/*
 * Copyright (C) 1996-2020 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */

/* DEBUG: section 14    IP Cache */

#include "squid.h"
#include "CacheManager.h"
#include "cbdata.h"
#include "dlink.h"
#include "dns/LookupDetails.h"
#include "dns/rfc3596.h"
#include "event.h"
#include "ip/Address.h"
#include "ip/tools.h"
#include "ipcache.h"
#include "mgr/Registration.h"
#include "SquidConfig.h"
#include "SquidTime.h"
#include "StatCounters.h"
#include "Store.h"
#include "util.h"
#include "wordlist.h"

#if SQUID_SNMP
#include "snmp_core.h"
#endif

/**
 \defgroup IPCacheAPI IP Cache API
 \ingroup Components
 \section Introduction Introduction
 \par
 *  The IP cache is a built-in component of squid providing
 *  Hostname to IP-Number translation functionality and managing
 *  the involved data-structures. Efficiency concerns require
 *  mechanisms that allow non-blocking access to these mappings.
 *  The IP cache usually doesn't block on a request except for
 *  special cases where this is desired (see below).
 *
 \todo IP Cache should have its own API *.h header file.
 */

/**
 \defgroup IPCacheInternal IP Cache Internals
 \ingroup IPCacheAPI
 \todo  when IP cache is provided as a class. These sub-groups will be obsolete
 *  for now they are used to separate the public and private functions.
 *  with the private ones all being in IPCachInternal and public in IPCacheAPI
 *
 \section InternalOperation Internal Operation
 *
 * Internally, the execution flow is as follows: On a miss,
 * ipcache_getnbhostbyname checks whether a request for
 * this name is already pending, and if positive, it creates
 * a new entry using ipcacheAddNew with the IP_PENDING
 * flag set . Then it calls ipcacheAddPending to add a
 * request to the queue together with data and handler.  Else,
 * ipcache_dnsDispatch() is called to directly create a
 * DNS query or to ipcacheEnqueue() if all no DNS port
 * is free.  ipcache_call_pending() is called regularly
 * to walk down the pending list and call handlers. LRU clean-up
 * is performed through ipcache_purgelru() according to
 * the ipcache_high threshold.
 */

/**
 \ingroup IPCacheAPI
 *
 * The data structure used for storing name-address mappings
 * is a small hashtable (static hash_table *ip_table),
 * where structures of type ipcache_entry whose most
 * interesting members are:
 */
class ipcache_entry
{
    MEMPROXY_CLASS(ipcache_entry);

public:
    ipcache_entry(const char *);
    ~ipcache_entry();

    hash_link hash;     /* must be first */
    time_t lastref;
    time_t expires;
    ipcache_addrs addrs;
    IPH *handler;
    void *handlerData;
    char *error_message;

    struct timeval request_time;
    dlink_node lru;
    unsigned short locks;
    struct Flags {
        Flags() : negcached(false), fromhosts(false) {}

        bool negcached;
        bool fromhosts;
    } flags;

    int age() const; ///< time passed since request_time or -1 if unknown
};

/// \ingroup IPCacheInternal
static struct _ipcache_stats {
    int requests;
    int replies;
    int hits;
    int misses;
    int negative_hits;
    int numeric_hits;
    int rr_a;
    int rr_aaaa;
    int rr_cname;
    int cname_only;
    int invalid;
} IpcacheStats;

/// \ingroup IPCacheInternal
static dlink_list lru_list;

// forward-decls
static void stat_ipcache_get(StoreEntry *);

static FREE ipcacheFreeEntry;
static IDNSCB ipcacheHandleReply;
static int ipcacheExpiredEntry(ipcache_entry *);
static ipcache_entry *ipcache_get(const char *);
static void ipcacheLockEntry(ipcache_entry *);
static void ipcacheStatPrint(ipcache_entry *, StoreEntry *);
static void ipcacheUnlockEntry(ipcache_entry *);
static void ipcacheRelease(ipcache_entry *, bool dofree = true);

/// \ingroup IPCacheInternal
static ipcache_addrs static_addrs;
/// \ingroup IPCacheInternal
static hash_table *ip_table = NULL;

/// \ingroup IPCacheInternal
static long ipcache_low = 180;
/// \ingroup IPCacheInternal
static long ipcache_high = 200;

