The Tor Browser: netwerk/dns/nsHostResolver.cpp@ca08bd8f51b2 (annotated)

netwerk/dns/nsHostResolver.cpp@ca08bd8f51b2 (annotated)

netwerk/dns/nsHostResolver.cpp

Wed, 31 Dec 2014 06:55:46 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:55:46 +0100
changeset 1: ca08bd8f51b2
permissions: -rw-r--r--

Added tag TORBROWSER_REPLICA for changeset 6474c204b198

 /* vim:set ts=4 sw=4 sts=4 et cin: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #if defined(MOZ_LOGGING)
 #define FORCE_PR_LOG
 #endif
 #if defined(HAVE_RES_NINIT)
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <arpa/nameser.h>
 #include <resolv.h>
 #define RES_RETRY_ON_FAILURE
 #endif
 #include <stdlib.h>
 #include "nsHostResolver.h"
 #include "nsError.h"
 #include "nsISupportsBase.h"
 #include "nsISupportsUtils.h"
 #include "nsAutoPtr.h"
 #include "prthread.h"
 #include "prerror.h"
 #include "prtime.h"
 #include "prlog.h"
 #include "pldhash.h"
 #include "plstr.h"
 #include "nsURLHelper.h"
 #include "nsThreadUtils.h"
 #include "mozilla/HashFunctions.h"
 #include "mozilla/TimeStamp.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/VisualEventTracer.h"
 using namespace mozilla;
 using namespace mozilla::net;
 //----------------------------------------------------------------------------
 // Use a persistent thread pool in order to avoid spinning up new threads all the time.
 // In particular, thread creation results in a res_init() call from libc which is
 // quite expensive.
 //
 // The pool dynamically grows between 0 and MAX_RESOLVER_THREADS in size. New requests
 // go first to an idle thread. If that cannot be found and there are fewer than MAX_RESOLVER_THREADS
 // currently in the pool a new thread is created for high priority requests. If
 // the new request is at a lower priority a new thread will only be created if
 // there are fewer than HighThreadThreshold currently outstanding. If a thread cannot be
 // created or an idle thread located for the request it is queued.
 //
 // When the pool is greater than HighThreadThreshold in size a thread will be destroyed after
 // ShortIdleTimeoutSeconds of idle time. Smaller pools use LongIdleTimeoutSeconds for a
 // timeout period.
 #define HighThreadThreshold     MAX_RESOLVER_THREADS_FOR_ANY_PRIORITY
 #define LongIdleTimeoutSeconds  300           // for threads 1 -> HighThreadThreshold
 #define ShortIdleTimeoutSeconds 60            // for threads HighThreadThreshold+1 -> MAX_RESOLVER_THREADS
 PR_STATIC_ASSERT (HighThreadThreshold <= MAX_RESOLVER_THREADS);
 //----------------------------------------------------------------------------
 #if defined(PR_LOGGING)
 static PRLogModuleInfo *gHostResolverLog = nullptr;
 #define LOG(args) PR_LOG(gHostResolverLog, PR_LOG_DEBUG, args)
 #else
 #define LOG(args)
 #endif
 //----------------------------------------------------------------------------
 static inline void
 MoveCList(PRCList &from, PRCList &to)
 {
     if (!PR_CLIST_IS_EMPTY(&from)) {
         to.next = from.next;
         to.prev = from.prev;
         to.next->prev = &to;
         to.prev->next = &to;
         PR_INIT_CLIST(&from);
     }
 }
 //----------------------------------------------------------------------------
 #if defined(RES_RETRY_ON_FAILURE)
 // this class represents the resolver state for a given thread.  if we
 // encounter a lookup failure, then we can invoke the Reset method on an
 // instance of this class to reset the resolver (in case /etc/resolv.conf
 // for example changed).  this is mainly an issue on GNU systems since glibc
 // only reads in /etc/resolv.conf once per thread.  it may be an issue on
 // other systems as well.
 class nsResState
 {
 public:
     nsResState()
         // initialize mLastReset to the time when this object
         // is created.  this means that a reset will not occur
         // if a thread is too young.  the alternative would be
         // to initialize this to the beginning of time, so that
         // the first failure would cause a reset, but since the
         // thread would have just started up, it likely would
         // already have current /etc/resolv.conf info.
         : mLastReset(PR_IntervalNow())
     {
     }
     bool Reset()
     {
         // reset no more than once per second
         if (PR_IntervalToSeconds(PR_IntervalNow() - mLastReset) < 1)
             return false;
         LOG(("Calling 'res_ninit'.\n"));
         mLastReset = PR_IntervalNow();
         return (res_ninit(&_res) == 0);
     }
 private:
     PRIntervalTime mLastReset;
 };
 #endif // RES_RETRY_ON_FAILURE
 //----------------------------------------------------------------------------
 static inline bool
 IsHighPriority(uint16_t flags)
 {
     return !(flags & (nsHostResolver::RES_PRIORITY_LOW | nsHostResolver::RES_PRIORITY_MEDIUM));
 }
 static inline bool
 IsMediumPriority(uint16_t flags)
 {
     return flags & nsHostResolver::RES_PRIORITY_MEDIUM;
 }
 static inline bool
 IsLowPriority(uint16_t flags)
 {
     return flags & nsHostResolver::RES_PRIORITY_LOW;
 }
 //----------------------------------------------------------------------------
 // this macro filters out any flags that are not used when constructing the
 // host key.  the significant flags are those that would affect the resulting
 // host record (i.e., the flags that are passed down to PR_GetAddrInfoByName).
