mDNSResponder/mDNSCore/uDNS.c

/*
 * Copyright (c) 2002-2020 Apple Inc. All rights reserved.
 *
 * 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.

 * To Do:
 * Elimate all mDNSPlatformMemAllocate/mDNSPlatformMemFree from this code -- the core code
 * is supposed to be malloc-free so that it runs in constant memory determined at compile-time.
 * Any dynamic run-time requirements should be handled by the platform layer below or client layer above
 */

#include "uDNS.h"

#if MDNSRESPONDER_SUPPORTS(APPLE, METRICS)
#include "Metrics.h"
#endif

#if MDNSRESPONDER_SUPPORTS(APPLE, SYMPTOMS)
#include "SymptomReporter.h"
#endif

#if MDNSRESPONDER_SUPPORTS(APPLE, QUERIER)
#include "QuerierSupport.h"
#endif

#if MDNSRESPONDER_SUPPORTS(APPLE, DNSSECv2)
#include "dnssec_v2.h"
#endif // MDNSRESPONDER_SUPPORTS(APPLE, DNSSECv2)

#if (defined(_MSC_VER))
// Disable "assignment within conditional expression".
// Other compilers understand the convention that if you place the assignment expression within an extra pair
// of parentheses, this signals to the compiler that you really intended an assignment and no warning is necessary.
// The Microsoft compiler doesn't understand this convention, so in the absense of any other way to signal
// to the compiler that the assignment is intentional, we have to just turn this warning off completely.
    #pragma warning(disable:4706)
#endif

// For domain enumeration and automatic browsing
// This is the user's DNS search list.
// In each of these domains we search for our special pointer records (lb._dns-sd._udp.<domain>, etc.)
// to discover recommended domains for domain enumeration (browse, default browse, registration,
// default registration) and possibly one or more recommended automatic browsing domains.
mDNSexport SearchListElem *SearchList = mDNSNULL;

// The value can be set to true by the Platform code e.g., MacOSX uses the plist mechanism
mDNSBool StrictUnicastOrdering = mDNSfalse;

extern mDNS mDNSStorage;

// We keep track of the number of unicast DNS servers and log a message when we exceed 64.
// Currently the unicast queries maintain a 128 bit map to track the valid DNS servers for that
// question. Bit position is the index into the DNS server list. This is done so to try all
// the servers exactly once before giving up. If we could allocate memory in the core, then
// arbitrary limitation of 128 DNSServers can be removed.
#define MAX_UNICAST_DNS_SERVERS 128

#define SetNextuDNSEvent(m, rr) { \
        if ((m)->NextuDNSEvent - ((rr)->LastAPTime + (rr)->ThisAPInterval) >= 0)                                                                              \
            (m)->NextuDNSEvent = ((rr)->LastAPTime + (rr)->ThisAPInterval);                                                                         \
}

#ifndef UNICAST_DISABLED

// ***************************************************************************
#if COMPILER_LIKES_PRAGMA_MARK
#pragma mark - General Utility Functions
#endif

// set retry timestamp for record with exponential backoff
mDNSlocal void SetRecordRetry(mDNS *const m, AuthRecord *rr, mDNSu32 random)
{
    rr->LastAPTime = m->timenow;

    if (rr->expire && rr->refreshCount < MAX_UPDATE_REFRESH_COUNT)
    {
        mDNSs32 remaining = rr->expire - m->timenow;
        rr->refreshCount++;
        if (remaining > MIN_UPDATE_REFRESH_TIME)
        {
            // Refresh at 70% + random (currently it is 0 to 10%)
            rr->ThisAPInterval =  7 * (remaining/10) + (random ? random : mDNSRandom(remaining/10));
            // Don't update more often than 5 minutes
            if (rr->ThisAPInterval < MIN_UPDATE_REFRESH_TIME)
                rr->ThisAPInterval = MIN_UPDATE_REFRESH_TIME;
            LogInfo("SetRecordRetry refresh in %d of %d for %s",
                    rr->ThisAPInterval/mDNSPlatformOneSecond, (rr->expire - m->timenow)/mDNSPlatformOneSecond, ARDisplayString(m, rr));
        }
        else
        {
            rr->ThisAPInterval = MIN_UPDATE_REFRESH_TIME;
            LogInfo("SetRecordRetry clamping to min refresh in %d of %d for %s",
                    rr->ThisAPInterval/mDNSPlatformOneSecond, (rr->expire - m->timenow)/mDNSPlatformOneSecond, ARDisplayString(m, rr));
        }
        return;
    }

    rr->expire = 0;

    rr->ThisAPInterval = rr->ThisAPInterval * QuestionIntervalStep; // Same Retry logic as Unicast Queries
    if (rr->ThisAPInterval < INIT_RECORD_REG_INTERVAL)
        rr->ThisAPInterval = INIT_RECORD_REG_INTERVAL;
    if (rr->ThisAPInterval > MAX_RECORD_REG_INTERVAL)
        rr->ThisAPInterval = MAX_RECORD_REG_INTERVAL;

    LogInfo("SetRecordRetry retry in %d ms for %s", rr->ThisAPInterval, ARDisplayString(m, rr));
}

// ***************************************************************************
#if COMPILER_LIKES_PRAGMA_MARK
#pragma mark - Name Server List Management
#endif

#if !MDNSRESPONDER_SUPPORTS(APPLE, QUERIER)
mDNSexport DNSServer *mDNS_AddDNSServer(mDNS *const m, const domainname *domain, const mDNSInterfaceID interface,
    const mDNSs32 serviceID, const mDNSAddr *addr, const mDNSIPPort port, ScopeType scopeType, mDNSu32 timeout,
    mDNSBool isCell, mDNSBool isExpensive, mDNSBool isConstrained, mDNSBool isCLAT46, mDNSu32 resGroupID,
    mDNSBool usableA, mDNSBool usableAAAA, mDNSBool reqDO)
{
    DNSServer **p;
    DNSServer *server;
    int       dnsCount = CountOfUnicastDNSServers(m);
    if (dnsCount >= MAX_UNICAST_DNS_SERVERS)
    {
        LogMsg("mDNS_AddDNSServer: DNS server count of %d reached, not adding this server", dnsCount);
        return mDNSNULL;
    }

    if (!domain) domain = (const domainname *)"";

    LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO,
        "mDNS_AddDNSServer(%d): Adding " PRI_IP_ADDR " for " PRI_DM_NAME " interface " PUB_S " (%p), serviceID %u, "
        "scopeType %d, resGroupID %u" PUB_S PUB_S PUB_S PUB_S PUB_S PUB_S PUB_S,
        dnsCount + 1, addr, DM_NAME_PARAM(domain), InterfaceNameForID(&mDNSStorage, interface), interface, serviceID,
        (int)scopeType, resGroupID,
        usableA       ? ", usableA"     : "",
        usableAAAA    ? ", usableAAAA"  : "",
        isCell        ? ", cell"        : "",
        isExpensive   ? ", expensive"   : "",
        isConstrained ? ", constrained" : "",
        isCLAT46      ? ", CLAT46"      : "",
        reqDO         ? ", reqDO"       : "");

    // Scan our existing list to see if we already have a matching record for this DNS resolver
    for (p = &m->DNSServers; (server = *p) != mDNSNULL; p = &server->next)
    {
        if (server->interface       != interface)       continue;
        if (server->serviceID       != serviceID)       continue;
        if (!mDNSSameAddress(&server->addr, addr))      continue;
        if (!mDNSSameIPPort(server->port, port))        continue;
        if (!SameDomainName(&server->domain, domain))   continue;
        if (server->scopeType       != scopeType)       continue;
        if (server->timeout         != timeout)         continue;
        if (!server->usableA        != !usableA)        continue;
        if (!server->usableAAAA     != !usableAAAA)     continue;
        if (!server->isCell         != !isCell)         continue;
        if (!(server->flags & DNSServerFlag_Delete))
        {
            debugf("Note: DNS Server %#a:%d for domain %##s (%p) registered more than once",
                addr, mDNSVal16(port), domain->c, interface);
        }
        // If we found a matching record, cut it from the list
        // (and if we’re *not* resurrecting a record that was marked for deletion, it’s a duplicate,
        // and the debugf message signifies that we’re collapsing duplicate entries into one)
        *p = server->next;
        server->next = mDNSNULL;
        break;
    }

    // If we broke out because we found an existing matching record, advance our pointer to the end of the list
    while (*p)
    {
        p = &(*p)->next;
    }

    if (server)
    {
        if (server->flags & DNSServerFlag_Delete)
        {
#if MDNSRESPONDER_SUPPORTS(APPLE, SYMPTOMS)
            server->flags &= ~DNSServerFlag_Unreachable;
#endif
            server->flags &= ~DNSServerFlag_Delete;
        }
        server->isExpensive   = isExpensive;
        server->isConstrained = isConstrained;
        server->isCLAT46      = isCLAT46;
        *p = server;    // Append resurrected record at end of list
    }
    else
    {
        server = (DNSServer *) mDNSPlatformMemAllocateClear(sizeof(*server));
        if (!server)
        {
            LogMsg("Error: mDNS_AddDNSServer - malloc");
        }
        else
        {
            server->interface     = interface;
            server->serviceID     = serviceID;
            server->addr          = *addr;
            server->port          = port;
            server->scopeType     = scopeType;
            server->timeout       = timeout;
            server->usableA       = usableA;
            server->usableAAAA    = usableAAAA;
            server->isCell        = isCell;
            server->isExpensive   = isExpensive;
            server->isConstrained = isConstrained;
            server->isCLAT46      = isCLAT46;
            AssignDomainName(&server->domain, domain);
            *p = server; // Append new record at end of list
        }
    }
    if (server)
    {
        server->penaltyTime = 0;
        // We always update the ID (not just when we allocate a new instance) because we want
        // all the resGroupIDs for a particular domain to match.
        server->resGroupID  = resGroupID;
    }
    return(server);
}

// PenalizeDNSServer is called when the number of queries to the unicast
// DNS server exceeds MAX_UCAST_UNANSWERED_QUERIES or when we receive an
// error e.g., SERV_FAIL from DNS server.
mDNSexport void PenalizeDNSServer(mDNS *const m, DNSQuestion *q, mDNSOpaque16 responseFlags)
{
    DNSServer *new;
    DNSServer *orig = q->qDNSServer;
    mDNSu8 rcode = '\0';

    mDNS_CheckLock(m);

    LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO,
              "PenalizeDNSServer: Penalizing DNS server " PRI_IP_ADDR " question for question %p " PRI_DM_NAME " (" PUB_S ") SuppressUnusable %d",
              (q->qDNSServer ? &q->qDNSServer->addr : mDNSNULL), q, DM_NAME_PARAM(&q->qname), DNSTypeName(q->qtype), q->SuppressUnusable);

    // If we get error from any DNS server, remember the error. If all of the servers,
    // return the error, then return the first error.
    if (mDNSOpaque16IsZero(q->responseFlags))
        q->responseFlags = responseFlags;

    rcode = (mDNSu8)(responseFlags.b[1] & kDNSFlag1_RC_Mask);

    // After we reset the qDNSServer to NULL, we could get more SERV_FAILS that might end up
    // penalizing again.
    if (!q->qDNSServer)
        goto end;

    // If strict ordering of unicast servers needs to be preserved, we just lookup
    // the next best match server below
    //
    // If strict ordering is not required which is the default behavior, we penalize the server
    // for DNSSERVER_PENALTY_TIME. We may also use additional logic e.g., don't penalize for PTR
    // in the future.

    if (!StrictUnicastOrdering)
    {
        LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO, "PenalizeDNSServer: Strict Unicast Ordering is FALSE");
        // We penalize the server so that new queries don't pick this server for DNSSERVER_PENALTY_TIME
        // XXX Include other logic here to see if this server should really be penalized
        //
        if (q->qtype == kDNSType_PTR)
        {
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO, "PenalizeDNSServer: Not Penalizing PTR question");
        }
        else if ((rcode == kDNSFlag1_RC_FormErr) || (rcode == kDNSFlag1_RC_ServFail) || (rcode == kDNSFlag1_RC_NotImpl))
        {
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO,
                      "PenalizeDNSServer: Not Penalizing DNS Server since it at least responded with rcode %d", rcode);
        }
        else
        {
            const char *reason = "";
            if (rcode == kDNSFlag1_RC_Refused)
            {
                reason = " because server refused to answer";
            }
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO, "PenalizeDNSServer: Penalizing question type %d" PUB_S,
                      q->qtype, reason);
            q->qDNSServer->penaltyTime = NonZeroTime(m->timenow + DNSSERVER_PENALTY_TIME);
        }
    }
    else
    {
        LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_DEFAULT, "PenalizeDNSServer: Strict Unicast Ordering is TRUE");
    }

end:
    new = GetServerForQuestion(m, q);

    if (new == orig)
    {
        if (new)
        {
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_DEFAULT,
                      "PenalizeDNSServer: ERROR!! GetServerForQuestion returned the same server " PRI_IP_ADDR ":%d",
                      &new->addr, mDNSVal16(new->port));
            q->ThisQInterval = 0;   // Inactivate this question so that we dont bombard the network
        }
        else
        {
            // When we have no more DNS servers, we might end up calling PenalizeDNSServer multiple
            // times when we receive SERVFAIL from delayed packets in the network e.g., DNS server
            // is slow in responding and we have sent three queries. When we repeatedly call, it is
            // okay to receive the same NULL DNS server. Next time we try to send the query, we will
            // realize and re-initialize the DNS servers.
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO, "PenalizeDNSServer: GetServerForQuestion returned the same server NULL");
        }
    }
    else
    {
        // The new DNSServer is set in DNSServerChangeForQuestion
        DNSServerChangeForQuestion(m, q, new);

        if (new)
        {
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO,
                      "PenalizeDNSServer: Server for " PRI_DM_NAME " (" PUB_S ") changed to " PRI_IP_ADDR ":%d (" PRI_DM_NAME ")",
                      DM_NAME_PARAM(&q->qname), DNSTypeName(q->qtype), &q->qDNSServer->addr, mDNSVal16(q->qDNSServer->port), DM_NAME_PARAM(&q->qDNSServer->domain));
            // We want to try the next server immediately. As the question may already have backed off, reset
            // the interval. We do this only the first time when we try all the DNS servers. Once we reached the end of
            // list and retrying all the servers again e.g., at least one server failed to respond in the previous try, we
            // use the normal backoff which is done in uDNS_CheckCurrentQuestion when we send the packet out.
            if (!q->triedAllServersOnce)
            {
                q->ThisQInterval = InitialQuestionInterval;
                q->LastQTime  = m->timenow - q->ThisQInterval;
                SetNextQueryTime(m, q);
            }
        }
        else
        {
            // We don't have any more DNS servers for this question. If some server in the list did not return
            // any response, we need to keep retrying till we get a response. uDNS_CheckCurrentQuestion handles
            // this case.
            //
            // If all servers responded with a negative response, We need to do two things. First, generate a
            // negative response so that applications get a reply. We also need to reinitialize the DNS servers
            // so that when the cache expires, we can restart the query.  We defer this up until we generate
            // a negative cache response in uDNS_CheckCurrentQuestion.
            //
            // Be careful not to touch the ThisQInterval here. For a normal question, when we answer the question
            // in AnswerCurrentQuestionWithResourceRecord will set ThisQInterval to MaxQuestionInterval and hence
            // the next query will not happen until cache expiry. If it is a long lived question,
            // AnswerCurrentQuestionWithResourceRecord will not set it to MaxQuestionInterval. In that case,
            // we want the normal backoff to work.
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_INFO,
                      "PenalizeDNSServer: Server for %p, " PRI_DM_NAME " (" PUB_S ") changed to NULL, Interval %d",
                      q, DM_NAME_PARAM(&q->qname), DNSTypeName(q->qtype), q->ThisQInterval);
        }
        q->unansweredQueries = 0;