#if LIBRESOLV_DNS_TTL_HACK
extern int _dns_ttl_;
#endif

/// \ingroup IPCacheInternal
inline int ipcacheCount() { return ip_table ? ip_table->count : 0; }

int
ipcache_entry::age() const
{
    return request_time.tv_sec ? tvSubMsec(request_time, current_time) : -1;
}

/**
 \ingroup IPCacheInternal
 *
 * removes the given ipcache entry
 */
static void
ipcacheRelease(ipcache_entry * i, bool dofree)
{
    if (!i) {
        debugs(14, DBG_CRITICAL, "ipcacheRelease: Releasing entry with i=<NULL>");
        return;
    }

    if (!i || !i->hash.key) {
        debugs(14, DBG_CRITICAL, "ipcacheRelease: Releasing entry without hash link!");
        return;
    }

    debugs(14, 3, "ipcacheRelease: Releasing entry for '" << (const char *) i->hash.key << "'");

    hash_remove_link(ip_table, (hash_link *) i);
    dlinkDelete(&i->lru, &lru_list);
    if (dofree)
        ipcacheFreeEntry(i);
}

/// \ingroup IPCacheInternal
static ipcache_entry *
ipcache_get(const char *name)
{
    if (ip_table != NULL)
        return (ipcache_entry *) hash_lookup(ip_table, name);
    else
        return NULL;
}

/// \ingroup IPCacheInternal
static int
ipcacheExpiredEntry(ipcache_entry * i)
{
    /* all static entries are locked, so this takes care of them too */

    if (i->locks != 0)
        return 0;

    if (i->addrs.count == 0)
        if (0 == i->flags.negcached)
            return 1;

    if (i->expires > squid_curtime)
        return 0;

    return 1;
}

/// \ingroup IPCacheAPI
void
ipcache_purgelru(void *)
{
    dlink_node *m;
    dlink_node *prev = NULL;
    ipcache_entry *i;
    int removed = 0;
    eventAdd("ipcache_purgelru", ipcache_purgelru, NULL, 10.0, 1);

    for (m = lru_list.tail; m; m = prev) {
        if (ipcacheCount() < ipcache_low)
            break;

        prev = m->prev;

        i = (ipcache_entry *)m->data;

        if (i->locks != 0)
            continue;

        ipcacheRelease(i);

        ++removed;
    }

    debugs(14, 9, "ipcache_purgelru: removed " << removed << " entries");
}

/**
 \ingroup IPCacheInternal
 *
 * purges entries added from /etc/hosts (or whatever).
 */
static void
purge_entries_fromhosts(void)
{
    dlink_node *m = lru_list.head;
    ipcache_entry *i = NULL, *t;

    while (m) {
        if (i != NULL) {    /* need to delay deletion */
            ipcacheRelease(i);  /* we just override locks */
            i = NULL;
        }

        t = (ipcache_entry*)m->data;

        if (t->flags.fromhosts)
            i = t;

        m = m->next;
    }

    if (i != NULL)
        ipcacheRelease(i);
}

ipcache_entry::ipcache_entry(const char *name) :
    lastref(0),
    expires(0),
    handler(nullptr),
    handlerData(nullptr),
    error_message(nullptr),
    locks(0) // XXX: use Lock type ?
{
    hash.key = xstrdup(name);
    Tolower(static_cast<char*>(hash.key));
    expires = squid_curtime + Config.negativeDnsTtl;

    memset(&request_time, 0, sizeof(request_time));
}

/// \ingroup IPCacheInternal
static void
ipcacheAddEntry(ipcache_entry * i)
{
    hash_link *e = (hash_link *)hash_lookup(ip_table, i->hash.key);

    if (NULL != e) {
        /* avoid colission */
        ipcache_entry *q = (ipcache_entry *) e;
        ipcacheRelease(q);
    }

    hash_join(ip_table, &i->hash);
    dlinkAdd(i, &i->lru, &lru_list);
    i->lastref = squid_curtime;
}

