[net/dns] Don't abandon a DnsUDPAttempt when the response does not match the query.

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 00d8064f6e8d6f263423659519e9691a99e406aa..a9390a2547dc0e8aaef8eec8bc1317d6214796aa 100644
--- a/net/dns/dns_transaction.cc
+++ b/net/dns/dns_transaction.cc
@@ -71,6 +71,7 @@ class DnsUDPAttempt {
                 scoped_ptr<DnsQuery> query,
                 const CompletionCallback& callback)
       : next_state_(STATE_NONE),
+        received_malformed_response_(false),
         socket_(socket.Pass()),
         server_(server),
         query_(query.Pass()),
@@ -150,8 +151,7 @@ class DnsUDPAttempt {
           break;
       }
     } while (rv != ERR_IO_PENDING && next_state_ != STATE_NONE);
-
-    return rv;
+    return received_malformed_response_ ? ERR_DNS_MALFORMED_RESPONSE : rv;

[mmenke, 2012/08/28 14:15:54]

Err...How does this work?  It looks like if we ever get a malformed response, we
set |received_malformed_response_| to true, and never switch it to false if we
subsequently get a non-malformed response, we'll still return
ERR_DNS_MALFORMED_RESPONSE here.

[szym, 2012/08/28 14:59:44]

You're right. This isn't finished yet, and the test I wrote doesn't really
exercise it. I'll upload a fixed patch soon.

   }
 
   int DoConnect() {
@@ -196,12 +196,14 @@ class DnsUDPAttempt {
 
     DCHECK(rv);
     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;
+      // Our solution is to make another attempt, in case the query truly
+      // failed, but keep this attempt alive, in case it was a false alarm.
+      received_malformed_response_ = true;
+      next_state_ = STATE_READ_RESPONSE;
+      return ERR_IO_PENDING;
     }
     if (response_->flags() & dns_protocol::kFlagTC)
       return ERR_DNS_SERVER_REQUIRES_TCP;
@@ -222,6 +224,7 @@ class DnsUDPAttempt {
   }
 
   State next_state_;
+  bool received_malformed_response_;
 
   scoped_ptr<DatagramClientSocket> socket_;
   IPEndPoint server_;