Abehjati/add fee to ipyth (#19)

* Add fee for updating prices

* Accept only native currency.

* Update events

* Update names and comments

According to Jayant comments

* update abi

* update docs

* Make fee a fixed amount

Author: ali-behjati

IPyth.sol

@@ -27,9 +27,10 @@ interface IPyth {
     event BatchPriceFeedUpdate(int8 chainId, uint64 sequenceNumber, uint batchSize, uint freshPricesInBatch);
 
     /// @dev Emitted when a call to `updatePriceFeeds` is processed successfully.
-    /// @param sender Sender of this call (`msg.sender`).
+    /// @param sender Sender of the call (`msg.sender`).
     /// @param batchCount Number of batches that this function processed.
-    event UpdatePriceFeeds(address indexed sender, uint batchCount);
+    /// @param fee Amount of paid fee for updating the prices.
+    event UpdatePriceFeeds(address indexed sender, uint batchCount, uint fee);
 
 
     /// @notice Returns the current price and confidence interval.
@@ -50,8 +51,17 @@ interface IPyth {
     /// @return publishTime - the UNIX timestamp of when this price was computed.
     function getPrevPriceUnsafe(bytes32 id) external view returns (PythStructs.Price memory price, uint64 publishTime);
 
-    /// @notice Update price feeds with given update messages if they are more recent than the current stored prices.
+    /// @notice Update price feeds with given update messages.
+    /// This method requires the caller to pay a fee in wei; the required fee can be computed by calling
+    /// `getUpdateFee` with the length of the `updateData` array.
+    /// Prices will be updated if they are more recent than the current stored prices.
     /// The call will succeed even if the update is not the most recent.
-    /// @dev Reverts if the updateData is invalid.
-    function updatePriceFeeds(bytes[] memory updateData) external;
+    /// @dev Reverts if the transferred fee is not sufficient or the updateData is invalid.
+    /// @param updateData Array of price update data.
+    function updatePriceFeeds(bytes[] memory updateData) external payable;
+
+    /// @notice Returns the required fee to update an array of price updates.
+    /// @param updateDataSize Number of price updates.
+    /// @return feeAmount The required fee in Wei.
+    function getUpdateFee(uint updateDataSize) external view returns (uint feeAmount);
 }

IPythAbi.json

@@ -99,6 +99,12 @@
         "internalType": "uint256",
         "name": "batchCount",
         "type": "uint256"
+      },
+      {
+        "indexed": false,
+        "internalType": "uint256",
+        "name": "fee",
+        "type": "uint256"
       }
     ],
     "name": "UpdatePriceFeeds",
@@ -217,6 +223,25 @@
     "stateMutability": "view",
     "type": "function"
   },
+  {
+    "inputs": [
+      {
+        "internalType": "uint256",
+        "name": "updateDataSize",
+        "type": "uint256"
+      }
+    ],
+    "name": "getUpdateFee",
+    "outputs": [
+      {
+        "internalType": "uint256",
+        "name": "feeAmount",
+        "type": "uint256"
+      }
+    ],
+    "stateMutability": "view",
+    "type": "function"
+  },
   {
     "inputs": [
       {
@@ -227,7 +252,7 @@
     ],
     "name": "updatePriceFeeds",
     "outputs": [],
-    "stateMutability": "nonpayable",
+    "stateMutability": "payable",
     "type": "function"
   }
 ]

MockPyth.sol

@@ -8,14 +8,24 @@ contract MockPyth is AbstractPyth {
     mapping(bytes32 => PythStructs.PriceFeed) priceFeeds;
     uint64 sequenceNumber;
 
+    uint singleUpdateFeeInWei;
+
+    constructor(uint _singleUpdateFeeInWei) {
+        singleUpdateFeeInWei = _singleUpdateFeeInWei;
+    }
+
     function queryPriceFeed(bytes32 id) public override view returns (PythStructs.PriceFeed memory priceFeed) {
         return priceFeeds[id];
     }
 
     // Takes an array of encoded price feeds and stores them.
     // You can create this data either by calling createPriceFeedData or
     // by using web3.js or ethers abi utilities.
-    function updatePriceFeeds(bytes[] memory updateData) public override {
+    function updatePriceFeeds(bytes[] memory updateData) public override payable {
+        uint requiredFee = getUpdateFee(updateData.length);
+        require(msg.value >= requiredFee, "Insufficient paid fee amount");
+        payable(msg.sender).transfer(msg.value - requiredFee);
+
         uint freshPrices = 0;
 
         // Chain ID is id of the source chain that the price update comes from. Since it is just a mock contract
@@ -46,7 +56,11 @@ contract MockPyth is AbstractPyth {
         sequenceNumber += 1;
 
         // There is only 1 batch of prices
-        emit UpdatePriceFeeds(msg.sender, 1);
+        emit UpdatePriceFeeds(msg.sender, 1, requiredFee);
+    }
+
+    function getUpdateFee(uint updateDataSize) public override view returns (uint feeAmount) {
+        return singleUpdateFeeInWei * updateDataSize;
     }
 
     function createPriceFeedUpdateData(