[webview_flutter_wkwebview] Fix crash when calling setOnConsoleMessage multiple times

Author: rickhohler

packages/webview_flutter/webview_flutter_wkwebview/darwin/Tests/UserContentControllerProxyAPITests.swift

@@ -95,3 +95,53 @@ class TestUserContentController: WKUserContentController {
     removeAllUserScriptsCalled = true
   }
 }
+
+// Mock that simulates WKUserContentController's behavior of crashing/complaining
+// when adding a duplicate script message handler.
+// Mock that verifies remove is called before add, and enforces uniqueness
+class MockVerifyingUserContentController: WKUserContentController {
+  var registeredNames: Set<String> = []
+  var removeCalledFor: String? = nil
+
+  override func add(_ scriptMessageHandler: WKScriptMessageHandler, name: String) {
+    if registeredNames.contains(name) {
+      // If we are here, it means remove wasn't called or failed to remove
+      // In logical flow, remove() should have been called first.
+      // But implementation-wise, we just want to ensure we don't crash.
+      // Ideally, the 'remove' call below should have cleared it.
+      NSException(name: NSExceptionName.invalidArgumentException, reason: "Duplicate handler name", userInfo: nil).raise()
+    }
+    registeredNames.insert(name)
+  }
+
+  override func removeScriptMessageHandler(forName name: String) {
+    removeCalledFor = name
+    registeredNames.remove(name)
+  }
+}
+
+extension UserContentControllerProxyAPITests {
+  @MainActor func testAddScriptMessageHandlerHandlesDuplicates() {
+    let registrar = TestProxyApiRegistrar()
+    let api = registrar.apiDelegate.pigeonApiWKUserContentController(registrar)
+    
+    let instance = MockVerifyingUserContentController()
+    let handler = ScriptMessageHandlerImpl(
+      api: registrar.apiDelegate.pigeonApiWKScriptMessageHandler(registrar), registrar: registrar)
+    let name = "myString"
+
+    // First add
+    try? api.pigeonDelegate.addScriptMessageHandler(
+      pigeonApi: api, pigeonInstance: instance, handler: handler, name: name)
+    XCTAssertTrue(instance.registeredNames.contains(name))
+
+    // Second add - should NOT crash because implementation calls remove first
+    try? api.pigeonDelegate.addScriptMessageHandler(
+        pigeonApi: api, pigeonInstance: instance, handler: handler, name: name)
+    
+    // Check that it's still registered (or re-registered)
+    XCTAssertTrue(instance.registeredNames.contains(name))
+    // Verify remove was called
+    XCTAssertEqual(instance.removeCalledFor, name)
+  }
+}

packages/webview_flutter/webview_flutter_wkwebview/darwin/webview_flutter_wkwebview/Sources/webview_flutter_wkwebview/UserContentControllerProxyAPIDelegate.swift

@@ -13,6 +13,9 @@ class UserContentControllerProxyAPIDelegate: PigeonApiDelegateWKUserContentContr
     pigeonApi: PigeonApiWKUserContentController, pigeonInstance: WKUserContentController,
     handler: WKScriptMessageHandler, name: String
   ) throws {
+    // WKUserContentController will crash if a script message handler with the same name
+    // is added twice. We remove the existing one (if any) to ensure the new one replaces it.
+    pigeonInstance.removeScriptMessageHandler(forName: name)
     pigeonInstance.add(handler, name: name)
   }