/**
 \ingroup IPCacheInternal
 *
 * walks down the pending list, calling handlers
 */
static void
ipcacheCallback(ipcache_entry *i, int wait)
{
    IPH *callback = i->handler;
    void *cbdata = NULL;
    i->lastref = squid_curtime;

    if (!i->handler)
        return;

    ipcacheLockEntry(i);

    callback = i->handler;

    i->handler = NULL;

    if (cbdataReferenceValidDone(i->handlerData, &cbdata)) {
        const Dns::LookupDetails details(i->error_message, wait);
        callback((i->addrs.count ? &i->addrs : NULL), details, cbdata);
    }

    ipcacheUnlockEntry(i);
}

static void
ipcacheParse(ipcache_entry *i, const rfc1035_rr * answers, int nr, const char *error_message)
{
    int k;
    int j = 0;
    int na = 0;
    int ttl = 0;
    const char *name = (const char *)i->hash.key;
    int cname_found = 0;

    i->expires = squid_curtime + Config.negativeDnsTtl;
    i->flags.negcached = true;
    safe_free(i->addrs.in_addrs);
    assert(i->addrs.in_addrs == NULL);
    safe_free(i->addrs.bad_mask);
    assert(i->addrs.bad_mask == NULL);
    safe_free(i->error_message);
    assert(i->error_message == NULL);
    i->addrs.count = 0;

    if (nr < 0) {
        debugs(14, 3, "Lookup failed '" << error_message << "' for '" << (const char *)i->hash.key << "'");
        i->error_message = xstrdup(error_message);
        return;
    }

    if (nr == 0) {
        debugs(14, 3, "No DNS records in response to '" << name << "'");
        i->error_message = xstrdup("No DNS records");
        return;
    }

    debugs(14, 3, nr << " answers for '" << name << "'");
    assert(answers);

    for (k = 0; k < nr; ++k) {

        if (Ip::EnableIpv6 && answers[k].type == RFC1035_TYPE_AAAA) {
            if (answers[k].rdlength != sizeof(struct in6_addr)) {
                debugs(14, DBG_IMPORTANT, MYNAME << "Invalid IPv6 address in response to '" << name << "'");
                continue;
            }
            ++na;
            ++IpcacheStats.rr_aaaa;
            continue;
        }

        if (answers[k].type == RFC1035_TYPE_A) {
            if (answers[k].rdlength != sizeof(struct in_addr)) {
                debugs(14, DBG_IMPORTANT, MYNAME << "Invalid IPv4 address in response to '" << name << "'");
                continue;
            }
            ++na;
            ++IpcacheStats.rr_a;
            continue;
        }

        /* With A and AAAA, the CNAME does not necessarily come with additional records to use. */
        if (answers[k].type == RFC1035_TYPE_CNAME) {
            cname_found=1;
            ++IpcacheStats.rr_cname;
            continue;
        }

        // otherwise its an unknown RR. debug at level 9 since we usually want to ignore these and they are common.
        debugs(14, 9, "Unknown RR type received: type=" << answers[k].type << " starting at " << &(answers[k]) );
    }
    if (na == 0) {
        debugs(14, DBG_IMPORTANT, MYNAME << "No Address records in response to '" << name << "'");
        i->error_message = xstrdup("No Address records");
        if (cname_found)
            ++IpcacheStats.cname_only;
        return;
    }

    i->addrs.in_addrs = static_cast<Ip::Address *>(xcalloc(na, sizeof(Ip::Address)));
    for (int l = 0; l < na; ++l)
        i->addrs.in_addrs[l].setEmpty(); // perform same init actions as constructor would.
    i->addrs.bad_mask = (unsigned char *)xcalloc(na, sizeof(unsigned char));

    for (j = 0, k = 0; k < nr; ++k) {

        if (answers[k].type == RFC1035_TYPE_A) {
            if (answers[k].rdlength != sizeof(struct in_addr))
                continue;

            struct in_addr temp;
            memcpy(&temp, answers[k].rdata, sizeof(struct in_addr));
            i->addrs.in_addrs[j] = temp;

            debugs(14, 3, name << " #" << j << " " << i->addrs.in_addrs[j]);
            ++j;

        } else if (Ip::EnableIpv6 && answers[k].type == RFC1035_TYPE_AAAA) {
            if (answers[k].rdlength != sizeof(struct in6_addr))
                continue;

            struct in6_addr temp;
            memcpy(&temp, answers[k].rdata, sizeof(struct in6_addr));
            i->addrs.in_addrs[j] = temp;

            debugs(14, 3, name << " #" << j << " " << i->addrs.in_addrs[j] );
            ++j;
        }
        if (ttl == 0 || (int) answers[k].ttl < ttl)
            ttl = answers[k].ttl;
    }

    assert(j == na);

    if (na < 256)
        i->addrs.count = (unsigned char) na;
    else
        i->addrs.count = 255;