    }
}
#endif // !MDNSRESPONDER_SUPPORTS(APPLE, QUERIER)

// ***************************************************************************
#if COMPILER_LIKES_PRAGMA_MARK
#pragma mark - authorization management
#endif

mDNSlocal DomainAuthInfo *GetAuthInfoForName_direct(mDNS *m, const domainname *const name)
{
    const domainname *n = name;
    while (n->c[0])
    {
        DomainAuthInfo *ptr;
        for (ptr = m->AuthInfoList; ptr; ptr = ptr->next)
            if (SameDomainName(&ptr->domain, n))
            {
                debugf("GetAuthInfoForName %##s Matched %##s Key name %##s", name->c, ptr->domain.c, ptr->keyname.c);
                return(ptr);
            }
        n = (const domainname *)(n->c + 1 + n->c[0]);
    }
    //LogInfo("GetAuthInfoForName none found for %##s", name->c);
    return mDNSNULL;
}

// MUST be called with lock held
mDNSexport DomainAuthInfo *GetAuthInfoForName_internal(mDNS *m, const domainname *const name)
{
    DomainAuthInfo **p = &m->AuthInfoList;

    mDNS_CheckLock(m);

    // First purge any dead keys from the list
    while (*p)
    {
        if ((*p)->deltime && m->timenow - (*p)->deltime >= 0)
        {
            DNSQuestion *q;
            DomainAuthInfo *info = *p;
            LogInfo("GetAuthInfoForName_internal deleting expired key %##s %##s", info->domain.c, info->keyname.c);
            *p = info->next;    // Cut DomainAuthInfo from list *before* scanning our question list updating AuthInfo pointers
            for (q = m->Questions; q; q=q->next)
                if (q->AuthInfo == info)
                {
                    q->AuthInfo = GetAuthInfoForName_direct(m, &q->qname);
                    debugf("GetAuthInfoForName_internal updated q->AuthInfo from %##s to %##s for %##s (%s)",
                           info->domain.c, q->AuthInfo ? q->AuthInfo->domain.c : mDNSNULL, q->qname.c, DNSTypeName(q->qtype));
                }

            // Probably not essential, but just to be safe, zero out the secret key data
            // so we don't leave it hanging around in memory
            // (where it could potentially get exposed via some other bug)
            mDNSPlatformMemZero(info, sizeof(*info));
            mDNSPlatformMemFree(info);
        }
        else
            p = &(*p)->next;
    }

    return(GetAuthInfoForName_direct(m, name));
}

mDNSexport DomainAuthInfo *GetAuthInfoForName(mDNS *m, const domainname *const name)
{
    DomainAuthInfo *d;
    mDNS_Lock(m);
    d = GetAuthInfoForName_internal(m, name);
    mDNS_Unlock(m);
    return(d);
}

// MUST be called with the lock held
mDNSexport mStatus mDNS_SetSecretForDomain(mDNS *m, DomainAuthInfo *info,
                                           const domainname *domain, const domainname *keyname, const char *b64keydata, const domainname *hostname, mDNSIPPort *port)
{
    DNSQuestion *q;
    DomainAuthInfo **p = &m->AuthInfoList;
    if (!info || !b64keydata) { LogMsg("mDNS_SetSecretForDomain: ERROR: info %p b64keydata %p", info, b64keydata); return(mStatus_BadParamErr); }

    LogInfo("mDNS_SetSecretForDomain: domain %##s key %##s", domain->c, keyname->c);

    AssignDomainName(&info->domain,  domain);
    AssignDomainName(&info->keyname, keyname);
    if (hostname)
        AssignDomainName(&info->hostname, hostname);
    else
        info->hostname.c[0] = 0;
    if (port)
        info->port = *port;
    else
        info->port = zeroIPPort;
    mDNS_snprintf(info->b64keydata, sizeof(info->b64keydata), "%s", b64keydata);

    if (DNSDigest_ConstructHMACKeyfromBase64(info, b64keydata) < 0)
    {
        LogMsg("mDNS_SetSecretForDomain: ERROR: Could not convert shared secret from base64: domain %##s key %##s %s", domain->c, keyname->c, mDNS_LoggingEnabled ? b64keydata : "");
        return(mStatus_BadParamErr);
    }

    // Don't clear deltime until after we've ascertained that b64keydata is valid
    info->deltime = 0;

    while (*p && (*p) != info) p=&(*p)->next;
    if (*p) {LogInfo("mDNS_SetSecretForDomain: Domain %##s Already in list", (*p)->domain.c); return(mStatus_AlreadyRegistered);}

    info->next = mDNSNULL;
    *p = info;

    // Check to see if adding this new DomainAuthInfo has changed the credentials for any of our questions
    for (q = m->Questions; q; q=q->next)
    {
        DomainAuthInfo *newinfo = GetAuthInfoForQuestion(m, q);
        if (q->AuthInfo != newinfo)
        {
            debugf("mDNS_SetSecretForDomain updating q->AuthInfo from %##s to %##s for %##s (%s)",
                   q->AuthInfo ? q->AuthInfo->domain.c : mDNSNULL,
                   newinfo     ? newinfo->domain.c : mDNSNULL, q->qname.c, DNSTypeName(q->qtype));
            q->AuthInfo = newinfo;
        }
    }

    return(mStatus_NoError);
}

// ***************************************************************************
#if COMPILER_LIKES_PRAGMA_MARK
#pragma mark -
#pragma mark - NAT Traversal
#endif

// Keep track of when to request/refresh the external address using NAT-PMP or UPnP/IGD,
// and do so when necessary
mDNSlocal mStatus uDNS_RequestAddress(mDNS *m)
{
    mStatus err = mStatus_NoError;

    if (!m->NATTraversals)
    {
        m->retryGetAddr = NonZeroTime(m->timenow + FutureTime);
        LogInfo("uDNS_RequestAddress: Setting retryGetAddr to future");
    }
    else if (m->timenow - m->retryGetAddr >= 0)
    {
        if (mDNSv4AddrIsRFC1918(&m->Router.ip.v4))
        {
            static NATAddrRequest req = {NATMAP_VERS, NATOp_AddrRequest};
            static mDNSu8* start = (mDNSu8*)&req;
            mDNSu8* end = start + sizeof(NATAddrRequest);
            err = mDNSPlatformSendUDP(m, start, end, 0, mDNSNULL, &m->Router, NATPMPPort, mDNSfalse);
            debugf("uDNS_RequestAddress: Sent NAT-PMP external address request %d", err);

#ifdef _LEGACY_NAT_TRAVERSAL_
            if (mDNSIPPortIsZero(m->UPnPRouterPort) || mDNSIPPortIsZero(m->UPnPSOAPPort))
            {
                LNT_SendDiscoveryMsg(m);
                debugf("uDNS_RequestAddress: LNT_SendDiscoveryMsg");
            }
            else
            {
                mStatus lnterr = LNT_GetExternalAddress(m);
                if (lnterr)
                    LogMsg("uDNS_RequestAddress: LNT_GetExternalAddress returned error %d", lnterr);

                err = err ? err : lnterr; // NAT-PMP error takes precedence
            }
#endif // _LEGACY_NAT_TRAVERSAL_
        }

        // Always update the interval and retry time, so that even if we fail to send the
        // packet, we won't spin in an infinite loop repeatedly failing to send the packet
        if (m->retryIntervalGetAddr < NATMAP_INIT_RETRY)
        {
            m->retryIntervalGetAddr = NATMAP_INIT_RETRY;
        }
        else if (m->retryIntervalGetAddr < NATMAP_MAX_RETRY_INTERVAL / 2)
        {
            m->retryIntervalGetAddr *= 2;
        }
        else
        {
            m->retryIntervalGetAddr = NATMAP_MAX_RETRY_INTERVAL;
        }

        m->retryGetAddr = NonZeroTime(m->timenow + m->retryIntervalGetAddr);
    }
    else
    {
        debugf("uDNS_RequestAddress: Not time to send address request");
    }

    // Always update NextScheduledNATOp, even if we didn't change retryGetAddr, so we'll
    // be called when we need to send the request(s)
    if (m->NextScheduledNATOp - m->retryGetAddr > 0)
        m->NextScheduledNATOp = m->retryGetAddr;

    return err;
}

mDNSlocal mStatus uDNS_SendNATMsg(mDNS *m, NATTraversalInfo *info, mDNSBool usePCP, mDNSBool unmapping)
{
    mStatus err = mStatus_NoError;

    if (!info)
    {
        LogMsg("uDNS_SendNATMsg called unexpectedly with NULL info");
        return mStatus_BadParamErr;
    }

    // send msg if the router's address is private (which means it's non-zero)
    if (mDNSv4AddrIsRFC1918(&m->Router.ip.v4))
    {
        if (!usePCP)
        {
            if (!info->sentNATPMP)
            {
                if (info->Protocol)
                {
                    static NATPortMapRequest NATPortReq;
                    static const mDNSu8* end = (mDNSu8 *)&NATPortReq + sizeof(NATPortMapRequest);
                    mDNSu8 *p = (mDNSu8 *)&NATPortReq.NATReq_lease;

                    NATPortReq.vers    = NATMAP_VERS;
                    NATPortReq.opcode  = info->Protocol;
                    NATPortReq.unused  = zeroID;
                    NATPortReq.intport = info->IntPort;
                    NATPortReq.extport = info->RequestedPort;
                    p[0] = (mDNSu8)((info->NATLease >> 24) &  0xFF);
                    p[1] = (mDNSu8)((info->NATLease >> 16) &  0xFF);
                    p[2] = (mDNSu8)((info->NATLease >>  8) &  0xFF);
                    p[3] = (mDNSu8)( info->NATLease        &  0xFF);

                    err = mDNSPlatformSendUDP(m, (mDNSu8 *)&NATPortReq, end, 0, mDNSNULL, &m->Router, NATPMPPort, mDNSfalse);
                    debugf("uDNS_SendNATMsg: Sent NAT-PMP mapping request %d", err);
                }

                // In case the address request already went out for another NAT-T,
                // set the NewAddress to the currently known global external address, so
                // Address-only operations will get the callback immediately
                info->NewAddress = m->ExtAddress;

                // Remember that we just sent a NAT-PMP packet, so we won't resend one later.
                // We do this because the NAT-PMP "Unsupported Version" response has no
                // information about the (PCP) request that triggered it, so we must send
                // NAT-PMP requests for all operations. Without this, we'll send n PCP
                // requests for n operations, receive n NAT-PMP "Unsupported Version"
                // responses, and send n NAT-PMP requests for each of those responses,
                // resulting in (n + n^2) packets sent. We only want to send 2n packets:
                // n PCP requests followed by n NAT-PMP requests.
                info->sentNATPMP = mDNStrue;
            }
        }
        else
        {
            PCPMapRequest req;
            mDNSu8* start = (mDNSu8*)&req;
            mDNSu8* end = start + sizeof(req);
            mDNSu8* p = (mDNSu8*)&req.lifetime;

            req.version = PCP_VERS;
            req.opCode = PCPOp_Map;
            req.reserved = zeroID;

            p[0] = (mDNSu8)((info->NATLease >> 24) &  0xFF);
            p[1] = (mDNSu8)((info->NATLease >> 16) &  0xFF);
            p[2] = (mDNSu8)((info->NATLease >>  8) &  0xFF);
            p[3] = (mDNSu8)( info->NATLease        &  0xFF);

            mDNSAddrMapIPv4toIPv6(&m->AdvertisedV4.ip.v4, &req.clientAddr);

            req.nonce[0] = m->PCPNonce[0];
            req.nonce[1] = m->PCPNonce[1];
            req.nonce[2] = m->PCPNonce[2];

            req.protocol = (info->Protocol == NATOp_MapUDP ? PCPProto_UDP : PCPProto_TCP);

            req.reservedMapOp[0] = 0;
            req.reservedMapOp[1] = 0;
            req.reservedMapOp[2] = 0;

            req.intPort = info->Protocol ? info->IntPort : DiscardPort;
            req.extPort = info->RequestedPort;

            // Since we only support IPv4, even if using the all-zeros address, map it, so
            // the PCP gateway will give us an IPv4 address & not an IPv6 address.
            mDNSAddrMapIPv4toIPv6(&info->NewAddress, &req.extAddress);

            err = mDNSPlatformSendUDP(m, start, end, 0, mDNSNULL, &m->Router, NATPMPPort, mDNSfalse);
            debugf("uDNS_SendNATMsg: Sent PCP Mapping request %d", err);

            // Unset the sentNATPMP flag, so that we'll send a NAT-PMP packet if we
            // receive a NAT-PMP "Unsupported Version" packet. This will result in every
            // renewal, retransmission, etc. being tried first as PCP, then if a NAT-PMP
            // "Unsupported Version" response is received, fall-back & send the request
            // using NAT-PMP.
            info->sentNATPMP = mDNSfalse;

#ifdef _LEGACY_NAT_TRAVERSAL_
            // If an unmapping is being performed, then don't send an LNT discovery message or an LNT port map request.
            if (!unmapping)
            {
                if (mDNSIPPortIsZero(m->UPnPRouterPort) || mDNSIPPortIsZero(m->UPnPSOAPPort))
                {
                    LNT_SendDiscoveryMsg(m);
                    debugf("uDNS_SendNATMsg: LNT_SendDiscoveryMsg");
                }
                else
                {
                    mStatus lnterr = LNT_MapPort(m, info);
                    if (lnterr)
                        LogMsg("uDNS_SendNATMsg: LNT_MapPort returned error %d", lnterr);

                    err = err ? err : lnterr; // PCP error takes precedence
                }
            }
#else
            (void)unmapping; // Unused
#endif // _LEGACY_NAT_TRAVERSAL_
        }
    }

    return(err);
}

mDNSexport void RecreateNATMappings(mDNS *const m, const mDNSu32 waitTicks)
{
    mDNSu32 when = NonZeroTime(m->timenow + waitTicks);
    NATTraversalInfo *n;
    for (n = m->NATTraversals; n; n=n->next)
    {
        n->ExpiryTime    = 0;       // Mark this mapping as expired
        n->retryInterval = NATMAP_INIT_RETRY;
        n->retryPortMap  = when;
        n->lastSuccessfulProtocol = NATTProtocolNone;
        if (!n->Protocol) n->NewResult = mStatus_NoError;
#ifdef _LEGACY_NAT_TRAVERSAL_
        if (n->tcpInfo.sock) { mDNSPlatformTCPCloseConnection(n->tcpInfo.sock); n->tcpInfo.sock = mDNSNULL; }
#endif // _LEGACY_NAT_TRAVERSAL_
    }

    m->PCPNonce[0] = mDNSRandom(-1);
    m->PCPNonce[1] = mDNSRandom(-1);
    m->PCPNonce[2] = mDNSRandom(-1);
    m->retryIntervalGetAddr = 0;
    m->retryGetAddr = when;

