/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <arpa/inet.h>
#include <dirent.h>
#include <errno.h>
#include <linux/if.h>
#include <math.h>
#include <netdb.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <string.h>
#include <pthread.h>
#include <net/if.h>

#define LOG_TAG "DnsProxyListener"
#define DBG 0
#define VDBG 0

#include <algorithm>
#include <chrono>
#include <list>
#include <vector>

#include <android-base/stringprintf.h>
#include <cutils/misc.h>
#include <log/log.h>
#include <netdutils/OperationLimiter.h>
#include <netdutils/Slice.h>
#include <resolv.h>
#include <sysutils/SocketClient.h>
#include <utils/String16.h>

#include <binder/IServiceManager.h>

#include "Controllers.h"
#include "DnsProxyListener.h"
#include "Fwmark.h"
#include "NetdClient.h"
#include "NetdConstants.h"
#include "NetworkController.h"
#include "ResponseCode.h"
#include "Stopwatch.h"
#include "android/net/metrics/INetdEventListener.h"
#include "thread_util.h"

#include <netd_resolv/resolv_stub.h>

using android::String16;
using android::base::StringPrintf;
using android::net::metrics::INetdEventListener;

namespace android {
namespace net {

namespace {

// TODO: move to a separate file (with other constants from FwmarkService and NetdNativeService)
constexpr const char CONNECTIVITY_USE_RESTRICTED_NETWORKS[] =
    "android.permission.CONNECTIVITY_USE_RESTRICTED_NETWORKS";
constexpr const char NETWORK_BYPASS_PRIVATE_DNS[] =
    "android.permission.NETWORK_BYPASS_PRIVATE_DNS";

// Limits the number of outstanding DNS queries by client UID.
constexpr int MAX_QUERIES_PER_UID = 256;

// Max packet size for answer, sync with getaddrinfo.c
constexpr int MAXPACKET = 8 * 1024;

android::netdutils::OperationLimiter<uid_t> queryLimiter(MAX_QUERIES_PER_UID);

void logArguments(int argc, char** argv) {
    for (int i = 0; i < argc; i++) {
        ALOGD("argv[%i]=%s", i, argv[i]);
    }
}

template<typename T>
void tryThreadOrError(SocketClient* cli, T* handler) {
    cli->incRef();

    const int rval = threadLaunch(handler);
    if (rval == 0) {
        // SocketClient decRef() happens in the handler's run() method.
        return;
    }

    char* msg = nullptr;
    asprintf(&msg, "%s (%d)", strerror(-rval), -rval);
    cli->sendMsg(ResponseCode::OperationFailed, msg, false);
    free(msg);

    delete handler;
    cli->decRef();
}

bool checkAndClearUseLocalNameserversFlag(unsigned* netid) {
    if (netid == nullptr || ((*netid) & NETID_USE_LOCAL_NAMESERVERS) == 0) {
        return false;
    }
    *netid = (*netid) & ~NETID_USE_LOCAL_NAMESERVERS;
    return true;
}

constexpr bool requestingUseLocalNameservers(unsigned flags) {
    return (flags & NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS) != 0;
}

inline bool queryingViaTls(unsigned dns_netid) {
    ExternalPrivateDnsStatus privateDnsStatus = {PrivateDnsMode::OFF, 0, {}};
    RESOLV_STUB.resolv_get_private_dns_status_for_net(dns_netid, &privateDnsStatus);
    switch (static_cast<PrivateDnsMode>(privateDnsStatus.mode)) {
        case PrivateDnsMode::OPPORTUNISTIC:
            for (unsigned i = 0; i < privateDnsStatus.numServers; i++) {
                if (privateDnsStatus.serverStatus[i].validation == Validation::success) {
                    return true;
                }
            }
            return false;
        case PrivateDnsMode::STRICT:
            return true;
        default:
            return false;
    }
}

bool hasPermissionToBypassPrivateDns(uid_t uid) {
    static_assert(AID_SYSTEM >= 0 && AID_SYSTEM < FIRST_APPLICATION_UID,
        "Calls from AID_SYSTEM must not result in a permission check to avoid deadlock.");
    if (uid >= 0 && uid < FIRST_APPLICATION_UID) {
        return true;
    }

    for (const char* const permission :
         {CONNECTIVITY_USE_RESTRICTED_NETWORKS, NETWORK_BYPASS_PRIVATE_DNS}) {
        if (checkCallingPermission(String16(permission))) {
            return true;
        }
    }
    return false;
}

void maybeFixupNetContext(android_net_context* ctx) {
    if (requestingUseLocalNameservers(ctx->flags) && !hasPermissionToBypassPrivateDns(ctx->uid)) {
        // Not permitted; clear the flag.
        ctx->flags &= ~NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
    }

    if (!requestingUseLocalNameservers(ctx->flags)) {
        // If we're not explicitly bypassing DNS-over-TLS servers, check whether
        // DNS-over-TLS is in use as an indicator for when to use more modern
        // DNS resolution mechanics.
        if (queryingViaTls(ctx->dns_netid)) {
            ctx->flags |= NET_CONTEXT_FLAG_USE_EDNS;
        }
    }
}

void addIpAddrWithinLimit(std::vector<android::String16>* ip_addrs, const sockaddr* addr,
                          socklen_t addrlen);

int extractIpAddressAnswers(const uint8_t* answer, size_t anslen, int ipType,
                            std::vector<String16>* ip_addrs) {
    int total_ip_addr_count = 0;
    ns_msg handle;
    if (ns_initparse((const uint8_t*) answer, anslen, &handle) < 0) {
        return 0;
    }
    int ancount = ns_msg_count(handle, ns_s_an);
    ns_rr rr;
    for (int i = 0; i < ancount; i++) {
        if (ns_parserr(&handle, ns_s_an, i, &rr) < 0) {
            continue;
        }
        const uint8_t* rdata = ns_rr_rdata(rr);
        if (ipType == ns_t_a) {
            sockaddr_in sin = {.sin_family = AF_INET};
            memcpy(&sin.sin_addr, rdata, sizeof(sin.sin_addr));
            addIpAddrWithinLimit(ip_addrs, (sockaddr*) &sin, sizeof(sin));
            total_ip_addr_count++;
        } else if (ipType == ns_t_aaaa) {
            struct in6_addr in6;
            memcpy(&in6, rdata, IN6ADDRSZ);
            sockaddr_in6 sin6 = {.sin6_family = AF_INET6, .sin6_addr = in6};
            addIpAddrWithinLimit(ip_addrs, (sockaddr*) &sin6, sizeof(sin6));
            total_ip_addr_count++;
        }
    }