 #define RES_KEY_FLAGS(_f) ((_f) & nsHostResolver::RES_CANON_NAME)
 nsHostRecord::nsHostRecord(const nsHostKey *key)
     : addr_info_lock("nsHostRecord.addr_info_lock")
     , addr_info_gencnt(0)
     , addr_info(nullptr)
     , addr(nullptr)
     , negative(false)
     , resolving(false)
     , onQueue(false)
     , usingAnyThread(false)
     , mDoomed(false)
 {
     host = ((char *) this) + sizeof(nsHostRecord);
     memcpy((char *) host, key->host, strlen(key->host) + 1);
     flags = key->flags;
     af = key->af;
     expiration = TimeStamp::NowLoRes();
     PR_INIT_CLIST(this);
     PR_INIT_CLIST(&callbacks);
 }
 nsresult
 nsHostRecord::Create(const nsHostKey *key, nsHostRecord **result)
 {
     size_t hostLen = strlen(key->host) + 1;
     size_t size = hostLen + sizeof(nsHostRecord);
     // Use placement new to create the object with room for the hostname
     // allocated after it.
     void *place = ::operator new(size);
     *result = new(place) nsHostRecord(key);
     NS_ADDREF(*result);
     MOZ_EVENT_TRACER_NAME_OBJECT(*result, key->host);
     return NS_OK;
 }
 nsHostRecord::~nsHostRecord()
 {
     delete addr_info;
     delete addr;
 }
 bool
 nsHostRecord::Blacklisted(NetAddr *aQuery)
 {
     // must call locked
     LOG(("Checking blacklist for host [%s], host record [%p].\n", host, this));
     // skip the string conversion for the common case of no blacklist
     if (!mBlacklistedItems.Length()) {
         return false;
     }
     char buf[kIPv6CStrBufSize];
     if (!NetAddrToString(aQuery, buf, sizeof(buf))) {
         return false;
     }
     nsDependentCString strQuery(buf);
     for (uint32_t i = 0; i < mBlacklistedItems.Length(); i++) {
         if (mBlacklistedItems.ElementAt(i).Equals(strQuery)) {
             LOG(("Address [%s] is blacklisted for host [%s].\n", buf, host));
             return true;
         }
     }
     return false;
 }
 void
 nsHostRecord::ReportUnusable(NetAddr *aAddress)
 {
     // must call locked
     LOG(("Adding address to blacklist for host [%s], host record [%p].\n", host, this));
     if (negative)
         mDoomed = true;
     char buf[kIPv6CStrBufSize];
     if (NetAddrToString(aAddress, buf, sizeof(buf))) {
         LOG(("Successfully adding address [%s] to blacklist for host [%s].\n", buf, host));
         mBlacklistedItems.AppendElement(nsCString(buf));
     }
 }
 void
 nsHostRecord::ResetBlacklist()
 {
     // must call locked
     LOG(("Resetting blacklist for host [%s], host record [%p].\n", host, this));
     mBlacklistedItems.Clear();
 }
 bool
 nsHostRecord::HasUsableResult(uint16_t queryFlags) const
 {
     if (mDoomed)
         return false;
     // don't use cached negative results for high priority queries.
     if (negative && IsHighPriority(queryFlags))
         return false;
     return addr_info || addr || negative;
 }
 static size_t
 SizeOfResolveHostCallbackListExcludingHead(const PRCList *head,
                                            MallocSizeOf mallocSizeOf)
 {
     size_t n = 0;
     PRCList *curr = head->next;
     while (curr != head) {
         nsResolveHostCallback *callback =
             static_cast<nsResolveHostCallback*>(curr);
         n += callback->SizeOfIncludingThis(mallocSizeOf);
         curr = curr->next;
     }
     return n;
 }
 size_t
 nsHostRecord::SizeOfIncludingThis(MallocSizeOf mallocSizeOf) const
 {
     size_t n = mallocSizeOf(this);
     // The |host| field (inherited from nsHostKey) actually points to extra
     // memory that is allocated beyond the end of the nsHostRecord (see
     // nsHostRecord::Create()).  So it will be included in the
     // |mallocSizeOf(this)| call above.
     n += SizeOfResolveHostCallbackListExcludingHead(&callbacks, mallocSizeOf);
     n += addr_info ? addr_info->SizeOfIncludingThis(mallocSizeOf) : 0;
     n += mallocSizeOf(addr);
     n += mBlacklistedItems.SizeOfExcludingThis(mallocSizeOf);
     for (size_t i = 0; i < mBlacklistedItems.Length(); i++) {
         n += mBlacklistedItems[i].SizeOfExcludingThisMustBeUnshared(mallocSizeOf);
     }
     return n;
 }
 //----------------------------------------------------------------------------
 struct nsHostDBEnt : PLDHashEntryHdr
 {
     nsHostRecord *rec;
 };
 static PLDHashNumber
 HostDB_HashKey(PLDHashTable *table, const void *key)
 {
     const nsHostKey *hk = static_cast<const nsHostKey *>(key);
     return AddToHash(HashString(hk->host), RES_KEY_FLAGS(hk->flags), hk->af);
 }
 static bool
 HostDB_MatchEntry(PLDHashTable *table,
                   const PLDHashEntryHdr *entry,
                   const void *key)
 {
     const nsHostDBEnt *he = static_cast<const nsHostDBEnt *>(entry);
     const nsHostKey *hk = static_cast<const nsHostKey *>(key);
     return !strcmp(he->rec->host, hk->host) &&
             RES_KEY_FLAGS (he->rec->flags) == RES_KEY_FLAGS(hk->flags) &&
             he->rec->af == hk->af;
 }
 static void
 HostDB_MoveEntry(PLDHashTable *table,
                  const PLDHashEntryHdr *from,
                  PLDHashEntryHdr *to)
 {
     static_cast<nsHostDBEnt *>(to)->rec =
             static_cast<const nsHostDBEnt *>(from)->rec;
 }
 static void
 HostDB_ClearEntry(PLDHashTable *table,
                   PLDHashEntryHdr *entry)
 {
     nsHostDBEnt *he = static_cast<nsHostDBEnt*>(entry);
     MOZ_ASSERT(he, "nsHostDBEnt is null!");
