[marketplace] Add tests for freeing a slot

contracts/Collateral.sol

@@ -47,17 +47,19 @@ contract Collateral is AccountLocks {
     assert(token.transfer(msg.sender, amount));
   }
 
+  function _slashAmount(address account, uint256 percentage)
+    internal
+    view
+    returns (uint256)
+  {
+    return (balanceOf(account) * percentage) / 100;
+  }
+
   function _slash(address account, uint256 percentage)
     internal
     collateralInvariant
   {
-    // TODO: perhaps we need to add a minCollateral parameter so that
-    // a host's collateral can't drop below a certain amount, possibly
-    // preventing malicious behaviour when collateral drops too low for it
-    // to matter that it will be lost. Also, we need collateral to be high
-    // enough to cover repair costs in case of repair as well as marked
-    // proofs as missing fees.
-    uint256 amount = (balanceOf(account) * percentage) / 100;
+    uint256 amount = _slashAmount(account, percentage);
     funds.slashed += amount;
     subtract(account, amount);
   }

contracts/Marketplace.sol

@@ -50,13 +50,11 @@ contract Marketplace is Collateral, Proofs {
   function _freeSlot(
     bytes32 slotId
   ) internal marketplaceInvariant {
-    bytes32 requestId = _getRequestIdForSlot(slotId);
+    Slot storage slot = _slot(slotId);
+    bytes32 requestId = slot.requestId;
     RequestContext storage context = requestContexts[requestId];
     require(context.state == RequestState.Started, "Invalid state");
-    require(!_isCancelled(requestId), "Request cancelled");
 
-    Slot storage slot = _slot(slotId);
-    require(slot.host != address(0), "Slot not filled");
 
     _removeAccountLock(slot.host, requestId);
     // TODO: burn host's collateral except for repair costs + mark proof

contracts/Storage.sol

@@ -9,7 +9,7 @@ contract Storage is Collateral, Marketplace {
   uint256 public collateralAmount;
   uint256 public slashMisses;
   uint256 public slashPercentage;
-  uint256 public missThreshold;
+  uint256 public minCollateralThreshold;
 
   constructor(
     IERC20 token,
@@ -19,7 +19,7 @@ contract Storage is Collateral, Marketplace {
     uint256 _collateralAmount,
     uint256 _slashMisses,
     uint256 _slashPercentage,
-    uint256 _missThreshold
+    uint256 _minCollateralThreshold
   )
     Marketplace(
       token,
@@ -32,7 +32,7 @@ contract Storage is Collateral, Marketplace {
     collateralAmount = _collateralAmount;
     slashMisses = _slashMisses;
     slashPercentage = _slashPercentage;
-    missThreshold = _missThreshold;
+    minCollateralThreshold = _minCollateralThreshold;
   }
 
   function getRequest(bytes32 requestId) public view returns (Request memory) {
@@ -43,8 +43,8 @@ contract Storage is Collateral, Marketplace {
     return _slot(slotId);
   }
 
-  function getHost(bytes32 requestId) public view returns (address) {
-    return _host(requestId);
+  function getHost(bytes32 slotId) public view returns (address) {
+    return _host(slotId);
   }
 
   function missingProofs(bytes32 slotId) public view returns (uint256) {
@@ -85,12 +85,20 @@ contract Storage is Collateral, Marketplace {
     slotMustAcceptProofs(slotId)
   {
     _markProofAsMissing(slotId, period);
-    uint256 missed = _missed(slotId);
-    if (missed % slashMisses == 0) {
-      _slash(_host(slotId), slashPercentage);
-    }
-    if (missed > missThreshold) {
-      _freeSlot(slotId);
+    address host = _host(slotId);
+    if (_missed(slotId) % slashMisses == 0) {
+
+      uint256 slashAmount = _slashAmount(host, slashPercentage);
+      if (balanceOf(host) - slashAmount < minCollateralThreshold) {
+        // If host has been slashed enough such that the next slashing would
+        // cause the collateral to drop below the minimum threshold, the slot
+        // needs to be freed as the remaining collateral must be used for
+        // repairs and rewards (with any leftover to be burnt).
+        _freeSlot(slotId);
+      }
+      else {
+        _slash(host, slashPercentage);
+      }
     }
   }
 }

contracts/TestCollateral.sol

@@ -23,4 +23,8 @@ contract TestCollateral is Collateral {
   function unlock(bytes32 id) public {
     _unlock(id);
   }
+
+  function removeAccountLock(address account, bytes32 lockId) public {
+    _removeAccountLock(account, lockId);
+  }
 }

contracts/TestMarketplace.sol

@@ -25,4 +25,12 @@ contract TestMarketplace is Marketplace {
   function isSlotCancelled(bytes32 slotId) public view returns (bool) {
     return _isSlotCancelled(slotId);
   }
+  
+  function freeSlot(bytes32 slotId) public {
+    _freeSlot(slotId);
+  }
+
+  function slot(bytes32 slotId) public view returns (Slot memory) {
+    return _slot(slotId);
+  }
 }

contracts/TestProofs.sol

@@ -40,6 +40,10 @@ contract TestProofs is Proofs {
     _expectProofs(id, _probability, _duration);
   }
 
