feat: cannot hold 2 responses for the same attestation

src/interfaces/IResolver.sol

@@ -25,6 +25,9 @@ interface IResolver {
   /// @dev Checks if a title is allowed to be attested.
   function allowedAttestationTitles(string memory title) external view returns (bool);
 
+  /// @dev Validates if an attestation can have a response.
+  function cannotReply(bytes32 uid) external view returns (bool);
+
   /// @dev Checks which action a role can perform on a schema.
   function allowedSchemas(bytes32 uid) external view returns (Action);
 

src/resolver/Resolver.sol

@@ -8,6 +8,7 @@ import { AccessControl } from "@openzeppelin/contracts/access/AccessControl.sol"
 import { AccessDenied, InvalidEAS, InvalidLength, uncheckedInc, EMPTY_UID, NO_EXPIRATION_TIME } from "../Common.sol";
 
 error AlreadyCheckedOut();
+error AlreadyHasResponse();
 error InsufficientValue();
 error InvalidAttestationTitle();
 error InvalidExpiration();
@@ -32,12 +33,15 @@ contract Resolver is IResolver, AccessControl {
   // Maps addresses to booleans to check if a Villager has checked out
   mapping(address => bool) private _checkedOutVillagers;
 
-  // Maps schemas ID and role ID to action
-  mapping(bytes32 => Action) private _allowedSchemas;
-
   // Maps allowed attestations (Hashed titles that can be attested)
   mapping(bytes32 => bool) private _allowedAttestationTitles;
 
+  // Maps attestation IDs to boolans (each attestation can only have one active response)
+  mapping(bytes32 => bool) private _cannotReply;
+
+  // Maps schemas ID and role ID to action
+  mapping(bytes32 => Action) private _allowedSchemas;
+
   /// @dev Creates a new resolver.
   /// @param eas The address of the global EAS contract.
   constructor(IEAS eas) {
@@ -76,6 +80,11 @@ contract Resolver is IResolver, AccessControl {
     return _allowedAttestationTitles[keccak256(abi.encode(title))];
   }
 
+  /// @inheritdoc IResolver
+  function cannotReply(bytes32 uid) public view returns (bool) {
+    return _cannotReply[uid];
+  }
+
   /// @inheritdoc IResolver
   function allowedSchemas(bytes32 uid) public view returns (Action) {
     return _allowedSchemas[uid];
@@ -126,6 +135,7 @@ contract Resolver is IResolver, AccessControl {
     // Schema to revoke a response ( true / false )
     if (isActionAllowed(attestation.schema, Action.REPLY)) {
       _checkRole(VILLAGER_ROLE, attestation.attester);
+      _cannotReply[attestation.refUID] = false;
       return true;
     }
 
@@ -201,8 +211,9 @@ contract Resolver is IResolver, AccessControl {
   }
 
   /// @dev Attest a response to an event badge emitted by {attestEvent}.
-  function attestResponse(Attestation calldata attestation) internal view returns (bool) {
+  function attestResponse(Attestation calldata attestation) internal returns (bool) {
     if (!attestation.revocable) revert InvalidRevocability();
+    if (_cannotReply[attestation.refUID]) revert AlreadyHasResponse();
     _checkRole(VILLAGER_ROLE, attestation.attester);
 
     // Checks if the attestation has a non empty reference
@@ -212,6 +223,9 @@ contract Resolver is IResolver, AccessControl {
     // The response is designed to be a reply to a previous attestation
     if (attesterRef.recipient != attestation.attester) revert InvalidRefUID();
 
+    // Cannot create new responses until this attestation is revoked
+    _cannotReply[attestation.refUID] = true;
+
     return true;
   }
 

test/EAS.t.sol

@@ -48,10 +48,18 @@ contract ResolverTest is Test {
     vm.startPrank(villager);
     bytes32 eventUID = attest_event(uids[2], manager, titles[0], "This address changed my mind");
 
-    // Attest Responses, then revoke it
+    // Attest Response
     vm.startPrank(manager);
     bytes32 responseUID = attest_response(uids[3], villager, eventUID, true);
+    assert(resolver.cannotReply(eventUID));
+    // Should fail to attest response again
+    assert(!try_attest_response(uids[3], villager, eventUID, true));
+    // Should be able to revoke the response
     attest_response_revoke(uids[3], responseUID);
+    assert(!resolver.cannotReply(eventUID));
+    // Should be able to re-attest response
+    attest_response(uids[3], villager, eventUID, false);
+    assert(resolver.cannotReply(eventUID));
 
     // Check-Out Villager as Himself
     vm.startPrank(villager);
@@ -284,6 +292,33 @@ contract ResolverTest is Test {
     }
   }
 
+  function try_attest_response(
+    bytes32 schemaUID,
+    address recipient,
+    bytes32 refUID,
+    bool status
+  ) public returns (bool) {
+    try
+      eas.attest(
+        AttestationRequest({
+          schema: schemaUID,
+          data: AttestationRequestData({
+            recipient: recipient,
+            expirationTime: 0,
+            revocable: true,
+            refUID: refUID,
+            data: abi.encode(status),
+            value: 0
+          })
+        })
+      )
+    {
+      return true;
+    } catch {
+      return false;
+    }
+  }
+
   function attest_response_revoke(bytes32 schemaUID, bytes32 attestationUID) public {
     eas.revoke(
       RevocationRequest({

test/Resolver.t.sol

@@ -145,6 +145,8 @@ contract ResolverTest is Test {
     assert(!hasRole(ROOT_ROLE, deployer));
   }
 
+  function test_return_all_badge_titles() public {}
+
   function hasRole(bytes32 role, address account) public view returns (bool) {
     return IAccessControl(address(resolver)).hasRole(role, account);
   }