#ifdef _LEGACY_NAT_TRAVERSAL_
    LNT_ClearState(m);
#endif // _LEGACY_NAT_TRAVERSAL_

    m->NextScheduledNATOp = m->timenow;     // Need to send packets immediately
}

mDNSexport void natTraversalHandleAddressReply(mDNS *const m, mDNSu16 err, mDNSv4Addr ExtAddr)
{
    static mDNSu16 last_err = 0;
    NATTraversalInfo *n;

    if (err)
    {
        if (err != last_err) LogMsg("Error getting external address %d", err);
        ExtAddr = zerov4Addr;
    }
    else
    {
        LogInfo("Received external IP address %.4a from NAT", &ExtAddr);
        if (mDNSv4AddrIsRFC1918(&ExtAddr))
            LogMsg("Double NAT (external NAT gateway address %.4a is also a private RFC 1918 address)", &ExtAddr);
        if (mDNSIPv4AddressIsZero(ExtAddr))
            err = NATErr_NetFail; // fake error to handle routers that pathologically report success with the zero address
    }

    // Globally remember the most recently discovered address, so it can be used in each
    // new NATTraversal structure
    m->ExtAddress = ExtAddr;

    if (!err) // Success, back-off to maximum interval
        m->retryIntervalGetAddr = NATMAP_MAX_RETRY_INTERVAL;
    else if (!last_err) // Failure after success, retry quickly (then back-off exponentially)
        m->retryIntervalGetAddr = NATMAP_INIT_RETRY;
    // else back-off normally in case of pathological failures

    m->retryGetAddr = m->timenow + m->retryIntervalGetAddr;
    if (m->NextScheduledNATOp - m->retryGetAddr > 0)
        m->NextScheduledNATOp = m->retryGetAddr;

    last_err = err;

    for (n = m->NATTraversals; n; n=n->next)
    {
        // We should change n->NewAddress only when n is one of:
        // 1) a mapping operation that most recently succeeded using NAT-PMP or UPnP/IGD,
        //    because such an operation needs the update now. If the lastSuccessfulProtocol
        //    is currently none, then natTraversalHandlePortMapReplyWithAddress() will be
        //    called should NAT-PMP or UPnP/IGD succeed in the future.
        // 2) an address-only operation that did not succeed via PCP, because when such an
        //    operation succeeds via PCP, it's for the TCP discard port just to learn the
        //    address. And that address may be different than the external address
        //    discovered via NAT-PMP or UPnP/IGD. If the lastSuccessfulProtocol
        //    is currently none, we must update the NewAddress as PCP may not succeed.
        if (!mDNSSameIPv4Address(n->NewAddress, ExtAddr) &&
             (n->Protocol ?
               (n->lastSuccessfulProtocol == NATTProtocolNATPMP || n->lastSuccessfulProtocol == NATTProtocolUPNPIGD) :
               (n->lastSuccessfulProtocol != NATTProtocolPCP)))
        {
            // Needs an update immediately
            n->NewAddress    = ExtAddr;
            n->ExpiryTime    = 0;
            n->retryInterval = NATMAP_INIT_RETRY;
            n->retryPortMap  = m->timenow;
#ifdef _LEGACY_NAT_TRAVERSAL_
            if (n->tcpInfo.sock) { mDNSPlatformTCPCloseConnection(n->tcpInfo.sock); n->tcpInfo.sock = mDNSNULL; }
#endif // _LEGACY_NAT_TRAVERSAL_

            m->NextScheduledNATOp = m->timenow;     // Need to send packets immediately
        }
    }
}

// Both places that call NATSetNextRenewalTime() update m->NextScheduledNATOp correctly afterwards
mDNSlocal void NATSetNextRenewalTime(mDNS *const m, NATTraversalInfo *n)
{
    n->retryInterval = (n->ExpiryTime - m->timenow)/2;
    if (n->retryInterval < NATMAP_MIN_RETRY_INTERVAL)   // Min retry interval is 2 seconds
        n->retryInterval = NATMAP_MIN_RETRY_INTERVAL;
    n->retryPortMap = m->timenow + n->retryInterval;
}

mDNSlocal void natTraversalHandlePortMapReplyWithAddress(mDNS *const m, NATTraversalInfo *n, const mDNSInterfaceID InterfaceID, mDNSu16 err, mDNSv4Addr extaddr, mDNSIPPort extport, mDNSu32 lease, NATTProtocol protocol)
{
    const char *prot = n->Protocol == 0 ? "Add" : n->Protocol == NATOp_MapUDP ? "UDP" : n->Protocol == NATOp_MapTCP ? "TCP" : "???";
    (void)prot;
    n->NewResult = err;
    if (err || lease == 0 || mDNSIPPortIsZero(extport))
    {
        LogInfo("natTraversalHandlePortMapReplyWithAddress: %p Response %s Port %5d External %.4a:%d lease %d error %d",
                n, prot, mDNSVal16(n->IntPort), &extaddr, mDNSVal16(extport), lease, err);
        n->retryInterval = NATMAP_MAX_RETRY_INTERVAL;
        n->retryPortMap = m->timenow + NATMAP_MAX_RETRY_INTERVAL;
        // No need to set m->NextScheduledNATOp here, since we're only ever extending the m->retryPortMap time
        if      (err == NATErr_Refused) n->NewResult = mStatus_NATPortMappingDisabled;
        else if (err > NATErr_None && err <= NATErr_Opcode) n->NewResult = mStatus_NATPortMappingUnsupported;
    }
    else
    {
        if (lease > 999999999UL / mDNSPlatformOneSecond)
            lease = 999999999UL / mDNSPlatformOneSecond;
        n->ExpiryTime = NonZeroTime(m->timenow + lease * mDNSPlatformOneSecond);

        if (!mDNSSameIPv4Address(n->NewAddress, extaddr) || !mDNSSameIPPort(n->RequestedPort, extport))
            LogInfo("natTraversalHandlePortMapReplyWithAddress: %p %s Response %s Port %5d External %.4a:%d changed to %.4a:%d lease %d",
                    n,
                    (n->lastSuccessfulProtocol == NATTProtocolNone    ? "None    " :
                     n->lastSuccessfulProtocol == NATTProtocolNATPMP  ? "NAT-PMP " :
                     n->lastSuccessfulProtocol == NATTProtocolUPNPIGD ? "UPnP/IGD" :
                     n->lastSuccessfulProtocol == NATTProtocolPCP     ? "PCP     " :
                     /* else */                                         "Unknown " ),
                    prot, mDNSVal16(n->IntPort), &n->NewAddress, mDNSVal16(n->RequestedPort),
                    &extaddr, mDNSVal16(extport), lease);

        n->InterfaceID   = InterfaceID;
        n->NewAddress    = extaddr;
        if (n->Protocol) n->RequestedPort = extport; // Don't report the (PCP) external port to address-only operations
        n->lastSuccessfulProtocol = protocol;

        NATSetNextRenewalTime(m, n);            // Got our port mapping; now set timer to renew it at halfway point
        m->NextScheduledNATOp = m->timenow;     // May need to invoke client callback immediately
    }
}

// To be called for NAT-PMP or UPnP/IGD mappings, to use currently discovered (global) address
mDNSexport void natTraversalHandlePortMapReply(mDNS *const m, NATTraversalInfo *n, const mDNSInterfaceID InterfaceID, mDNSu16 err, mDNSIPPort extport, mDNSu32 lease, NATTProtocol protocol)
{
    natTraversalHandlePortMapReplyWithAddress(m, n, InterfaceID, err, m->ExtAddress, extport, lease, protocol);
}

// Must be called with the mDNS_Lock held
mDNSexport mStatus mDNS_StartNATOperation_internal(mDNS *const m, NATTraversalInfo *traversal)
{
    NATTraversalInfo **n;

    LogInfo("mDNS_StartNATOperation_internal %p Protocol %d IntPort %d RequestedPort %d NATLease %d", traversal,
            traversal->Protocol, mDNSVal16(traversal->IntPort), mDNSVal16(traversal->RequestedPort), traversal->NATLease);

    // Note: It important that new traversal requests are appended at the *end* of the list, not prepended at the start
    for (n = &m->NATTraversals; *n; n=&(*n)->next)
    {
        if (traversal == *n)
        {
            LogFatalError("Error! Tried to add a NAT traversal that's already in the active list: request %p Prot %d Int %d TTL %d",
                   traversal, traversal->Protocol, mDNSVal16(traversal->IntPort), traversal->NATLease);
            return(mStatus_AlreadyRegistered);
        }
        if (traversal->Protocol && traversal->Protocol == (*n)->Protocol && mDNSSameIPPort(traversal->IntPort, (*n)->IntPort) &&
            !mDNSSameIPPort(traversal->IntPort, SSHPort))
            LogMsg("Warning: Created port mapping request %p Prot %d Int %d TTL %d "
                   "duplicates existing port mapping request %p Prot %d Int %d TTL %d",
                   traversal, traversal->Protocol, mDNSVal16(traversal->IntPort), traversal->NATLease,
                   *n,        (*n)->Protocol, mDNSVal16((*n)->IntPort), (*n)->NATLease);
    }

    // Initialize necessary fields
    traversal->next            = mDNSNULL;
    traversal->ExpiryTime      = 0;
    traversal->retryInterval   = NATMAP_INIT_RETRY;
    traversal->retryPortMap    = m->timenow;
    traversal->NewResult       = mStatus_NoError;
    traversal->lastSuccessfulProtocol = NATTProtocolNone;
    traversal->sentNATPMP      = mDNSfalse;
    traversal->ExternalAddress = onesIPv4Addr;
    traversal->NewAddress      = zerov4Addr;
    traversal->ExternalPort    = zeroIPPort;
    traversal->Lifetime        = 0;
    traversal->Result          = mStatus_NoError;

    // set default lease if necessary
    if (!traversal->NATLease) traversal->NATLease = NATMAP_DEFAULT_LEASE;

#ifdef _LEGACY_NAT_TRAVERSAL_
    mDNSPlatformMemZero(&traversal->tcpInfo, sizeof(traversal->tcpInfo));
#endif // _LEGACY_NAT_TRAVERSAL_

    if (!m->NATTraversals)      // If this is our first NAT request, kick off an address request too
    {
        m->retryGetAddr         = m->timenow;
        m->retryIntervalGetAddr = NATMAP_INIT_RETRY;
    }

    // If this is an address-only operation, initialize to the current global address,
    // or (in non-PCP environments) we won't know the address until the next external
    // address request/response.
    if (!traversal->Protocol)
    {
        traversal->NewAddress = m->ExtAddress;
    }

    m->NextScheduledNATOp = m->timenow; // This will always trigger sending the packet ASAP, and generate client callback if necessary

    *n = traversal;     // Append new NATTraversalInfo to the end of our list

    return(mStatus_NoError);
}

// Must be called with the mDNS_Lock held
mDNSexport mStatus mDNS_StopNATOperation_internal(mDNS *m, NATTraversalInfo *traversal)
{
    mDNSBool unmap = mDNStrue;
    NATTraversalInfo *p;
    NATTraversalInfo **ptr = &m->NATTraversals;

    while (*ptr && *ptr != traversal) ptr=&(*ptr)->next;
    if (*ptr) *ptr = (*ptr)->next;      // If we found it, cut this NATTraversalInfo struct from our list
    else
    {
        LogMsg("mDNS_StopNATOperation_internal: NATTraversalInfo %p not found in list", traversal);
        return(mStatus_BadReferenceErr);
    }

    LogInfo("mDNS_StopNATOperation_internal %p %d %d %d %d", traversal,
            traversal->Protocol, mDNSVal16(traversal->IntPort), mDNSVal16(traversal->RequestedPort), traversal->NATLease);

    if (m->CurrentNATTraversal == traversal)
        m->CurrentNATTraversal = m->CurrentNATTraversal->next;

    // If there is a match for the operation being stopped, don't send a deletion request (unmap)
    for (p = m->NATTraversals; p; p=p->next)
    {
        if (traversal->Protocol ?
            ((traversal->Protocol == p->Protocol && mDNSSameIPPort(traversal->IntPort, p->IntPort)) ||
             (!p->Protocol && traversal->Protocol == NATOp_MapTCP && mDNSSameIPPort(traversal->IntPort, DiscardPort))) :
            (!p->Protocol || (p->Protocol == NATOp_MapTCP && mDNSSameIPPort(p->IntPort, DiscardPort))))
        {
            LogInfo("Warning: Removed port mapping request %p Prot %d Int %d TTL %d "
                    "duplicates existing port mapping request %p Prot %d Int %d TTL %d",
                    traversal, traversal->Protocol, mDNSVal16(traversal->IntPort), traversal->NATLease,
                            p,         p->Protocol, mDNSVal16(        p->IntPort),         p->NATLease);
            unmap = mDNSfalse;
        }
    }

    // Even if we DIDN'T make a successful UPnP mapping yet, we might still have a partially-open TCP connection we need to clean up
    // Before zeroing traversal->RequestedPort below, perform the LNT unmapping, which requires the mapping's external port,
    // held by the traversal->RequestedPort variable.
    #ifdef _LEGACY_NAT_TRAVERSAL_
    {
        mStatus err = LNT_UnmapPort(m, traversal);
        if (err) LogMsg("Legacy NAT Traversal - unmap request failed with error %d", err);
    }
    #endif // _LEGACY_NAT_TRAVERSAL_

    if (traversal->ExpiryTime && unmap)
    {
        traversal->NATLease = 0;
        traversal->retryInterval = 0;

        // In case we most recently sent NAT-PMP, we need to set sentNATPMP to false so
        // that we'll send a NAT-PMP request to destroy the mapping. We do this because
        // the NATTraversal struct has already been cut from the list, and the client
        // layer will destroy the memory upon returning from this function, so we can't
        // try PCP first and then fall-back to NAT-PMP. That is, if we most recently
        // created/renewed the mapping using NAT-PMP, we need to destroy it using NAT-PMP
        // now, because we won't get a chance later.
        traversal->sentNATPMP = mDNSfalse;

        // Both NAT-PMP & PCP RFCs state that the suggested port in deletion requests
        // should be zero. And for PCP, the suggested external address should also be
        // zero, specifically, the all-zeros IPv4-mapped address, since we would only
        // would have requested an IPv4 address.
        traversal->RequestedPort = zeroIPPort;
        traversal->NewAddress = zerov4Addr;

        uDNS_SendNATMsg(m, traversal, traversal->lastSuccessfulProtocol != NATTProtocolNATPMP, mDNStrue);
    }

    return(mStatus_NoError);
}

mDNSexport mStatus mDNS_StartNATOperation(mDNS *const m, NATTraversalInfo *traversal)
{
    mStatus status;
    mDNS_Lock(m);
    status = mDNS_StartNATOperation_internal(m, traversal);
    mDNS_Unlock(m);
    return(status);
}

mDNSexport mStatus mDNS_StopNATOperation(mDNS *const m, NATTraversalInfo *traversal)
{
    mStatus status;
    mDNS_Lock(m);
    status = mDNS_StopNATOperation_internal(m, traversal);
    mDNS_Unlock(m);
    return(status);
}

// ***************************************************************************
#if COMPILER_LIKES_PRAGMA_MARK
#pragma mark -
#pragma mark - Long-Lived Queries
#endif

// Lock must be held -- otherwise m->timenow is undefined
mDNSlocal void StartLLQPolling(mDNS *const m, DNSQuestion *q)
{
    debugf("StartLLQPolling: %##s", q->qname.c);
    q->state = LLQ_Poll;
    q->ThisQInterval = INIT_UCAST_POLL_INTERVAL;
    // We want to send our poll query ASAP, but the "+ 1" is because if we set the time to now,
    // we risk causing spurious "SendQueries didn't send all its queries" log messages
    q->LastQTime     = m->timenow - q->ThisQInterval + 1;
    SetNextQueryTime(m, q);
}

mDNSlocal mDNSu8 *putLLQ(DNSMessage *const msg, mDNSu8 *ptr, const DNSQuestion *const question, const LLQOptData *const data)
{
    AuthRecord rr;
    ResourceRecord *opt = &rr.resrec;
    rdataOPT *optRD;