     nsHostRecord *hr = he->rec;
     MOZ_ASSERT(hr, "nsHostDBEnt has null host record!");
     LOG(("Clearing cache db entry for host [%s].\n", hr->host));
 #if defined(DEBUG) && defined(PR_LOGGING)
     {
         MutexAutoLock lock(hr->addr_info_lock);
         if (!hr->addr_info) {
             LOG(("No address info for host [%s].\n", hr->host));
         } else {
             TimeDuration diff = hr->expiration - TimeStamp::NowLoRes();
             LOG(("Record for [%s] expires in %f seconds.\n", hr->host, diff.ToSeconds()));
             NetAddrElement *addrElement = nullptr;
             char buf[kIPv6CStrBufSize];
             do {
                 if (!addrElement) {
                     addrElement = hr->addr_info->mAddresses.getFirst();
                 } else {
                     addrElement = addrElement->getNext();
                 }
                 if (addrElement) {
                     NetAddrToString(&addrElement->mAddress, buf, sizeof(buf));
                     LOG(("  [%s]\n", buf));
                 }
             }
             while (addrElement);
         }
     }
 #endif
     NS_RELEASE(he->rec);
 }
 static bool
 HostDB_InitEntry(PLDHashTable *table,
                  PLDHashEntryHdr *entry,
                  const void *key)
 {
     nsHostDBEnt *he = static_cast<nsHostDBEnt *>(entry);
     nsHostRecord::Create(static_cast<const nsHostKey *>(key), &he->rec);
     return true;
 }
 static const PLDHashTableOps gHostDB_ops =
 {
     PL_DHashAllocTable,
     PL_DHashFreeTable,
     HostDB_HashKey,
     HostDB_MatchEntry,
     HostDB_MoveEntry,
     HostDB_ClearEntry,
     PL_DHashFinalizeStub,
     HostDB_InitEntry,
 };
 static PLDHashOperator
 HostDB_RemoveEntry(PLDHashTable *table,
                    PLDHashEntryHdr *hdr,
                    uint32_t number,
                    void *arg)
 {
     return PL_DHASH_REMOVE;
 }
 //----------------------------------------------------------------------------
 nsHostResolver::nsHostResolver(uint32_t maxCacheEntries,
                                uint32_t maxCacheLifetime,
                                uint32_t lifetimeGracePeriod)
     : mMaxCacheEntries(maxCacheEntries)
     , mMaxCacheLifetime(TimeDuration::FromSeconds(maxCacheLifetime))
     , mGracePeriod(TimeDuration::FromSeconds(lifetimeGracePeriod))
     , mLock("nsHostResolver.mLock")
     , mIdleThreadCV(mLock, "nsHostResolver.mIdleThreadCV")
     , mNumIdleThreads(0)
     , mThreadCount(0)
     , mActiveAnyThreadCount(0)
     , mEvictionQSize(0)
     , mPendingCount(0)
     , mShutdown(true)
 {
     mCreationTime = PR_Now();
     PR_INIT_CLIST(&mHighQ);
     PR_INIT_CLIST(&mMediumQ);
     PR_INIT_CLIST(&mLowQ);
     PR_INIT_CLIST(&mEvictionQ);
     mLongIdleTimeout  = PR_SecondsToInterval(LongIdleTimeoutSeconds);
     mShortIdleTimeout = PR_SecondsToInterval(ShortIdleTimeoutSeconds);
 }
 nsHostResolver::~nsHostResolver()
 {
     PL_DHashTableFinish(&mDB);
 }
 nsresult
 nsHostResolver::Init()
 {
     PL_DHashTableInit(&mDB, &gHostDB_ops, nullptr, sizeof(nsHostDBEnt), 0);
     mShutdown = false;
 #if defined(HAVE_RES_NINIT)
     // We want to make sure the system is using the correct resolver settings,
     // so we force it to reload those settings whenever we startup a subsequent
     // nsHostResolver instance.  We assume that there is no reason to do this
     // for the first nsHostResolver instance since that is usually created
     // during application startup.
     static int initCount = 0;
     if (initCount++ > 0) {
         LOG(("Calling 'res_ninit'.\n"));
         res_ninit(&_res);
     }
 #endif
     return NS_OK;
 }
 void
 nsHostResolver::ClearPendingQueue(PRCList *aPendingQ)
 {
     // loop through pending queue, erroring out pending lookups.
     if (!PR_CLIST_IS_EMPTY(aPendingQ)) {
         PRCList *node = aPendingQ->next;
         while (node != aPendingQ) {
             nsHostRecord *rec = static_cast<nsHostRecord *>(node);
             node = node->next;
             OnLookupComplete(rec, NS_ERROR_ABORT, nullptr);
         }
     }
 }
 void
 nsHostResolver::Shutdown()
 {
     LOG(("Shutting down host resolver.\n"));
     PRCList pendingQHigh, pendingQMed, pendingQLow, evictionQ;
     PR_INIT_CLIST(&pendingQHigh);
     PR_INIT_CLIST(&pendingQMed);
     PR_INIT_CLIST(&pendingQLow);
     PR_INIT_CLIST(&evictionQ);
     {
         MutexAutoLock lock(mLock);
         mShutdown = true;
         MoveCList(mHighQ, pendingQHigh);
         MoveCList(mMediumQ, pendingQMed);
         MoveCList(mLowQ, pendingQLow);
         MoveCList(mEvictionQ, evictionQ);
         mEvictionQSize = 0;
         mPendingCount = 0;
         if (mNumIdleThreads)
             mIdleThreadCV.NotifyAll();
         // empty host database
         PL_DHashTableEnumerate(&mDB, HostDB_RemoveEntry, nullptr);
     }
     ClearPendingQueue(&pendingQHigh);
     ClearPendingQueue(&pendingQMed);
     ClearPendingQueue(&pendingQLow);
     if (!PR_CLIST_IS_EMPTY(&evictionQ)) {
         PRCList *node = evictionQ.next;
         while (node != &evictionQ) {
             nsHostRecord *rec = static_cast<nsHostRecord *>(node);
             node = node->next;
             NS_RELEASE(rec);
         }
     }
 #ifdef NS_BUILD_REFCNT_LOGGING
     // Logically join the outstanding worker threads with a timeout.
