PIP36: Replay Failed StateSyncs

contracts/StateReceiver.sol

@@ -1,43 +1,102 @@
 pragma solidity ^0.5.11;
 
-import { RLPReader } from "solidity-rlp/contracts/RLPReader.sol";
-
-import { System } from "./System.sol";
+import {RLPReader} from "solidity-rlp/contracts/RLPReader.sol";
+import {System} from "./System.sol";
+import {IStateReceiver} from "./IStateReceiver.sol";
 
 contract StateReceiver is System {
   using RLPReader for bytes;
   using RLPReader for RLPReader.RLPItem;
 
   uint256 public lastStateId;
 
+  bytes32 public failedStateSyncsRoot;
+  mapping(bytes32 => bool) public nullifier;
+
+  mapping(uint256 => bytes) public failedStateSyncs;
+
+  address public rootSetter;
+  uint256 public constant TREE_DEPTH = 6;
+
   event StateCommitted(uint256 indexed stateId, bool success);
+  event StateSyncReplay(uint256 indexed stateId);
+
+  constructor(address _rootSetter) public {
+    rootSetter = _rootSetter;
+  }
 
-  function commitState(uint256 syncTime, bytes calldata recordBytes) external onlySystem returns(bool success) {
+  function commitState(uint256 syncTime, bytes calldata recordBytes) external onlySystem returns (bool success) {
     // parse state data
     RLPReader.RLPItem[] memory dataList = recordBytes.toRlpItem().toList();
     uint256 stateId = dataList[0].toUint();
-    require(
-      lastStateId + 1 == stateId,
-      "StateIds are not sequential"
-    );
+    require(lastStateId + 1 == stateId, "StateIds are not sequential");
     lastStateId++;
-
     address receiver = dataList[1].toAddress();
     bytes memory stateData = dataList[2].toBytes();
     // notify state receiver contract, in a non-revert manner
     if (isContract(receiver)) {
       uint256 txGas = 5000000;
+
       bytes memory data = abi.encodeWithSignature("onStateReceive(uint256,bytes)", stateId, stateData);
       // solium-disable-next-line security/no-inline-assembly
       assembly {
         success := call(txGas, receiver, 0, add(data, 0x20), mload(data), 0, 0)
       }
       emit StateCommitted(stateId, success);
+      if (!success) failedStateSyncs[stateId] = abi.encode(receiver, stateData);
     }
   }
 
+  function replayFailedStateSync(uint256 stateId) external {
+    bytes memory stateSyncData = failedStateSyncs[stateId];
+    require(stateSyncData.length != 0, "!found");
+    delete failedStateSyncs[stateId];
+
+    (address receiver, bytes memory stateData) = abi.decode(stateSyncData, (address, bytes));
+    emit StateSyncReplay(stateId);
+    IStateReceiver(receiver).onStateReceive(stateId, stateData); // revertable
+  }
+
+  function setRoot(bytes32 _root) external {
+    require(msg.sender == rootSetter, "!rootSetter");
+    require(failedStateSyncsRoot == bytes32(0), "already set");
+    failedStateSyncsRoot = _root;
+  }
+
+  function replayHistoricFailedStateSync(
+    bytes32[TREE_DEPTH] calldata proof,
+    uint256 proofIndex,
+    uint256 stateId,
+    address receiver,
+    bytes calldata data
+  ) external {
+    bytes32 root = failedStateSyncsRoot;
+    require(root != bytes32(0), "!root");
+
+    bytes32 leafHash = keccak256(abi.encode(stateId, receiver, data));
+    bytes32 zeroHash = keccak256(abi.encode(uint256(0), address(0), new bytes(0)));
+    require(leafHash != zeroHash && !nullifier[leafHash], "used");
+    nullifier[leafHash] = true;
+
+    require(root == _getRoot(proof, proofIndex, leafHash), "!proof");
+
+    emit StateSyncReplay(stateId);
+    IStateReceiver(receiver).onStateReceive(stateId, data);
+  }
+
+  function _getRoot(bytes32[TREE_DEPTH] memory proof, uint256 index, bytes32 leafHash) private pure returns (bytes32) {
+    bytes32 node = leafHash;
+
+    for (uint256 height = 0; height < TREE_DEPTH; height++) {
+      if (((index >> height) & 1) == 1) node = keccak256(abi.encodePacked(proof[height], node));
+      else node = keccak256(abi.encodePacked(node, proof[height]));
+    }
+
+    return node;
+  }
+
   // check if address is contract
-  function isContract(address _addr) private view returns (bool){
+  function isContract(address _addr) private view returns (bool) {
     uint32 size;
     // solium-disable-next-line security/no-inline-assembly
     assembly {