    //!!!KRS when we implement multiple llqs per message, we'll need to memmove anything past the question section
    ptr = putQuestion(msg, ptr, msg->data + AbsoluteMaxDNSMessageData, &question->qname, question->qtype, question->qclass);
    if (!ptr) { LogMsg("ERROR: putLLQ - putQuestion"); return mDNSNULL; }

    // locate OptRR if it exists, set pointer to end
    // !!!KRS implement me

    // format opt rr (fields not specified are zero-valued)
    mDNS_SetupResourceRecord(&rr, mDNSNULL, mDNSInterface_Any, kDNSType_OPT, kStandardTTL, kDNSRecordTypeKnownUnique, AuthRecordAny, mDNSNULL, mDNSNULL);
    opt->rrclass    = NormalMaxDNSMessageData;
    opt->rdlength   = sizeof(rdataOPT); // One option in this OPT record
    opt->rdestimate = sizeof(rdataOPT);

    optRD = &rr.resrec.rdata->u.opt[0];
    optRD->opt = kDNSOpt_LLQ;
    optRD->u.llq = *data;
    ptr = PutResourceRecordTTLJumbo(msg, ptr, &msg->h.numAdditionals, opt, 0);
    if (!ptr) { LogMsg("ERROR: putLLQ - PutResourceRecordTTLJumbo"); return mDNSNULL; }

    return ptr;
}

// Normally we'd just request event packets be sent directly to m->LLQNAT.ExternalPort, except...
// with LLQs over TLS/TCP we're doing a weird thing where instead of requesting packets be sent to ExternalAddress:ExternalPort
// we're requesting that packets be sent to ExternalPort, but at the source address of our outgoing TCP connection.
// Normally, after going through the NAT gateway, the source address of our outgoing TCP connection is the same as ExternalAddress,
// so this is fine, except when the TCP connection ends up going over a VPN tunnel instead.
// To work around this, if we find that the source address for our TCP connection is not a private address, we tell the Dot Mac
// LLQ server to send events to us directly at port 5353 on that address, instead of at our mapped external NAT port.

mDNSlocal mDNSu16 GetLLQEventPort(const mDNS *const m, const mDNSAddr *const dst)
{
    mDNSAddr src;
    mDNSPlatformSourceAddrForDest(&src, dst);
    //LogMsg("GetLLQEventPort: src %#a for dst %#a (%d)", &src, dst, mDNSv4AddrIsRFC1918(&src.ip.v4) ? mDNSVal16(m->LLQNAT.ExternalPort) : 0);
    return(mDNSv4AddrIsRFC1918(&src.ip.v4) ? mDNSVal16(m->LLQNAT.ExternalPort) : mDNSVal16(MulticastDNSPort));
}

// Normally called with llq set.
// May be called with llq NULL, when retransmitting a lost Challenge Response
mDNSlocal void sendChallengeResponse(mDNS *const m, DNSQuestion *const q, const LLQOptData *llq)
{
    mDNSu8 *responsePtr = m->omsg.data;
    LLQOptData llqBuf;

    if (q->tcp) { LogMsg("sendChallengeResponse: ERROR!!: question %##s (%s) tcp non-NULL", q->qname.c, DNSTypeName(q->qtype)); return; }

    if (q->ntries++ == kLLQ_MAX_TRIES)
    {
        LogMsg("sendChallengeResponse: %d failed attempts for LLQ %##s", kLLQ_MAX_TRIES, q->qname.c);
        StartLLQPolling(m,q);
        return;
    }

    if (!llq)       // Retransmission: need to make a new LLQOptData
    {
        llqBuf.vers     = kLLQ_Vers;
        llqBuf.llqOp    = kLLQOp_Setup;
        llqBuf.err      = LLQErr_NoError;   // Don't need to tell server UDP notification port when sending over UDP
        llqBuf.id       = q->id;
        llqBuf.llqlease = q->ReqLease;
        llq = &llqBuf;
    }

    q->LastQTime     = m->timenow;
    q->ThisQInterval = q->tcp ? 0 : (kLLQ_INIT_RESEND * q->ntries * mDNSPlatformOneSecond);     // If using TCP, don't need to retransmit
    SetNextQueryTime(m, q);

    // To simulate loss of challenge response packet, uncomment line below
    //if (q->ntries == 1) return;

    InitializeDNSMessage(&m->omsg.h, q->TargetQID, uQueryFlags);
    responsePtr = putLLQ(&m->omsg, responsePtr, q, llq);
    if (responsePtr)
    {
        mStatus err = mDNSSendDNSMessage(m, &m->omsg, responsePtr, mDNSInterface_Any, mDNSNULL, q->LocalSocket, &q->servAddr, q->servPort, mDNSNULL, mDNSfalse);
        if (err) { LogMsg("sendChallengeResponse: mDNSSendDNSMessage%s failed: %d", q->tcp ? " (TCP)" : "", err); }
    }
    else StartLLQPolling(m,q);
}

mDNSlocal void SetLLQTimer(mDNS *const m, DNSQuestion *const q, const LLQOptData *const llq)
{
    mDNSs32 lease = (mDNSs32)llq->llqlease * mDNSPlatformOneSecond;
    q->ReqLease      = llq->llqlease;
    q->LastQTime     = m->timenow;
    q->expire        = m->timenow + lease;
    q->ThisQInterval = lease/2 + mDNSRandom(lease/10);
    debugf("SetLLQTimer setting %##s (%s) to %d %d", q->qname.c, DNSTypeName(q->qtype), lease/mDNSPlatformOneSecond, q->ThisQInterval/mDNSPlatformOneSecond);
    SetNextQueryTime(m, q);
}

mDNSlocal void recvSetupResponse(mDNS *const m, mDNSu8 rcode, DNSQuestion *const q, const LLQOptData *const llq)
{
    if (rcode && rcode != kDNSFlag1_RC_NXDomain)
    { LogMsg("ERROR: recvSetupResponse %##s (%s) - rcode && rcode != kDNSFlag1_RC_NXDomain", q->qname.c, DNSTypeName(q->qtype)); return; }

    if (llq->llqOp != kLLQOp_Setup)
    { LogMsg("ERROR: recvSetupResponse %##s (%s) - bad op %d", q->qname.c, DNSTypeName(q->qtype), llq->llqOp); return; }

    if (llq->vers != kLLQ_Vers)
    { LogMsg("ERROR: recvSetupResponse %##s (%s) - bad vers %d", q->qname.c, DNSTypeName(q->qtype), llq->vers); return; }

    if (q->state == LLQ_InitialRequest)
    {
        //LogInfo("Got LLQ_InitialRequest");

        if (llq->err) { LogMsg("recvSetupResponse - received llq->err %d from server", llq->err); StartLLQPolling(m,q); return; }

        if (q->ReqLease != llq->llqlease)
            debugf("recvSetupResponse: requested lease %lu, granted lease %lu", q->ReqLease, llq->llqlease);

        // cache expiration in case we go to sleep before finishing setup
        q->ReqLease = llq->llqlease;
        q->expire = m->timenow + ((mDNSs32)llq->llqlease * mDNSPlatformOneSecond);

        // update state
        q->state  = LLQ_SecondaryRequest;
        q->id     = llq->id;
        q->ntries = 0; // first attempt to send response
        sendChallengeResponse(m, q, llq);
    }
    else if (q->state == LLQ_SecondaryRequest)
    {
        if (llq->err) { LogMsg("ERROR: recvSetupResponse %##s (%s) code %d from server", q->qname.c, DNSTypeName(q->qtype), llq->err); StartLLQPolling(m,q); return; }
        if (!mDNSSameOpaque64(&q->id, &llq->id))
        { LogMsg("recvSetupResponse - ID changed.  discarding"); return; }     // this can happen rarely (on packet loss + reordering)
        q->state         = LLQ_Established;
        q->ntries        = 0;
        SetLLQTimer(m, q, llq);
    }
}

mDNSexport uDNS_LLQType uDNS_recvLLQResponse(mDNS *const m, const DNSMessage *const msg, const mDNSu8 *const end,
                                             const mDNSAddr *const srcaddr, const mDNSIPPort srcport, DNSQuestion **matchQuestion)
{
    DNSQuestion pktQ, *q;
    if (msg->h.numQuestions && getQuestion(msg, msg->data, end, 0, &pktQ))
    {
        const rdataOPT *opt = GetLLQOptData(m, msg, end);

        for (q = m->Questions; q; q = q->next)
        {
            if (!mDNSOpaque16IsZero(q->TargetQID) && q->LongLived && q->qtype == pktQ.qtype && q->qnamehash == pktQ.qnamehash && SameDomainName(&q->qname, &pktQ.qname))
            {
                debugf("uDNS_recvLLQResponse found %##s (%s) %d %#a %#a %X %X %X %X %d",
                       q->qname.c, DNSTypeName(q->qtype), q->state, srcaddr, &q->servAddr,
                       opt ? opt->u.llq.id.l[0] : 0, opt ? opt->u.llq.id.l[1] : 0, q->id.l[0], q->id.l[1], opt ? opt->u.llq.llqOp : 0);
                if (q->state == LLQ_Poll) debugf("uDNS_LLQ_Events: q->state == LLQ_Poll msg->h.id %d q->TargetQID %d", mDNSVal16(msg->h.id), mDNSVal16(q->TargetQID));
                if (q->state == LLQ_Poll && mDNSSameOpaque16(msg->h.id, q->TargetQID))
                {
                    m->rec.r.resrec.RecordType = 0;     // Clear RecordType to show we're not still using it

                    // Don't reset the state to IntialRequest as we may write that to the dynamic store
                    // and PrefPane might wrongly think that we are "Starting" instead of "Polling". If
                    // we are in polling state because of PCP/NAT-PMP disabled or DoubleNAT, next LLQNATCallback
                    // would kick us back to LLQInitialRequest. So, resetting the state here may not be useful.
                    //
                    // If we have a good NAT (neither PCP/NAT-PMP disabled nor Double-NAT), then we should not be
                    // possibly in polling state. To be safe, we want to retry from the start in that case
                    // as there may not be another LLQNATCallback
                    //
                    // NOTE: We can be in polling state if we cannot resolve the SOA record i.e, servAddr is set to
                    // all ones. In that case, we would set it in LLQ_InitialRequest as it overrides the PCP/NAT-PMP or
                    // Double-NAT state.
                    if (!mDNSAddressIsOnes(&q->servAddr) && !mDNSIPPortIsZero(m->LLQNAT.ExternalPort) &&
                        !m->LLQNAT.Result)
                    {
                        debugf("uDNS_recvLLQResponse got poll response; moving to LLQ_InitialRequest for %##s (%s)", q->qname.c, DNSTypeName(q->qtype));
                        q->state         = LLQ_InitialRequest;
                    }
                    q->servPort      = zeroIPPort;      // Clear servPort so that startLLQHandshake will retry the GetZoneData processing
                    q->ThisQInterval = LLQ_POLL_INTERVAL + mDNSRandom(LLQ_POLL_INTERVAL/10);    // Retry LLQ setup in approx 15 minutes
                    q->LastQTime     = m->timenow;
                    SetNextQueryTime(m, q);
                    *matchQuestion = q;
                    return uDNS_LLQ_Entire;     // uDNS_LLQ_Entire means flush stale records; assume a large effective TTL
                }
                // Note: In LLQ Event packets, the msg->h.id does not match our q->TargetQID, because in that case the msg->h.id nonce is selected by the server
                else if (opt && q->state == LLQ_Established && opt->u.llq.llqOp == kLLQOp_Event && mDNSSameOpaque64(&opt->u.llq.id, &q->id))
                {
                    mDNSu8 *ackEnd;
                    //debugf("Sending LLQ ack for %##s (%s)", q->qname.c, DNSTypeName(q->qtype));
                    InitializeDNSMessage(&m->omsg.h, msg->h.id, ResponseFlags);
                    ackEnd = putLLQ(&m->omsg, m->omsg.data, q, &opt->u.llq);
                    if (ackEnd) mDNSSendDNSMessage(m, &m->omsg, ackEnd, mDNSInterface_Any, mDNSNULL, q->LocalSocket, srcaddr, srcport, mDNSNULL, mDNSfalse);
                    m->rec.r.resrec.RecordType = 0;     // Clear RecordType to show we're not still using it
                    debugf("uDNS_LLQ_Events: q->state == LLQ_Established msg->h.id %d q->TargetQID %d", mDNSVal16(msg->h.id), mDNSVal16(q->TargetQID));
                    *matchQuestion = q;
                    return uDNS_LLQ_Events;
                }
                if (opt && mDNSSameOpaque16(msg->h.id, q->TargetQID))
                {
                    if (q->state == LLQ_Established && opt->u.llq.llqOp == kLLQOp_Refresh && mDNSSameOpaque64(&opt->u.llq.id, &q->id) && msg->h.numAdditionals && !msg->h.numAnswers)
                    {
                        if (opt->u.llq.err != LLQErr_NoError) LogMsg("recvRefreshReply: received error %d from server", opt->u.llq.err);
                        else
                        {
                            //LogInfo("Received refresh confirmation ntries %d for %##s (%s)", q->ntries, q->qname.c, DNSTypeName(q->qtype));
                            // If we're waiting to go to sleep, then this LLQ deletion may have been the thing
                            // we were waiting for, so schedule another check to see if we can sleep now.
                            if (opt->u.llq.llqlease == 0 && m->SleepLimit) m->NextScheduledSPRetry = m->timenow;
                            GrantCacheExtensions(m, q, opt->u.llq.llqlease);
                            SetLLQTimer(m, q, &opt->u.llq);
                            q->ntries = 0;
                        }
                        m->rec.r.resrec.RecordType = 0;     // Clear RecordType to show we're not still using it
                        *matchQuestion = q;
                        return uDNS_LLQ_Ignore;
                    }
                    if (q->state < LLQ_Established && mDNSSameAddress(srcaddr, &q->servAddr))
                    {
                        LLQ_State oldstate = q->state;
                        recvSetupResponse(m, msg->h.flags.b[1] & kDNSFlag1_RC_Mask, q, &opt->u.llq);
                        m->rec.r.resrec.RecordType = 0;     // Clear RecordType to show we're not still using it
                        // We have a protocol anomaly here in the LLQ definition.
                        // Both the challenge packet from the server and the ack+answers packet have opt->u.llq.llqOp == kLLQOp_Setup.
                        // However, we need to treat them differently:
                        // The challenge packet has no answers in it, and tells us nothing about whether our cache entries
                        // are still valid, so this packet should not cause us to do anything that messes with our cache.
                        // The ack+answers packet gives us the whole truth, so we should handle it by updating our cache
                        // to match the answers in the packet, and only the answers in the packet.
                        *matchQuestion = q;
                        return (oldstate == LLQ_SecondaryRequest ? uDNS_LLQ_Entire : uDNS_LLQ_Ignore);
                    }
                }
            }
        }
        m->rec.r.resrec.RecordType = 0;     // Clear RecordType to show we're not still using it
    }
    *matchQuestion = mDNSNULL;
    return uDNS_LLQ_Not;
}