    return total_ip_addr_count;
}

template <typename IntegralType>
bool simpleStrtoul(const char* input, IntegralType* output, int base = 10) {
    char* endPtr;
    errno = 0;
    auto result = strtoul(input, &endPtr, base);
    // Check the length in order to ensure there is no "-" sign
    if (!*input || *endPtr || (endPtr - input) != static_cast<ptrdiff_t>(strlen(input)) ||
        (errno == ERANGE && (result == ULONG_MAX))) {
        return false;
    }
    *output = result;
    return true;
}

bool parseQuery(const uint8_t* msg, size_t msgLen, int* rr_type, std::string* rr_name) {
    ns_msg handle;
    ns_rr rr;
    if (ns_initparse((const uint8_t*) msg, msgLen, &handle) < 0 ||
        ns_parserr(&handle, ns_s_qd, 0, &rr) < 0) {
        return false;
    }

    *rr_name = ns_rr_name(rr);
    *rr_type = ns_rr_type(rr);
    return true;
}

bool onlyIPv4Answers(const struct addrinfo* res) {
    // Null addrinfo pointer isn't checked because the caller doesn't pass null pointer.

    for (const struct addrinfo* ai = res; ai; ai = ai->ai_next)
        if (ai->ai_family != AF_INET) return false;

    return true;
}

bool isSpecialUseIPv4Address(const struct in_addr& ia) {
    const uint32_t addr = ntohl(ia.s_addr);

    // Only check necessary IP ranges in RFC 5735 section 4
    return ((addr & 0xff000000) == 0x00000000) ||  // "This" Network
           ((addr & 0xff000000) == 0x7f000000) ||  // Loopback
           ((addr & 0xffff0000) == 0xa9fe0000) ||  // Link Local
           ((addr & 0xf0000000) == 0xe0000000) ||  // Multicast
           (addr == INADDR_BROADCAST);             // Limited Broadcast
}

bool isSpecialUseIPv4Address(const struct sockaddr* sa) {
    if (sa->sa_family != AF_INET) return false;

    return isSpecialUseIPv4Address(((struct sockaddr_in*) sa)->sin_addr);
}

bool onlyNonSpecialUseIPv4Addresses(struct hostent* hp) {
    // Null hostent pointer isn't checked because the caller doesn't pass null pointer.

    if (hp->h_addrtype != AF_INET) return false;

    for (int i = 0; hp->h_addr_list[i] != nullptr; i++)
        if (isSpecialUseIPv4Address(*(struct in_addr*) hp->h_addr_list[i])) return false;

    return true;
}

bool onlyNonSpecialUseIPv4Addresses(const struct addrinfo* res) {
    // Null addrinfo pointer isn't checked because the caller doesn't pass null pointer.

    for (const struct addrinfo* ai = res; ai; ai = ai->ai_next) {
        if (ai->ai_family != AF_INET) return false;
        if (isSpecialUseIPv4Address(ai->ai_addr)) return false;
    }

    return true;
}

void logDnsQueryResult(const struct hostent* hp) {
    if (hp == nullptr) return;

    ALOGD("DNS records:");
    for (int i = 0; hp->h_addr_list[i] != nullptr; i++) {
        char ip_addr[INET6_ADDRSTRLEN];
        if (inet_ntop(hp->h_addrtype, hp->h_addr_list[i], ip_addr, sizeof(ip_addr)) != nullptr) {
            ALOGD("[%d] %s, %d, %d, %s (%p)", i, hp->h_name ? hp->h_name : "null", hp->h_addrtype,
                  hp->h_length, ip_addr, hp->h_addr_list[i]);
        } else {
            ALOGD("[%d] numeric hostname translation fail (%d)", i, errno);
        }
    }
}

void logDnsQueryResult(const struct addrinfo* res) {
    if (res == nullptr) return;

    int i;
    const struct addrinfo* ai;
    ALOGD("DNS records:");
    for (ai = res, i = 0; ai; ai = ai->ai_next, i++) {
        if ((ai->ai_family != AF_INET) && (ai->ai_family != AF_INET6)) continue;
        char ip_addr[INET6_ADDRSTRLEN];
        int ret = getnameinfo(ai->ai_addr, ai->ai_addrlen, ip_addr, sizeof(ip_addr), nullptr, 0,
                              NI_NUMERICHOST);
        if (!ret) {
            ALOGD("[%d] 0x%x,%d,%d,%d,%d,%s,%s,%p", i, ai->ai_flags, ai->ai_family, ai->ai_socktype,
                  ai->ai_protocol, ai->ai_addrlen, ai->ai_canonname ? ai->ai_canonname : "null",
                  ip_addr, ai);
        } else {
            ALOGD("[%d] numeric hostname translation fail (%d)", i, ret);
        }
    }
}

bool isValidNat64Prefix(const netdutils::IPPrefix prefix) {
    if (prefix.family() != AF_INET6) {
        ALOGE("Only IPv6 NAT64 prefixes are supported (%u)", prefix.family());
        return false;
    }
    if (prefix.length() != 96) {
        ALOGE("Only /96 NAT64 prefixes are supported (%d)", prefix.length());
        return false;
    }
    return true;
}

bool synthesizeNat64PrefixWithARecord(const netdutils::IPPrefix& prefix, struct hostent* hp) {
    if (hp == nullptr) return false;
    if (!onlyNonSpecialUseIPv4Addresses(hp)) return false;
    if (!isValidNat64Prefix(prefix)) return false;

    struct sockaddr_storage ss = netdutils::IPSockAddr(prefix.ip());
    struct sockaddr_in6* v6prefix = (struct sockaddr_in6*) &ss;
    for (int i = 0; hp->h_addr_list[i] != nullptr; i++) {
        struct in_addr iaOriginal = *(struct in_addr*) hp->h_addr_list[i];
        struct in6_addr* ia6 = (struct in6_addr*) hp->h_addr_list[i];
        memset(ia6, 0, sizeof(struct in6_addr));