    if (ttl > Config.positiveDnsTtl)
        ttl = Config.positiveDnsTtl;

    if (ttl < Config.negativeDnsTtl)
        ttl = Config.negativeDnsTtl;

    i->expires = squid_curtime + ttl;

    i->flags.negcached = false;
}

/// \ingroup IPCacheInternal
static void
ipcacheHandleReply(void *data, const rfc1035_rr * answers, int na, const char *error_message)
{
    ipcache_entry *i;
    static_cast<generic_cbdata *>(data)->unwrap(&i);
    ++IpcacheStats.replies;
    const int age = i->age();
    statCounter.dns.svcTime.count(age);

    ipcacheParse(i, answers, na, error_message);
    ipcacheAddEntry(i);
    ipcacheCallback(i, age);
}

/**
 \ingroup IPCacheAPI
 *
 \param name        Host to resolve.
 \param handler     Pointer to the function to be called when the reply
 *          from the IP cache (or the DNS if the IP cache misses)
 \param handlerData Information that is passed to the handler and does not affect the IP cache.
 *
 * XXX: on hits and some errors, the handler is called immediately instead
 * of scheduling an async call. This reentrant behavior means that the
 * user job must be extra careful after calling ipcache_nbgethostbyname,
 * especially if the handler destroys the job. Moreover, the job has
 * no way of knowing whether the reentrant call happened.
 * Comm::Connection setup usually protects the job by scheduling an async call,
 * but some user code calls ipcache_nbgethostbyname directly.
 */
void
ipcache_nbgethostbyname(const char *name, IPH * handler, void *handlerData)
{
    ipcache_entry *i = NULL;
    const ipcache_addrs *addrs = NULL;
    generic_cbdata *c;
    debugs(14, 4, "ipcache_nbgethostbyname: Name '" << name << "'.");
    ++IpcacheStats.requests;

    if (name == NULL || name[0] == '\0') {
        debugs(14, 4, "ipcache_nbgethostbyname: Invalid name!");
        ++IpcacheStats.invalid;
        const Dns::LookupDetails details("Invalid hostname", -1); // error, no lookup
        if (handler)
            handler(NULL, details, handlerData);
        return;
    }

    if ((addrs = ipcacheCheckNumeric(name))) {
        debugs(14, 4, "ipcache_nbgethostbyname: BYPASS for '" << name << "' (already numeric)");
        ++IpcacheStats.numeric_hits;
        const Dns::LookupDetails details; // no error, no lookup
        if (handler)
            handler(addrs, details, handlerData);
        return;
    }

    i = ipcache_get(name);

    if (NULL == i) {
        /* miss */
        (void) 0;
    } else if (ipcacheExpiredEntry(i)) {
        /* hit, but expired -- bummer */
        ipcacheRelease(i);
        i = NULL;
    } else {
        /* hit */
        debugs(14, 4, "ipcache_nbgethostbyname: HIT for '" << name << "'");

        if (i->flags.negcached)
            ++IpcacheStats.negative_hits;
        else
            ++IpcacheStats.hits;

        i->handler = handler;

        i->handlerData = cbdataReference(handlerData);

        ipcacheCallback(i, -1); // no lookup

        return;
    }

    debugs(14, 5, "ipcache_nbgethostbyname: MISS for '" << name << "'");
    ++IpcacheStats.misses;
    i = new ipcache_entry(name);
    i->handler = handler;
    i->handlerData = cbdataReference(handlerData);
    i->request_time = current_time;
    c = new generic_cbdata(i);
    idnsALookup(hashKeyStr(&i->hash), ipcacheHandleReply, c);
}

/// \ingroup IPCacheInternal
static void
ipcacheRegisterWithCacheManager(void)
{
    Mgr::RegisterAction("ipcache",
                        "IP Cache Stats and Contents",
                        stat_ipcache_get, 0, 1);
}

