allow sending to same blockchain but not exact same instance

contracts/src/TeleporterTokenDestination.sol

@@ -62,25 +62,38 @@ abstract contract TeleporterTokenDestination is
      * @notice Sends tokens to the specified destination token bridge instance.
      *
      * @dev Burns the bridged amount, and uses Teleporter to send a cross chain message.
+     * Tokens can be sent to the same blockchain this bridge instance is deployed on,
+     * to another destination bridge instance.
      * Requirements:
      *
-     * - `input.destinationBlockchainID` cannot be the same as the current blockchainID
      * - `input.destinationBridgeAddress` cannot be the zero address
      * - `input.recipient` cannot be the zero address
      * - `amount` must be greater than 0
      * - `amount` must be greater than `input.primaryFee`
      */
     function _send(SendTokensInput calldata input, uint256 amount) internal virtual {
-        require(
-            input.destinationBlockchainID != blockchainID,
-            "TeleporterTokenDestination: cannot bridge to same chain"
-        );
         require(
             input.destinationBridgeAddress != address(0),
             "TeleporterTokenDestination: zero destination bridge address"
         );
         require(input.recipient != address(0), "TeleporterTokenDestination: zero recipient address");
 
+        // If the destination blockchain is the source bridge instance's blockchain,
+        // the destination bridge address must match the token source address.
+        if (input.destinationBlockchainID == sourceBlockchainID) {
+            require(
+                input.destinationBridgeAddress == tokenSourceAddress,
+                "TeleporterTokenDestination: invalid destination bridge address"
+            );
+        }
+
+        if (input.destinationBlockchainID == blockchainID) {
+            require(
+                input.destinationBridgeAddress != address(this),
+                "TeleporterTokenDestination: invalid destination bridge address"
+            );
+        }
+
         // Deposit the funds sent from the user to the bridge,
         // and set to adjusted amount after deposit
         amount = _deposit(amount);

contracts/test/TeleporterTokenDestinationTests.t.sol

@@ -102,14 +102,6 @@ contract TeleporterTokenDestinationTest is Test {
     /**
      * Send tokens unit tests
      */
-
-    function testSendToSameChain() public {
-        SendTokensInput memory input = _createDefaultSendTokensInput();
-        input.destinationBlockchainID = DEFAULT_DESTINATION_BLOCKCHAIN_ID;
-        vm.expectRevert(_formatTokenDestinationErrorMessage("cannot bridge to same chain"));
-        app.send(input, 0);
-    }
-
     function testZeroDestinationBridge() public {
         SendTokensInput memory input = _createDefaultSendTokensInput();
         input.destinationBridgeAddress = address(0);
@@ -124,6 +116,21 @@ contract TeleporterTokenDestinationTest is Test {
         app.send(input, 0);
     }
 
+    function testInvalidSendingBackToSourceBlockchain() public {
+        SendTokensInput memory input = _createDefaultSendTokensInput();
+        input.destinationBridgeAddress = address(this);
+        vm.expectRevert(_formatTokenDestinationErrorMessage("invalid destination bridge address"));
+        app.send(input, 0);
+    }
+
+    function testSendingToSameInstance() public {
+        SendTokensInput memory input = _createDefaultSendTokensInput();
+        input.destinationBlockchainID = app.blockchainID();
+        input.destinationBridgeAddress = address(app);
+        vm.expectRevert(_formatTokenDestinationErrorMessage("invalid destination bridge address"));
+        app.send(input, 0);
+    }
+
     function testZeroSendAmount() public {
         vm.expectRevert(_formatTokenDestinationErrorMessage("zero send amount"));
         app.send(_createDefaultSendTokensInput(), 0);
@@ -148,6 +155,21 @@ contract TeleporterTokenDestinationTest is Test {
         _sendSuccess(amount, primaryFee);
     }
 
+    function testSendToSameBlockchainDifferentDestination() public {
+        // Send a transfer to the same app itself
+        uint256 amount = 2;
+        SendTokensInput memory input = _createDefaultSendTokensInput();
+        input.destinationBlockchainID = app.blockchainID();
+        input.destinationBridgeAddress = address(this);
+
+        uint256 bridgedAmount = amount - input.primaryFee;
+        _checkExpectedTeleporterCalls(input, bridgedAmount);
+
+        vm.expectEmit(true, true, true, true, address(app));
+        emit SendTokens(_MOCK_MESSAGE_ID, address(this), bridgedAmount);
+        app.send(input, amount);
+    }
+
     /**
      * Receive tokens unit tests
      */

tests/flows/basic_erc20_send_receive.go

@@ -104,9 +104,9 @@ func BasicERC20SendReceive(network interfaces.Network) {
 	utils.CheckERC20DestinationWithdrawal(
 		ctx,
 		erc20Destination,
+		receipt,
 		recipientAddress,
 		bridgedAmount,
-		receipt,
 	)
 
 	// Check that the recipient received the tokens
@@ -158,9 +158,9 @@ func BasicERC20SendReceive(network interfaces.Network) {
 		ctx,
 		erc20SourceAddress,
 		sourceToken,
+		receipt,
 		recipientAddress,
 		bridgedAmount,
-		receipt,
 	)
 
 	// Check that the recipient received the tokens