feat: collateral fractions (#47)

Co-authored-by: Eric Mastro <github@egonat.me>

contracts/Configuration.sol

@@ -9,9 +9,15 @@ struct MarketplaceConfig {
 }
 
 struct CollateralConfig {
-  uint256 minimumAmount; // frees slot when collateral drops below this minimum
-  uint256 slashCriterion; // amount of proofs missed that lead to slashing
-  uint256 slashPercentage; // percentage of the collateral that is slashed
+  /// @dev percentage of remaining collateral slot after it has been freed
+  /// (equivalent to `collateral - (collateral*maxNumberOfSlashes*slashPercentage)/100`)
+  /// TODO: to be aligned more closely with actual cost of repair once bandwidth incentives are known,
+  /// see https://github.com/status-im/codex-contracts-eth/pull/47#issuecomment-1465511949.
+  uint8 repairRewardPercentage;
+
+  uint8 maxNumberOfSlashes; // frees slot when the number of slashing reaches this value
+  uint16 slashCriterion; // amount of proofs missed that lead to slashing
+  uint8 slashPercentage; // percentage of the collateral that is slashed
 }
 
 struct ProofConfig {

contracts/Marketplace.sol

@@ -44,6 +44,10 @@ contract Marketplace is Proofs, StateRetrieval {
     MarketplaceConfig memory configuration
   ) Proofs(configuration.proofs) marketplaceInvariant {
     token = token_;
+
+    require(configuration.collateral.repairRewardPercentage <= 100, "Must be less than 100");
+    require(configuration.collateral.slashPercentage <= 100, "Must be less than 100");
+    require(configuration.collateral.maxNumberOfSlashes * configuration.collateral.slashPercentage <= 100, "Total slash percentage must be less then 100");
     config = configuration;
   }
 
@@ -126,17 +130,17 @@ contract Marketplace is Proofs, StateRetrieval {
     require(slotState(slotId) == SlotState.Filled, "Slot not accepting proofs");
     _markProofAsMissing(slotId, period);
     Slot storage slot = _slots[slotId];
+    Request storage request = _requests[slot.requestId];
 
     if (missingProofs(slotId) % config.collateral.slashCriterion == 0) {
-      uint256 slashedAmount = (slot.currentCollateral * config.collateral.slashPercentage) / 100;
+      uint256 slashedAmount = (request.ask.collateral * config.collateral.slashPercentage) / 100;
       slot.currentCollateral -= slashedAmount;
       _funds.slashed += slashedAmount;
       _funds.balance -= slashedAmount;
 
-      if (slot.currentCollateral < config.collateral.minimumAmount) {
-        // When the collateral drops below the minimum threshold, the slot
-        // needs to be freed so that there is enough remaining collateral to be
-        // distributed for repairs and rewards (with any leftover to be burnt).
+      if (missingProofs(slotId) / config.collateral.slashCriterion >= config.collateral.maxNumberOfSlashes) {
+        // When the number of slashings is at or above the allowed amount,
+        // free the slot.
         _forciblyFreeSlot(slotId);
       }
     }

contracts/Requests.sol

@@ -8,7 +8,7 @@ struct Request {
   address client;
   Ask ask;
   Content content;
-  uint256 expiry; // time at which this request timeouts if all slots are not filled and is pronounced cancelled
+  uint256 expiry; // timestamp as seconds since unix epoch at which this request expires
   bytes32 nonce; // random nonce to differentiate between similar requests
 }
 

deploy/marketplace.js

@@ -2,7 +2,8 @@ async function deployMarketplace({ deployments, getNamedAccounts }) {
   const token = await deployments.get("TestToken")
   const configuration = {
     collateral: {
-      minimumAmount: 40,
+      repairRewardPercentage: 10,
+      maxNumberOfSlashes: 5,
       slashCriterion: 3,
       slashPercentage: 10,
     },

package.json

@@ -4,6 +4,7 @@
   "scripts": {
     "test": "npm run lint && hardhat test",
     "start": "hardhat node --export deployment-localhost.json",
+    "compile": "hardhat compile",
     "format": "prettier --write contracts/**/*.sol test/**/*.js",
     "lint": "solhint contracts/**.sol"
   },

test/Marketplace.test.js

@@ -29,6 +29,47 @@ const {
   currentTime,
 } = require("./evm")
 
+describe('Marketplace constructor', function () {
+  let Marketplace, token, config
+
+  beforeEach(async function () {
+    await snapshot()
+    await ensureMinimumBlockHeight(256)
+
+    const TestToken = await ethers.getContractFactory("TestToken")
+    token = await TestToken.deploy()
+
+    Marketplace = await ethers.getContractFactory("TestMarketplace")
+    config = exampleConfiguration()
+  })
+
+  afterEach(async function () {
+    await revert()
+  })
+
+  function testPercentageOverflow(property) {
+    it(`should reject for ${property} overflowing percentage values`, async () => {
+      config.collateral[property] = 101
+
+      await expect(Marketplace.deploy(token.address, config)).to.be.revertedWith(
+        "Must be less than 100"
+      )
+    })
+  }
+
+  testPercentageOverflow('repairRewardPercentage')
+  testPercentageOverflow('slashPercentage')
+
+  it('should reject when total slash percentage exceeds 100%', async () => {
+    config.collateral.slashPercentage = 1
+    config.collateral.maxNumberOfSlashes = 101
+
+    await expect(Marketplace.deploy(token.address, config)).to.be.revertedWith(
+      "Total slash percentage must be less then 100"
+    )
+  })
+})
+
 describe("Marketplace", function () {
   const proof = hexlify(randomBytes(42))
   const config = exampleConfiguration()
@@ -765,7 +806,7 @@ describe("Marketplace", function () {
     })
 
     it("frees slot when collateral slashed below minimum threshold", async function () {
-      const minimum = config.collateral.minimumAmount
+      const minimum = request.ask.collateral - (request.ask.collateral*config.collateral.maxNumberOfSlashes*config.collateral.slashPercentage)/100
       await waitUntilStarted(marketplace, request, proof, token)
       while ((await marketplace.slotState(slotId(slot))) === SlotState.Filled) {
         expect(await marketplace.getSlotCollateral(slotId(slot))).to.be.gt(minimum)
@@ -779,7 +820,7 @@ describe("Marketplace", function () {
     })
 
     it("free slot when minimum reached and resets missed proof counter", async function () {
-      const minimum = config.collateral.minimumAmount
+      const minimum = request.ask.collateral - (request.ask.collateral*config.collateral.maxNumberOfSlashes*config.collateral.slashPercentage)/100
       await waitUntilStarted(marketplace, request, proof, token)
       let missedProofs = 0
       while ((await marketplace.slotState(slotId(slot))) === SlotState.Filled) {

test/examples.js

@@ -5,7 +5,8 @@ const { hexlify, randomBytes } = ethers.utils
 
 const exampleConfiguration = () => ({
   collateral: {
-    minimumAmount: 40,
+    repairRewardPercentage: 10,
+    maxNumberOfSlashes: 5,
     slashCriterion: 3,
     slashPercentage: 10,
   },