Add a uniswap anchored view

This commit adds a Uniswap anchored Open Oracle view.
We intend to propose switching the Compound Protocol to use this oracle, together with the Coinbase reporter feed.

The idea is that the price can only be set to a value coming from the reporter, but must be reasonably close to the anchor price.
The configuration for the oracle is passed up entirely in the constructor, including which uniswap market to use as an anchor for each reported price.

Tokens can also be configured to have FIXED_ETH or FIXED_USD prices.
FIXED_USD prices are constant (since the oracle returns prices denominated in USD).
FIXED_ETH prices are a multiple of the ETH price, which must be reported in order to be used.

The view also directly exposes the interface for compatibility with the Compound Protocol, which currently expects to fetch prices by CToken address.

In the unexpected event that the reporter believes their key to be compromised, they may sign a 'rotate' message which can be used to invalidate the reporter.
In such an event, the view is configured to fall back to using the anchor price directly.

In order to track the Uniswap price, the price accumulators those markets expose are tracked by block timestamp.
Whenever prices are posted, the tracked accumulators are updated in such a way as to always have an accumulator from at least a certain period ago.
When a current anchor price is needed, it is always the time-weighted average price over at least the configured anchor period.

.circleci/config.yml

@@ -10,7 +10,7 @@ jobs:
           docker_layer_caching: true
       - run:
         |
-          sudo wget https://github.com/ethereum/solidity/releases/download/v0.6.6/solc-static-linux -O /usr/local/bin/solc
+          sudo wget https://github.com/ethereum/solidity/releases/download/v0.6.10/solc-static-linux -O /usr/local/bin/solc
           sudo chmod +x /usr/local/bin/solc
       - checkout
       - restore_cache:

Dockerfile

@@ -1,6 +1,6 @@
 FROM node:13.6.0-alpine3.10
 WORKDIR /open-oracle
-RUN wget https://github.com/ethereum/solidity/releases/download/v0.6.6/solc-static-linux -O /usr/local/bin/solc && chmod +x /usr/local/bin/solc
+RUN wget https://github.com/ethereum/solidity/releases/download/v0.6.10/solc-static-linux -O /usr/local/bin/solc && chmod +x /usr/local/bin/solc
 RUN apk update && apk add --no-cache --virtual .gyp \
     python \
     make \

contracts/AnchoredView/AnchoredView.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.6;
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity ^0.6.10;
 pragma experimental ABIEncoderV2;
 
 import "./SymbolConfiguration.sol";
@@ -45,14 +47,13 @@ contract AnchoredView is SymbolConfiguration {
     /// @notice The Open Oracle Price Data contract
     OpenOraclePriceData public immutable priceData;
 
-    /// @notice The highest ratio of the new median price to the anchor price that will still trigger the median price to be updated
+    /// @dev The highest ratio of the new median price to the anchor price that will still trigger the median price to be updated
     uint immutable upperBoundAnchorRatio;
 
-    /// @notice The lowest ratio of the new median price to the anchor price that will still trigger the median price to be updated
+    /// @dev The lowest ratio of the new median price to the anchor price that will still trigger the median price to be updated
     uint immutable lowerBoundAnchorRatio;
 
-    /// @notice Average blocks per day, for checking anchor staleness
-    /// @dev 1 day / 15
+    /// @dev Average blocks per day, for checking anchor staleness (1 day / 15)
     uint constant blocksInADay = 5760;
 
     /// @notice The event emitted when the median price is updated
@@ -114,7 +115,6 @@ contract AnchoredView is SymbolConfiguration {
 
             uint reporterPrice = priceData.getPrice(reporter, tokenConfig.openOracleKey);
             uint anchorPrice = getAnchorInUsd(tokenConfig, usdcPrice);
-
             uint anchorRatio = mul(anchorPrice, 100e16) / reporterPrice;
             bool withinAnchor = anchorRatio <= upperBoundAnchorRatio && anchorRatio >= lowerBoundAnchorRatio;
 