contracts/test/TestReenterer.sol

@@ -0,0 +1,19 @@
+pragma solidity ^0.5.11;
+
+contract TestReenterer {
+    uint256 public reenterCount;
+
+    function onStateReceive(uint256 id, bytes calldata _data) external {
+        if (reenterCount++ == 0) {
+            (bool success, bytes memory ret) = msg.sender.call(
+                abi.encodeWithSignature("replayFailedStateSync(uint256)", id)
+            );
+            // bubble up revert for tests
+            if (!success) {
+                assembly {
+                    revert(add(ret, 0x20), mload(ret))
+                }
+            }
+        }
+    }
+}

contracts/test/TestRevertingReceiver.sol

@@ -0,0 +1,12 @@
+pragma solidity ^0.5.11;
+
+contract TestRevertingReceiver {
+    bool public shouldIRevert = true;
+    function onStateReceive(uint256 _id, bytes calldata _data) external {
+        if (shouldIRevert) revert("TestRevertingReceiver");
+    }
+
+    function toggle() external {
+        shouldIRevert = !shouldIRevert;
+    }
+}

contracts/test/TestStateReceiver.sol

@@ -4,4 +4,6 @@ pragma experimental ABIEncoderV2;
 import {StateReceiver} from "../StateReceiver.sol";
 import {TestSystem} from "./TestSystem.sol";
 
-contract TestStateReceiver is StateReceiver, TestSystem {}
+contract TestStateReceiver is StateReceiver, TestSystem {
+  constructor(address _rootSetter) public StateReceiver(_rootSetter) {}
+}

migrations/2_genesis_contracts_deploy.js

@@ -10,6 +10,8 @@ const SafeMath = artifacts.require('SafeMath')
 const StateReciever = artifacts.require('StateReceiver')
 const TestStateReceiver = artifacts.require('TestStateReceiver')
 const TestCommitState = artifacts.require('TestCommitState')
+const TestReenterer = artifacts.require('TestReenterer')
+const TestRevertingReceiver = artifacts.require('TestRevertingReceiver')
 const System = artifacts.require('System')
 const ValidatorVerifier = artifacts.require('ValidatorVerifier')
 
@@ -44,13 +46,17 @@ module.exports = async function (deployer, network) {
             deployer.link(e.lib, e.contracts)
         }
 
-        console.log("Deploying contracts...")
+        const rootSetter = deployer.networks[network].from
+
+        console.log("Deploying contracts with rootSetter %s...", rootSetter)
         await deployer.deploy(BorValidatorSet)
         await deployer.deploy(TestBorValidatorSet)
-        await deployer.deploy(StateReciever)
-        await deployer.deploy(TestStateReceiver)
+        await deployer.deploy(StateReciever, rootSetter)
+        await deployer.deploy(TestStateReceiver, rootSetter)
         await deployer.deploy(System)
         await deployer.deploy(ValidatorVerifier)
         await deployer.deploy(TestCommitState)
+        await deployer.deploy(TestReenterer)
+        await deployer.deploy(TestRevertingReceiver)
     })
 }