Handle stale price

contracts/PriceOracle/PriceOracleProxy.sol

@@ -172,13 +172,15 @@ contract PriceOracleProxy is PriceOracle, Exponential, Denominations {
 
         AggregatorInfo memory aggregatorInfo = aggregators[token];
         if (aggregatorInfo.isUsed) {
-            uint256 price = getPriceFromChainlink(aggregatorInfo.base, aggregatorInfo.quote);
-            if (aggregatorInfo.quote == Denominations.USD) {
-                // Convert the price to ETH based if it's USD based.
-                price = mul_(price, Exp({mantissa: getUsdcEthPrice()}));
+            (bool success, uint256 price) = getPriceFromChainlink(aggregatorInfo.base, aggregatorInfo.quote);
+            if (success) {
+                if (aggregatorInfo.quote == Denominations.USD) {
+                    // Convert the price to ETH based if it's USD based.
+                    price = mul_(price, Exp({mantissa: getUsdcEthPrice()}));
+                }
+                uint256 underlyingDecimals = EIP20Interface(token).decimals();
+                return mul_(price, 10**(18 - underlyingDecimals));
             }
-            uint256 underlyingDecimals = EIP20Interface(token).decimals();
-            return mul_(price, 10**(18 - underlyingDecimals));
         }
         return getPriceFromV1(token);
     }
@@ -187,14 +189,17 @@ contract PriceOracleProxy is PriceOracle, Exponential, Denominations {
      * @notice Get price from ChainLink
      * @param base The base token that ChainLink aggregator gets the price of
      * @param quote The quote token, currenlty support ETH and USD
-     * @return The price, scaled by 1e18
+     * @return (Success, The price, scaled by 1e18)
      */
-    function getPriceFromChainlink(address base, address quote) internal view returns (uint256) {
-        (, int256 price, , , ) = registry.latestRoundData(base, quote);
-        require(price > 0, "invalid price");
+    function getPriceFromChainlink(address base, address quote) internal view returns (bool, uint256) {
+        (, int256 price, , uint256 updatedAt, ) = registry.latestRoundData(base, quote);
+        // If the price from ChainLink hasn't been updated for 1 day, we consider it stale.
+        if (price == 0 || add_(updatedAt, 1 days) < getBlockTimestamp()) {
+            return (false, 0);
+        }
 
         // Extend the decimals to 1e18.
-        return mul_(uint256(price), 10**(18 - uint256(registry.decimals(base, quote))));
+        return (true, mul_(uint256(price), 10**(18 - uint256(registry.decimals(base, quote)))));
     }
 
     /**
@@ -279,6 +284,14 @@ contract PriceOracleProxy is PriceOracle, Exponential, Denominations {
         return v1PriceOracle.assetPrices(token);
     }
 
+    /**
+     * @notice Get the curent block timestamp
+     * @return The curent block timestamp
+     */
+    function getBlockTimestamp() internal view returns (uint256) {
+        return block.timestamp;
+    }
+
     /*** Admin or guardian functions ***/
 
     event AggregatorUpdated(address tokenAddress, address base, address quote, bool isUsed);

tests/Contracts/MockAggregator.sol

@@ -42,6 +42,7 @@ contract MockAggregator {
 
     uint8 public decimals = 18;
     int256 public answer;
+    uint256 public blockTimestamp = 100000;
 
     constructor(int256 _answer) public {
         answer = _answer;
@@ -61,7 +62,7 @@ contract MockAggregator {
         // Shh
         _roundId;
 
-        return (roundId, answer, block.timestamp, block.timestamp, roundId);
+        return (roundId, answer, blockTimestamp, blockTimestamp, roundId);
     }
 
     function latestRoundData()
@@ -75,7 +76,7 @@ contract MockAggregator {
             uint80
         )
     {
-        return (roundId, answer, block.timestamp, block.timestamp, roundId);
+        return (roundId, answer, blockTimestamp, blockTimestamp, roundId);
     }
 
     function setAnswer(int256 _answer) external {
@@ -85,6 +86,10 @@ contract MockAggregator {
     function setDecimals(uint8 _decimals) external {
         decimals = _decimals;
     }
+
+    function setBlockTimestamp(uint256 newBlockTimestamp) external {
+        blockTimestamp = newBlockTimestamp;
+    }
 }
 