/**
 \ingroup IPCacheAPI
 *
 * Initialize the ipcache.
 * Is called from mainInitialize() after disk initialization
 * and prior to the reverse FQDNCache initialization
 */
void
ipcache_init(void)
{
    int n;
    debugs(14, DBG_IMPORTANT, "Initializing IP Cache...");
    memset(&IpcacheStats, '\0', sizeof(IpcacheStats));
    lru_list = dlink_list();

    static_addrs.in_addrs = static_cast<Ip::Address *>(xcalloc(1, sizeof(Ip::Address)));
    static_addrs.in_addrs->setEmpty(); // properly setup the Ip::Address!
    static_addrs.bad_mask = (unsigned char *)xcalloc(1, sizeof(unsigned char));
    ipcache_high = (long) (((float) Config.ipcache.size *
                            (float) Config.ipcache.high) / (float) 100);
    ipcache_low = (long) (((float) Config.ipcache.size *
                           (float) Config.ipcache.low) / (float) 100);
    n = hashPrime(ipcache_high / 4);
    ip_table = hash_create((HASHCMP *) strcmp, n, hash4);

    ipcacheRegisterWithCacheManager();
}

/**
 \ingroup IPCacheAPI
 *
 * Is different from ipcache_nbgethostbyname in that it only checks
 * if an entry exists in the cache and does not by default contact the DNS,
 * unless this is requested, by setting the flags.
 *
 \param name        Host name to resolve.
 \param flags       Default is NULL, set to IP_LOOKUP_IF_MISS
 *          to explicitly perform DNS lookups.
 *
 \retval NULL   An error occurred during lookup
 \retval NULL   No results available in cache and no lookup specified
 \retval *  Pointer to the ipcahce_addrs structure containing the lookup results
 */
const ipcache_addrs *
ipcache_gethostbyname(const char *name, int flags)
{
    ipcache_entry *i = NULL;
    ipcache_addrs *addrs;
    assert(name);
    debugs(14, 3, "ipcache_gethostbyname: '" << name  << "', flags=" << std::hex << flags);
    ++IpcacheStats.requests;
    i = ipcache_get(name);

    if (NULL == i) {
        (void) 0;
    } else if (ipcacheExpiredEntry(i)) {
        ipcacheRelease(i);
        i = NULL;
    } else if (i->flags.negcached) {
        ++IpcacheStats.negative_hits;
        // ignore i->error_message: the caller just checks IP cache presence
        return NULL;
    } else {
        ++IpcacheStats.hits;
        i->lastref = squid_curtime;
        // ignore i->error_message: the caller just checks IP cache presence
        return &i->addrs;
    }

    /* no entry [any more] */

    if ((addrs = ipcacheCheckNumeric(name))) {
        ++IpcacheStats.numeric_hits;
        return addrs;
    }

    ++IpcacheStats.misses;

    if (flags & IP_LOOKUP_IF_MISS)
        ipcache_nbgethostbyname(name, NULL, NULL);

    return NULL;
}

/// \ingroup IPCacheInternal
static void
ipcacheStatPrint(ipcache_entry * i, StoreEntry * sentry)
{
    int k;
    char buf[MAX_IPSTRLEN];

    if (!sentry) {
        debugs(14, DBG_CRITICAL, HERE << "CRITICAL: sentry is NULL!");
        return;
    }

    if (!i) {
        debugs(14, DBG_CRITICAL, HERE << "CRITICAL: ipcache_entry is NULL!");
        storeAppendPrintf(sentry, "CRITICAL ERROR\n");
        return;
    }

    int count = i->addrs.count;

    storeAppendPrintf(sentry, " %-32.32s %c%c %6d %6d %2d(%2d)",
                      hashKeyStr(&i->hash),
                      i->flags.fromhosts ? 'H' : ' ',
                      i->flags.negcached ? 'N' : ' ',
                      (int) (squid_curtime - i->lastref),
                      (int) ((i->flags.fromhosts ? -1 : i->expires - squid_curtime)),
                      (int) i->addrs.count,
                      (int) i->addrs.badcount);

    /** \par
     * Negative-cached entries have no IPs listed. */
    if (i->flags.negcached) {
        storeAppendPrintf(sentry, "\n");
        return;
    }

    /** \par
     * Cached entries have IPs listed with a BNF of:   ip-address '-' ('OK'|'BAD') */
    for (k = 0; k < count; ++k) {
        /* Display tidy-up: IPv6 are so big make the list vertical */
        if (k == 0)
            storeAppendPrintf(sentry, " %45.45s-%3s\n",
                              i->addrs.in_addrs[k].toStr(buf,MAX_IPSTRLEN),
                              i->addrs.bad_mask[k] ? "BAD" : "OK ");
        else
            storeAppendPrintf(sentry, "%s %45.45s-%3s\n",
                              "                                                         ", /* blank-space indenting IP list */
                              i->addrs.in_addrs[k].toStr(buf,MAX_IPSTRLEN),
                              i->addrs.bad_mask[k] ? "BAD" : "OK ");
    }
}