        // Synthesize /96 NAT64 prefix in place. The space has reserved by getanswer() and
        // _hf_gethtbyname2() in system/netd/resolv/gethnamaddr.cpp and
        // system/netd/resolv/sethostent.cpp.
        *ia6 = v6prefix->sin6_addr;
        ia6->s6_addr32[3] = iaOriginal.s_addr;

        if (DBG) {
            char buf[INET6_ADDRSTRLEN];  // big enough for either IPv4 or IPv6
            inet_ntop(AF_INET, &iaOriginal.s_addr, buf, sizeof(buf));
            ALOGD("DNS A record: %s", buf);
            inet_ntop(AF_INET6, &v6prefix->sin6_addr, buf, sizeof(buf));
            ALOGD("NAT64 prefix: %s", buf);
            inet_ntop(AF_INET6, ia6, buf, sizeof(buf));
            ALOGD("DNS64 Synthesized AAAA record: %s", buf);
        }
    }
    hp->h_addrtype = AF_INET6;
    hp->h_length = sizeof(in6_addr);

    if (DBG) logDnsQueryResult(hp);
    return true;
}

bool synthesizeNat64PrefixWithARecord(const netdutils::IPPrefix& prefix, struct addrinfo* result) {
    if (result == nullptr) return false;
    if (!onlyNonSpecialUseIPv4Addresses(result)) return false;
    if (!isValidNat64Prefix(prefix)) return false;

    struct sockaddr_storage ss = netdutils::IPSockAddr(prefix.ip());
    struct sockaddr_in6* v6prefix = (struct sockaddr_in6*) &ss;
    for (struct addrinfo* ai = result; ai; ai = ai->ai_next) {
        struct sockaddr_in sinOriginal = *(struct sockaddr_in*) ai->ai_addr;
        struct sockaddr_in6* sin6 = (struct sockaddr_in6*) ai->ai_addr;
        memset(sin6, 0, sizeof(sockaddr_in6));

        // Synthesize /96 NAT64 prefix in place. The space has reserved by get_ai() in
        // system/netd/resolv/getaddrinfo.cpp.
        sin6->sin6_addr = v6prefix->sin6_addr;
        sin6->sin6_addr.s6_addr32[3] = sinOriginal.sin_addr.s_addr;
        sin6->sin6_family = AF_INET6;
        sin6->sin6_port = sinOriginal.sin_port;
        ai->ai_addrlen = sizeof(struct sockaddr_in6);
        ai->ai_family = AF_INET6;

        if (DBG) {
            char buf[INET6_ADDRSTRLEN];  // big enough for either IPv4 or IPv6
            inet_ntop(AF_INET, &sinOriginal.sin_addr.s_addr, buf, sizeof(buf));
            ALOGD("DNS A record: %s", buf);
            inet_ntop(AF_INET6, &v6prefix->sin6_addr, buf, sizeof(buf));
            ALOGD("NAT64 prefix: %s", buf);
            inet_ntop(AF_INET6, &sin6->sin6_addr, buf, sizeof(buf));
            ALOGD("DNS64 Synthesized AAAA record: %s", buf);
        }
    }
    if (DBG) logDnsQueryResult(result);
    return true;
}

}  // namespace

DnsProxyListener::DnsProxyListener(const NetworkController* netCtrl, EventReporter* eventReporter) :
        FrameworkListener(SOCKET_NAME), mNetCtrl(netCtrl), mEventReporter(eventReporter) {
    registerCmd(new GetAddrInfoCmd(this));
    registerCmd(new GetHostByAddrCmd(this));
    registerCmd(new GetHostByNameCmd(this));
    registerCmd(new ResNSendCommand(this));
}

DnsProxyListener::GetAddrInfoHandler::GetAddrInfoHandler(
        SocketClient *c, char* host, char* service, struct addrinfo* hints,
        const android_net_context& netcontext, const int reportingLevel,
        const android::sp<android::net::metrics::INetdEventListener>& netdEventListener)
        : mClient(c),
          mHost(host),
          mService(service),
          mHints(hints),
          mNetContext(netcontext),
          mReportingLevel(reportingLevel),
          mNetdEventListener(netdEventListener) {
}

DnsProxyListener::GetAddrInfoHandler::~GetAddrInfoHandler() {
    free(mHost);
    free(mService);
    free(mHints);
}

static bool sendBE32(SocketClient* c, uint32_t data) {
    uint32_t be_data = htonl(data);
    return c->sendData(&be_data, sizeof(be_data)) == 0;
}

// Sends 4 bytes of big-endian length, followed by the data.
// Returns true on success.
static bool sendLenAndData(SocketClient* c, const int len, const void* data) {
    return sendBE32(c, len) && (len == 0 || c->sendData(data, len) == 0);
}

// Returns true on success
static bool sendhostent(SocketClient *c, struct hostent *hp) {
    bool success = true;
    int i;
    if (hp->h_name != nullptr) {
        success &= sendLenAndData(c, strlen(hp->h_name)+1, hp->h_name);
    } else {
        success &= sendLenAndData(c, 0, "") == 0;
    }

    for (i=0; hp->h_aliases[i] != nullptr; i++) {
        success &= sendLenAndData(c, strlen(hp->h_aliases[i])+1, hp->h_aliases[i]);
    }
    success &= sendLenAndData(c, 0, ""); // null to indicate we're done

    uint32_t buf = htonl(hp->h_addrtype);
    success &= c->sendData(&buf, sizeof(buf)) == 0;

    buf = htonl(hp->h_length);
    success &= c->sendData(&buf, sizeof(buf)) == 0;

    for (i=0; hp->h_addr_list[i] != nullptr; i++) {
        success &= sendLenAndData(c, 16, hp->h_addr_list[i]);
    }
    success &= sendLenAndData(c, 0, ""); // null to indicate we're done
    return success;
}

static bool sendaddrinfo(SocketClient* c, struct addrinfo* ai) {
    // struct addrinfo {
    //      int     ai_flags;       /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST */
    //      int     ai_family;      /* PF_xxx */
    //      int     ai_socktype;    /* SOCK_xxx */
    //      int     ai_protocol;    /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
    //      socklen_t ai_addrlen;   /* length of ai_addr */
    //      char    *ai_canonname;  /* canonical name for hostname */
    //      struct  sockaddr *ai_addr;      /* binary address */
    //      struct  addrinfo *ai_next;      /* next structure in linked list */
    // };