// Stub definition of TCPSocket_struct so we can access flags field. (Rest of TCPSocket_struct is platform-dependent.)
struct TCPSocket_struct { mDNSIPPort port; TCPSocketFlags flags; /* ... */ };

// tcpCallback is called to handle events (e.g. connection opening and data reception) on TCP connections for
// Private DNS operations -- private queries, private LLQs, private record updates and private service updates
mDNSlocal void tcpCallback(TCPSocket *sock, void *context, mDNSBool ConnectionEstablished, mStatus err)
{
    tcpInfo_t *tcpInfo = (tcpInfo_t *)context;
    mDNSBool closed  = mDNSfalse;
    mDNS      *m       = tcpInfo->m;
    DNSQuestion *const q = tcpInfo->question;
    tcpInfo_t **backpointer =
        q                 ? &q->tcp :
        tcpInfo->rr       ? &tcpInfo->rr->tcp : mDNSNULL;
    if (backpointer && *backpointer != tcpInfo)
        LogMsg("tcpCallback: %d backpointer %p incorrect tcpInfo %p question %p rr %p",
               mDNSPlatformTCPGetFD(tcpInfo->sock), *backpointer, tcpInfo, q, tcpInfo->rr);

    if (err) goto exit;

    if (ConnectionEstablished)
    {
        mDNSu8    *end = ((mDNSu8*) &tcpInfo->request) + tcpInfo->requestLen;
        DomainAuthInfo *AuthInfo;

        // Defensive coding for <rdar://problem/5546824> Crash in mDNSResponder at GetAuthInfoForName_internal + 366
        // Don't know yet what's causing this, but at least we can be cautious and try to avoid crashing if we find our pointers in an unexpected state
        if (tcpInfo->rr && tcpInfo->rr->resrec.name != &tcpInfo->rr->namestorage)
            LogMsg("tcpCallback: ERROR: tcpInfo->rr->resrec.name %p != &tcpInfo->rr->namestorage %p",
                   tcpInfo->rr->resrec.name, &tcpInfo->rr->namestorage);
        if (tcpInfo->rr  && tcpInfo->rr->resrec.name != &tcpInfo->rr->namestorage) return;

        AuthInfo =  tcpInfo->rr  ? GetAuthInfoForName(m, tcpInfo->rr->resrec.name)         : mDNSNULL;

        // connection is established - send the message
        if (q && q->LongLived && q->state == LLQ_Established)
        {
            // Lease renewal over TCP, resulting from opening a TCP connection in sendLLQRefresh
            end = ((mDNSu8*) &tcpInfo->request) + tcpInfo->requestLen;
        }
        else if (q && q->LongLived && q->state != LLQ_Poll && !mDNSIPPortIsZero(m->LLQNAT.ExternalPort) && !mDNSIPPortIsZero(q->servPort))
        {
            // Notes:
            // If we have a NAT port mapping, ExternalPort is the external port
            // If we have a routable address so we don't need a port mapping, ExternalPort is the same as our own internal port
            // If we need a NAT port mapping but can't get one, then ExternalPort is zero
            LLQOptData llqData;         // set llq rdata
            llqData.vers  = kLLQ_Vers;
            llqData.llqOp = kLLQOp_Setup;
            llqData.err   = GetLLQEventPort(m, &tcpInfo->Addr); // We're using TCP; tell server what UDP port to send notifications to
            LogInfo("tcpCallback: eventPort %d", llqData.err);
            llqData.id    = zeroOpaque64;
            llqData.llqlease = kLLQ_DefLease;
            InitializeDNSMessage(&tcpInfo->request.h, q->TargetQID, uQueryFlags);
            end = putLLQ(&tcpInfo->request, tcpInfo->request.data, q, &llqData);
            if (!end) { LogMsg("ERROR: tcpCallback - putLLQ"); err = mStatus_UnknownErr; goto exit; }
            AuthInfo = q->AuthInfo;     // Need to add TSIG to this message
            q->ntries = 0; // Reset ntries so that tcp/tls connection failures don't affect sendChallengeResponse failures
        }
        else if (q)
        {
            mDNSOpaque16 HeaderFlags = uQueryFlags;

            // LLQ Polling mode or non-LLQ uDNS over TCP
            InitializeDNSMessage(&tcpInfo->request.h, q->TargetQID, HeaderFlags);
            end = putQuestion(&tcpInfo->request, tcpInfo->request.data, tcpInfo->request.data + AbsoluteMaxDNSMessageData, &q->qname, q->qtype, q->qclass);

            AuthInfo = q->AuthInfo;     // Need to add TSIG to this message
        }

        err = mDNSSendDNSMessage(m, &tcpInfo->request, end, mDNSInterface_Any, sock, mDNSNULL, &tcpInfo->Addr, tcpInfo->Port, AuthInfo, mDNSfalse);
        if (err) { debugf("ERROR: tcpCallback: mDNSSendDNSMessage - %d", err); err = mStatus_UnknownErr; goto exit; }
#if MDNSRESPONDER_SUPPORTS(APPLE, METRICS)
        if (mDNSSameIPPort(tcpInfo->Port, UnicastDNSPort))
        {
            MetricsUpdateDNSQuerySize((mDNSu32)(end - (mDNSu8 *)&tcpInfo->request));
        }
#endif

        // Record time we sent this question
        if (q)
        {
            mDNS_Lock(m);
            q->LastQTime = m->timenow;
            if (q->ThisQInterval < (256 * mDNSPlatformOneSecond))   // Now we have a TCP connection open, make sure we wait at least 256 seconds before retrying
                q->ThisQInterval = (256 * mDNSPlatformOneSecond);
            SetNextQueryTime(m, q);
            mDNS_Unlock(m);
        }
    }
    else
    {
        long n;
        const mDNSBool Read_replylen = (tcpInfo->nread < 2);  // Do we need to read the replylen field first?
        if (Read_replylen)         // First read the two-byte length preceeding the DNS message
        {
            mDNSu8 *lenptr = (mDNSu8 *)&tcpInfo->replylen;
            n = mDNSPlatformReadTCP(sock, lenptr + tcpInfo->nread, 2 - tcpInfo->nread, &closed);
            if (n < 0)
            {
                LogMsg("ERROR: tcpCallback - attempt to read message length failed (%d)", n);
                err = mStatus_ConnFailed;
                goto exit;
            }
            else if (closed)
            {
                // It's perfectly fine for this socket to close after the first reply. The server might
                // be sending gratuitous replies using UDP and doesn't have a need to leave the TCP socket open.
                // We'll only log this event if we've never received a reply before.
                // BIND 9 appears to close an idle connection after 30 seconds.
                if (tcpInfo->numReplies == 0)
                {
                    LogMsg("ERROR: socket closed prematurely tcpInfo->nread = %d", tcpInfo->nread);
                    err = mStatus_ConnFailed;
                    goto exit;
                }
                else
                {
                    // Note that we may not be doing the best thing if an error occurs after we've sent a second request
                    // over this tcp connection.  That is, we only track whether we've received at least one response
                    // which may have been to a previous request sent over this tcp connection.
                    if (backpointer) *backpointer = mDNSNULL; // Clear client backpointer FIRST so we don't risk double-disposing our tcpInfo_t
                    DisposeTCPConn(tcpInfo);
                    return;
                }
            }

            tcpInfo->nread += n;
            if (tcpInfo->nread < 2) goto exit;

            tcpInfo->replylen = (mDNSu16)((mDNSu16)lenptr[0] << 8 | lenptr[1]);
            if (tcpInfo->replylen < sizeof(DNSMessageHeader))
            { LogMsg("ERROR: tcpCallback - length too short (%d bytes)", tcpInfo->replylen); err = mStatus_UnknownErr; goto exit; }

            tcpInfo->reply = (DNSMessage *) mDNSPlatformMemAllocate(tcpInfo->replylen);
            if (!tcpInfo->reply) { LogMsg("ERROR: tcpCallback - malloc failed"); err = mStatus_NoMemoryErr; goto exit; }
        }

        n = mDNSPlatformReadTCP(sock, ((char *)tcpInfo->reply) + (tcpInfo->nread - 2), tcpInfo->replylen - (tcpInfo->nread - 2), &closed);

        if (n < 0)
        {
            // If this is our only read for this invokation, and it fails, then that's bad.
            // But if we did successfully read some or all of the replylen field this time through,
            // and this is now our second read from the socket, then it's expected that sometimes
            // there may be no more data present, and that's perfectly okay.
            // Assuming failure of the second read is a problem is what caused this bug:
            // <rdar://problem/15043194> mDNSResponder fails to read DNS over TCP packet correctly
            if (!Read_replylen) { LogMsg("ERROR: tcpCallback - read returned %d", n); err = mStatus_ConnFailed; }
            goto exit;
        }
        else if (closed)
        {
            if (tcpInfo->numReplies == 0)
            {
                LogMsg("ERROR: socket closed prematurely tcpInfo->nread = %d", tcpInfo->nread);
                err = mStatus_ConnFailed;
                goto exit;
            }
            else
            {
                // Note that we may not be doing the best thing if an error occurs after we've sent a second request
                // over this tcp connection.  That is, we only track whether we've received at least one response
                // which may have been to a previous request sent over this tcp connection.
                if (backpointer) *backpointer = mDNSNULL; // Clear client backpointer FIRST so we don't risk double-disposing our tcpInfo_t
                DisposeTCPConn(tcpInfo);
                return;
            }
        }

        tcpInfo->nread += n;

        if ((tcpInfo->nread - 2) == tcpInfo->replylen)
        {
            mDNSBool tls;
            DNSMessage *reply = tcpInfo->reply;
            mDNSu8     *end   = (mDNSu8 *)tcpInfo->reply + tcpInfo->replylen;
            mDNSAddr Addr  = tcpInfo->Addr;
            mDNSIPPort Port  = tcpInfo->Port;
            mDNSIPPort srcPort = zeroIPPort;
            tcpInfo->numReplies++;
            tcpInfo->reply    = mDNSNULL;   // Detach reply buffer from tcpInfo_t, to make sure client callback can't cause it to be disposed
            tcpInfo->nread    = 0;
            tcpInfo->replylen = 0;

            // If we're going to dispose this connection, do it FIRST, before calling client callback
            // Note: Sleep code depends on us clearing *backpointer here -- it uses the clearing of rr->tcp
            // as the signal that the DNS deregistration operation with the server has completed, and the machine may now sleep
            // If we clear the tcp pointer in the question, mDNSCoreReceiveResponse cannot find a matching question. Hence
            // we store the minimal information i.e., the source port of the connection in the question itself.
            // Dereference sock before it is disposed in DisposeTCPConn below.

            if (sock->flags & kTCPSocketFlags_UseTLS) tls = mDNStrue;
            else tls = mDNSfalse;

            if (q && q->tcp) {srcPort = q->tcp->SrcPort; q->tcpSrcPort = srcPort;}

            if (backpointer)
                if (!q || !q->LongLived || m->SleepState)
                { *backpointer = mDNSNULL; DisposeTCPConn(tcpInfo); }

            mDNSCoreReceive(m, reply, end, &Addr, Port, tls ? (mDNSAddr *)1 : mDNSNULL, srcPort, 0);
            // USE CAUTION HERE: Invoking mDNSCoreReceive may have caused the environment to change, including canceling this operation itself

            mDNSPlatformMemFree(reply);
            return;
        }
    }

exit:

    if (err)
    {
        // Clear client backpointer FIRST -- that way if one of the callbacks cancels its operation
        // we won't end up double-disposing our tcpInfo_t
        if (backpointer) *backpointer = mDNSNULL;

        mDNS_Lock(m);       // Need to grab the lock to get m->timenow

        if (q)
        {
            if (q->ThisQInterval == 0)
            {
                // We get here when we fail to establish a new TCP/TLS connection that would have been used for a new LLQ request or an LLQ renewal.
                // Note that ThisQInterval is also zero when sendChallengeResponse resends the LLQ request on an extant TCP/TLS connection.
                q->LastQTime = m->timenow;
                if (q->LongLived)
                {
                    // We didn't get the chance to send our request packet before the TCP/TLS connection failed.
                    // We want to retry quickly, but want to back off exponentially in case the server is having issues.
                    // Since ThisQInterval was 0, we can't just multiply by QuestionIntervalStep, we must track the number
                    // of TCP/TLS connection failures using ntries.
                    mDNSu32 count = q->ntries + 1; // want to wait at least 1 second before retrying

                    q->ThisQInterval = InitialQuestionInterval;

                    for (; count; count--)
                        q->ThisQInterval *= QuestionIntervalStep;

                    if (q->ThisQInterval > LLQ_POLL_INTERVAL)
                        q->ThisQInterval = LLQ_POLL_INTERVAL;
                    else
                        q->ntries++;

                    LogMsg("tcpCallback: stream connection for LLQ %##s (%s) failed %d times, retrying in %d ms", q->qname.c, DNSTypeName(q->qtype), q->ntries, q->ThisQInterval);
                }
                else
                {
                    q->ThisQInterval = MAX_UCAST_POLL_INTERVAL;
                    LogMsg("tcpCallback: stream connection for %##s (%s) failed, retrying in %d ms", q->qname.c, DNSTypeName(q->qtype), q->ThisQInterval);
                }
                SetNextQueryTime(m, q);
            }
            else if (NextQSendTime(q) - m->timenow > (q->LongLived ? LLQ_POLL_INTERVAL : MAX_UCAST_POLL_INTERVAL))
            {
                // If we get an error and our next scheduled query for this question is more than the max interval from now,
                // reset the next query to ensure we wait no longer the maximum interval from now before trying again.
                q->LastQTime     = m->timenow;
                q->ThisQInterval = q->LongLived ? LLQ_POLL_INTERVAL : MAX_UCAST_POLL_INTERVAL;
                SetNextQueryTime(m, q);
                LogMsg("tcpCallback: stream connection for %##s (%s) failed, retrying in %d ms", q->qname.c, DNSTypeName(q->qtype), q->ThisQInterval);
            }

            // We're about to dispose of the TCP connection, so we must reset the state to retry over TCP/TLS
            // because sendChallengeResponse will send the query via UDP if we don't have a tcp pointer.
            // Resetting to LLQ_InitialRequest will cause uDNS_CheckCurrentQuestion to call startLLQHandshake, which
            // will attempt to establish a new tcp connection.
            if (q->LongLived && q->state == LLQ_SecondaryRequest)
                q->state = LLQ_InitialRequest;

            // ConnFailed may happen if the server sends a TCP reset or TLS fails, in which case we want to retry establishing the LLQ
            // quickly rather than switching to polling mode.  This case is handled by the above code to set q->ThisQInterval just above.
            // If the error isn't ConnFailed, then the LLQ is in bad shape, so we switch to polling mode.
            if (err != mStatus_ConnFailed)
            {
                if (q->LongLived && q->state != LLQ_Poll) StartLLQPolling(m, q);
            }
        }

        mDNS_Unlock(m);

        DisposeTCPConn(tcpInfo);
    }
}

mDNSlocal tcpInfo_t *MakeTCPConn(mDNS *const m, const DNSMessage *const msg, const mDNSu8 *const end,
                                 TCPSocketFlags flags, const mDNSAddr *const Addr, const mDNSIPPort Port, domainname *hostname,
                                 DNSQuestion *const question, AuthRecord *const rr)
{
    mStatus err;
    mDNSIPPort srcport = zeroIPPort;
    tcpInfo_t *info;
    mDNSBool useBackgroundTrafficClass;

    useBackgroundTrafficClass = question ? question->UseBackgroundTraffic : mDNSfalse;

    if ((flags & kTCPSocketFlags_UseTLS) && (!hostname || !hostname->c[0]))
    { LogMsg("MakeTCPConn: TLS connection being setup with NULL hostname"); return mDNSNULL; }

    info = (tcpInfo_t *) mDNSPlatformMemAllocateClear(sizeof(*info));
    if (!info) { LogMsg("ERROR: MakeTCP - memallocate failed"); return(mDNSNULL); }

    if (msg)
    {
        const mDNSu8 *const start = (const mDNSu8 *)msg;
        if ((end < start) || ((end - start) > (int)sizeof(info->request)))
        {
            LogRedact(MDNS_LOG_CATEGORY_DEFAULT, MDNS_LOG_ERROR,
                "MakeTCPConn: invalid DNS message pointers -- msg: %p, end: %p", msg, end);
            mDNSPlatformMemFree(info);
            return mDNSNULL;
        }
        info->requestLen = (int)(end - start);
        mDNSPlatformMemCopy(&info->request, msg, info->requestLen);
    }

    info->m          = m;
    info->sock       = mDNSPlatformTCPSocket(flags, Addr->type, &srcport, hostname, useBackgroundTrafficClass);
    info->question   = question;
    info->rr         = rr;
    info->Addr       = *Addr;
    info->Port       = Port;
    info->reply      = mDNSNULL;
    info->replylen   = 0;
    info->nread      = 0;
    info->numReplies = 0;
    info->SrcPort = srcport;

    if (!info->sock) { LogMsg("MakeTCPConn: unable to create TCP socket"); mDNSPlatformMemFree(info); return(mDNSNULL); }
    mDNSPlatformSetSocktOpt(info->sock, mDNSTransport_TCP, Addr->type, question);
    err = mDNSPlatformTCPConnect(info->sock, Addr, Port, (question ? question->InterfaceID : mDNSNULL), tcpCallback, info);

    // Probably suboptimal here.
    // Instead of returning mDNSNULL here on failure, we should probably invoke the callback with an error code.
    // That way clients can put all the error handling and retry/recovery code in one place,
    // instead of having to handle immediate errors in one place and async errors in another.
    // Also: "err == mStatus_ConnEstablished" probably never happens.

