Validator: Store and record change to stake

Currently, changes to stake are indirectly recorded and handshake may start
to return different result any time. With this change, we ensure that we
have a single point from which changes are performed, and tracked.

source/agora/node/Validator.d

@@ -82,6 +82,9 @@ public class Validator : FullNode, API
     /// but LocalScheduler is not instantiated yet.
     private bool started;
 
+    /// The identity we present on `handshake`
+    private Identity identity;
+
     /// Ctor
     public this (Config config)
     {
@@ -101,7 +104,12 @@ public class Validator : FullNode, API
         // does not call `onAcceptedBlock`.
         PreImageInfo self;
         if (this.enroll_man.getNextPreimage(self, this.ledger.getBlockHeight()))
+        {
             this.ledger.addPreimage(self);
+            this.setIdentity(self.utxo);
+        }
+        else
+            this.setIdentity(this.getFrozenUTXO());
 
         // currently we are not saving preimage info,
         // we only have the commitment in the genesis block
@@ -334,9 +342,7 @@ public class Validator : FullNode, API
 
         this.recordReq("public_key");
 
-        auto enroll_key = this.enroll_man.getEnrollmentKey();
-        Identity id = Identity(this.config.validator.key_pair.address,
-            enroll_key == Hash.init ? this.getFrozenUTXO() : enroll_key);
+        Identity id = Identity(this.identity.key, this.identity.utxo);
         if (key == PublicKey.init)
             return id;
 
@@ -657,14 +663,28 @@ public class Validator : FullNode, API
         Hash enroll_key = this.enroll_man.getEnrolledUTXO(height,
             this.ledger.getUTXOFinder());
 
-        if (enroll_key == Hash.init &&
-            (enroll_key = this.getFrozenUTXO()) == Hash.init)
+        if (enroll_key == Hash.init)
+        {
+            enroll_key = this.getFrozenUTXO();
+            if (enroll_key == Hash.init)
             {
                 log.dbg("checkAndEnroll: No frozen UTXO for validator {}",
                     this.config.validator.key_pair.address);
                 return Enrollment.init; // Not enrolled and no frozen UTXO
             }
 
+            if (this.identity.utxo != enroll_key)
+                this.setIdentity(enroll_key);
+        }
+        // We're enrolled but not aware of it, perhaps a restart, although
+        // the ctor should have caught this.
+        else if (this.identity.utxo is Hash.init)
+            this.setIdentity(enroll_key);
+        // Something fishy is happening, keep the same identity
+        else if (enroll_key != this.identity.utxo)
+            log.error("Identity differs from enrolled UTXO: {} (id) - {} (enrolled)",
+                      enroll_key, this.identity.utxo);
+
         const enrolled = this.enroll_man.validator_set.getEnrolledHeight(next_height, enroll_key);
 
         // This validators enrollment will expire next cycle or not enrolled at all
@@ -706,6 +726,29 @@ public class Validator : FullNode, API
         return Hash.init;
     }
 
+    /***************************************************************************
+
+        Set the `Identity` we use while communicating with other nodes
+
+        The identity is derived from the stake, hence it is set once when
+        the stake appears, and could be changed if the stake is slashed
+        and another one appears.
+
+        Params:
+          utxo = The UTXO hash of the stake we are tracking
+
+    ***************************************************************************/
+
+    private void setIdentity (in Hash utxo) @safe
+    {
+        if (this.identity.utxo is Hash.init)
+            log.info("Node identity initialized to {}", utxo);
+        else
+            log.warn("Node identity changed from {} to {}", this.identity.utxo, utxo);
+
+        this.identity = Identity(this.config.validator.key_pair.address, utxo);
+    }
+
     /***************************************************************************
 
         A delegate to be called by Nominator when node's own nomination is