Kernel opening should be provable and confirmed on auxiliary

contracts/core/AuxiliaryBlockStore.sol

@@ -18,7 +18,8 @@ import "../lib/Block.sol";
 import "../lib/MetaBlock.sol";
 import "../lib/SafeMath.sol";
 import "./BlockStore.sol";
-
+import "./PollingPlaceInterface.sol";
+import "./KernelGatewayInterface.sol";
 /**
  * @title The auxiliary block store stores observations about the auxiliary
  *        chain.
@@ -52,12 +53,30 @@ contract AuxiliaryBlockStore is BlockStore {
      */
     mapping(bytes32 => bytes32) public originBlockHashes;
 
-    /** The hash of the currently active kernel. */
-    bytes32 public kernelHash;
 
     /** The corresponding origin block store that tracks the origin chain. */
     BlockStore public originBlockStore;
 
+    /**
+     * The meta-block gate kernel gateway is the only contract that is allowed
+     * to inform opening of new kernel gateway.
+     */
+    KernelGatewayInterface public kernelGateway;
+
+    /* Modifiers */
+
+    /**
+     * @notice Functions with this modifier can only be called from the address
+     *         that is registered as the kernel gateway.
+     */
+    modifier onlyKernelGateway() {
+        require(
+            msg.sender == address(kernelGateway),
+            "This method must be called from the registered kernel gateway."
+        );
+        _;
+    }
+
     /* Constructor */
 
     /**
@@ -125,6 +144,27 @@ contract AuxiliaryBlockStore is BlockStore {
 
     /* External Functions */
 
+    /**
+     * @notice Set kernel gateway
+     *
+     * @param _kernelGateway The kernel gateway address
+     */
+    function initializeKernelGateway(address _kernelGateway)
+        external
+    {
+        require(
+            _kernelGateway != address(0),
+            "Kernel gateway address must not be zero."
+        );
+
+        require(
+            kernelGateway == address(0),
+            "Kernel gateway must not be already initialized."
+        );
+
+        kernelGateway = KernelGatewayInterface(_kernelGateway);
+    }
+
     /**
      * @notice Report a block. A reported block header is stored and can then
      *         be part of subsequent votes.
@@ -236,7 +276,7 @@ contract AuxiliaryBlockStore is BlockStore {
      *
      * @return transitionHash_ Hash of transition object at the checkpoint.
      */
-    function  auxiliaryTransitionHashAtBlock(
+    function transitionHashAtBlock(
         bytes32 _blockHash
     )
         external
@@ -316,7 +356,7 @@ contract AuxiliaryBlockStore is BlockStore {
     {
         bytes32 expectedTransitionHash = MetaBlock.hashAuxiliaryTransition(
             coreIdentifier,
-            kernelHash,
+            kernelHashes[_blockHash],
             checkpoints[_blockHash].dynasty,
             _blockHash,
             accumulatedGases[_blockHash],
@@ -328,6 +368,29 @@ contract AuxiliaryBlockStore is BlockStore {
         valid_ = _transitionHash == expectedTransitionHash;
     }
 
+    /**
+     * @notice Marks a block in the block store as justified. The source and
+     *         the target are required to know when a block is finalised.
+     *         Only the polling place may call this method.
+     *
+     * @dev This is an external function which can be called by polling place.
+     *      This function call justify_ function which is internal defined in
+     *      super class
+     *
+     * @param _sourceBlockHash The block hash of the source of the super-
+     *                         majority link.
+     * @param _targetBlockHash The block hash of the block that is justified.
+     */
+    function justify(
+        bytes32 _sourceBlockHash,
+        bytes32 _targetBlockHash
+    )
+        external
+        onlyPollingPlace()
+    {
+        super.justify_(_sourceBlockHash, _targetBlockHash);
+        updateKernel(_targetBlockHash);
+    }
     /* Private Functions */
 
     /**
@@ -378,4 +441,47 @@ contract AuxiliaryBlockStore is BlockStore {
 
         isAncestor_ = currentCheckpoint.blockHash == _ancestor;
     }
+
+    /**
+     * @notice Stores the kernel observation for the dynasty number.
+     *         It also activates already reported kernel
+     *
+     * @param _blockHash The checkpoint that shall be finalized.
+     */
+    function updateKernel(bytes32 _blockHash)
+        private
+    {
+
+        bytes32 openKernelHash =
+            kernelGateway.getOpenKernelHash(currentDynasty);
+
+        // Check if any kernel is reported for activation.
+        if(openKernelHash != bytes32(0)) {
+
+            address[] memory updatedValidators;
+            uint256[] memory updatedWeights;
+
+            (updatedValidators, updatedWeights) =
+                kernelGateway.getUpdatedValidators(openKernelHash);
+
+            /*
+             * Report polling place about new validators and new finalized
+             * block heights.
+             */
+            PollingPlaceInterface(pollingPlace).updateMetaBlockHeight(
+                updatedValidators,
+                updatedWeights,
+                originBlockStore.getCurrentDynasty(),
+                currentDynasty
+            );
+
+            // Update the active kernel hash.
+            kernelGateway.activateKernel(openKernelHash);
+        }
+
+        // Store the kernel observations for the block hash.
+        kernelHashes[_blockHash] = kernelGateway.getActiveKernelHash();
+
+    }
+
 }

