[net] HostResolverImpl + DnsTransaction + DnsConfigService = Asynchronous DNS ready for experiments.

net/dns/dns_transaction.cc

Index: net/dns/dns_transaction.cc
diff --git a/net/dns/dns_transaction.cc b/net/dns/dns_transaction.cc
index 6cd02a33bd5b707945971bf300d3540d7a031c0d..3f127823058d23afec6a2c7423b1acb9cb9c3a20 100644
--- a/net/dns/dns_transaction.cc
+++ b/net/dns/dns_transaction.cc
@@ -78,7 +78,7 @@ class ResponseParameters : public NetLog::EventParameters {
     DictionaryValue* dict = new DictionaryValue();
     dict->SetInteger("rcode", rcode_);
     dict->SetInteger("answer_count", answer_count_);
-    dict->Set("socket_source", source_.ToValue());
+    dict->Set("source_dependency", source_.ToValue());
     return dict;
   }
 
@@ -211,8 +211,14 @@ class DnsUDPAttempt {
       return rv;
 
     DCHECK(rv);
-    if (!response_->InitParse(rv, *query_))
+    if (!response_->InitParse(rv, *query_)) {
+      // TODO(szym): Consider making this reaction less aggressive.
+      // Other implementations simply ignore mismatched responses. Since each
+      // DnsUDPAttempt binds to a different port, we might find that responses
+      // to previously timed out queries lead to failures in the future.
+      // http://crbug.com/107413
       return ERR_DNS_MALFORMED_RESPONSE;
+    }
     if (response_->flags() & dns_protocol::kFlagTC)
       return ERR_DNS_SERVER_REQUIRES_TCP;
     if (response_->rcode() != dns_protocol::kRcodeNOERROR &&
@@ -303,6 +309,10 @@ class DnsTransactionImpl : public DnsTransaction, public base::NonThreadSafe {
     return rv;
   }
 
+  virtual const BoundNetLog& net_log() const {

[mmenke, 2012/02/15 19:54:16]

nit:  OVERRIDE

+    return net_log_;
+  }
+
  private:
   // Prepares |qnames_| according to the DnsConfig.
   int PrepareSearch() {
@@ -387,7 +397,8 @@ class DnsTransactionImpl : public DnsTransaction, public base::NonThreadSafe {
     }
 
     net_log_.AddEvent(NetLog::TYPE_DNS_TRANSACTION_ATTEMPT, make_scoped_refptr(
-        new NetLogSourceParameter("socket_source", socket->NetLog().source())));
+        new NetLogSourceParameter("source_dependency",
+                                  socket->NetLog().source())));
 
     const DnsConfig& config = session_->config();
 
@@ -451,7 +462,7 @@ class DnsTransactionImpl : public DnsTransaction, public base::NonThreadSafe {
         DoCallback(rv, attempt);
         return;
       default:
-        // TODO(szym): Some nameservers could fail so try the next one.
+        // Some nameservers could fail so try the next one.
         const DnsConfig& config = session_->config();
         if (attempts_.size() < config.attempts * config.nameservers.size()) {
           rv = MakeAttempt();