    // Write the struct piece by piece because we might be a 64-bit netd
    // talking to a 32-bit process.
    bool success =
            sendBE32(c, ai->ai_flags) &&
            sendBE32(c, ai->ai_family) &&
            sendBE32(c, ai->ai_socktype) &&
            sendBE32(c, ai->ai_protocol);
    if (!success) {
        return false;
    }

    // ai_addrlen and ai_addr.
    if (!sendLenAndData(c, ai->ai_addrlen, ai->ai_addr)) {
        return false;
    }

    // strlen(ai_canonname) and ai_canonname.
    if (!sendLenAndData(c, ai->ai_canonname ? strlen(ai->ai_canonname) + 1 : 0, ai->ai_canonname)) {
        return false;
    }

    return true;
}

void DnsProxyListener::GetAddrInfoHandler::doDns64Synthesis(int32_t* rv, struct addrinfo** res) {
    if (mHost == nullptr) return;

    const bool ipv6WantedButNoData = (mHints && mHints->ai_family == AF_INET6 && *rv == EAI_NODATA);
    const bool unspecWantedButNoIPv6 =
            ((!mHints || mHints->ai_family == AF_UNSPEC) && *rv == 0 && onlyIPv4Answers(*res));

    if (!ipv6WantedButNoData && !unspecWantedButNoIPv6) {
        return;
    }

    netdutils::IPPrefix prefix{};
    if (net::gCtls->resolverCtrl.getPrefix64(mNetContext.dns_netid, &prefix)) {
        return;
    }

    if (ipv6WantedButNoData) {
        // If caller wants IPv6 answers but no data, try to query IPv4 answers for synthesis
        const uid_t uid = mClient->getUid();
        if (queryLimiter.start(uid)) {
            mHints->ai_family = AF_INET;
            // Don't need to do freeaddrinfo(res) before starting new DNS lookup because previous
            // DNS lookup is failed with error EAI_NODATA.
            *rv = RESOLV_STUB.android_getaddrinfofornetcontext(mHost, mService, mHints,
                                                               &mNetContext, res);
            queryLimiter.finish(uid);
            if (*rv) {
                *rv = EAI_NODATA;  // return original error code
                return;
            }
        } else {
            ALOGE("getaddrinfo: from UID %d, max concurrent queries reached", uid);
            return;
        }
    }

    if (!synthesizeNat64PrefixWithARecord(prefix, *res)) {
        if (ipv6WantedButNoData) {
            // If caller wants IPv6 answers but no data and failed to synthesize IPv6 answers,
            // don't return the IPv4 answers.
            *rv = EAI_NODATA;  // return original error code
            if (*res) {
                freeaddrinfo(*res);
                *res = nullptr;
            }
        }
    }
}

void DnsProxyListener::GetAddrInfoHandler::run() {
    if (DBG) {
        ALOGD("GetAddrInfoHandler, now for %s / %s / {%u,%u,%u,%u,%u,%u}", mHost, mService,
                mNetContext.app_netid, mNetContext.app_mark,
                mNetContext.dns_netid, mNetContext.dns_mark,
                mNetContext.uid, mNetContext.flags);
    }

    struct addrinfo* result = nullptr;
    Stopwatch s;
    maybeFixupNetContext(&mNetContext);
    const uid_t uid = mClient->getUid();
    int32_t rv = 0;
    if (queryLimiter.start(uid)) {
        rv = RESOLV_STUB.android_getaddrinfofornetcontext(mHost, mService, mHints, &mNetContext,
                                                          &result);
        queryLimiter.finish(uid);
    } else {
        // Note that this error code is currently not passed down to the client.
        // android_getaddrinfo_proxy() returns EAI_NODATA on any error.
        rv = EAI_MEMORY;
        ALOGE("getaddrinfo: from UID %d, max concurrent queries reached", uid);
    }
    const int latencyMs = lround(s.timeTaken());

    doDns64Synthesis(&rv, &result);

    if (rv) {
        // getaddrinfo failed
        mClient->sendBinaryMsg(ResponseCode::DnsProxyOperationFailed, &rv, sizeof(rv));
    } else {
        bool success = !mClient->sendCode(ResponseCode::DnsProxyQueryResult);
        struct addrinfo* ai = result;
        while (ai && success) {
            success = sendBE32(mClient, 1) && sendaddrinfo(mClient, ai);
            ai = ai->ai_next;
        }
        success = success && sendBE32(mClient, 0);
        if (!success) {
            ALOGW("Error writing DNS result to client");
        }
    }
    std::vector<String16> ip_addrs;
    int total_ip_addr_count = 0;
    if (result) {
        if (mNetdEventListener != nullptr
                && mReportingLevel == INetdEventListener::REPORTING_LEVEL_FULL) {
            for (addrinfo* ai = result; ai; ai = ai->ai_next) {
                sockaddr* ai_addr = ai->ai_addr;
                if (ai_addr) {
                    addIpAddrWithinLimit(&ip_addrs, ai_addr, ai->ai_addrlen);
                    total_ip_addr_count++;
                }
            }
        }
        freeaddrinfo(result);
    }
    mClient->decRef();
    if (mNetdEventListener != nullptr) {
        switch (mReportingLevel) {
            case INetdEventListener::REPORTING_LEVEL_NONE:
                // Skip reporting.
                break;
            case INetdEventListener::REPORTING_LEVEL_METRICS:
                // Metrics reporting is on. Send metrics.
                mNetdEventListener->onDnsEvent(mNetContext.dns_netid,
                                               INetdEventListener::EVENT_GETADDRINFO, rv,
                                               latencyMs, String16(""), {}, -1, -1);
                break;
            case INetdEventListener::REPORTING_LEVEL_FULL:
                // Full event info reporting is on. Send full info.
                mNetdEventListener->onDnsEvent(mNetContext.dns_netid,
                                               INetdEventListener::EVENT_GETADDRINFO, rv,
                                               latencyMs, String16(mHost), ip_addrs,
                                               total_ip_addr_count, mNetContext.uid);
                break;
        }
    } else {
        ALOGW("Netd event listener is not available; skipping.");
    }
}