contracts/core/BlockStore.sol

@@ -260,33 +260,7 @@ contract BlockStore is BlockStoreInterface {
         external
         onlyPollingPlace()
     {
-        bool blockValid;
-        string memory reason;
-
-        (blockValid, reason) = isSourceValid(_sourceBlockHash);
-        require(blockValid, reason);
-
-        (blockValid, reason) = isTargetValid(
-            _sourceBlockHash,
-            _targetBlockHash
-        );
-        require(blockValid, reason);
-
-        // Finalise first as it may increase the dynasty number of target.
-        if (distanceInEpochs(_sourceBlockHash, _targetBlockHash) == 1) {
-            finalise(_sourceBlockHash);
-        }
-
-        Checkpoint memory checkpoint = Checkpoint(
-            _targetBlockHash,
-            _sourceBlockHash,
-            true,
-            false,
-            currentDynasty
-        );
-        checkpoints[_targetBlockHash] = checkpoint;
-
-        emit BlockJustified(_targetBlockHash);
+        justify_(_sourceBlockHash, _targetBlockHash);
     }
 
     /**
@@ -493,6 +467,50 @@ contract BlockStore is BlockStoreInterface {
 
     /* Internal Functions */
 
+    /**
+     * @notice Marks a block in the block store as justified. The source and
+     *         the target are required to know when a block is finalised.
+     *         Only the polling place may call this method.
+     *
+     * @param _sourceBlockHash The block hash of the source of the super-
+     *                         majority link.
+     * @param _targetBlockHash The block hash of the block that is justified.
+     */
+    function justify_(
+        bytes32 _sourceBlockHash,
+        bytes32 _targetBlockHash
+    )
+        internal
+    {
+        bool blockValid;
+        string memory reason;
+
+        (blockValid, reason) = isSourceValid(_sourceBlockHash);
+        require(blockValid, reason);
+
+        (blockValid, reason) = isTargetValid(
+            _sourceBlockHash,
+            _targetBlockHash
+        );
+        require(blockValid, reason);
+
+        // Finalise first as it may increase the dynasty number of target.
+        if (distanceInEpochs(_sourceBlockHash, _targetBlockHash) == 1) {
+            finalise(_sourceBlockHash);
+        }
+
+        Checkpoint memory checkpoint = Checkpoint(
+            _targetBlockHash,
+            _sourceBlockHash,
+            true,
+            false,
+            currentDynasty
+        );
+        checkpoints[_targetBlockHash] = checkpoint;
+
+        emit BlockJustified(_targetBlockHash);
+    }
+
     /**
      * @notice Report a block. A reported block header is stored and can then
      *         be part of subsequent votes.
@@ -616,8 +634,6 @@ contract BlockStore is BlockStoreInterface {
         isCheckpoint_ = checkpoints[_blockHash].blockHash == _blockHash;
     }
 
-    /* Private Functions */
-
     /**
      * @notice Finalises the checkpoint at the given block hash. Updates the
      *         current head and dynasty if it is above the old head.
@@ -635,6 +651,8 @@ contract BlockStore is BlockStoreInterface {
         emit BlockFinalised(_blockHash);
     }
 
+    /* Private Functions */
+
     /**
      * @notice Checks if a source block is valid. The same criteria apply for
      *         voting and justifying, as justifying results from voting.

contracts/core/BlockStoreInterface.sol

@@ -136,4 +136,22 @@ interface BlockStoreInterface {
         external
         view
         returns (bool reported_);
+
+    /**
+     * @notice Returns auxiliary transition hash at the checkpoint defined
+     *         at given block hash.
+     *
+     * @dev It reverts transaction if checkpoint is not defined at given
+     *      block hash.
+     *
+     * @param _blockHash The hash of the block for which transition object
+     *                   is requested.
+     *
+     * @return transitionHash_ Hash of transition object at the checkpoint.
+     */
+    function  transitionHashAtBlock(bytes32 _blockHash)
+        external
+        view
+        returns(bytes32 transitionHash_);
+
 }

contracts/core/InitializeGatewayKernelInterface.sol

@@ -0,0 +1,29 @@
+pragma solidity ^0.4.23;
+
+// Copyright 2018 OpenST Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/** @title The interface for opening the new kernel on auxiliary. */
+
+interface InitializeGatewayKernelInterface {
+
+    /**
+     * @notice Set kernel gateway
+     *
+     * @param _kernelGateway The kernel gateway address
+     */
+    function initializeKernelGateway(address _kernelGateway)
+        external;
+
+}