 contract MockRegistry is FeedRegistryInterface {
@@ -93,6 +98,7 @@ contract MockRegistry is FeedRegistryInterface {
     mapping(address => mapping(address => int256)) private answer;
     bool public getFeedFailed;
     bool public feedDisabled;
+    uint256 public blockTimestamp = 100000;
 
     function getRoundData(
         address base,
@@ -109,7 +115,7 @@ contract MockRegistry is FeedRegistryInterface {
             uint80
         )
     {
-        return (roundId, answer[base][quote], block.timestamp, block.timestamp, _roundId);
+        return (roundId, answer[base][quote], blockTimestamp, blockTimestamp, _roundId);
     }
 
     function latestRoundData(address base, address quote)
@@ -123,7 +129,7 @@ contract MockRegistry is FeedRegistryInterface {
             uint80
         )
     {
-        return (roundId, answer[base][quote], block.timestamp, block.timestamp, roundId);
+        return (roundId, answer[base][quote], blockTimestamp, blockTimestamp, roundId);
     }
 
     function decimals(address base, address quote) external view returns (uint8) {
@@ -183,4 +189,8 @@ contract MockRegistry is FeedRegistryInterface {
     ) external {
         answer[base][quote] = _answer;
     }
+
+    function setBlockTimestamp(uint256 newBlockTimestamp) external {
+        blockTimestamp = newBlockTimestamp;
+    }
 }

tests/Contracts/PriceOracleProxyHarness.sol

@@ -0,0 +1,22 @@
+pragma solidity ^0.5.16;
+
+import "../../contracts/PriceOracle/PriceOracleProxy.sol";
+
+contract PriceOracleProxyHarness is PriceOracleProxy {
+    uint256 public blockTimestamp = 100000;
+
+    constructor(
+        address admin_,
+        address v1PriceOracle_,
+        address cEthAddress_,
+        address registry_
+    ) public PriceOracleProxy(admin_, v1PriceOracle_, cEthAddress_, registry_) {}
+
+    function getBlockTimestamp() internal view returns (uint256) {
+        return blockTimestamp;
+    }
+
+    function setBlockTimestamp(uint256 newBlockTimestamp) public {
+        blockTimestamp = newBlockTimestamp;
+    }
+}

tests/PriceOracleProxyTest.js

@@ -47,7 +47,7 @@ describe('PriceOracleProxy', () => {
     cYv2CrvLP = await makeCToken({comptroller: cEth.comptroller, supportMarket: true, underlying: yv2CrvLP});
 
     backingOracle = await makePriceOracle();
-    oracle = await deploy('PriceOracleProxy',
+    oracle = await deploy('PriceOracleProxyHarness',
       [
         root,
         backingOracle._address,
@@ -196,6 +196,30 @@ describe('PriceOracleProxy', () => {
       let proxyPrice = await call(oracle, "getUnderlyingPrice", [cOther._address]);
       expect(Number(proxyPrice)).toEqual(0.0005 * 1e18);
     });
+
+    it("fallbacks to v1 if the price from chainlink is invalid", async () => {
+      const v1Price = 10;
+      const oraclePrice = '0';
+
+      await setAndVerifyBackingPrice(cOther, v1Price);
+      await setPrice(cOther.underlying._address, cOther.underlying._address, ethAddress, oraclePrice);
+      await readAndVerifyProxyPrice(cOther, v1Price);
+    });
+
+    it("fallbacks to v1 if the price from chainlink is stale", async () => {
+      const v1Price = 10;
+      const oraclePrice = '2';
+
+      const timestamp1 = 10000;
+      const timestamp2 = 96500; // greater than timestamp1 + 86400 (1 day)
+      await send(mockAggregator, "setBlockTimestamp", [timestamp1]);
+      await send(oracle, "setBlockTimestamp", [timestamp2]);
+
+      await setAndVerifyBackingPrice(cOther, v1Price);
+      await setPrice(cOther.underlying._address, cOther.underlying._address, ethAddress, oraclePrice);
+
+      await readAndVerifyProxyPrice(cOther, v1Price);
+    });
   });
 
   describe("_setAdmin", () => {