add eraseNode tool

contracts/registry/UsernameRegistrar.sol

@@ -274,6 +274,28 @@ contract UsernameRegistrar is Controlled, ApproveAndCallFallBack {
         slashUsername(username, _reserveSecret);
     }
 
+    /**
+     * @notice Clear resolver and ownership of unowned subdomians.
+     * @param _labels Sequence to erase.
+     */
+    function eraseNode(
+        bytes32[] _labels
+    ) 
+        external 
+    {
+        uint len = _labels.length;
+        require(len != 0, "Nothing to erase");
+        bytes32 label = _labels[len - 1];
+        bytes32 subnode = keccak256(abi.encodePacked(ensNode, label));
+        require(ensRegistry.owner(subnode) == address(0), "First slash/release top level subdomain");
+        ensRegistry.setSubnodeOwner(ensNode, label, address(this));
+        if(len > 1) {
+            eraseNodeHierarchy(len - 2, _labels, subnode);
+        }
+        ensRegistry.setResolver(subnode, 0);
+        ensRegistry.setOwner(subnode, 0);
+    }
+
     /**
      * @notice Migrate account to new registry, opt-in to new contract.
      * @param _label Username hash.
@@ -697,7 +719,34 @@ contract UsernameRegistrar is Controlled, ApproveAndCallFallBack {
         state = _state;
         emit RegistryState(_state);
     }
-
+
+    /**
+     * @notice recursively erase all _labels in _subnode
+     * @param _idx recursive position of _labels to erase
+     * @param _labels list of subnode labes
+     * @param _subnode subnode being erased
+     */
+    function eraseNodeHierarchy(
+        uint _idx,
+        bytes32[] _labels,
+        bytes32 _subnode
+    ) 
+        private 
+    {
+        // Take ownership of the node
+        ensRegistry.setSubnodeOwner(_subnode, _labels[_idx], address(this));
+        bytes32 subnode = keccak256(abi.encodePacked(_subnode, _labels[_idx]));
+
+        // Recurse if there are more labels
+        if (_idx > 0) {
+            eraseNodeHierarchy(_idx - 1, _labels, subnode);
+        }
+
+        // Erase the resolver and owner records
+        ensRegistry.setResolver(subnode, 0);
+        ensRegistry.setOwner(subnode, 0);
+    }
+
     /**
      * @dev Decodes abi encoded data with selector for "register(bytes32,address,bytes32,bytes32)".
      * @param _data Abi encoded data.

test/usernameregistrar.spec.js

@@ -986,6 +986,74 @@ contract('UsernameRegistrar', function () {
     });
   });
 
+describe('eraseNode(bytes32[])', function() {
+  it('should clear unowned subdomains of users', async () => {;
+    const registrant = accountsArr[6];
+    const anyone = accountsArr[5];
+    await TestToken.methods.mint(registry.price).send({from: registrant});
+    await TestToken.methods.approve(UsernameRegistrar.address, registry.price).send({from: registrant});  
+    const username = "root";
+    const usernameHash = namehash.hash(username + '.' + registry.registry);
+    const label = web3Utils.sha3(username);
+    const labels = [
+      web3Utils.sha3("10"),
+      web3Utils.sha3("9"),
+      web3Utils.sha3("8"),
+      web3Utils.sha3("7"),
+      web3Utils.sha3("6"),
+      web3Utils.sha3("5"),
+      web3Utils.sha3("4"),
+      web3Utils.sha3("3"),
+      web3Utils.sha3("2"),
+      web3Utils.sha3("1"),
+      web3Utils.sha3("0"),
+      web3Utils.sha3(username),
+    ];
+    await UsernameRegistrar.methods.register(
+      label,
+      utils.zeroAddress,
+      utils.zeroBytes32,
+      utils.zeroBytes32
+    ).send({from: registrant});
+    assert.equal(await ens.methods.owner(usernameHash).call(), registrant);    
+    const releaseDelay = await UsernameRegistrar.methods.releaseDelay().call();
+    await utils.increaseTime(releaseDelay)
+    await utils.increaseTime(1000)
+    await utils.increaseTime(1000)
+    let subnode = usernameHash;
+    for (let index = labels.length - 1; index > 0; index--) {
+      const label = labels[index - 1];
+      await ENSRegistry.methods.setSubnodeOwner(subnode, label, registrant).send({from: registrant}); 
+      subnode = web3Utils.soliditySha3(subnode, label);
+      assert.equal(await ens.methods.owner(subnode).call(), registrant);   
+
+    }
+
+    const resultRelease = await UsernameRegistrar.methods.release(web3Utils.sha3(username)).send({from: registrant});
+
+    subnode = usernameHash;
+    for (let index = labels.length - 1; index > 0; index--) {
+      const label = labels[index - 1];
+      subnode = web3Utils.soliditySha3(subnode, label);
+      assert.equal(await ens.methods.owner(subnode).call(), registrant);   
+    }
+
+    const resultErase = await UsernameRegistrar.methods.eraseNode(
+      labels
+    ).send({from: anyone});
+    //TODO: check events
+
+    subnode = usernameHash;
+    for (let index = labels.length - 1; index > 0; index--) {
+      const label = labels[index - 1];
+      subnode = web3Utils.soliditySha3(subnode, label);
+      assert.equal(await ens.methods.owner(subnode).call(), utils.zeroAddress);   
+    }
+  });
+
+
+});
+
   describe('moveRegistry(address)', function() {
     it('should move registry to new registry and migrate', async () => {
       const result = await UsernameRegistrar.methods.moveRegistry(UpdatedUsernameRegistrar.address).send();