/**
 \ingroup IPCacheInternal
 *
 * process objects list
 */
void
stat_ipcache_get(StoreEntry * sentry)
{
    dlink_node *m;
    assert(ip_table != NULL);
    storeAppendPrintf(sentry, "IP Cache Statistics:\n");
    storeAppendPrintf(sentry, "IPcache Entries In Use:  %d\n",
                      ipcache_entry::UseCount());
    storeAppendPrintf(sentry, "IPcache Entries Cached:  %d\n",
                      ipcacheCount());
    storeAppendPrintf(sentry, "IPcache Requests: %d\n",
                      IpcacheStats.requests);
    storeAppendPrintf(sentry, "IPcache Hits:            %d\n",
                      IpcacheStats.hits);
    storeAppendPrintf(sentry, "IPcache Negative Hits:       %d\n",
                      IpcacheStats.negative_hits);
    storeAppendPrintf(sentry, "IPcache Numeric Hits:        %d\n",
                      IpcacheStats.numeric_hits);
    storeAppendPrintf(sentry, "IPcache Misses:          %d\n",
                      IpcacheStats.misses);
    storeAppendPrintf(sentry, "IPcache Retrieved A:     %d\n",
                      IpcacheStats.rr_a);
    storeAppendPrintf(sentry, "IPcache Retrieved AAAA:  %d\n",
                      IpcacheStats.rr_aaaa);
    storeAppendPrintf(sentry, "IPcache Retrieved CNAME: %d\n",
                      IpcacheStats.rr_cname);
    storeAppendPrintf(sentry, "IPcache CNAME-Only Response: %d\n",
                      IpcacheStats.cname_only);
    storeAppendPrintf(sentry, "IPcache Invalid Request: %d\n",
                      IpcacheStats.invalid);
    storeAppendPrintf(sentry, "\n\n");
    storeAppendPrintf(sentry, "IP Cache Contents:\n\n");
    storeAppendPrintf(sentry, " %-31.31s %3s %6s %6s  %4s\n",
                      "Hostname",
                      "Flg",
                      "lstref",
                      "TTL",
                      "N(b)");

    for (m = lru_list.head; m; m = m->next) {
        assert( m->next != m );
        ipcacheStatPrint((ipcache_entry *)m->data, sentry);
    }
}

/// \ingroup IPCacheAPI
void
ipcacheInvalidate(const char *name)
{
    ipcache_entry *i;

    if ((i = ipcache_get(name)) == NULL)
        return;

    i->expires = squid_curtime;

    /*
     * NOTE, don't call ipcacheRelease here because we might be here due
     * to a thread started from a callback.
     */
}

/// \ingroup IPCacheAPI
void
ipcacheInvalidateNegative(const char *name)
{
    ipcache_entry *i;

    if ((i = ipcache_get(name)) == NULL)
        return;

    if (i->flags.negcached)
        i->expires = squid_curtime;

    /*
     * NOTE, don't call ipcacheRelease here because we might be here due
     * to a thread started from a callback.
     */
}

/// \ingroup IPCacheAPI
ipcache_addrs *
ipcacheCheckNumeric(const char *name)
{
    Ip::Address ip;
    /* check if it's already a IP address in text form. */

    /* it may be IPv6-wrapped */
    if (name[0] == '[') {
        char *tmp = xstrdup(&name[1]);
        tmp[strlen(tmp)-1] = '\0';
        if (!(ip = tmp)) {
            delete tmp;
            return NULL;
        }
        delete tmp;
    } else if (!(ip = name))
        return NULL;

    debugs(14, 4, "ipcacheCheckNumeric: HIT_BYPASS for '" << name << "' == " << ip );

    static_addrs.count = 1;

    static_addrs.cur = 0;

    static_addrs.in_addrs[0] = ip;

    static_addrs.bad_mask[0] = FALSE;

    static_addrs.badcount = 0;

    return &static_addrs;
}

/// \ingroup IPCacheInternal
static void
ipcacheLockEntry(ipcache_entry * i)
{
    if (i->locks++ == 0) {
        dlinkDelete(&i->lru, &lru_list);
        dlinkAdd(i, &i->lru, &lru_list);
    }
}