    // Don't need to log "connection failed" in customer builds -- it happens quite often during sleep, wake, configuration changes, etc.
    if      (err == mStatus_ConnEstablished) { tcpCallback(info->sock, info, mDNStrue, mStatus_NoError); }
    else if (err != mStatus_ConnPending    ) { LogInfo("MakeTCPConn: connection failed"); DisposeTCPConn(info); return(mDNSNULL); }
    return(info);
}

mDNSexport void DisposeTCPConn(struct tcpInfo_t *tcp)
{
    mDNSPlatformTCPCloseConnection(tcp->sock);
    if (tcp->reply) mDNSPlatformMemFree(tcp->reply);
    mDNSPlatformMemFree(tcp);
}

// Lock must be held
mDNSexport void startLLQHandshake(mDNS *m, DNSQuestion *q)
{
    // States prior to LLQ_InitialRequest should not react to NAT Mapping changes.
    // startLLQHandshake is never called with q->state < LLQ_InitialRequest except
    // from LLQNATCallback.   When we are actually trying to do LLQ, then q->state will
    // be equal to or greater than LLQ_InitialRequest when LLQNATCallback calls
    // startLLQHandshake.
    if (q->state < LLQ_InitialRequest)
    {
        return;
    }

    if (m->LLQNAT.clientContext != mDNSNULL) // LLQNAT just started, give it some time
    {
        LogInfo("startLLQHandshake: waiting for NAT status for %##s (%s)", q->qname.c, DNSTypeName(q->qtype));
        q->ThisQInterval = LLQ_POLL_INTERVAL + mDNSRandom(LLQ_POLL_INTERVAL/10);    // Retry in approx 15 minutes
        q->LastQTime = m->timenow;
        SetNextQueryTime(m, q);
        return;
    }

    // Either we don't have {PCP, NAT-PMP, UPnP/IGD} support (ExternalPort is zero) or behind a Double NAT that may or
    // may not have {PCP, NAT-PMP, UPnP/IGD} support (NATResult is non-zero)
    if (mDNSIPPortIsZero(m->LLQNAT.ExternalPort) || m->LLQNAT.Result)
    {
        LogInfo("startLLQHandshake: Cannot receive inbound packets; will poll for %##s (%s) External Port %d, NAT Result %d",
                q->qname.c, DNSTypeName(q->qtype), mDNSVal16(m->LLQNAT.ExternalPort), m->LLQNAT.Result);
        StartLLQPolling(m, q);
        return;
    }

    if (mDNSIPPortIsZero(q->servPort))
    {
        debugf("startLLQHandshake: StartGetZoneData for %##s (%s)", q->qname.c, DNSTypeName(q->qtype));
        q->ThisQInterval = LLQ_POLL_INTERVAL + mDNSRandom(LLQ_POLL_INTERVAL/10);    // Retry in approx 15 minutes
        q->LastQTime     = m->timenow;
        SetNextQueryTime(m, q);
        q->servAddr = zeroAddr;
        // We know q->servPort is zero because of check above
        if (q->nta) CancelGetZoneData(m, q->nta);
        q->nta = StartGetZoneData(m, &q->qname, ZoneServiceLLQ, LLQGotZoneData, q);
        return;
    }

    debugf("startLLQHandshake: m->AdvertisedV4 %#a%s Server %#a:%d%s %##s (%s)",
           &m->AdvertisedV4,                     mDNSv4AddrIsRFC1918(&m->AdvertisedV4.ip.v4) ? " (RFC 1918)" : "",
           &q->servAddr, mDNSVal16(q->servPort), mDNSAddrIsRFC1918(&q->servAddr)             ? " (RFC 1918)" : "",
           q->qname.c, DNSTypeName(q->qtype));

    if (q->ntries++ >= kLLQ_MAX_TRIES)
    {
        LogMsg("startLLQHandshake: %d failed attempts for LLQ %##s Polling.", kLLQ_MAX_TRIES, q->qname.c);
        StartLLQPolling(m, q);
    }
    else
    {
        mDNSu8 *end;
        LLQOptData llqData;

        // set llq rdata
        llqData.vers  = kLLQ_Vers;
        llqData.llqOp = kLLQOp_Setup;
        llqData.err   = LLQErr_NoError; // Don't need to tell server UDP notification port when sending over UDP
        llqData.id    = zeroOpaque64;
        llqData.llqlease = kLLQ_DefLease;

        InitializeDNSMessage(&m->omsg.h, q->TargetQID, uQueryFlags);
        end = putLLQ(&m->omsg, m->omsg.data, q, &llqData);
        if (!end) { LogMsg("ERROR: startLLQHandshake - putLLQ"); StartLLQPolling(m,q); return; }

        mDNSSendDNSMessage(m, &m->omsg, end, mDNSInterface_Any, mDNSNULL, q->LocalSocket, &q->servAddr, q->servPort , mDNSNULL, mDNSfalse);

        // update question state
        q->state         = LLQ_InitialRequest;
        q->ReqLease      = kLLQ_DefLease;
        q->ThisQInterval = (kLLQ_INIT_RESEND * mDNSPlatformOneSecond);
        q->LastQTime     = m->timenow;
        SetNextQueryTime(m, q);
    }
}


// forward declaration so GetServiceTarget can do reverse lookup if needed
mDNSlocal void GetStaticHostname(mDNS *m);

mDNSexport const domainname *GetServiceTarget(mDNS *m, AuthRecord *const rr)
{
    debugf("GetServiceTarget %##s", rr->resrec.name->c);

    if (!rr->AutoTarget)        // If not automatically tracking this host's current name, just return the existing target
        return(&rr->resrec.rdata->u.srv.target);
    else
    {
        {
            const int srvcount = CountLabels(rr->resrec.name);
            HostnameInfo *besthi = mDNSNULL, *hi;
            int best = 0;
            for (hi = m->Hostnames; hi; hi = hi->next)
                if (hi->arv4.state == regState_Registered || hi->arv4.state == regState_Refresh ||
                    hi->arv6.state == regState_Registered || hi->arv6.state == regState_Refresh)
                {
                    int x, hostcount = CountLabels(&hi->fqdn);
                    for (x = hostcount < srvcount ? hostcount : srvcount; x > 0 && x > best; x--)
                        if (SameDomainName(SkipLeadingLabels(rr->resrec.name, srvcount - x), SkipLeadingLabels(&hi->fqdn, hostcount - x)))
                        { best = x; besthi = hi; }
                }

            if (besthi) return(&besthi->fqdn);
        }
        if (m->StaticHostname.c[0]) return(&m->StaticHostname);
        else GetStaticHostname(m); // asynchronously do reverse lookup for primary IPv4 address
        LogInfo("GetServiceTarget: Returning NULL for %s", ARDisplayString(m, rr));
        return(mDNSNULL);
    }
}

mDNSlocal const domainname *PUBLIC_UPDATE_SERVICE_TYPE         = (const domainname*)"\x0B_dns-update"     "\x04_udp";
mDNSlocal const domainname *PUBLIC_LLQ_SERVICE_TYPE            = (const domainname*)"\x08_dns-llq"        "\x04_udp";

mDNSlocal const domainname *PRIVATE_UPDATE_SERVICE_TYPE        = (const domainname*)"\x0F_dns-update-tls" "\x04_tcp";
mDNSlocal const domainname *PRIVATE_QUERY_SERVICE_TYPE         = (const domainname*)"\x0E_dns-query-tls"  "\x04_tcp";
mDNSlocal const domainname *PRIVATE_LLQ_SERVICE_TYPE           = (const domainname*)"\x0C_dns-llq-tls"    "\x04_tcp";
mDNSlocal const domainname *DNS_PUSH_NOTIFICATION_SERVICE_TYPE = (const domainname*)"\x0D_dns-push-tls"   "\x04_tcp";

#define ZoneDataSRV(X) ( \
        (X)->ZoneService == ZoneServiceUpdate  ? ((X)->ZonePrivate ? PRIVATE_UPDATE_SERVICE_TYPE : PUBLIC_UPDATE_SERVICE_TYPE) : \
        (X)->ZoneService == ZoneServiceQuery   ? ((X)->ZonePrivate ? PRIVATE_QUERY_SERVICE_TYPE  : (const domainname*)""     ) : \
        (X)->ZoneService == ZoneServiceLLQ     ? ((X)->ZonePrivate ? PRIVATE_LLQ_SERVICE_TYPE    : PUBLIC_LLQ_SERVICE_TYPE   ) : \
        (X)->ZoneService == ZoneServiceDNSPush ? DNS_PUSH_NOTIFICATION_SERVICE_TYPE : (const domainname*)"")

// Forward reference: GetZoneData_StartQuery references GetZoneData_QuestionCallback, and
// GetZoneData_QuestionCallback calls GetZoneData_StartQuery
mDNSlocal mStatus GetZoneData_StartQuery(mDNS *const m, ZoneData *zd, mDNSu16 qtype);

// GetZoneData_QuestionCallback is called from normal client callback context (core API calls allowed)
mDNSlocal void GetZoneData_QuestionCallback(mDNS *const m, DNSQuestion *question, const ResourceRecord *const answer, QC_result AddRecord)
{
    ZoneData *zd = (ZoneData*)question->QuestionContext;

    debugf("GetZoneData_QuestionCallback: %s %s", AddRecord ? "Add" : "Rmv", RRDisplayString(m, answer));

    if (!AddRecord) return;                                             // Don't care about REMOVE events
    if (AddRecord == QC_addnocache && answer->rdlength == 0) return;    // Don't care about transient failure indications
    if (answer->rrtype != question->qtype) return;                      // Don't care about CNAMEs

    if (answer->rrtype == kDNSType_SOA)
    {
        debugf("GetZoneData GOT SOA %s", RRDisplayString(m, answer));
        mDNS_StopQuery(m, question);
        if (question->ThisQInterval != -1)
            LogMsg("GetZoneData_QuestionCallback: Question %##s (%s) ThisQInterval %d not -1", question->qname.c, DNSTypeName(question->qtype), question->ThisQInterval);
        if (answer->rdlength)
        {
            AssignDomainName(&zd->ZoneName, answer->name);
            zd->ZoneClass = answer->rrclass;
            GetZoneData_StartQuery(m, zd, kDNSType_SRV);
        }
        else if (zd->CurrentSOA->c[0])
        {
            zd->CurrentSOA = (domainname *)(zd->CurrentSOA->c + zd->CurrentSOA->c[0]+1);
            AssignDomainName(&zd->question.qname, zd->CurrentSOA);
            GetZoneData_StartQuery(m, zd, kDNSType_SOA);
        }
        else
        {
            LogInfo("GetZoneData recursed to root label of %##s without finding SOA", zd->ChildName.c);
            zd->ZoneDataCallback(m, mStatus_NoSuchNameErr, zd);
        }
    }
    else if (answer->rrtype == kDNSType_SRV)
    {
        debugf("GetZoneData GOT SRV %s", RRDisplayString(m, answer));
        mDNS_StopQuery(m, question);
        if (question->ThisQInterval != -1)
            LogMsg("GetZoneData_QuestionCallback: Question %##s (%s) ThisQInterval %d not -1", question->qname.c, DNSTypeName(question->qtype), question->ThisQInterval);
// Right now we don't want to fail back to non-encrypted operations
// If the AuthInfo has the AutoTunnel field set, then we want private or nothing
// <rdar://problem/5687667> BTMM: Don't fallback to unencrypted operations when SRV lookup fails
#if 0
        if (!answer->rdlength && zd->ZonePrivate && zd->ZoneService != ZoneServiceQuery)
        {
            zd->ZonePrivate = mDNSfalse;    // Causes ZoneDataSRV() to yield a different SRV name when building the query
            GetZoneData_StartQuery(m, zd, kDNSType_SRV);        // Try again, non-private this time
        }
        else
#endif
        {
            if (answer->rdlength)
            {
                AssignDomainName(&zd->Host, &answer->rdata->u.srv.target);
                zd->Port = answer->rdata->u.srv.port;
                // The MakeTCPConn path, which is used by everything but DNS Push, won't work at all for
                // IPv6.  This should be fixed for all cases we care about, but for now we make an exception
                // for Push notifications: we do not look up the a record here, but rather rely on the DSO
                // infrastructure to do a GetAddrInfo call on the name and try each IP address in sequence
                // until one connects.  We can't do this for the other use cases because this is in the DSO
                // code, not in MakeTCPConn.  Ultimately the fix for this is to use Network Framework to do
                // the connection establishment for all of these use cases.
                //
                // One implication of this is that if two different zones have DNS push server SRV records
                // pointing to the same server using a different domain name, we will not see these as being
                // the same server, and will not share the connection.   This isn't something we can easily
                // fix, and so the advice if someone runs into this and considers it a problem should be to
                // use the same name.
                //
                // Another issue with this code is that at present, we do not wait for more than one SRV
                // record--we cancel the query as soon as the first one comes in.   This isn't ideal: it
                // would be better to wait until we've gotten all our answers and then pick the one with
                // the highest priority.   Of course, this is unlikely to cause an operational problem in
                // practice, and as with the previous point, the fix is easy: figure out which server you
                // want people to use and don't list any other servers.   Fully switching to Network
                // Framework for this would (I think!) address this problem, or at least make it someone
                // else's problem.
                if (zd->ZoneService != ZoneServiceDNSPush)
                {
                    AssignDomainName(&zd->question.qname, &zd->Host);
                    GetZoneData_StartQuery(m, zd, kDNSType_A);
                }
                else
                {
                    zd->ZoneDataCallback(m, mStatus_NoError, zd);
                }
            }
            else
            {
                zd->ZonePrivate = mDNSfalse;
                zd->Host.c[0] = 0;
                zd->Port = zeroIPPort;
                zd->Addr = zeroAddr;
                zd->ZoneDataCallback(m, mStatus_NoError, zd);
            }
        }
    }
    else if (answer->rrtype == kDNSType_A)
    {
        debugf("GetZoneData GOT A %s", RRDisplayString(m, answer));
        mDNS_StopQuery(m, question);
        if (question->ThisQInterval != -1)
            LogMsg("GetZoneData_QuestionCallback: Question %##s (%s) ThisQInterval %d not -1", question->qname.c, DNSTypeName(question->qtype), question->ThisQInterval);
        zd->Addr.type  = mDNSAddrType_IPv4;
	if (answer->rdlength == 4)
            zd->Addr.ip.v4 = answer->rdata->u.ipv4;
	else
            zd->Addr.ip.v4 = zerov4Addr;
        // In order to simulate firewalls blocking our outgoing TCP connections, returning immediate ICMP errors or TCP resets,
        // the code below will make us try to connect to loopback, resulting in an immediate "port unreachable" failure.
        // This helps us test to make sure we handle this case gracefully
        // <rdar://problem/5607082> BTMM: mDNSResponder taking 100 percent CPU after upgrading to 10.5.1
#if 0
        zd->Addr.ip.v4.b[0] = 127;
        zd->Addr.ip.v4.b[1] = 0;
        zd->Addr.ip.v4.b[2] = 0;
        zd->Addr.ip.v4.b[3] = 1;
#endif
        // The caller needs to free the memory when done with zone data
        zd->ZoneDataCallback(m, mStatus_NoError, zd);
    }
}