+  function unexpectProofs(bytes32 id) public {
+    _unexpectProofs(id);
+  }
+
   function isProofRequired(bytes32 id) public view returns (bool) {
     return _isProofRequired(id);
   }

contracts/TestStorage.sol

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "./Storage.sol";
+
+// exposes internal functions of Storage for testing
+contract TestStorage is Storage {
+  constructor(
+    IERC20 token,
+    uint256 _proofPeriod,
+    uint256 _proofTimeout,
+    uint8 _proofDowntime,
+    uint256 _collateralAmount,
+    uint256 _slashMisses,
+    uint256 _slashPercentage,
+    uint256 _minCollateralThreshold
+  )
+    Storage(
+      token,
+      _proofPeriod,
+      _proofTimeout,
+      _proofDowntime,
+      _collateralAmount,
+      _slashMisses,
+      _slashPercentage,
+      _minCollateralThreshold
+    )
+  // solhint-disable-next-line no-empty-blocks
+  {
+
+  }
+
+  function slashAmount(address account, uint256 percentage) public view returns (uint256) {
+    return _slashAmount(account, percentage);
+  }
+}

deploy/storage.js

@@ -6,7 +6,7 @@ async function deployStorage({ deployments, getNamedAccounts }) {
   const collateralAmount = 100
   const slashMisses = 3
   const slashPercentage = 10
-  const missThreshold = 20
+  const minCollateralThreshold = 40
   const args = [
     token.address,
     proofPeriod,
@@ -15,10 +15,10 @@ async function deployStorage({ deployments, getNamedAccounts }) {
     collateralAmount,
     slashMisses,
     slashPercentage,
-    missThreshold,
+    minCollateralThreshold,
   ]
   const { deployer } = await getNamedAccounts()
-  await deployments.deploy("Storage", { args, from: deployer })
+  await deployments.deploy("TestStorage", { args, from: deployer })
 }
 
 async function mine256blocks({ network, ethers }) {
@@ -32,5 +32,5 @@ module.exports = async (environment) => {
   await deployStorage(environment)
 }
 
-module.exports.tags = ["Storage"]
+module.exports.tags = ["TestStorage"]
 module.exports.dependencies = ["TestToken"]

test/Collateral.test.js

@@ -110,5 +110,10 @@ describe("Collateral", function () {
       await collateral.unlock(lock.id)
       await expect(collateral.withdraw()).not.to.be.reverted
     })
+
+    it("withdrawal succeeds when account lock has been removed", async function () {
+      await collateral.removeAccountLock(account0.address, lock.id)
+      await expect(collateral.withdraw()).not.to.be.reverted
+    })
   })
 })

test/Marketplace.test.js

@@ -103,6 +103,61 @@ describe("Marketplace", function () {
     })
   })
 
+  describe("freeing a slot", function () {
+    var id
+    beforeEach(async function () {
+      slot.index = 0
+      id = slotId(slot)
+
+      switchAccount(client)
+      await token.approve(marketplace.address, price(request))
+      await marketplace.requestStorage(request)
+      switchAccount(host)
+      await token.approve(marketplace.address, collateral)
+      await marketplace.deposit(collateral)
+
+      // await marketplace.fillSlot(slot.request, slot.index, proof)
+    })
+
+    async function waitUntilAllSlotsFilled() {
+      const lastSlot = request.ask.slots - 1
+      for (let i = 0; i <= lastSlot; i++) {
+        await marketplace.fillSlot(slot.request, i, proof)
+      }
+    }
+
+    it("fails to free slot when slot not filled", async function () {
+      slot.index = 5
+      let nonExistentId = slotId(slot)
+      await expect(marketplace.freeSlot(nonExistentId)).to.be.revertedWith(
+        "Slot empty"
+      )
+    })
+
+    it("fails to free slot when not started", async function () {
+      await marketplace.fillSlot(slot.request, slot.index, proof)
+      await expect(marketplace.freeSlot(id)).to.be.revertedWith("Invalid state")
+    })
+
+    it("successfully frees slot", async function () {
+      await waitUntilAllSlotsFilled()
+      await expect(marketplace.freeSlot(id)).not.to.be.reverted
+    })
+
+    it("emits event once slot is freed", async function () {
+      await waitUntilAllSlotsFilled()
+      await expect(await marketplace.freeSlot(id))
+        .to.emit(marketplace, "SlotFreed")
+        .withArgs(slot.request, id)
+    })
+
+    it("cannot get slot once freed", async function () {
+      await waitUntilAllSlotsFilled()
+      await marketplace.freeSlot(id)
+      await expect(marketplace.slot(id)).to.be.revertedWith("Slot empty")
+    })
+  })
+
   describe("filling a slot", function () {
     beforeEach(async function () {
       switchAccount(client)

