[GitHub] [incubator-pekko] He-Pin commented on a diff in pull request #371: Generate random DNS id's

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin commented on code in PR #371:
URL: https://github.com/apache/incubator-pekko/pull/371#discussion_r1221553158


##########
actor/src/main/scala/org/apache/pekko/io/dns/internal/AsyncDnsResolver.scala:
##########
@@ -85,11 +86,25 @@ private[io] final class AsyncDnsResolver(
     settings.SearchDomains,
     settings.NDots)
 
-  private var requestId: Short = 0
+  private var (idIndex, idIncrement) = {
+    val secureRandom = new SecureRandom()
+    (secureRandom.nextLong(), secureRandom.nextLong())
+  }
+
+  private var idCount = 1
 
+  // DNS id's need to be random, see https://datatracker.ietf.org/doc/html/rfc5452#section-4.3.
+  // Uses enhanced double hashing technique from
+  // https://en.wikipedia.org/wiki/Double_hashing#Enhanced_double_hashing
   private def nextId(): Short = {
-    requestId = (requestId + 1).toShort
-    requestId
+    val result = (0xFFFFFFFF & idIndex).asInstanceOf[Short]
+    idIndex -= idIncrement
+    // Incorporate the counter into the increment to create a
+    // tetrahedral number additional term.
+    idIncrement -= {
+      idCount += 1; idCount - 1
+    }
+    result

Review Comment:
   `nextId` can be called concurrently, so I think two thread can get the same result.



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