Slash host stake when too many proofs are missing

contracts/Storage.sol

@@ -8,11 +8,22 @@ import "./Stakes.sol";
 contract Storage is Contracts, Proofs, Stakes {
 
   uint private stakeAmount;
+  uint private slashMisses;
+  uint private slashPercentage;
 
   mapping(bytes32=>bool) private finished;
 
-  constructor(IERC20 token, uint _stakeAmount) Stakes(token) {
+  constructor(
+    IERC20 token,
+    uint _stakeAmount,
+    uint _slashMisses,
+    uint _slashPercentage
+  )
+    Stakes(token)
+  {
     stakeAmount = _stakeAmount;
+    slashMisses = _slashMisses;
+    slashPercentage = _slashPercentage;
   }
 
   function newContract(
@@ -101,6 +112,10 @@ contract Storage is Contracts, Proofs, Stakes {
     return _missed(contractId);
   }
 
+  function stake(address account) public view returns (uint) {
+    return _stake(account);
+  }
+
   function isProofRequired(
     bytes32 contractId,
     uint blocknumber
@@ -133,6 +148,9 @@ contract Storage is Contracts, Proofs, Stakes {
 
   function markProofAsMissing(bytes32 contractId, uint blocknumber) public {
     _markProofAsMissing(contractId, blocknumber);
+    if (_missed(contractId) % slashMisses == 0) {
+      _slash(host(contractId), slashPercentage);
+    }
   }
 
   function increaseStake(uint amount) public {

test/Storage.test.js

@@ -7,6 +7,8 @@ const { mineBlock, minedBlockNumber } = require ("./mining")
 describe("Storage", function () {
 
   const stakeAmount = 100
+  const slashMisses = 3
+  const slashPercentage = 10
   const request = exampleRequest()
   const bid = exampleBid()
 
@@ -19,7 +21,9 @@ describe("Storage", function () {
     let Token = await ethers.getContractFactory("TestToken")
     let StorageContracts = await ethers.getContractFactory("Storage")
     token = await Token.deploy([client.address, host.address])
-    storage = await StorageContracts.deploy(token.address, stakeAmount)
+    storage = await StorageContracts.deploy(
+      token.address, stakeAmount, slashMisses, slashPercentage
+    )
   })
 
   describe("creating a new storage contract", function () {
@@ -123,6 +127,29 @@ describe("Storage", function () {
         ).to.be.revertedWith("Contract already finished")
       })
     })
+
+    describe("slashing when missing proofs", function () {
+
+      async function ensureProofIsMissing() {
+        while (!await storage.isProofRequired(id, await minedBlockNumber())) {
+          mineBlock()
+        }
+        const blocknumber = await minedBlockNumber()
+        for (let i=0; i<request.proofTimeout; i++) {
+          mineBlock()
+        }
+        await storage.markProofAsMissing(id, blocknumber)
+      }
+
+      it("reduces stake when too many proofs are missing", async function () {
+        await storage.connect(host).startContract(id)
+        for (let i=0; i<slashMisses; i++) {
+          await ensureProofIsMissing()
+        }
+        const expectedStake = stakeAmount * (100 - slashPercentage) / 100
+        expect(await storage.stake(host.address)).to.equal(expectedStake)
+    })
+    })
   })
 
   it("doesn't create contract with insufficient stake", async function () {
@@ -168,9 +195,7 @@ describe("Storage", function () {
   })
 })
 
-// TODO: contract start and timeout
 // TODO: failure to start contract burns host and client
 // TODO: implement checking of actual proofs of storage, instead of dummy bool
-// TODO: slash stake when too many missed proofs
 // TODO: allow other host to take over contract when too many missed proofs
 // TODO: small partial payouts when proofs are being submitted