     // Use this approach instead of PR_JoinThread() because that does
     // not allow a timeout which may be necessary for a semi-responsive
     // shutdown if the thread is blocked on a very slow DNS resolution.
     // mThreadCount is read outside of mLock, but the worst case
     // scenario for that race is one extra 25ms sleep.
     PRIntervalTime delay = PR_MillisecondsToInterval(25);
     PRIntervalTime stopTime = PR_IntervalNow() + PR_SecondsToInterval(20);
     while (mThreadCount && PR_IntervalNow() < stopTime)
         PR_Sleep(delay);
 #endif
 }
 void
 nsHostResolver::MoveQueue(nsHostRecord *aRec, PRCList &aDestQ)
 {
     NS_ASSERTION(aRec->onQueue, "Moving Host Record Not Currently Queued");
     PR_REMOVE_LINK(aRec);
     PR_APPEND_LINK(aRec, &aDestQ);
 }
 nsresult
 nsHostResolver::ResolveHost(const char            *host,
                             uint16_t               flags,
                             uint16_t               af,
                             nsResolveHostCallback *callback)
 {
     NS_ENSURE_TRUE(host && *host, NS_ERROR_UNEXPECTED);
     LOG(("Resolving host [%s]%s.\n",
          host, flags & RES_BYPASS_CACHE ? " - bypassing cache" : ""));
     // ensure that we are working with a valid hostname before proceeding.  see
     // bug 304904 for details.
     if (!net_IsValidHostName(nsDependentCString(host)))
         return NS_ERROR_UNKNOWN_HOST;
     // if result is set inside the lock, then we need to issue the
     // callback before returning.
     nsRefPtr<nsHostRecord> result;
     nsresult status = NS_OK, rv = NS_OK;
     {
         MutexAutoLock lock(mLock);
         if (mShutdown)
             rv = NS_ERROR_NOT_INITIALIZED;
         else {
             // Used to try to parse to an IP address literal.
             PRNetAddr tempAddr;
             // Unfortunately, PR_StringToNetAddr does not properly initialize
             // the output buffer in the case of IPv6 input. See bug 223145.
             memset(&tempAddr, 0, sizeof(PRNetAddr));
             // check to see if there is already an entry for this |host|
             // in the hash table.  if so, then check to see if we can't
             // just reuse the lookup result.  otherwise, if there are
             // any pending callbacks, then add to pending callbacks queue,
             // and return.  otherwise, add ourselves as first pending
             // callback, and proceed to do the lookup.
             nsHostKey key = { host, flags, af };
             nsHostDBEnt *he = static_cast<nsHostDBEnt *>
                                          (PL_DHashTableOperate(&mDB, &key, PL_DHASH_ADD));
             // if the record is null, then HostDB_InitEntry failed.
             if (!he || !he->rec) {
                 LOG(("  Out of memory: no cache entry for [%s].\n", host));
                 rv = NS_ERROR_OUT_OF_MEMORY;
             }
             // do we have a cached result that we can reuse?
             else if (!(flags & RES_BYPASS_CACHE) &&
                      he->rec->HasUsableResult(flags) &&
                      TimeStamp::NowLoRes() <= (he->rec->expiration + mGracePeriod)) {
                 LOG(("  Using cached record for host [%s].\n", host));
                 // put reference to host record on stack...
                 result = he->rec;
                 Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2, METHOD_HIT);
                 // For entries that are in the grace period
                 // or all cached negative entries, use the cache but start a new
                 // lookup in the background
                 ConditionallyRefreshRecord(he->rec, host);
                 if (he->rec->negative) {
                     LOG(("  Negative cache entry for[%s].\n", host));
                     Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                           METHOD_NEGATIVE_HIT);
                     status = NS_ERROR_UNKNOWN_HOST;
                 }
             }
             // if the host name is an IP address literal and has been parsed,
             // go ahead and use it.
             else if (he->rec->addr) {
                 LOG(("  Using cached address for IP Literal [%s].\n", host));
                 Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                       METHOD_LITERAL);
                 result = he->rec;
             }
             // try parsing the host name as an IP address literal to short
             // circuit full host resolution.  (this is necessary on some
             // platforms like Win9x.  see bug 219376 for more details.)
             else if (PR_StringToNetAddr(host, &tempAddr) == PR_SUCCESS) {
                 LOG(("  Host is IP Literal [%s].\n", host));
                 // ok, just copy the result into the host record, and be done
                 // with it! ;-)
                 he->rec->addr = new NetAddr();
                 PRNetAddrToNetAddr(&tempAddr, he->rec->addr);
                 // put reference to host record on stack...
