[net/dns] Resolve AF_UNSPEC on dual-stacked systems. Sort addresses according to RFC3484.

net/base/host_resolver_impl.cc

Index: net/base/host_resolver_impl.cc
diff --git a/net/base/host_resolver_impl.cc b/net/base/host_resolver_impl.cc
index 9ec0a379e197f59bebc3e506545fc55a973e4f6c..59288236538db9c2c15041b62a5c5c9fb07dbb7e 100644
--- a/net/base/host_resolver_impl.cc
+++ b/net/base/host_resolver_impl.cc
@@ -38,6 +38,7 @@
 #include "net/base/net_errors.h"
 #include "net/base/net_log.h"
 #include "net/base/net_util.h"
+#include "net/dns/address_sorter.h"
 #include "net/dns/dns_client.h"
 #include "net/dns/dns_config_service.h"
 #include "net/dns/dns_protocol.h"
@@ -609,7 +610,7 @@ class HostResolverImpl::ProcTask
   void Cancel() {
     DCHECK(origin_loop_->BelongsToCurrentThread());
 
-    if (was_canceled())
+    if (was_canceled() || was_completed())
       return;
 
     callback_.Reset();
@@ -1048,26 +1049,27 @@ class HostResolverImpl::DnsTask {
                               const AddressList& addr_list,
                               base::TimeDelta ttl)> Callback;
 
-  DnsTask(DnsTransactionFactory* factory,
+  DnsTask(DnsClient* client,

[cbentzel, 2012/07/30 15:53:43]

Wondering if it would be better to pass in DnsTransactionFactory and
AddressSorter rather than DnsClient. Since this is not a public interface, I
don't lean too strongly one way or another. 

[szym, 2012/08/06 23:22:20]

It seems simpler to use DnsClient.

           const Key& key,
           const Callback& callback,
           const BoundNetLog& job_net_log)
-      : callback_(callback), net_log_(job_net_log) {
-    DCHECK(factory);
+      : client_(client),
+        family_(key.address_family),
+        callback_(callback),
+        net_log_(job_net_log) {
+    DCHECK(client);
     DCHECK(!callback.is_null());
 
-    // For now we treat ADDRESS_FAMILY_UNSPEC as if it was IPV4.
-    uint16 qtype = (key.address_family == ADDRESS_FAMILY_IPV6)
-                   ? dns_protocol::kTypeAAAA
-                   : dns_protocol::kTypeA;
-    // TODO(szym): Implement "happy eyeballs".
-    transaction_ = factory->CreateTransaction(
+    // If unspecified, do IPv4 first, because suffix search will be faster.
+    uint16 qtype = (family_ == ADDRESS_FAMILY_IPV6) ?
+                   dns_protocol::kTypeAAAA :
+                   dns_protocol::kTypeA;
+    transaction_ = client_->GetTransactionFactory()->CreateTransaction(
         key.hostname,
         qtype,
         base::Bind(&DnsTask::OnTransactionComplete, base::Unretained(this),
-                   base::TimeTicks::Now()),
+                   true /* first_query */, base::TimeTicks::Now()),
         net_log_);
-    DCHECK(transaction_.get());
   }
 
   int Start() {
@@ -1075,47 +1077,120 @@ class HostResolverImpl::DnsTask {
     return transaction_->Start();
   }
 
-  void OnTransactionComplete(const base::TimeTicks& start_time,
+ private:
+  void OnTransactionComplete(bool first_query,
+                             const base::TimeTicks& start_time,
                              DnsTransaction* transaction,
                              int net_error,
                              const DnsResponse* response) {
     DCHECK(transaction);
     // Run |callback_| last since the owning Job will then delete this DnsTask.
-    DnsResponse::Result result = DnsResponse::DNS_SUCCESS;
-    if (net_error == OK) {
-      CHECK(response);
-      DNS_HISTOGRAM("AsyncDNS.TransactionSuccess",
+    if (net_error != OK) {
+      DNS_HISTOGRAM("AsyncDNS.TransactionFailure",
                     base::TimeTicks::Now() - start_time);
-      AddressList addr_list;
-      base::TimeDelta ttl;
-      result = response->ParseToAddressList(&addr_list, &ttl);
-      UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ParseToAddressList",
-                                result,
-                                DnsResponse::DNS_PARSE_RESULT_MAX);
-      if (result == DnsResponse::DNS_SUCCESS) {
-        net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
-                          addr_list.CreateNetLogCallback());
-        callback_.Run(net_error, addr_list, ttl);
+      OnFailure(net_error, DnsResponse::DNS_PARSE_OK);

[mmenke, 2012/07/30 15:37:00]

Might want to distinguish in histograms the first query failing and the second
one, so we have a chance of noticing AAAA-hostile DNS servers in our stats.

May also be interesting to have a histogram with the ratio of A time to AAAA
time for the same request.

No need to do anything in this CL, just throwing ideas out.

+      return;
+    }
+
+    CHECK(response);
+    DNS_HISTOGRAM("AsyncDNS.TransactionSuccess",
+                  base::TimeTicks::Now() - start_time);
+    AddressList addr_list;
+    base::TimeDelta ttl;
+    DnsResponse::Result result = response->ParseToAddressList(&addr_list, &ttl);
+    UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ParseToAddressList",
+                              result,
+                              DnsResponse::DNS_PARSE_RESULT_MAX);
+    if (result != DnsResponse::DNS_PARSE_OK) {
+      // Fail even if the other query succeeds.
+      OnFailure(ERR_DNS_MALFORMED_RESPONSE, result);
+      return;
+    }
+
+    bool needs_sort = false;
+    if (first_query) {
+      if (family_ == ADDRESS_FAMILY_IPV6) {
+        needs_sort = true;
+      } else if (family_ == ADDRESS_FAMILY_UNSPECIFIED) {
+        first_addr_list_ = addr_list;
+        first_ttl_ = ttl;
+        // Use fully-qualified domain name to avoid search.
+        transaction_ = client_->GetTransactionFactory()->CreateTransaction(
+            response->GetDottedName() + ".",
+            dns_protocol::kTypeAAAA,

[cbentzel, 2012/07/30 15:53:43]

Why don't we issue A and AAAA in parallel for all search suffixes? Is there a
plan to eventually do that?