namespace {

void addIpAddrWithinLimit(std::vector<android::String16>* ip_addrs, const sockaddr* addr,
                          socklen_t addrlen) {
    // ipAddresses array is limited to first INetdEventListener::DNS_REPORTED_IP_ADDRESSES_LIMIT
    // addresses for A and AAAA. Total count of addresses is provided, to be able to tell whether
    // some addresses didn't get logged.
    if (ip_addrs->size() < INetdEventListener::DNS_REPORTED_IP_ADDRESSES_LIMIT) {
        char ip_addr[INET6_ADDRSTRLEN];
        if (getnameinfo(addr, addrlen, ip_addr, sizeof(ip_addr), nullptr, 0, NI_NUMERICHOST) == 0) {
            ip_addrs->push_back(String16(ip_addr));
        }
    }
}

}  // namespace

DnsProxyListener::GetAddrInfoCmd::GetAddrInfoCmd(DnsProxyListener* dnsProxyListener) :
    NetdCommand("getaddrinfo"),
    mDnsProxyListener(dnsProxyListener) {
}

int DnsProxyListener::GetAddrInfoCmd::runCommand(SocketClient *cli,
                                            int argc, char **argv) {
    if (DBG) logArguments(argc, argv);

    if (argc != 8) {
        char* msg = nullptr;
        asprintf( &msg, "Invalid number of arguments to getaddrinfo: %i", argc);
        ALOGW("%s", msg);
        cli->sendMsg(ResponseCode::CommandParameterError, msg, false);
        free(msg);
        return -1;
    }

    char* name = argv[1];
    if (strcmp("^", name) == 0) {
        name = nullptr;
    } else {
        name = strdup(name);
    }

    char* service = argv[2];
    if (strcmp("^", service) == 0) {
        service = nullptr;
    } else {
        service = strdup(service);
    }

    struct addrinfo* hints = nullptr;
    int ai_flags = strtol(argv[3], nullptr, 10);
    int ai_family = strtol(argv[4], nullptr, 10);
    int ai_socktype = strtol(argv[5], nullptr, 10);
    int ai_protocol = strtol(argv[6], nullptr, 10);
    unsigned netId = strtoul(argv[7], nullptr, 10);
    const bool useLocalNameservers = checkAndClearUseLocalNameserversFlag(&netId);
    const uid_t uid = cli->getUid();

    android_net_context netcontext;
    mDnsProxyListener->mNetCtrl->getNetworkContext(netId, uid, &netcontext);
    if (useLocalNameservers) {
        netcontext.flags |= NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
    }

    if (ai_flags != -1 || ai_family != -1 ||
        ai_socktype != -1 || ai_protocol != -1) {
        hints = (struct addrinfo*) calloc(1, sizeof(struct addrinfo));
        hints->ai_flags = ai_flags;
        hints->ai_family = ai_family;
        hints->ai_socktype = ai_socktype;
        hints->ai_protocol = ai_protocol;
    }

    if (DBG) {
        ALOGD("GetAddrInfoHandler for %s / %s / {%u,%u,%u,%u,%u}",
             name ? name : "[nullhost]",
             service ? service : "[nullservice]",
             netcontext.app_netid, netcontext.app_mark,
             netcontext.dns_netid, netcontext.dns_mark,
             netcontext.uid);
    }

    const int metricsLevel = mDnsProxyListener->mEventReporter->getMetricsReportingLevel();

    DnsProxyListener::GetAddrInfoHandler* handler =
            new DnsProxyListener::GetAddrInfoHandler(cli, name, service, hints, netcontext,
                    metricsLevel, mDnsProxyListener->mEventReporter->getNetdEventListener());
    tryThreadOrError(cli, handler);
    return 0;
}

/*******************************************************
 *                  ResNSendCommand                  *
 *******************************************************/
DnsProxyListener::ResNSendCommand::ResNSendCommand(DnsProxyListener* dnsProxyListener)
    : NetdCommand("resnsend"), mDnsProxyListener(dnsProxyListener) {}

int DnsProxyListener::ResNSendCommand::runCommand(SocketClient* cli, int argc, char** argv) {
    if (DBG) logArguments(argc, argv);

    const uid_t uid = cli->getUid();
    if (argc != 3) {
        ALOGW("resnsend: from UID %d, invalid number of arguments to resnsend: %d", uid, argc);
        sendBE32(cli, -EINVAL);
        return -1;
    }

    unsigned netId;
    if (!simpleStrtoul(argv[2], &netId)) {
        ALOGW("resnsend: from UID %d, invalid netId", uid);
        sendBE32(cli, -EINVAL);
        return -1;
    }

    android_net_context netcontext;
    mDnsProxyListener->mNetCtrl->getNetworkContext(netId, uid, &netcontext);
    if (checkAndClearUseLocalNameserversFlag(&netId)) {
        netcontext.flags |= NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
    }
    const int metricsLevel = mDnsProxyListener->mEventReporter->getMetricsReportingLevel();

    DnsProxyListener::ResNSendHandler* handler = new DnsProxyListener::ResNSendHandler(
            cli, argv[1], netcontext, metricsLevel,
            mDnsProxyListener->mEventReporter->getNetdEventListener());
    tryThreadOrError(cli, handler);
    return 0;
}