/// \ingroup IPCacheInternal
static void
ipcacheUnlockEntry(ipcache_entry * i)
{
    if (i->locks < 1) {
        debugs(14, DBG_IMPORTANT, "WARNING: ipcacheEntry unlocked with no lock! locks=" << i->locks);
        return;
    }

    -- i->locks;

    if (ipcacheExpiredEntry(i))
        ipcacheRelease(i);
}

/// \ingroup IPCacheAPI
void
ipcacheCycleAddr(const char *name, ipcache_addrs * ia)
{
    ipcache_entry *i;
    unsigned char k;
    assert(name || ia);

    if (NULL == ia) {
        if ((i = ipcache_get(name)) == NULL)
            return;

        if (i->flags.negcached)
            return;

        ia = &i->addrs;
    }

    for (k = 0; k < ia->count; ++k) {
        if (++ia->cur == ia->count)
            ia->cur = 0;

        if (!ia->bad_mask[ia->cur])
            break;
    }

    if (k == ia->count) {
        /* All bad, reset to All good */
        debugs(14, 3, "ipcacheCycleAddr: Changing ALL " << name << " addrs from BAD to OK");

        for (k = 0; k < ia->count; ++k)
            ia->bad_mask[k] = 0;

        ia->badcount = 0;

        ia->cur = 0;
    }

    /* NP: zero-based so we increase the human-readable number of our position */
    debugs(14, 3, "ipcacheCycleAddr: " << name << " now at " << ia->in_addrs[ia->cur] << " (" << (ia->cur+1) << " of " << ia->count << ")");
}

/**
 \ingroup IPCacheAPI
 *
 \param name    domain name to have an IP marked bad
 \param addr    specific addres to be marked bad
 */
void
ipcacheMarkBadAddr(const char *name, const Ip::Address &addr)
{
    ipcache_entry *i;
    ipcache_addrs *ia;
    int k;

    /** Does nothing if the domain name does not exist. */
    if ((i = ipcache_get(name)) == NULL)
        return;

    ia = &i->addrs;

    for (k = 0; k < (int) ia->count; ++k) {
        if (addr == ia->in_addrs[k] )
            break;
    }

    /** Does nothing if the IP does not exist for the doamin. */
    if (k == (int) ia->count)
        return;

    /** Marks the given address as BAD */
    if (!ia->bad_mask[k]) {
        ia->bad_mask[k] = TRUE;
        ++ia->badcount;
        debugs(14, 2, "ipcacheMarkBadAddr: " << name << " " << addr );
    }

    /** then calls ipcacheCycleAddr() to advance the current pointer to the next OK address. */
    ipcacheCycleAddr(name, ia);
}

/// \ingroup IPCacheAPI
void
ipcacheMarkAllGood(const char *name)
{
    ipcache_entry *i;
    ipcache_addrs *ia;
    int k;

    if ((i = ipcache_get(name)) == NULL)
        return;

    ia = &i->addrs;

    /* All bad, reset to All good */
    debugs(14, 3, "ipcacheMarkAllGood: Changing ALL " << name << " addrs to OK (" << ia->badcount << "/" << ia->count << " bad)");

    for (k = 0; k < ia->count; ++k)
        ia->bad_mask[k] = 0;

    ia->badcount = 0;
}

/// \ingroup IPCacheAPI
void
ipcacheMarkGoodAddr(const char *name, const Ip::Address &addr)
{
    ipcache_entry *i;
    ipcache_addrs *ia;
    int k;

    if ((i = ipcache_get(name)) == NULL)
        return;

    ia = &i->addrs;

    for (k = 0; k < (int) ia->count; ++k) {
        if (addr == ia->in_addrs[k])
            break;
    }

    if (k == (int) ia->count)   /* not found */
        return;

    if (!ia->bad_mask[k])   /* already OK */
        return;

    ia->bad_mask[k] = FALSE;

    -- ia->badcount;

    debugs(14, 2, "ipcacheMarkGoodAddr: " << name << " " << addr );
}

/// \ingroup IPCacheInternal
static void
ipcacheFreeEntry(void *data)
{
    ipcache_entry *i = (ipcache_entry *)data;
    delete i;
}

ipcache_entry::~ipcache_entry()
{
    xfree(addrs.in_addrs);
    xfree(addrs.bad_mask);
    xfree(error_message);
    xfree(hash.key);
}