                 Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                       METHOD_LITERAL);
                 result = he->rec;
             }
             else if (mPendingCount >= MAX_NON_PRIORITY_REQUESTS &&
                      !IsHighPriority(flags) &&
                      !he->rec->resolving) {
                 LOG(("  Lookup queue full: dropping %s priority request for "
                      "[%s].\n",
                      IsMediumPriority(flags) ? "medium" : "low", host));
                 Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                       METHOD_OVERFLOW);
                 // This is a lower priority request and we are swamped, so refuse it.
                 rv = NS_ERROR_DNS_LOOKUP_QUEUE_FULL;
             }
             else if (flags & RES_OFFLINE) {
                 LOG(("  Offline request for [%s]; ignoring.\n", host));
                 rv = NS_ERROR_OFFLINE;
             }
             // If this is an IPV4 or IPV6 specific request, check if there is
             // an AF_UNSPEC entry we can use. Otherwise, hit the resolver...
             else if (!he->rec->resolving) {
                 if (!(flags & RES_BYPASS_CACHE) &&
                     ((af == PR_AF_INET) || (af == PR_AF_INET6))) {
                     // First, search for an entry with AF_UNSPEC
                     const nsHostKey unspecKey = { host, flags, PR_AF_UNSPEC };
                     nsHostDBEnt *unspecHe = static_cast<nsHostDBEnt *>
                         (PL_DHashTableOperate(&mDB, &unspecKey, PL_DHASH_LOOKUP));
                     NS_ASSERTION(PL_DHASH_ENTRY_IS_FREE(unspecHe) ||
                                  (PL_DHASH_ENTRY_IS_BUSY(unspecHe) &&
                                   unspecHe->rec),
                                 "Valid host entries should contain a record");
                     if (PL_DHASH_ENTRY_IS_BUSY(unspecHe) &&
                         unspecHe->rec &&
                         unspecHe->rec->HasUsableResult(flags) &&
                         TimeStamp::NowLoRes() <= (he->rec->expiration + mGracePeriod)) {
                         MOZ_ASSERT(unspecHe->rec->addr_info || unspecHe->rec->negative,
                                    "Entry should be resolved or negative.");
                         LOG(("  Trying AF_UNSPEC entry for [%s] af: %s.\n",
                             host, (af == PR_AF_INET) ? "AF_INET" : "AF_INET6"));
                         he->rec->addr_info = nullptr;
                         if (unspecHe->rec->negative) {
                             he->rec->negative = unspecHe->rec->negative;
                         } else if (unspecHe->rec->addr_info) {
                             // Search for any valid address in the AF_UNSPEC entry
                             // in the cache (not blacklisted and from the right
                             // family).
                             NetAddrElement *addrIter =
                                 unspecHe->rec->addr_info->mAddresses.getFirst();
                             while (addrIter) {
                                 if ((af == addrIter->mAddress.inet.family) &&
                                      !unspecHe->rec->Blacklisted(&addrIter->mAddress)) {
                                     if (!he->rec->addr_info) {
                                         he->rec->addr_info = new AddrInfo(
                                             unspecHe->rec->addr_info->mHostName,
                                             unspecHe->rec->addr_info->mCanonicalName);
                                     }
                                     he->rec->addr_info->AddAddress(
                                         new NetAddrElement(*addrIter));
                                 }
                                 addrIter = addrIter->getNext();
                             }
                         }
                         if (he->rec->HasUsableResult(flags)) {
                             result = he->rec;
                             Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                                   METHOD_HIT);
                             ConditionallyRefreshRecord(he->rec, host);
                         }
                         // For AF_INET6, a new lookup means another AF_UNSPEC
                         // lookup. We have already iterated through the
                         // AF_UNSPEC addresses, so we mark this record as
                         // negative.
                         else if (af == PR_AF_INET6) {
                             LOG(("  No AF_INET6 in AF_UNSPEC entry: "
                                  "[%s] unknown host", host));
                             result = he->rec;
                             he->rec->negative = true;
                             status = NS_ERROR_UNKNOWN_HOST;
                             Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                                   METHOD_NEGATIVE_HIT);
                         }
                     }
                 }
                 // If no valid address was found in the cache or this is an
                 // AF_UNSPEC request, then start a new lookup.
                 if (!result) {
                     LOG(("  No usable address in cache for [%s]", host));
                     // Add callback to the list of pending callbacks.
                     PR_APPEND_LINK(callback, &he->rec->callbacks);
                     he->rec->flags = flags;
                     rv = IssueLookup(he->rec);
                     Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                           METHOD_NETWORK_FIRST);
                     if (NS_FAILED(rv)) {
                         PR_REMOVE_AND_INIT_LINK(callback);
                     }
                     else {
                         LOG(("  DNS lookup for host [%s] blocking pending "
                              "'getaddrinfo' query: callback [%p]",
                              host, callback));
                     }
                 }
             }
             else {
                 LOG(("  Host [%s] is being resolved. Appending callback [%p].",
                      host, callback));
                 PR_APPEND_LINK(callback, &he->rec->callbacks);
                 if (he->rec->onQueue) {
                     Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                                           METHOD_NETWORK_SHARED);
                     // Consider the case where we are on a pending queue of
                     // lower priority than the request is being made at.
                     // In that case we should upgrade to the higher queue.
                     if (IsHighPriority(flags) &&
                         !IsHighPriority(he->rec->flags)) {
                         // Move from (low|med) to high.
                         MoveQueue(he->rec, mHighQ);
                         he->rec->flags = flags;
                         ConditionallyCreateThread(he->rec);
                     } else if (IsMediumPriority(flags) &&
                                IsLowPriority(he->rec->flags)) {
                         // Move from low to med.
                         MoveQueue(he->rec, mMediumQ);
                         he->rec->flags = flags;
                         mIdleThreadCV.Notify();
                     }
                 }
             }
         }
     }
     if (result)
         callback->OnLookupComplete(this, result, status);
     return rv;
 }
 void
 nsHostResolver::DetachCallback(const char            *host,
                                uint16_t               flags,
                                uint16_t               af,
                                nsResolveHostCallback *callback,
                                nsresult               status)
 {
     nsRefPtr<nsHostRecord> rec;
     {
         MutexAutoLock lock(mLock);
         nsHostKey key = { host, flags, af };
         nsHostDBEnt *he = static_cast<nsHostDBEnt *>
                                      (PL_DHashTableOperate(&mDB, &key, PL_DHASH_LOOKUP));
         if (he && he->rec) {
             // walk list looking for |callback|... we cannot assume
             // that it will be there!