DnsProxyListener::ResNSendHandler::ResNSendHandler(
        SocketClient* c, std::string msg, const android_net_context& netcontext,
        const int reportingLevel,
        const android::sp<android::net::metrics::INetdEventListener>& netdEventListener)
    : mClient(c),
      mMsg(std::move(msg)),
      mNetContext(netcontext),
      mReportingLevel(reportingLevel),
      mNetdEventListener(netdEventListener) {}

DnsProxyListener::ResNSendHandler::~ResNSendHandler() {
    mClient->decRef();
}

void DnsProxyListener::ResNSendHandler::run() {
    if (DBG) {
        ALOGD("ResNSendHandler, now for %s / {%u,%u,%u,%u,%u,%u}", mMsg.c_str(),
              mNetContext.app_netid, mNetContext.app_mark, mNetContext.dns_netid,
              mNetContext.dns_mark, mNetContext.uid, mNetContext.flags);
    }

    Stopwatch s;
    maybeFixupNetContext(&mNetContext);

    // Decode
    std::vector<uint8_t> msg(MAXPACKET, 0);

    // Max length of mMsg is less than 1024 since the CMD_BUF_SIZE in FrameworkListener is 1024
    int msgLen = b64_pton(mMsg.c_str(), msg.data(), MAXPACKET);
    if (msgLen == -1) {
        // Decode fail
        sendBE32(mClient, -EILSEQ);
        return;
    }

    const uid_t uid = mClient->getUid();
    int rr_type = 0;
    std::string rr_name;

    // TODO: Handle the case which is msg contains more than one query
    // Parse and store query type/name
    if (!parseQuery(msg.data(), msgLen, &rr_type, &rr_name)) {
        // If the query couldn't be parsed, block the request.
        ALOGW("resnsend: from UID %d, invalid query", uid);
        sendBE32(mClient, -EINVAL);
        return;
    }

    // Send DNS query
    std::vector<uint8_t> ansBuf(MAXPACKET, 0);
    int arcode, nsendAns = -1;
    if (queryLimiter.start(uid)) {
        nsendAns = RESOLV_STUB.resolv_res_nsend(&mNetContext, msg.data(), msgLen, ansBuf.data(),
                                                MAXPACKET, &arcode);
        queryLimiter.finish(uid);
    } else {
        ALOGW("resnsend: from UID %d, max concurrent queries reached", uid);
        nsendAns = -EBUSY;
    }

    const int latencyMs = lround(s.timeTaken());

    // Fail, send -errno
    if (nsendAns < 0) {
        sendBE32(mClient, nsendAns);
        return;
    }

    // Send rcode
    if (!sendBE32(mClient, arcode)) {
        ALOGW("resnsend: failed to send rcode to uid %d: %s", uid, strerror(errno));
        return;
    }

    // Send answer
    if (!sendLenAndData(mClient, nsendAns, ansBuf.data())) {
        ALOGW("resnsend: failed to send answer to uid %d: %s", uid, strerror(errno));
        return;
    }

    // Parse result for statistics
    if (mNetdEventListener != nullptr) {
        // TODO: Enable this when we have a INetdEventListener::EVENT_RES_NSEND constant
        if (0) {
            switch (mReportingLevel) {
                case INetdEventListener::REPORTING_LEVEL_NONE:
                    // Reporting is off.
                    break;
                case INetdEventListener::REPORTING_LEVEL_METRICS:
                    // Metrics reporting is on. Send metrics.
                    mNetdEventListener->onDnsEvent(
                            mNetContext.dns_netid, INetdEventListener::EVENT_GETHOSTBYNAME,
                            nsendAns > 0 ? 0 : nsendAns, latencyMs, String16(""), {}, -1, -1);
                    break;
                case INetdEventListener::REPORTING_LEVEL_FULL:
                    // Full event info reporting is on. Send full info.
                    std::vector<String16> ip_addrs;
                    int total_ip_addr_count =
                            extractIpAddressAnswers(ansBuf.data(), nsendAns, rr_type, &ip_addrs);
                    mNetdEventListener->onDnsEvent(
                            mNetContext.dns_netid, INetdEventListener::EVENT_GETHOSTBYNAME,
                            nsendAns > 0 ? 0 : nsendAns, latencyMs, String16(rr_name.c_str()),
                            ip_addrs, total_ip_addr_count, uid);
                    break;
            }
        }
    }
}

/*******************************************************
 *                  GetHostByName                      *
 *******************************************************/
DnsProxyListener::GetHostByNameCmd::GetHostByNameCmd(DnsProxyListener* dnsProxyListener) :
      NetdCommand("gethostbyname"),
      mDnsProxyListener(dnsProxyListener) {
}

int DnsProxyListener::GetHostByNameCmd::runCommand(SocketClient *cli,
                                            int argc, char **argv) {
    if (DBG) logArguments(argc, argv);

    if (argc != 4) {
        char* msg = nullptr;
        asprintf(&msg, "Invalid number of arguments to gethostbyname: %i", argc);
        ALOGW("%s", msg);
        cli->sendMsg(ResponseCode::CommandParameterError, msg, false);
        free(msg);
        return -1;
    }

    uid_t uid = cli->getUid();
    unsigned netId = strtoul(argv[1], nullptr, 10);
    const bool useLocalNameservers = checkAndClearUseLocalNameserversFlag(&netId);
    char* name = argv[2];
    int af = strtol(argv[3], nullptr, 10);

    if (strcmp(name, "^") == 0) {
        name = nullptr;
    } else {
        name = strdup(name);
    }

    android_net_context netcontext;
    mDnsProxyListener->mNetCtrl->getNetworkContext(netId, uid, &netcontext);
    if (useLocalNameservers) {
        netcontext.flags |= NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
    }

    const int metricsLevel = mDnsProxyListener->mEventReporter->getMetricsReportingLevel();

    DnsProxyListener::GetHostByNameHandler* handler =
            new DnsProxyListener::GetHostByNameHandler(cli, name, af, netcontext, metricsLevel,
                    mDnsProxyListener->mEventReporter->getNetdEventListener());
    tryThreadOrError(cli, handler);
    return 0;
}

