Fix PingPong Unit Test

Resolves #119.  This change includes the following:

* Adds a _totalPings argument to the ping() function.  This is needed to limit the Unit Test to one ping/pong.
  This was done to avoid re-entrancy limitations of the LZEndpointMock, which can only call send one time per
  chain endpoint.  It is also nice to be able to limit the number of pings sent.
* Adjusts unit tests to correspond with the changed behavior.
* Adds documentation to `PingPong.sol`.

Signed-off-by: Ryan Goulding <[email protected]>

README.md

@@ -11,7 +11,7 @@
  ### Install & Run tests
 ```shell
 yarn install
-npx hardhat test 
+yarn test
 ```
 
 * The code in the `/contracts` folder demonstrates LayerZero behaviours.

contracts/examples/PingPong.sol

@@ -1,10 +1,10 @@
 // SPDX-License-Identifier: MIT
 
 //
-// Note: you will need to fund each deployed contract with gas
+// Note: You will need to fund each deployed contract with gas.
 //
 // PingPong sends a LayerZero message back and forth between chains
-// until it is paused or runs out of gas!
+// a predetermined number of times (or until it runs out of gas).
 //
 // Demonstrates:
 //  1. a recursive feature of calling send() from inside lzReceive()
@@ -16,57 +16,74 @@ pragma abicoder v2;
 
 import "../lzApp/NonblockingLzApp.sol";
 
+/// @title PingPong
+/// @notice Sends a LayerZero message back and forth between chains a predetermined number of times.
 contract PingPong is NonblockingLzApp {
-    // event emitted every ping() to keep track of consecutive pings count
-    event Ping(uint pings);
 
-    // constructor requires the LayerZero endpoint for this chain
+    /// @dev event emitted every ping() to keep track of consecutive pings count
+    event Ping(uint256 pingCount);
+
+    /// @param _endpoint The LayerZero endpoint address.
     constructor(address _endpoint) NonblockingLzApp(_endpoint) {}
 
-    // pings the destination chain, along with the current number of pings sent
+    /// @notice Pings the destination chain, along with the current number of pings sent.
+    /// @param _dstChainId The destination chain ID.
+    /// @param _totalPings The total number of pings to send.
     function ping(
-        uint16 _dstChainId
+        uint16 _dstChainId,
+        uint256 _totalPings
     ) public {
-        _ping(_dstChainId, 0);
+        _ping(_dstChainId, 0, _totalPings);
     }
 
-    // pings the destination chain, along with the current number of pings sent
+    /// @dev Internal function to ping the destination chain, along with the current number of pings sent.
+    /// @param _dstChainId The destination chain ID.
+    /// @param _pings The current ping count.
+    /// @param _totalPings The total number of pings to send.
     function _ping(
         uint16 _dstChainId,
-        uint _ping
+        uint256 _pings,
+        uint256 _totalPings
     ) internal {
         require(address(this).balance > 0, "This contract ran out of money.");
 
         // encode the payload with the number of pings
-        bytes memory payload = abi.encode(_ping);
+        bytes memory payload = abi.encode(_pings, _totalPings);
 
+        // encode the adapter parameters
         uint16 version = 1;
         uint256 gasForDestinationLzReceive = 350000;
         bytes memory adapterParams = abi.encodePacked(version, gasForDestinationLzReceive);
 
         // send LayerZero message
-        _lzSend( // {value: messageFee} will be paid out of this contract!
-            _dstChainId, // destination chainId
-            payload, // abi.encode()'ed bytes
-            payable(this), // (msg.sender will be this contract) refund address (LayerZero will refund any extra gas back to caller of send()
-            address(0x0), // future param, unused for this example
+        _lzSend(           // {value: messageFee} will be paid out of this contract!
+            _dstChainId,   // destination chainId
+            payload,       // abi.encode()'ed bytes
+            payable(this), // (msg.sender will be this contract) refund address (LayerZero will refund any extra gas back to caller of send())
+            address(0x0),  // future param, unused for this example
             adapterParams, // v1 adapterParams, specify custom destination gas qty
             address(this).balance
         );
     }
 
+    /// @dev Internal function to handle incoming Ping messages.
+    /// @param _srcChainId The source chain ID from which the message originated.
+    /// @param _payload The payload of the incoming message.
     function _nonblockingLzReceive(
         uint16 _srcChainId,
-        bytes memory _srcAddress,
+        bytes memory, /*_srcAddress*/
         uint64, /*_nonce*/
         bytes memory _payload
     ) internal override {
         // decode the number of pings sent thus far
-        uint pings = abi.decode(_payload, (uint)) + 1;
-        emit Ping(pings);
+        (uint256 pingCount, uint256 totalPings) = abi.decode(_payload, (uint256, uint256));
+        ++pingCount;
+        emit Ping(pingCount);
 
         // *pong* back to the other side
-        _ping(_srcChainId,pings);
+        if (pingCount < totalPings) {
+            _ping(_srcChainId, pingCount, totalPings);
+        }
     }
 
     // allow this contract to receive ether

contracts/lzApp/NonblockingLzApp.sol

@@ -32,7 +32,6 @@ abstract contract NonblockingLzApp is LzApp {
             150,
             abi.encodeWithSelector(this.nonblockingLzReceive.selector, _srcChainId, _srcAddress, _nonce, _payload)
         );
-        // try-catch all errors/exceptions
         if (!success) {
             _storeFailedMessage(_srcChainId, _srcAddress, _nonce, _payload, reason);
         }