             PRCList *node = he->rec->callbacks.next;
             while (node != &he->rec->callbacks) {
                 if (static_cast<nsResolveHostCallback *>(node) == callback) {
                     PR_REMOVE_LINK(callback);
                     rec = he->rec;
                     break;
                 }
                 node = node->next;
             }
         }
     }
     // complete callback with the given status code; this would only be done if
     // the record was in the process of being resolved.
     if (rec)
         callback->OnLookupComplete(this, rec, status);
 }
 nsresult
 nsHostResolver::ConditionallyCreateThread(nsHostRecord *rec)
 {
     if (mNumIdleThreads) {
         // wake up idle thread to process this lookup
         mIdleThreadCV.Notify();
     }
     else if ((mThreadCount < HighThreadThreshold) ||
              (IsHighPriority(rec->flags) && mThreadCount < MAX_RESOLVER_THREADS)) {
         // dispatch new worker thread
         NS_ADDREF_THIS(); // owning reference passed to thread
         mThreadCount++;
         PRThread *thr = PR_CreateThread(PR_SYSTEM_THREAD,
                                         ThreadFunc,
                                         this,
                                         PR_PRIORITY_NORMAL,
                                         PR_GLOBAL_THREAD,
                                         PR_UNJOINABLE_THREAD,
 );
         if (!thr) {
             mThreadCount--;
             NS_RELEASE_THIS();
             return NS_ERROR_OUT_OF_MEMORY;
         }
     }
 #if defined(PR_LOGGING)
     else
       LOG(("  Unable to find a thread for looking up host [%s].\n", rec->host));
 #endif
     return NS_OK;
 }
 nsresult
 nsHostResolver::IssueLookup(nsHostRecord *rec)
 {
     MOZ_EVENT_TRACER_WAIT(rec, "net::dns::resolve");
     nsresult rv = NS_OK;
     NS_ASSERTION(!rec->resolving, "record is already being resolved");
     // Add rec to one of the pending queues, possibly removing it from mEvictionQ.
     // If rec is on mEvictionQ, then we can just move the owning
     // reference over to the new active queue.
     if (rec->next == rec)
         NS_ADDREF(rec);
     else {
         PR_REMOVE_LINK(rec);
         mEvictionQSize--;
     }
     if (IsHighPriority(rec->flags))
         PR_APPEND_LINK(rec, &mHighQ);
     else if (IsMediumPriority(rec->flags))
         PR_APPEND_LINK(rec, &mMediumQ);
     else
         PR_APPEND_LINK(rec, &mLowQ);
     mPendingCount++;
     rec->resolving = true;
     rec->onQueue = true;
     rv = ConditionallyCreateThread(rec);
     LOG (("  DNS thread counters: total=%d any-live=%d idle=%d pending=%d\n",
           mThreadCount,
           mActiveAnyThreadCount,
           mNumIdleThreads,
           mPendingCount));
     return rv;
 }
 nsresult
 nsHostResolver::ConditionallyRefreshRecord(nsHostRecord *rec, const char *host)
 {
     if (((TimeStamp::NowLoRes() > rec->expiration) || rec->negative) &&
         !rec->resolving) {
         LOG(("  Using %s cache entry for host [%s] but starting async renewal.",
             rec->negative ? "negative" :"positive", host));
         IssueLookup(rec);
         if (!rec->negative) {
             // negative entries are constantly being refreshed, only
             // track positive grace period induced renewals
             Telemetry::Accumulate(Telemetry::DNS_LOOKUP_METHOD2,
                 METHOD_RENEWAL);
         }
     }
     return NS_OK;
 }
 void
 nsHostResolver::DeQueue(PRCList &aQ, nsHostRecord **aResult)
 {
     *aResult = static_cast<nsHostRecord *>(aQ.next);
     PR_REMOVE_AND_INIT_LINK(*aResult);
     mPendingCount--;
     (*aResult)->onQueue = false;
 }
 bool
 nsHostResolver::GetHostToLookup(nsHostRecord **result)
 {
     bool timedOut = false;
     PRIntervalTime epoch, now, timeout;
     MutexAutoLock lock(mLock);
     timeout = (mNumIdleThreads >= HighThreadThreshold) ? mShortIdleTimeout : mLongIdleTimeout;
     epoch = PR_IntervalNow();
     while (!mShutdown) {
         // remove next record from Q; hand over owning reference. Check high, then med, then low
         if (!PR_CLIST_IS_EMPTY(&mHighQ)) {
             DeQueue (mHighQ, result);
             return true;
         }
         if (mActiveAnyThreadCount < HighThreadThreshold) {
             if (!PR_CLIST_IS_EMPTY(&mMediumQ)) {
                 DeQueue (mMediumQ, result);
                 mActiveAnyThreadCount++;
                 (*result)->usingAnyThread = true;
                 return true;
             }
             if (!PR_CLIST_IS_EMPTY(&mLowQ)) {
                 DeQueue (mLowQ, result);
                 mActiveAnyThreadCount++;
                 (*result)->usingAnyThread = true;
                 return true;
             }
         }
         // Determining timeout is racy, so allow one cycle through checking the queues
         // before exiting.
         if (timedOut)
             break;
         // wait for one or more of the following to occur:
         //  (1) the pending queue has a host record to process
         //  (2) the shutdown flag has been set
         //  (3) the thread has been idle for too long
         mNumIdleThreads++;
         mIdleThreadCV.Wait(timeout);
         mNumIdleThreads--;
         now = PR_IntervalNow();
         if ((PRIntervalTime)(now - epoch) >= timeout)
             timedOut = true;
         else {
             // It is possible that PR_WaitCondVar() was interrupted and returned early,
             // in which case we will loop back and re-enter it. In that case we want to
             // do so with the new timeout reduced to reflect time already spent waiting.
             timeout -= (PRIntervalTime)(now - epoch);
             epoch = now;
         }
     }
     // tell thread to exit...
     mThreadCount--;
     return false;
 }
 void
 nsHostResolver::OnLookupComplete(nsHostRecord *rec, nsresult status, AddrInfo *result)
 {
     // get the list of pending callbacks for this lookup, and notify
     // them that the lookup is complete.