DnsProxyListener::GetHostByNameHandler::GetHostByNameHandler(SocketClient* c, char* name, int af,
        const android_net_context& netcontext, const int metricsLevel,
        const android::sp<android::net::metrics::INetdEventListener>& netdEventListener)
        : mClient(c),
          mName(name),
          mAf(af),
          mNetContext(netcontext),
          mReportingLevel(metricsLevel),
          mNetdEventListener(netdEventListener) {
}

DnsProxyListener::GetHostByNameHandler::~GetHostByNameHandler() {
    free(mName);
}

void DnsProxyListener::GetHostByNameHandler::doDns64Synthesis(int32_t* rv, struct hostent** hpp) {
    netdutils::IPPrefix prefix{};
    // Don't have to consider family AF_UNSPEC case because gethostbyname{, 2} only supports
    // family AF_INET or AF_INET6.
    const bool ipv6WantedButNoData = (mAf == AF_INET6 && *rv == EAI_NODATA);

    if (!ipv6WantedButNoData) {
        return;
    }

    if (net::gCtls->resolverCtrl.getPrefix64(mNetContext.dns_netid, &prefix)) {
        return;
    }

    // If caller wants IPv6 answers but no data, try to query IPv4 answers for synthesis
    const uid_t uid = mClient->getUid();
    if (queryLimiter.start(uid)) {
        *rv = RESOLV_STUB.android_gethostbynamefornetcontext(mName, AF_INET, &mNetContext, hpp);
        queryLimiter.finish(uid);
        if (*rv) {
            *rv = EAI_NODATA;  // return original error code
            return;
        }
    } else {
        ALOGE("gethostbyname: from UID %d, max concurrent queries reached", uid);
        return;
    }

    if (!synthesizeNat64PrefixWithARecord(prefix, *hpp)) {
        // If caller wants IPv6 answers but no data and failed to synthesize IPv4 answers,
        // don't return the IPv4 answers.
        *hpp = nullptr;
    }
}

void DnsProxyListener::GetHostByNameHandler::run() {
    if (DBG) {
        ALOGD("DnsProxyListener::GetHostByNameHandler::run");
    }

    Stopwatch s;
    maybeFixupNetContext(&mNetContext);
    const uid_t uid = mClient->getUid();
    struct hostent* hp = nullptr;
    int32_t rv = 0;
    if (queryLimiter.start(uid)) {
        rv = RESOLV_STUB.android_gethostbynamefornetcontext(mName, mAf, &mNetContext, &hp);
        queryLimiter.finish(uid);
    } else {
        rv = EAI_MEMORY;
        ALOGE("gethostbyname: from UID %d, max concurrent queries reached", uid);
    }
    const int latencyMs = lround(s.timeTaken());

    doDns64Synthesis(&rv, &hp);

    if (DBG) {
        ALOGD("GetHostByNameHandler::run gethostbyname errno: %s hp->h_name = %s, name_len = %zu",
                hp ? "success" : strerror(errno),
                (hp && hp->h_name) ? hp->h_name : "null",
                (hp && hp->h_name) ? strlen(hp->h_name) + 1 : 0);
    }

    bool success = true;
    if (hp) {
        // hp is not nullptr iff. rv is 0.
        success = mClient->sendCode(ResponseCode::DnsProxyQueryResult) == 0;
        success &= sendhostent(mClient, hp);
    } else {
        success = mClient->sendBinaryMsg(ResponseCode::DnsProxyOperationFailed, nullptr, 0) == 0;
    }

    if (!success) {
        ALOGW("GetHostByNameHandler: Error writing DNS result to client");
    }

    if (mNetdEventListener != nullptr) {
        std::vector<String16> ip_addrs;
        int total_ip_addr_count = 0;
        if (mReportingLevel == INetdEventListener::REPORTING_LEVEL_FULL) {
            if (hp != nullptr && hp->h_addrtype == AF_INET) {
                in_addr** list = (in_addr**) hp->h_addr_list;
                for (int i = 0; list[i] != nullptr; i++) {
                    sockaddr_in sin = { .sin_family = AF_INET, .sin_addr = *list[i] };
                    addIpAddrWithinLimit(&ip_addrs, (sockaddr*) &sin, sizeof(sin));
                    total_ip_addr_count++;
                }
            } else if (hp != nullptr && hp->h_addrtype == AF_INET6) {
                in6_addr** list = (in6_addr**) hp->h_addr_list;
                for (int i = 0; list[i] != nullptr; i++) {
                    sockaddr_in6 sin6 = { .sin6_family = AF_INET6, .sin6_addr = *list[i] };
                    addIpAddrWithinLimit(&ip_addrs, (sockaddr*) &sin6, sizeof(sin6));
                    total_ip_addr_count++;
                }
            }
        }
        switch (mReportingLevel) {
            case INetdEventListener::REPORTING_LEVEL_NONE:
                // Reporting is off.
                break;
            case INetdEventListener::REPORTING_LEVEL_METRICS:
                // Metrics reporting is on. Send metrics.
                mNetdEventListener->onDnsEvent(mNetContext.dns_netid,
                                               INetdEventListener::EVENT_GETHOSTBYNAME,
                                               rv, latencyMs, String16(""), {}, -1, -1);
                break;
            case INetdEventListener::REPORTING_LEVEL_FULL:
                // Full event info reporting is on. Send full info.
                mNetdEventListener->onDnsEvent(mNetContext.dns_netid,
                                               INetdEventListener::EVENT_GETHOSTBYNAME,
                                               rv, latencyMs, String16(mName), ip_addrs,
                                               total_ip_addr_count, uid);
                break;
        }
    }

    mClient->decRef();
}


/*******************************************************
 *                  GetHostByAddr                      *
 *******************************************************/
DnsProxyListener::GetHostByAddrCmd::GetHostByAddrCmd(const DnsProxyListener* dnsProxyListener) :
        NetdCommand("gethostbyaddr"),
        mDnsProxyListener(dnsProxyListener) {
}