test/Proofs.test.js

@@ -138,6 +138,13 @@ describe("Proofs", function () {
       expect(await proofs.willProofBeRequired(id)).to.be.false
       expect(await proofs.isProofRequired(id)).to.be.true
     })
+
+    it("proofs won't be required when no longer expected", async function () {
+      expect(await proofs.getPointer(id)).to.be.lt(downtime)
+      expect(await proofs.willProofBeRequired(id)).to.be.true
+      await proofs.unexpectProofs(id)
+      expect(await proofs.willProofBeRequired(id)).to.be.false
+    })
   })
 
   describe("when proofs are required", function () {
@@ -256,5 +263,11 @@ describe("Proofs", function () {
         proofs.markProofAsMissing(id, missedPeriod)
       ).to.be.revertedWith("Proof already marked as missing")
     })
+
+    it("requires no proofs when no longer expected", async function () {
+      await waitUntilProofIsRequired(id)
+      await proofs.unexpectProofs(id)
+      await expect(await proofs.isProofRequired(id)).to.be.false
+    })
   })
 })

test/Storage.test.js

@@ -28,9 +28,9 @@ describe("Storage", function () {
   beforeEach(async function () {
     ;[client, host] = await ethers.getSigners()
 
-    await deployments.fixture(["TestToken", "Storage"])
+    await deployments.fixture(["TestToken", "TestStorage"])
     token = await ethers.getContract("TestToken")
-    storage = await ethers.getContract("Storage")
+    storage = await ethers.getContract("TestStorage")
 
     await token.mint(client.address, 1_000_000_000)
     await token.mint(host.address, 1_000_000_000)
@@ -38,6 +38,7 @@ describe("Storage", function () {
     collateralAmount = await storage.collateralAmount()
     slashMisses = await storage.slashMisses()
     slashPercentage = await storage.slashPercentage()
+    minCollateralThreshold = await storage.minCollateralThreshold()
 
     request = exampleRequest()
     request.client = client.address
@@ -190,6 +191,69 @@ describe("Storage", function () {
       expect(BigNumber.from(challenge2).isZero())
     })
   })
+  
+  describe("freeing a slot", function () {
+    beforeEach(async function () {
+      period = (await storage.proofPeriod()).toNumber()
+      ;({ periodOf, periodEnd } = periodic(period))
+    })
+
+    async function waitUntilAllSlotsFilled() {
+      const lastSlot = request.ask.slots - 1
+      for (let i = 0; i <= lastSlot; i++) {
+        await storage.fillSlot(slot.request, i, proof)
+      }
+    }
+
+    async function waitUntilProofIsRequired(id) {
+      await advanceTimeTo(periodEnd(periodOf(await currentTime())))
+      while (
+        !(
+          (await storage.isProofRequired(id)) &&
+          (await storage.getPointer(id)) < 250
+        )
+      ) {
+        await advanceTime(period)
+      }
+    }
+
+    async function markProofAsMissing(slotId, onMarkAsMissing) {
+      for (let i = 0; i < slashMisses; i++) {
+        await waitUntilProofIsRequired(slotId)
+        let missedPeriod = periodOf(await currentTime())
+        await advanceTime(period)
+        if (i === slashMisses - 1 && typeof onMarkAsMissing === "function") {
+          onMarkAsMissing(missedPeriod)
+        } else await storage.markProofAsMissing(slotId, missedPeriod)
+      }
+    }
+
+    it("frees slot when collateral slashed below minimum threshold", async function () {
+      const id = slotId(slot)
+
+      await waitUntilAllSlotsFilled()
+
+      while (true) {
+        await markProofAsMissing(id)
+        let balance = await storage.balanceOf(host.address)
+        let slashAmount = await storage.slashAmount(
+          host.address,
+          slashPercentage
+        )
+        if (balance - slashAmount < minCollateralThreshold) {
+          break
+        }
+      }
+
+      let onMarkAsMissing = async function (missedPeriod) {
+        await expect(
+          await storage.markProofAsMissing(id, missedPeriod)
+        ).to.emit(storage, "SlotFreed")
+      }
+      await markProofAsMissing(id, onMarkAsMissing)
+      await expect(storage.getSlot(id)).to.be.revertedWith("Slot empty")
+    })
+  })
 })
 
 // TODO: implement checking of actual proofs of storage, instead of dummy bool