evm: Always allow re-enabling a previously registered transceiver

Author: djb15

evm/src/NttManager/TransceiverRegistry.sol

@@ -120,13 +120,13 @@ abstract contract TransceiverRegistry {
             revert InvalidTransceiverZeroAddress();
         }
 
-        if (_numTransceivers.registered >= MAX_TRANSCEIVERS) {
-            revert TooManyTransceivers();
-        }
-
         if (transceiverInfos[transceiver].registered) {
             transceiverInfos[transceiver].enabled = true;
         } else {
+            if (_numTransceivers.registered >= MAX_TRANSCEIVERS) {
+                revert TooManyTransceivers();
+            }
+
             transceiverInfos[transceiver] = TransceiverInfo({
                 registered: true,
                 enabled: true,

evm/test/NttManager.t.sol

@@ -9,6 +9,7 @@ import "../src/interfaces/INttManager.sol";
 import "../src/interfaces/IRateLimiter.sol";
 import "../src/interfaces/INttManagerEvents.sol";
 import "../src/interfaces/IRateLimiterEvents.sol";
+import "../src/NttManager/TransceiverRegistry.sol";
 import {Utils} from "./libraries/Utils.sol";
 
 import "openzeppelin-contracts/contracts/token/ERC20/ERC20.sol";
@@ -226,6 +227,27 @@ contract TestNttManager is Test, INttManagerEvents, IRateLimiterEvents {
         nttManager.setTransceiver(address(0x123));
     }
 
+    function test_maxOutTransceivers() public {
+        // Let's register a transceiver and then disable it
+        DummyTransceiver e = new DummyTransceiver(address(nttManager));
+        nttManager.setTransceiver(address(e));
+        nttManager.removeTransceiver(address(e));
+
+        // We should be able to register 64 transceivers total
+        for (uint256 i = 0; i < 63; ++i) {
+            DummyTransceiver d = new DummyTransceiver(address(nttManager));
+            nttManager.setTransceiver(address(d));
+        }
+
+        // Registering a new transceiver should fail as we've hit the cap
+        DummyTransceiver c = new DummyTransceiver(address(nttManager));
+        vm.expectRevert(TransceiverRegistry.TooManyTransceivers.selector);
+        nttManager.setTransceiver(address(c));
+
+        // We should be able to renable an already registered transceiver at the cap
+        nttManager.setTransceiver(address(e));
+    }
+
     // == threshold
 
     function test_cantSetThresholdTooHigh() public {