     PRCList cbs;
     PR_INIT_CLIST(&cbs);
     {
         MutexAutoLock lock(mLock);
         // grab list of callbacks to notify
         MoveCList(rec->callbacks, cbs);
         // update record fields.  We might have a rec->addr_info already if a
         // previous lookup result expired and we're reresolving it..
         AddrInfo  *old_addr_info;
         {
             MutexAutoLock lock(rec->addr_info_lock);
             old_addr_info = rec->addr_info;
             rec->addr_info = result;
             rec->addr_info_gencnt++;
         }
         delete old_addr_info;
         rec->expiration = TimeStamp::NowLoRes();
         if (result) {
             rec->expiration += mMaxCacheLifetime;
             rec->negative = false;
         }
         else {
             rec->expiration += TimeDuration::FromSeconds(60); /* one minute for negative cache */
             rec->negative = true;
         }
         rec->resolving = false;
         if (rec->usingAnyThread) {
             mActiveAnyThreadCount--;
             rec->usingAnyThread = false;
         }
         if (!mShutdown) {
             // add to mEvictionQ
             PR_APPEND_LINK(rec, &mEvictionQ);
             NS_ADDREF(rec);
             if (mEvictionQSize < mMaxCacheEntries)
                 mEvictionQSize++;
             else {
                 // remove first element on mEvictionQ
                 nsHostRecord *head =
                     static_cast<nsHostRecord *>(PR_LIST_HEAD(&mEvictionQ));
                 PR_REMOVE_AND_INIT_LINK(head);
                 PL_DHashTableOperate(&mDB, (nsHostKey *) head, PL_DHASH_REMOVE);
                 if (!head->negative) {
                     // record the age of the entry upon eviction.
                     TimeDuration age = TimeStamp::NowLoRes() -
                                          (head->expiration - mMaxCacheLifetime);
                     Telemetry::Accumulate(Telemetry::DNS_CLEANUP_AGE,
                                           static_cast<uint32_t>(age.ToSeconds() / 60));
                 }
                 // release reference to rec owned by mEvictionQ
                 NS_RELEASE(head);
             }
         }
     }
     MOZ_EVENT_TRACER_DONE(rec, "net::dns::resolve");
     if (!PR_CLIST_IS_EMPTY(&cbs)) {
         PRCList *node = cbs.next;
         while (node != &cbs) {
             nsResolveHostCallback *callback =
                     static_cast<nsResolveHostCallback *>(node);
             node = node->next;
             callback->OnLookupComplete(this, rec, status);
             // NOTE: callback must not be dereferenced after this point!!
         }
     }
     NS_RELEASE(rec);
 }
 void
 nsHostResolver::CancelAsyncRequest(const char            *host,
                                    uint16_t               flags,
                                    uint16_t               af,
                                    nsIDNSListener        *aListener,
                                    nsresult               status)
 {
     MutexAutoLock lock(mLock);
     // Lookup the host record associated with host, flags & address family
     nsHostKey key = { host, flags, af };
     nsHostDBEnt *he = static_cast<nsHostDBEnt *>
                       (PL_DHashTableOperate(&mDB, &key, PL_DHASH_LOOKUP));
     if (he && he->rec) {
         nsHostRecord* recPtr = nullptr;
         PRCList *node = he->rec->callbacks.next;
         // Remove the first nsDNSAsyncRequest callback which matches the
         // supplied listener object
         while (node != &he->rec->callbacks) {
             nsResolveHostCallback *callback
                 = static_cast<nsResolveHostCallback *>(node);
             if (callback && (callback->EqualsAsyncListener(aListener))) {
                 // Remove from the list of callbacks
                 PR_REMOVE_LINK(callback);
                 recPtr = he->rec;
                 callback->OnLookupComplete(this, recPtr, status);
                 break;
             }
             node = node->next;
         }
         // If there are no more callbacks, remove the hash table entry
         if (recPtr && PR_CLIST_IS_EMPTY(&recPtr->callbacks)) {
             PL_DHashTableOperate(&mDB, (nsHostKey *)recPtr, PL_DHASH_REMOVE);
             // If record is on a Queue, remove it and then deref it
             if (recPtr->next != recPtr) {
                 PR_REMOVE_LINK(recPtr);
                 NS_RELEASE(recPtr);
             }
         }
     }
 }
 static size_t
 SizeOfHostDBEntExcludingThis(PLDHashEntryHdr* hdr, MallocSizeOf mallocSizeOf,
                              void*)
 {
     nsHostDBEnt* ent = static_cast<nsHostDBEnt*>(hdr);
     return ent->rec->SizeOfIncludingThis(mallocSizeOf);
 }
 size_t
 nsHostResolver::SizeOfIncludingThis(MallocSizeOf mallocSizeOf) const
 {
     MutexAutoLock lock(mLock);
     size_t n = mallocSizeOf(this);
     n += PL_DHashTableSizeOfExcludingThis(&mDB, SizeOfHostDBEntExcludingThis,
                                           mallocSizeOf);
     // The following fields aren't measured.