/// \ingroup IPCacheAPI
void
ipcacheFreeMemory(void)
{
    hashFreeItems(ip_table, ipcacheFreeEntry);
    hashFreeMemory(ip_table);
    ip_table = NULL;
}

/**
 \ingroup IPCacheAPI
 *
 * Recalculate IP cache size upon reconfigure.
 * Is called to clear the IPCache's data structures,
 * cancel all pending requests.
 */
void
ipcache_restart(void)
{
    ipcache_high = (long) (((float) Config.ipcache.size *
                            (float) Config.ipcache.high) / (float) 100);
    ipcache_low = (long) (((float) Config.ipcache.size *
                           (float) Config.ipcache.low) / (float) 100);
    purge_entries_fromhosts();
}

/**
 \ingroup IPCacheAPI
 *
 * Adds a "static" entry from /etc/hosts
 *
 \param name    Hostname to be linked with IP
 \param ipaddr  IP Address to be cached.
 *
 \retval 0  Success.
 \retval 1  IP address is invalid or other error.
 */
int
ipcacheAddEntryFromHosts(const char *name, const char *ipaddr)
{
    ipcache_entry *i;

    Ip::Address ip;

    if (!(ip = ipaddr)) {
        if (strchr(ipaddr, ':') && strspn(ipaddr, "0123456789abcdefABCDEF:") == strlen(ipaddr)) {
            debugs(14, 3, "ipcacheAddEntryFromHosts: Skipping IPv6 address '" << ipaddr << "'");
        } else {
            debugs(14, DBG_IMPORTANT, "ipcacheAddEntryFromHosts: Bad IP address '" << ipaddr << "'");
        }

        return 1;
    }

    if ((i = ipcache_get(name))) {
        if (1 == i->flags.fromhosts) {
            ipcacheUnlockEntry(i);
        } else if (i->locks > 0) {
            debugs(14, DBG_IMPORTANT, "ipcacheAddEntryFromHosts: can't add static entry for locked name '" << name << "'");
            return 1;
        } else {
            ipcacheRelease(i);
        }
    }

    i = new ipcache_entry(name);
    i->addrs.count = 1;
    i->addrs.cur = 0;
    i->addrs.badcount = 0;

    i->addrs.in_addrs = static_cast<Ip::Address *>(xcalloc(1, sizeof(Ip::Address)));
    i->addrs.bad_mask = (unsigned char *)xcalloc(1, sizeof(unsigned char));
    i->addrs.in_addrs[0] = ip;
    i->addrs.bad_mask[0] = FALSE;
    i->flags.fromhosts = true;
    ipcacheAddEntry(i);
    ipcacheLockEntry(i);
    return 0;
}

#if SQUID_SNMP
/**
 \ingroup IPCacheAPI
 *
 * The function to return the ip cache statistics to via SNMP
 */
variable_list *
snmp_netIpFn(variable_list * Var, snint * ErrP)
{
    variable_list *Answer = NULL;
    MemBuf tmp;
    debugs(49, 5, "snmp_netIpFn: Processing request:" << snmpDebugOid(Var->name, Var->name_length, tmp));
    *ErrP = SNMP_ERR_NOERROR;

    switch (Var->name[LEN_SQ_NET + 1]) {

    case IP_ENT:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      ipcacheCount(),
                                      SMI_GAUGE32);
        break;

    case IP_REQ:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      IpcacheStats.requests,
                                      SMI_COUNTER32);
        break;

    case IP_HITS:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      IpcacheStats.hits,
                                      SMI_COUNTER32);
        break;

    case IP_PENDHIT:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      0,
                                      SMI_GAUGE32);
        break;

    case IP_NEGHIT:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      IpcacheStats.negative_hits,
                                      SMI_COUNTER32);
        break;

    case IP_MISS:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      IpcacheStats.misses,
                                      SMI_COUNTER32);
        break;

    case IP_GHBN:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      0, /* deprecated */
                                      SMI_COUNTER32);
        break;

    case IP_LOC:
        Answer = snmp_var_new_integer(Var->name, Var->name_length,
                                      0, /* deprecated */
                                      SMI_COUNTER32);
        break;

    default:
        *ErrP = SNMP_ERR_NOSUCHNAME;
        snmp_var_free(Answer);
        return (NULL);
    }

    return Answer;
}

#endif /*SQUID_SNMP */