@@ -217,7 +217,7 @@ contract AnchoredView is SymbolConfiguration {
     /// @notice invalidate the reporter, and fall back to using anchor directly in all cases
     function invalidate(bytes memory message, bytes memory signature) public {
         (string memory decoded_message, ) = abi.decode(message, (string, address));
-        require(keccak256(abi.encodePacked(decoded_message)) == keccak256(abi.encodePacked("rotate")), "invalid message must be 'rotate'");
+        require(keccak256(abi.encodePacked(decoded_message)) == keccak256(abi.encodePacked("rotate")), "invalidation message must be 'rotate'");
         require(priceData.source(message, signature) == reporter, "invalidation message must come from the reporter");
 
         reporterBreaker = true;

contracts/AnchoredView/SymbolConfiguration.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.6;
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity ^0.6.10;
 pragma experimental ABIEncoderV2;
 
 
@@ -13,7 +15,7 @@ contract SymbolConfiguration {
     address public constant cDaiAnchorKey = address(2);
 
     /// @notice standard amount for the Dollar
-    uint constant oneDollar = 1e6;
+    uint public constant oneDollar = 1e6;
 
     // Address of the oracle key (underlying) for cTokens non special keyed tokens
     address public immutable cRepAnchorKey;

contracts/DelFiPrice.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.6;
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity ^0.6.10;
 pragma experimental ABIEncoderV2;
 
 import "./OpenOraclePriceData.sol";
@@ -15,13 +17,13 @@ contract DelFiPrice is OpenOracleView {
     /// @notice The event emitted when new prices are posted but the median price is not updated due to the anchor
     event PriceGuarded(string symbol, uint64 median, uint64 anchor);
 
-    /// @notice The reporter address whose prices checked against the median for safety
+    /// @dev The reporter address whose prices checked against the median for safety
     address anchor;
 
-    /// @notice The highest ratio of the new median price to the anchor price that will still trigger the median price to be updated
+    /// @dev The highest ratio of the new median price to the anchor price that will still trigger the median price to be updated
     uint256 upperBoundAnchorRatio;
 
-    /// @notice The lowest ratio of the new median price to the anchor price that will still trigger the median price to be updated
+    /// @dev The lowest ratio of the new median price to the anchor price that will still trigger the median price to be updated
     uint256 lowerBoundAnchorRatio;
 
     /// @notice The mapping of medianized prices per symbol

contracts/OpenOracleData.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.6;
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity ^0.6.10;
 pragma experimental ABIEncoderV2;
 
 /**

contracts/OpenOraclePriceData.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.6;
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity ^0.6.10;
 
 import "./OpenOracleData.sol";
 
@@ -20,8 +22,8 @@ contract OpenOraclePriceData is OpenOracleData {
     }
 
     /**
-     * @notice The most recent authenticated data from all sources
-     * @dev This is private because dynamic mapping keys preclude auto-generated getters.
+     * @dev The most recent authenticated data from all sources.
+     *  This is private because dynamic mapping keys preclude auto-generated getters.
      */
     mapping(address => mapping(string => Datum)) private data;
 
@@ -41,7 +43,7 @@ contract OpenOraclePriceData is OpenOracleData {
 
         // Only update if newer than stored, according to source
         Datum storage prior = data[source][key];
-        if (timestamp > prior.timestamp && timestamp < block.timestamp + 60 minutes) {
+        if (timestamp > prior.timestamp && timestamp < block.timestamp + 60 minutes && source != address(0)) {
             data[source][key] = Datum(timestamp, value);
             emit Write(source, key, timestamp, value);
         } else {

contracts/OpenOracleView.sol

@@ -1,4 +1,6 @@
-pragma solidity ^0.6.6;
+// SPDX-License-Identifier: GPL-3.0
+
+pragma solidity ^0.6.10;
 
 import "./OpenOracleData.sol";