     // - mHighQ, mMediumQ, mLowQ, mEvictionQ, because they just point to
     //   nsHostRecords that also pointed to by entries |mDB|, and measured when
     //   |mDB| is measured.
     return n;
 }
 void
 nsHostResolver::ThreadFunc(void *arg)
 {
     LOG(("DNS lookup thread - starting execution.\n"));
     static nsThreadPoolNaming naming;
     naming.SetThreadPoolName(NS_LITERAL_CSTRING("DNS Resolver"));
 #if defined(RES_RETRY_ON_FAILURE)
     nsResState rs;
 #endif
     nsHostResolver *resolver = (nsHostResolver *)arg;
     nsHostRecord *rec;
     PRAddrInfo *prai = nullptr;
     while (resolver->GetHostToLookup(&rec)) {
         LOG(("DNS lookup thread - Calling getaddrinfo for host [%s].\n",
              rec->host));
         int flags = PR_AI_ADDRCONFIG;
         if (!(rec->flags & RES_CANON_NAME))
             flags |= PR_AI_NOCANONNAME;
         TimeStamp startTime = TimeStamp::Now();
         MOZ_EVENT_TRACER_EXEC(rec, "net::dns::resolve");
         // We need to remove IPv4 records manually
         // because PR_GetAddrInfoByName doesn't support PR_AF_INET6.
         bool disableIPv4 = rec->af == PR_AF_INET6;
         uint16_t af = disableIPv4 ? PR_AF_UNSPEC : rec->af;
         prai = PR_GetAddrInfoByName(rec->host, af, flags);
 #if defined(RES_RETRY_ON_FAILURE)
         if (!prai && rs.Reset())
             prai = PR_GetAddrInfoByName(rec->host, af, flags);
 #endif
         TimeDuration elapsed = TimeStamp::Now() - startTime;
         uint32_t millis = static_cast<uint32_t>(elapsed.ToMilliseconds());
         // convert error code to nsresult
         nsresult status;
         AddrInfo *ai = nullptr;
         if (prai) {
             const char *cname = nullptr;
             if (rec->flags & RES_CANON_NAME)
                 cname = PR_GetCanonNameFromAddrInfo(prai);
             ai = new AddrInfo(rec->host, prai, disableIPv4, cname);
             PR_FreeAddrInfo(prai);
             if (ai->mAddresses.isEmpty()) {
                 delete ai;
                 ai = nullptr;
             }
         }
         if (ai) {
             status = NS_OK;
             Telemetry::Accumulate(!rec->addr_info_gencnt ?
                                     Telemetry::DNS_LOOKUP_TIME :
                                     Telemetry::DNS_RENEWAL_TIME,
                                   millis);
         }
         else {
             status = NS_ERROR_UNKNOWN_HOST;
             Telemetry::Accumulate(Telemetry::DNS_FAILED_LOOKUP_TIME, millis);
         }
         // OnLookupComplete may release "rec", log before we lose it.
         LOG(("DNS lookup thread - lookup completed for host [%s]: %s.\n",
              rec->host, ai ? "success" : "failure: unknown host"));
         resolver->OnLookupComplete(rec, status, ai);
     }
     NS_RELEASE(resolver);
     LOG(("DNS lookup thread - queue empty, thread finished.\n"));
 }
 nsresult
 nsHostResolver::Create(uint32_t         maxCacheEntries,
                        uint32_t         maxCacheLifetime,
                        uint32_t         lifetimeGracePeriod,
                        nsHostResolver **result)
 {
 #if defined(PR_LOGGING)
     if (!gHostResolverLog)
         gHostResolverLog = PR_NewLogModule("nsHostResolver");
 #endif
     nsHostResolver *res = new nsHostResolver(maxCacheEntries,
                                              maxCacheLifetime,
                                              lifetimeGracePeriod);
     if (!res)
         return NS_ERROR_OUT_OF_MEMORY;
     NS_ADDREF(res);
     nsresult rv = res->Init();
     if (NS_FAILED(rv))
         NS_RELEASE(res);
     *result = res;
     return rv;
 }
 PLDHashOperator
 CacheEntryEnumerator(PLDHashTable *table, PLDHashEntryHdr *entry,
                      uint32_t number, void *arg)
 {
     // We don't pay attention to address literals, only resolved domains.
     // Also require a host.
     nsHostRecord *rec = static_cast<nsHostDBEnt*>(entry)->rec;
     MOZ_ASSERT(rec, "rec should never be null here!");
     if (!rec || !rec->addr_info || !rec->host) {
         return PL_DHASH_NEXT;
     }
     DNSCacheEntries info;
     info.hostname = rec->host;
     info.family = rec->af;
     info.expiration = (int64_t)(rec->expiration - TimeStamp::NowLoRes()).ToSeconds();
     if (info.expiration <= 0) {
         // We only need valid DNS cache entries
         return PL_DHASH_NEXT;
     }
     {
         MutexAutoLock lock(rec->addr_info_lock);
         NetAddr *addr = nullptr;
         NetAddrElement *addrElement = rec->addr_info->mAddresses.getFirst();
         if (addrElement) {
             addr = &addrElement->mAddress;
         }
         while (addr) {
             char buf[kIPv6CStrBufSize];
             if (NetAddrToString(addr, buf, sizeof(buf))) {
                 info.hostaddr.AppendElement(buf);
             }
             addr = nullptr;
             addrElement = addrElement->getNext();
             if (addrElement) {
                 addr = &addrElement->mAddress;
             }
         }
     }
     nsTArray<DNSCacheEntries> *args = static_cast<nsTArray<DNSCacheEntries> *>(arg);
     args->AppendElement(info);
     return PL_DHASH_NEXT;
 }
 void
 nsHostResolver::GetDNSCacheEntries(nsTArray<DNSCacheEntries> *args)
 {
     PL_DHashTableEnumerate(&mDB, CacheEntryEnumerator, args);
 }

The Tor Browser / annotate

netwerk/dns/nsHostResolver.cpp@ca08bd8f51b2 (annotated)

netwerk/dns/nsHostResolver.cpp