[szym, 2012/08/06 23:22:20]

To avoid the "I'm a smart NAT and I'm going to protect the DNS server from DoS
attack by black-holing any packets over 7 simultaneous requests"-issue.

This initial approach aims to be conservative (<=1 outstanding query per Job).

+            base::Bind(&DnsTask::OnTransactionComplete, base::Unretained(this),
+                       false /* first_query */, base::TimeTicks::Now()),
+            net_log_);
+        net_error = transaction_->Start();
+        if (net_error != ERR_IO_PENDING)
+          OnFailure(net_error, DnsResponse::DNS_PARSE_OK);
         return;
       }
-      net_error = ERR_DNS_MALFORMED_RESPONSE;
     } else {
-      DNS_HISTOGRAM("AsyncDNS.TransactionFailure",
+      DCHECK_EQ(ADDRESS_FAMILY_UNSPECIFIED, family_);
+      if (!first_addr_list_.empty()) {
+        ttl = std::min(ttl, first_ttl_);
+        // Place IPv4 addresses after IPv6.
+        addr_list.insert(addr_list.end(), first_addr_list_.begin(),
+                                          first_addr_list_.end());
+        needs_sort = true;
+      }
+    }
+
+    if (addr_list.empty()) {
+      // TODO(szym): Don't fallback to ProcTask in this case.
+      OnFailure(ERR_NAME_NOT_RESOLVED, DnsResponse::DNS_NO_ADDRESSES);
+      return;
+    }
+
+    if (needs_sort) {
+      base::TimeTicks start_time = base::TimeTicks::Now();
+      if (!client_->GetAddressSorter()->Sort(&addr_list)) {
+        DNS_HISTOGRAM("AsyncDNS.SortFailure",
+                      base::TimeTicks::Now() - start_time);
+        OnFailure(ERR_DNS_SORT_ERROR, DnsResponse::DNS_PARSE_OK);
+        return;
+      }
+      DNS_HISTOGRAM("AsyncDNS.SortSuccess",
                     base::TimeTicks::Now() - start_time);
     }
+
+    // AddressSorter prunes unusable destinations.
+    if (addr_list.empty()) {
+      LOG(WARNING) << "Address list empty after RFC3484 sort";
+      OnFailure(ERR_NAME_NOT_RESOLVED, DnsResponse::DNS_PARSE_OK);

[mmenke, 2012/07/30 15:37:00]

Should we be recording DNS_NO_ADDRESSES here, or some new error?

+      return;
+    }
+
+    OnSuccess(addr_list, ttl);
+  }
+
+  void OnFailure(int net_error, DnsResponse::Result result) {
+    DCHECK_NE(OK, net_error);
     net_log_.EndEvent(
         NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
         base::Bind(&NetLogDnsTaskFailedCallback, net_error, result));
     callback_.Run(net_error, AddressList(), base::TimeDelta());
   }
 
- private:
+  void OnSuccess(const AddressList& addr_list, base::TimeDelta ttl) {
+    net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
+                      addr_list.CreateNetLogCallback());
+    callback_.Run(OK, addr_list, ttl);
+  }
+
+  DnsClient* client_;
+  AddressFamily family_;
   // The listener to the results of this DnsTask.
   Callback callback_;
-
   const BoundNetLog net_log_;
 
   scoped_ptr<DnsTransaction> transaction_;
+
+  // TODO(szym): wrap this up as HostResolver::Result, add canonical name.
+  // Results from the first transaction. Used only if |family_| is unspecified.

[mmenke, 2012/07/30 15:37:00]

nit:  Convention seems to be to put the TODOs after other comments, probably so
it's clear the other comments aren't part of the TODO.

+  AddressList first_addr_list_;
+  base::TimeDelta first_ttl_;
 };
 
 //-----------------------------------------------------------------------------
@@ -1214,7 +1289,7 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
   }
 
   // Marks |req| as cancelled. If it was the last active Request, also finishes
-  // this Job marking it either as aborted or cancelled, and deletes it.
+  // this Job marking it as cancelled, and deletes it.

[mmenke, 2012/07/30 15:37:00]

nit:  "Job, marking"

   void CancelRequest(Request* req) {
     DCHECK_EQ(key_.hostname, req->info().hostname());
     DCHECK(!req->was_canceled());
@@ -1381,7 +1456,7 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
   void StartDnsTask() {
     DCHECK(resolver_->HaveDnsConfig());
     dns_task_.reset(new DnsTask(
-        resolver_->dns_client_->GetTransactionFactory(),
+        resolver_->dns_client_.get(),
         key_,
         base::Bind(&Job::OnDnsTaskComplete, base::Unretained(this)),
         net_log_));
@@ -1415,6 +1490,7 @@ class HostResolverImpl::Job : public PrioritizedDispatcher::Job {
     }
 
     UmaAsyncDnsResolveStatus(RESOLVE_STATUS_DNS_SUCCESS);
+
     CompleteRequests(net_error, addr_list, ttl);
   }