bypass all the special netcontext flag
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// handling and the resolver event logging.
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struct addrinfo* res = nullptr;
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const int status =
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android_getaddrinfofornetcontext(kIPv4OnlyHost, nullptr, &hints, &netcontext, &res);
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ScopedAddrinfo result(res);
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if (status != 0) {
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ALOGW("(%u, %u) plat_prefix/dns(%s) status = %d/%s", cfg->netId, cfg->discoveryId,
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kIPv4OnlyHost, status, gai_strerror(status));
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return false;
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}
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// Use only the first result. If other records are present, possibly
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// with differing DNS64 prefixes they are ignored. Note that this is a
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// violation of https://tools.ietf.org/html/rfc7050#section-3
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//
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// "A node MUST look through all of the received AAAA resource records
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// to collect one or more Pref64::/n."
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//
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// TODO: Consider remedying this.
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if (result->ai_family != AF_INET6) {
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ALOGW("(%u, %u) plat_prefix/unexpected address family: %d", cfg->netId, cfg->discoveryId,
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result->ai_family);
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return false;
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}
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const IPAddress ipv6(reinterpret_cast<sockaddr_in6*>(result->ai_addr)->sin6_addr);
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// Only /96 DNS64 prefixes are supported at this time.
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cfg->prefix64 = IPPrefix(ipv6, 96);
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ALOGW("(%u, %u) Detected NAT64 prefix %s", cfg->netId, cfg->discoveryId,
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cfg->prefix64.toString().c_str());
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return true;
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}
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bool Dns64Configuration::isDiscoveryInProgress(const Dns64Config& cfg) const REQUIRES(mMutex) {
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const auto& iter = mDns64Configs.find(cfg.netId);
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if (iter == mDns64Configs.end()) return false;
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const Dns64Config& currentCfg = iter->second;
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return (currentCfg.discoveryId == cfg.discoveryId);
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}
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bool Dns64Configuration::reportNat64PrefixStatus(unsigned netId, bool added, const IPPrefix& pfx) {
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if (pfx.ip().family() != AF_INET6 || pfx.ip().scope_id() != 0) {
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ALOGW("Abort to send NAT64 prefix notification. Unexpected NAT64 prefix (%u, %d, %s).",
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netId, added, pfx.toString().c_str());
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return false;
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}
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Nat64PrefixInfo args = {netId, added, pfx.ip().toString(), (uint8_t)pfx.length()};
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mPrefixCallback(args);
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return true;
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}
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bool Dns64Configuration::shouldContinueDiscovery(const Dns64Config& cfg) {
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std::lock_guard guard(mMutex);
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return isDiscoveryInProgress(cfg);
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}
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void Dns64Configuration::removeDns64Config(unsigned netId) REQUIRES(mMutex) {
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IPPrefix prefix = getPrefix64Locked(netId);
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mDns64Configs.erase(netId);
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if (!prefix.isUninitialized()) {
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reportNat64PrefixStatus(netId, PREFIX_REMOVED, prefix);
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}
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}
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void Dns64Configuration::recordDns64Config(const Dns64Config& cfg) {
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std::lock_guard guard(mMutex);
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if (!isDiscoveryInProgress(cfg)) return;
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removeDns64Config(cfg.netId);
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mDns64Configs.emplace(std::make_pair(cfg.netId, cfg));
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reportNat64PrefixStatus(cfg.netId, PREFIX_ADDED, cfg.prefix64);
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// TODO: consider extending INetdEventListener to report the DNS64 prefix
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// up to ConnectivityService to potentially include this in LinkProperties.
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}
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} // namespace net
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} // namespace android
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