// GetZoneData_StartQuery is called from normal client context (lock not held, or client callback)
mDNSlocal mStatus GetZoneData_StartQuery(mDNS *const m, ZoneData *zd, mDNSu16 qtype)
{
    if (qtype == kDNSType_SRV)
    {
        AssignDomainName(&zd->question.qname, ZoneDataSRV(zd));
        AppendDomainName(&zd->question.qname, &zd->ZoneName);
        debugf("lookupDNSPort %##s", zd->question.qname.c);
    }

    // CancelGetZoneData can get called at any time. We should stop the question if it has not been
    // stopped already. A value of -1 for ThisQInterval indicates that the question is not active
    // yet.
    zd->question.ThisQInterval       = -1;
    zd->question.InterfaceID         = mDNSInterface_Any;
    zd->question.flags               = 0;
    //zd->question.qname.c[0]        = 0;           // Already set
    zd->question.qtype               = qtype;
    zd->question.qclass              = kDNSClass_IN;
    zd->question.LongLived           = mDNSfalse;
    zd->question.ExpectUnique        = mDNStrue;
    zd->question.ForceMCast          = mDNSfalse;
    zd->question.ReturnIntermed      = mDNStrue;
    zd->question.SuppressUnusable    = mDNSfalse;
    zd->question.AppendSearchDomains = 0;
    zd->question.TimeoutQuestion     = 0;
    zd->question.WakeOnResolve       = 0;
    zd->question.UseBackgroundTraffic = mDNSfalse;
    zd->question.ProxyQuestion      = 0;
    zd->question.pid                 = mDNSPlatformGetPID();
    zd->question.euid                = 0;
    zd->question.QuestionCallback    = GetZoneData_QuestionCallback;
    zd->question.QuestionContext     = zd;

    //LogMsg("GetZoneData_StartQuery %##s (%s) %p", zd->question.qname.c, DNSTypeName(zd->question.qtype), zd->question.Private);
    return(mDNS_StartQuery(m, &zd->question));
}

// StartGetZoneData is an internal routine (i.e. must be called with the lock already held)
mDNSexport ZoneData *StartGetZoneData(mDNS *const m, const domainname *const name, const ZoneService target, ZoneDataCallback callback, void *ZoneDataContext)
{
    ZoneData *zd = (ZoneData*) mDNSPlatformMemAllocateClear(sizeof(*zd));
    if (!zd) { LogMsg("ERROR: StartGetZoneData - mDNSPlatformMemAllocateClear failed"); return mDNSNULL; }
    AssignDomainName(&zd->ChildName, name);
    zd->ZoneService      = target;
    zd->CurrentSOA       = &zd->ChildName;
    zd->ZoneName.c[0]    = 0;
    zd->ZoneClass        = 0;
    zd->Host.c[0]        = 0;
    zd->Port             = zeroIPPort;
    zd->Addr             = zeroAddr;
    zd->ZonePrivate      = mDNSfalse;
    zd->ZoneDataCallback = callback;
    zd->ZoneDataContext  = ZoneDataContext;

    zd->question.QuestionContext = zd;

    mDNS_DropLockBeforeCallback();      // GetZoneData_StartQuery expects to be called from a normal callback, so we emulate that here
    AssignDomainName(&zd->question.qname, zd->CurrentSOA);
    GetZoneData_StartQuery(m, zd, kDNSType_SOA);
    mDNS_ReclaimLockAfterCallback();

    return zd;
}

// Returns if the question is a GetZoneData question. These questions are special in
// that they are created internally while resolving a private query or LLQs.
mDNSexport mDNSBool IsGetZoneDataQuestion(DNSQuestion *q)
{
    if (q->QuestionCallback == GetZoneData_QuestionCallback) return(mDNStrue);
    else return(mDNSfalse);
}

// GetZoneData queries are a special case -- even if we have a key for them, we don't do them privately,
// because that would result in an infinite loop (i.e. to do a private query we first need to get
// the _dns-query-tls SRV record for the zone, and we can't do *that* privately because to do so
// we'd need to already know the _dns-query-tls SRV record.
// Also, as a general rule, we never do SOA queries privately
mDNSexport DomainAuthInfo *GetAuthInfoForQuestion(mDNS *m, const DNSQuestion *const q)  // Must be called with lock held
{
    if (q->QuestionCallback == GetZoneData_QuestionCallback) return(mDNSNULL);
    if (q->qtype            == kDNSType_SOA                ) return(mDNSNULL);
    return(GetAuthInfoForName_internal(m, &q->qname));
}

// ***************************************************************************
#if COMPILER_LIKES_PRAGMA_MARK
#pragma mark - host name and interface management
#endif

mDNSlocal void SendRecordRegistration(mDNS *const m, AuthRecord *rr);
mDNSlocal void SendRecordDeregistration(mDNS *m, AuthRecord *rr);
mDNSlocal mDNSBool IsRecordMergeable(mDNS *const m, AuthRecord *rr, mDNSs32 time);

// When this function is called, service record is already deregistered. We just
// have to deregister the PTR and TXT records.
mDNSlocal void UpdateAllServiceRecords(mDNS *const m, AuthRecord *rr, mDNSBool reg)
{
    AuthRecord *r, *srvRR;

    if (rr->resrec.rrtype != kDNSType_SRV) { LogMsg("UpdateAllServiceRecords:ERROR!! ResourceRecord not a service record %s", ARDisplayString(m, rr)); return; }

    if (reg && rr->state == regState_NoTarget) { LogMsg("UpdateAllServiceRecords:ERROR!! SRV record %s in noTarget state during registration", ARDisplayString(m, rr)); return; }

    LogInfo("UpdateAllServiceRecords: ResourceRecord %s", ARDisplayString(m, rr));

    for (r = m->ResourceRecords; r; r=r->next)
    {
        if (!AuthRecord_uDNS(r)) continue;
        srvRR = mDNSNULL;
        if (r->resrec.rrtype == kDNSType_PTR)
            srvRR = r->Additional1;
        else if (r->resrec.rrtype == kDNSType_TXT)
            srvRR = r->DependentOn;
        if (srvRR && srvRR->resrec.rrtype != kDNSType_SRV)
            LogMsg("UpdateAllServiceRecords: ERROR!! Resource record %s wrong, expecting SRV type", ARDisplayString(m, srvRR));
        if (srvRR == rr)
        {
            if (!reg)
            {
                LogInfo("UpdateAllServiceRecords: deregistering %s", ARDisplayString(m, r));
                r->SRVChanged = mDNStrue;
                r->ThisAPInterval = INIT_RECORD_REG_INTERVAL;
                r->LastAPTime = m->timenow - INIT_RECORD_REG_INTERVAL;
                r->state = regState_DeregPending;
            }
            else
            {
                // Clearing SRVchanged is a safety measure. If our pevious dereg never
                // came back and we had a target change, we are starting fresh
                r->SRVChanged = mDNSfalse;
                // if it is already registered or in the process of registering, then don't
                // bother re-registering. This happens today for non-BTMM domains where the
                // TXT and PTR get registered before SRV records because of the delay in
                // getting the port mapping. There is no point in re-registering the TXT
                // and PTR records.
                if ((r->state == regState_Registered) ||
                    (r->state == regState_Pending && r->nta && !mDNSIPv4AddressIsZero(r->nta->Addr.ip.v4)))
                    LogInfo("UpdateAllServiceRecords: not registering %s, state %d", ARDisplayString(m, r), r->state);
                else
                {
                    LogInfo("UpdateAllServiceRecords: registering %s, state %d", ARDisplayString(m, r), r->state);
                    ActivateUnicastRegistration(m, r);
                }
            }
        }
    }
}

// Called in normal client context (lock not held)
// Currently only supports SRV records for nat mapping
mDNSlocal void CompleteRecordNatMap(mDNS *m, NATTraversalInfo *n)
{
    const domainname *target;
    domainname *srvt;
    AuthRecord *rr = (AuthRecord *)n->clientContext;
    debugf("SRVNatMap complete %.4a IntPort %u ExternalPort %u NATLease %u", &n->ExternalAddress, mDNSVal16(n->IntPort), mDNSVal16(n->ExternalPort), n->NATLease);

    if (!rr) { LogMsg("CompleteRecordNatMap called with unknown AuthRecord object"); return; }
    if (!n->NATLease) { LogMsg("CompleteRecordNatMap No NATLease for %s", ARDisplayString(m, rr)); return; }

    if (rr->resrec.rrtype != kDNSType_SRV) {LogMsg("CompleteRecordNatMap: Not a service record %s", ARDisplayString(m, rr)); return; }

    if (rr->resrec.RecordType == kDNSRecordTypeDeregistering) { LogInfo("CompleteRecordNatMap called for %s, Service deregistering", ARDisplayString(m, rr)); return; }

    if (rr->state == regState_DeregPending) { LogInfo("CompleteRecordNatMap called for %s, record in DeregPending", ARDisplayString(m, rr)); return; }

    // As we free the zone info after registering/deregistering with the server (See hndlRecordUpdateReply),
    // we need to restart the get zone data and nat mapping request to get the latest mapping result as we can't handle it
    // at this moment. Restart from the beginning.
    if (!rr->nta || mDNSIPv4AddressIsZero(rr->nta->Addr.ip.v4))
    {
        LogInfo("CompleteRecordNatMap called for %s but no zone information!", ARDisplayString(m, rr));
        // We need to clear out the NATinfo state so that it will result in re-acquiring the mapping
        // and hence this callback called again.
        if (rr->NATinfo.clientContext)
        {
            mDNS_StopNATOperation_internal(m, &rr->NATinfo);
            rr->NATinfo.clientContext = mDNSNULL;
        }
        rr->state = regState_Pending;
        rr->ThisAPInterval = INIT_RECORD_REG_INTERVAL;
        rr->LastAPTime = m->timenow - INIT_RECORD_REG_INTERVAL;
        return;
    }

    mDNS_Lock(m);
    // Reevaluate the target always as Target could have changed while
    // we were getting the port mapping (See UpdateOneSRVRecord)
    target = GetServiceTarget(m, rr);
    srvt = GetRRDomainNameTarget(&rr->resrec);
    if (!target || target->c[0] == 0 || mDNSIPPortIsZero(n->ExternalPort))
    {
        if (target && target->c[0])
            LogInfo("CompleteRecordNatMap - Target %##s for ResourceRecord %##s, ExternalPort %d", target->c, rr->resrec.name->c, mDNSVal16(n->ExternalPort));
        else
            LogInfo("CompleteRecordNatMap - no target for %##s, ExternalPort %d", rr->resrec.name->c, mDNSVal16(n->ExternalPort));
        if (srvt) srvt->c[0] = 0;
        rr->state = regState_NoTarget;
        rr->resrec.rdlength = rr->resrec.rdestimate = 0;
        mDNS_Unlock(m);
        UpdateAllServiceRecords(m, rr, mDNSfalse);
        return;
    }
    LogInfo("CompleteRecordNatMap - Target %##s for ResourceRecord %##s, ExternalPort %d", target->c, rr->resrec.name->c, mDNSVal16(n->ExternalPort));
    // This function might get called multiple times during a network transition event. Previosuly, we could
    // have put the SRV record in NoTarget state above and deregistered all the other records. When this
    // function gets called again with a non-zero ExternalPort, we need to set the target and register the
    // other records again.
    if (srvt && !SameDomainName(srvt, target))
    {
        AssignDomainName(srvt, target);
        SetNewRData(&rr->resrec, mDNSNULL, 0);      // Update rdlength, rdestimate, rdatahash
    }

    // SRVChanged is set when when the target of the SRV record changes (See UpdateOneSRVRecord).
    // As a result of the target change, we might register just that SRV Record if it was
    // previously registered and we have a new target OR deregister SRV (and the associated
    // PTR/TXT records) if we don't have a target anymore. When we get a response from the server,
    // SRVChanged state tells that we registered/deregistered because of a target change
    // and hence handle accordingly e.g., if we deregistered, put the records in NoTarget state OR
    // if we registered then put it in Registered state.
    //
    // Here, we are registering all the records again from the beginning. Treat this as first time
    // registration rather than a temporary target change.
    rr->SRVChanged = mDNSfalse;

    // We want IsRecordMergeable to check whether it is a record whose update can be
    // sent with others. We set the time before we call IsRecordMergeable, so that
    // it does not fail this record based on time. We are interested in other checks
    // at this time
    rr->state = regState_Pending;
    rr->ThisAPInterval = INIT_RECORD_REG_INTERVAL;
    rr->LastAPTime = m->timenow - INIT_RECORD_REG_INTERVAL;
    if (IsRecordMergeable(m, rr, m->timenow + MERGE_DELAY_TIME))
        // Delay the record registration by MERGE_DELAY_TIME so that we can merge them
        // into one update
        rr->LastAPTime += MERGE_DELAY_TIME;
    mDNS_Unlock(m);
    // We call this always even though it may not be necessary always e.g., normal registration
    // process where TXT and PTR gets registered followed by the SRV record after it gets
    // the port mapping. In that case, UpdateAllServiceRecords handles the optimization. The
    // update of TXT and PTR record is required if we entered noTargetState before as explained
    // above.
    UpdateAllServiceRecords(m, rr, mDNStrue);
}

mDNSlocal void StartRecordNatMap(mDNS *m, AuthRecord *rr)
{
    const mDNSu8 *p;
    mDNSu8 protocol;

    if (rr->resrec.rrtype != kDNSType_SRV)
    {
        LogInfo("StartRecordNatMap: Resource Record %##s type %d, not supported", rr->resrec.name->c, rr->resrec.rrtype);
        return;
    }
    p = rr->resrec.name->c;
    //Assume <Service Instance>.<App Protocol>.<Transport protocol>.<Name>
    // Skip the first two labels to get to the transport protocol
    if (p[0]) p += 1 + p[0];
    if (p[0]) p += 1 + p[0];
    if      (SameDomainLabel(p, (mDNSu8 *)"\x4" "_tcp")) protocol = NATOp_MapTCP;
    else if (SameDomainLabel(p, (mDNSu8 *)"\x4" "_udp")) protocol = NATOp_MapUDP;
    else { LogMsg("StartRecordNatMap: could not determine transport protocol of service %##s", rr->resrec.name->c); return; }

    //LogMsg("StartRecordNatMap: clientContext %p IntPort %d srv.port %d %s",
    //  rr->NATinfo.clientContext, mDNSVal16(rr->NATinfo.IntPort), mDNSVal16(rr->resrec.rdata->u.srv.port), ARDisplayString(m, rr));
    if (rr->NATinfo.clientContext) mDNS_StopNATOperation_internal(m, &rr->NATinfo);
    rr->NATinfo.Protocol       = protocol;

    // Shouldn't be trying to set IntPort here --
    // BuildUpdateMessage overwrites srs->RR_SRV.resrec.rdata->u.srv.port with external (mapped) port number
    rr->NATinfo.IntPort        = rr->resrec.rdata->u.srv.port;
    rr->NATinfo.RequestedPort  = rr->resrec.rdata->u.srv.port;
    rr->NATinfo.NATLease       = 0;     // Request default lease
    rr->NATinfo.clientCallback = CompleteRecordNatMap;
    rr->NATinfo.clientContext  = rr;
    mDNS_StartNATOperation_internal(m, &rr->NATinfo);
}

// Unlink an Auth Record from the m->ResourceRecords list.
// When a resource record enters regState_NoTarget initially, mDNS_Register_internal
// does not initialize completely e.g., it cannot check for duplicates etc. The resource
// record is temporarily left in the ResourceRecords list so that we can initialize later
// when the target is resolvable. Similarly, when host name changes, we enter regState_NoTarget
// and we do the same.