int DnsProxyListener::GetHostByAddrCmd::runCommand(SocketClient *cli,
                                            int argc, char **argv) {
    if (DBG) logArguments(argc, argv);

    if (argc != 5) {
        char* msg = nullptr;
        asprintf(&msg, "Invalid number of arguments to gethostbyaddr: %i", argc);
        ALOGW("%s", msg);
        cli->sendMsg(ResponseCode::CommandParameterError, msg, false);
        free(msg);
        return -1;
    }

    char* addrStr = argv[1];
    int addrLen = strtol(argv[2], nullptr, 10);
    int addrFamily = strtol(argv[3], nullptr, 10);
    uid_t uid = cli->getUid();
    unsigned netId = strtoul(argv[4], nullptr, 10);
    const bool useLocalNameservers = checkAndClearUseLocalNameserversFlag(&netId);

    void* addr = malloc(sizeof(struct in6_addr));
    errno = 0;
    int result = inet_pton(addrFamily, addrStr, addr);
    if (result <= 0) {
        char* msg = nullptr;
        asprintf(&msg, "inet_pton(\"%s\") failed %s", addrStr, strerror(errno));
        ALOGW("%s", msg);
        cli->sendMsg(ResponseCode::OperationFailed, msg, false);
        free(addr);
        free(msg);
        return -1;
    }

    android_net_context netcontext;
    mDnsProxyListener->mNetCtrl->getNetworkContext(netId, uid, &netcontext);
    if (useLocalNameservers) {
        netcontext.flags |= NET_CONTEXT_FLAG_USE_LOCAL_NAMESERVERS;
    }

    DnsProxyListener::GetHostByAddrHandler* handler =
            new DnsProxyListener::GetHostByAddrHandler(cli, addr, addrLen, addrFamily, netcontext);
    tryThreadOrError(cli, handler);
    return 0;
}

DnsProxyListener::GetHostByAddrHandler::GetHostByAddrHandler(
          SocketClient* c,
          void* address,
          int addressLen,
          int addressFamily,
          const android_net_context& netcontext)
        : mClient(c),
          mAddress(address),
          mAddressLen(addressLen),
          mAddressFamily(addressFamily),
          mNetContext(netcontext) {
}

DnsProxyListener::GetHostByAddrHandler::~GetHostByAddrHandler() {
    free(mAddress);
}

void DnsProxyListener::GetHostByAddrHandler::doDns64ReverseLookup(struct hostent** hpp) {
    if (*hpp != nullptr || mAddressFamily != AF_INET6 || !mAddress) {
        return;
    }

    netdutils::IPPrefix prefix{};
    if (net::gCtls->resolverCtrl.getPrefix64(mNetContext.dns_netid, &prefix)) {
        return;
    }

    if (!isValidNat64Prefix(prefix)) {
        return;
    }

    struct sockaddr_storage ss = netdutils::IPSockAddr(prefix.ip());
    struct sockaddr_in6* v6prefix = (struct sockaddr_in6*) &ss;
    struct in6_addr v6addr = *(in6_addr*) mAddress;
    // Check if address has NAT64 prefix. Only /96 IPv6 NAT64 prefixes are supported
    if ((v6addr.s6_addr32[0] != v6prefix->sin6_addr.s6_addr32[0]) ||
        (v6addr.s6_addr32[1] != v6prefix->sin6_addr.s6_addr32[1]) ||
        (v6addr.s6_addr32[2] != v6prefix->sin6_addr.s6_addr32[2])) {
        return;
    }

    const uid_t uid = mClient->getUid();
    if (queryLimiter.start(uid)) {
        // Remove NAT64 prefix and do reverse DNS query
        struct in_addr v4addr = {.s_addr = v6addr.s6_addr32[3]};
        *hpp = RESOLV_STUB.android_gethostbyaddrfornetcontext(&v4addr, sizeof(v4addr), AF_INET,
                                                              &mNetContext);
        queryLimiter.finish(uid);
        if (*hpp) {
            // Replace IPv4 address with original queried IPv6 address in place. The space has
            // reserved by _dns_gethtbyaddr() and netbsd_gethostent_r() in
            // system/netd/resolv/gethnamaddr.cpp.
            // Note that android_gethostbyaddrfornetcontext returns only one entry in result.
            memcpy((*hpp)->h_addr_list[0], &v6addr, sizeof(v6addr));
            (*hpp)->h_addrtype = AF_INET6;
            (*hpp)->h_length = sizeof(struct in6_addr);
        }
    } else {
        ALOGE("gethostbyaddr: from UID %d, max concurrent queries reached", uid);
    }
}

void DnsProxyListener::GetHostByAddrHandler::run() {
    if (DBG) {
        ALOGD("DnsProxyListener::GetHostByAddrHandler::run");
    }

    maybeFixupNetContext(&mNetContext);
    const uid_t uid = mClient->getUid();
    struct hostent* hp = nullptr;
    if (queryLimiter.start(uid)) {
        hp = RESOLV_STUB.android_gethostbyaddrfornetcontext(mAddress, mAddressLen, mAddressFamily,
                                                            &mNetContext);
        queryLimiter.finish(uid);
    } else {
        ALOGE("gethostbyaddr: from UID %d, max concurrent queries reached", uid);
    }

    doDns64ReverseLookup(&hp);

    if (DBG) {
        ALOGD("GetHostByAddrHandler::run gethostbyaddr errno: %s hp->h_name = %s, name_len = %zu",
                hp ? "success" : strerror(errno),
                (hp && hp->h_name) ? hp->h_name : "null",
                (hp && hp->h_name) ? strlen(hp->h_name) + 1 : 0);
    }

    bool success = true;
    if (hp) {
        success = mClient->sendCode(ResponseCode::DnsProxyQueryResult) == 0;
        success &= sendhostent(mClient, hp);
    } else {
        success = mClient->sendBinaryMsg(ResponseCode::DnsProxyOperationFailed, nullptr, 0) == 0;
    }

    if (!success) {
        ALOGW("GetHostByAddrHandler: Error writing DNS result to client");
    }
    mClient->decRef();
}

}  // namespace net
}  // namespace android