// This UnlinkResourceRecord routine is very worrying. It bypasses all the normal cleanup performed
// by mDNS_Deregister_internal and just unceremoniously cuts the record from the active list.
// This is why re-regsitering this record was producing syslog messages like this:
// "Error! Tried to add a NAT traversal that's already in the active list"
// Right now UnlinkResourceRecord is fortunately only called by RegisterAllServiceRecords,
// which then immediately calls mDNS_Register_internal to re-register the record, which probably
// masked more serious problems. Any other use of UnlinkResourceRecord is likely to lead to crashes.
// For now we'll workaround that specific problem by explicitly calling mDNS_StopNATOperation_internal,
// but long-term we should either stop cancelling the record registration and then re-registering it,
// or if we really do need to do this for some reason it should be done via the usual
// mDNS_Deregister_internal path instead of just cutting the record from the list.

mDNSlocal mStatus UnlinkResourceRecord(mDNS *const m, AuthRecord *const rr)
{
    AuthRecord **list = &m->ResourceRecords;
    while (*list && *list != rr) list = &(*list)->next;
    if (*list)
    {
        *list = rr->next;
        rr->next = mDNSNULL;

        // Temporary workaround to cancel any active NAT mapping operation
        if (rr->NATinfo.clientContext)
        {
            mDNS_StopNATOperation_internal(m, &rr->NATinfo);
            rr->NATinfo.clientContext = mDNSNULL;
            if (rr->resrec.rrtype == kDNSType_SRV) rr->resrec.rdata->u.srv.port = rr->NATinfo.IntPort;
        }

        return(mStatus_NoError);
    }
    LogMsg("UnlinkResourceRecord:ERROR!! - no such active record %##s", rr->resrec.name->c);
    return(mStatus_NoSuchRecord);
}

// We need to go through mDNS_Register again as we did not complete the
// full initialization last time e.g., duplicate checks.
// After we register, we will be in regState_GetZoneData.
mDNSlocal void RegisterAllServiceRecords(mDNS *const m, AuthRecord *rr)
{
    LogInfo("RegisterAllServiceRecords: Service Record %##s", rr->resrec.name->c);
    // First Register the service record, we do this differently from other records because
    // when it entered NoTarget state, it did not go through complete initialization
    rr->SRVChanged = mDNSfalse;
    UnlinkResourceRecord(m, rr);
    mDNS_Register_internal(m, rr);
    // Register the other records
    UpdateAllServiceRecords(m, rr, mDNStrue);
}

// Called with lock held
mDNSlocal void UpdateOneSRVRecord(mDNS *m, AuthRecord *rr)
{
    // Target change if:
    // We have a target and were previously waiting for one, or
    // We had a target and no longer do, or
    // The target has changed

    domainname *curtarget = &rr->resrec.rdata->u.srv.target;
    const domainname *const nt = GetServiceTarget(m, rr);
    const domainname *const newtarget = nt ? nt : (domainname*)"";
    mDNSBool TargetChanged = (newtarget->c[0] && rr->state == regState_NoTarget) || !SameDomainName(curtarget, newtarget);
    mDNSBool HaveZoneData  = rr->nta && !mDNSIPv4AddressIsZero(rr->nta->Addr.ip.v4);

    // Nat state change if:
    // We were behind a NAT, and now we are behind a new NAT, or
    // We're not behind a NAT but our port was previously mapped to a different external port
    // We were not behind a NAT and now we are

    mDNSIPPort port        = rr->resrec.rdata->u.srv.port;
    mDNSBool NowNeedNATMAP = (rr->AutoTarget == Target_AutoHostAndNATMAP && !mDNSIPPortIsZero(port) && mDNSv4AddrIsRFC1918(&m->AdvertisedV4.ip.v4) && rr->nta && !mDNSAddrIsRFC1918(&rr->nta->Addr));
    mDNSBool WereBehindNAT = (rr->NATinfo.clientContext != mDNSNULL);
    mDNSBool PortWasMapped = (rr->NATinfo.clientContext && !mDNSSameIPPort(rr->NATinfo.RequestedPort, port));       // I think this is always false -- SC Sept 07
    mDNSBool NATChanged    = (!WereBehindNAT && NowNeedNATMAP) || (!NowNeedNATMAP && PortWasMapped);

    (void)HaveZoneData; //unused

    LogInfo("UpdateOneSRVRecord: Resource Record %s TargetChanged %d, NewTarget %##s", ARDisplayString(m, rr), TargetChanged, nt->c);

    debugf("UpdateOneSRVRecord: %##s newtarget %##s TargetChanged %d HaveZoneData %d port %d NowNeedNATMAP %d WereBehindNAT %d PortWasMapped %d NATChanged %d",
           rr->resrec.name->c, newtarget,
           TargetChanged, HaveZoneData, mDNSVal16(port), NowNeedNATMAP, WereBehindNAT, PortWasMapped, NATChanged);

    mDNS_CheckLock(m);

    if (!TargetChanged && !NATChanged) return;

    // If we are deregistering the record, then ignore any NAT/Target change.
    if (rr->resrec.RecordType == kDNSRecordTypeDeregistering)
    {
        LogInfo("UpdateOneSRVRecord: Deregistering record, Ignoring TargetChanged %d, NATChanged %d for %##s, state %d", TargetChanged, NATChanged,
                rr->resrec.name->c, rr->state);
        return;
    }

    if (newtarget)
        LogInfo("UpdateOneSRVRecord: TargetChanged %d, NATChanged %d for %##s, state %d, newtarget %##s", TargetChanged, NATChanged, rr->resrec.name->c, rr->state, newtarget->c);
    else
        LogInfo("UpdateOneSRVRecord: TargetChanged %d, NATChanged %d for %##s, state %d, null newtarget", TargetChanged, NATChanged, rr->resrec.name->c, rr->state);
    switch(rr->state)
    {
    case regState_NATMap:
        // In these states, the SRV has either not yet been registered (it will get up-to-date information when it is)
        // or is in the process of, or has already been, deregistered. This assumes that whenever we transition out
        // of this state, we need to look at the target again.
        return;

    case regState_UpdatePending:
        // We are getting a Target change/NAT change while the SRV record is being updated ?
        // let us not do anything for now.
        return;

    case regState_NATError:
        if (!NATChanged) return;
    // if nat changed, register if we have a target (below)
	/* FALLTHROUGH */

    case regState_NoTarget:
        if (!newtarget->c[0])
        {
            LogInfo("UpdateOneSRVRecord: No target yet for Resource Record %s", ARDisplayString(m, rr));
            return;
        }
        RegisterAllServiceRecords(m, rr);
        return;
    case regState_DeregPending:
    // We are in DeregPending either because the service was deregistered from above or we handled
    // a NAT/Target change before and sent the deregistration below. There are a few race conditions
    // possible
    //
    // 1. We are handling a second NAT/Target change while the first dereg is in progress. It is possible
    //    that first dereg never made it through because there was no network connectivity e.g., disconnecting
    //    from network triggers this function due to a target change and later connecting to the network
    //    retriggers this function but the deregistration never made it through yet. Just fall through.
    //    If there is a target register otherwise deregister.
    //
    // 2. While we sent the dereg during a previous NAT/Target change, uDNS_DeregisterRecord gets
    //    called as part of service deregistration. When the response comes back, we call
    //    CompleteDeregistration rather than handle NAT/Target change because the record is in
    //    kDNSRecordTypeDeregistering state.
    //
    // 3. If the upper layer deregisters the service, we check for kDNSRecordTypeDeregistering both
    //    here in this function to avoid handling NAT/Target change and in hndlRecordUpdateReply to call
    //    CompleteDeregistration instead of handling NAT/Target change. Hence, we are not concerned
    //    about that case here.
    //
    // We just handle case (1) by falling through
    case regState_Pending:
    case regState_Refresh:
    case regState_Registered:
        // target or nat changed.  deregister service.  upon completion, we'll look for a new target
        rr->SRVChanged = mDNStrue;
        rr->ThisAPInterval = INIT_RECORD_REG_INTERVAL;
        rr->LastAPTime = m->timenow - INIT_RECORD_REG_INTERVAL;
        if (newtarget->c[0])
        {
            LogInfo("UpdateOneSRVRecord: SRV record changed for service %##s, registering with new target %##s",
                    rr->resrec.name->c, newtarget->c);
            rr->state = regState_Pending;
        }
        else
        {
            LogInfo("UpdateOneSRVRecord: SRV record changed for service %##s de-registering", rr->resrec.name->c);
            rr->state = regState_DeregPending;
            UpdateAllServiceRecords(m, rr, mDNSfalse);
        }
        return;
    case regState_Unregistered:
    default: LogMsg("UpdateOneSRVRecord: Unknown state %d for %##s", rr->state, rr->resrec.name->c);
    }
}

mDNSexport void UpdateAllSRVRecords(mDNS *m)
{
    m->NextSRVUpdate = 0;
    LogInfo("UpdateAllSRVRecords %d", m->SleepState);

    if (m->CurrentRecord)
        LogMsg("UpdateAllSRVRecords ERROR m->CurrentRecord already set %s", ARDisplayString(m, m->CurrentRecord));
    m->CurrentRecord = m->ResourceRecords;
    while (m->CurrentRecord)
    {
        AuthRecord *rptr = m->CurrentRecord;
        m->CurrentRecord = m->CurrentRecord->next;
        if (AuthRecord_uDNS(rptr) && rptr->resrec.rrtype == kDNSType_SRV)
            UpdateOneSRVRecord(m, rptr);
    }
}

// Forward reference: AdvertiseHostname references HostnameCallback, and HostnameCallback calls AdvertiseHostname
mDNSlocal void HostnameCallback(mDNS *const m, AuthRecord *const rr, mStatus result);

// Called in normal client context (lock not held)
mDNSlocal void hostnameGetPublicAddressCallback(mDNS *m, NATTraversalInfo *n)
{
    HostnameInfo *h = (HostnameInfo *)n->clientContext;

    if (!h) { LogMsg("RegisterHostnameRecord: registration cancelled"); return; }

    if (!n->Result)
    {
        if (mDNSIPv4AddressIsZero(n->ExternalAddress) || mDNSv4AddrIsRFC1918(&n->ExternalAddress)) return;

        if (h->arv4.resrec.RecordType)
        {
            if (mDNSSameIPv4Address(h->arv4.resrec.rdata->u.ipv4, n->ExternalAddress)) return;  // If address unchanged, do nothing
            LogInfo("Updating hostname %p %##s IPv4 from %.4a to %.4a (NAT gateway's external address)",n,
                    h->arv4.resrec.name->c, &h->arv4.resrec.rdata->u.ipv4, &n->ExternalAddress);
            mDNS_Deregister(m, &h->arv4);   // mStatus_MemFree callback will re-register with new address
        }
        else
        {
            LogInfo("Advertising hostname %##s IPv4 %.4a (NAT gateway's external address)", h->arv4.resrec.name->c, &n->ExternalAddress);
            h->arv4.resrec.RecordType = kDNSRecordTypeKnownUnique;
            h->arv4.resrec.rdata->u.ipv4 = n->ExternalAddress;
            mDNS_Register(m, &h->arv4);
        }
    }
}

// register record or begin NAT traversal
mDNSlocal void AdvertiseHostname(mDNS *m, HostnameInfo *h)
{
    if (!mDNSIPv4AddressIsZero(m->AdvertisedV4.ip.v4) && h->arv4.resrec.RecordType == kDNSRecordTypeUnregistered)
    {
        mDNS_SetupResourceRecord(&h->arv4, mDNSNULL, mDNSInterface_Any, kDNSType_A, kHostNameTTL, kDNSRecordTypeUnregistered, AuthRecordAny, HostnameCallback, h);
        AssignDomainName(&h->arv4.namestorage, &h->fqdn);
        h->arv4.resrec.rdata->u.ipv4 = m->AdvertisedV4.ip.v4;
        h->arv4.state = regState_Unregistered;
        if (mDNSv4AddrIsRFC1918(&m->AdvertisedV4.ip.v4))
        {
            // If we already have a NAT query active, stop it and restart it to make sure we get another callback
            if (h->natinfo.clientContext) mDNS_StopNATOperation_internal(m, &h->natinfo);
            h->natinfo.Protocol         = 0;
            h->natinfo.IntPort          = zeroIPPort;
            h->natinfo.RequestedPort    = zeroIPPort;
            h->natinfo.NATLease         = 0;
            h->natinfo.clientCallback   = hostnameGetPublicAddressCallback;
            h->natinfo.clientContext    = h;
            mDNS_StartNATOperation_internal(m, &h->natinfo);
        }
        else
        {
            LogInfo("Advertising hostname %##s IPv4 %.4a", h->arv4.resrec.name->c, &m->AdvertisedV4.ip.v4);
            h->arv4.resrec.RecordType = kDNSRecordTypeKnownUnique;
            mDNS_Register_internal(m, &h->arv4);
        }
    }

    if (!mDNSIPv6AddressIsZero(m->AdvertisedV6.ip.v6) && h->arv6.resrec.RecordType == kDNSRecordTypeUnregistered)
    {
        mDNS_SetupResourceRecord(&h->arv6, mDNSNULL, mDNSInterface_Any, kDNSType_AAAA, kHostNameTTL, kDNSRecordTypeKnownUnique, AuthRecordAny, HostnameCallback, h);
        AssignDomainName(&h->arv6.namestorage, &h->fqdn);
        h->arv6.resrec.rdata->u.ipv6 = m->