Fix method handler control flow in Windows and Linux text input plugins (#17964)

The existing logic incorrectly factored out a check that there were arguments too early, applying it to any message not already handled (including unhandled methods, such as methods added after the initial implementation) and thus failing if any unhandled message had no arguments.

Fixes https://github.com/flutter/flutter/issues/55653

shell/platform/glfw/text_input_plugin.cc

@@ -114,61 +114,61 @@ void TextInputPlugin::HandleMethodCall(
     // These methods are no-ops.
   } else if (method.compare(kClearClientMethod) == 0) {
     active_model_ = nullptr;
-  } else {
-    // Every following method requires args.
+  } else if (method.compare(kSetClientMethod) == 0) {
+    if (!method_call.arguments() || method_call.arguments()->IsNull()) {
+      result->Error(kBadArgumentError, "Method invoked without args");
+      return;
+    }
+    const rapidjson::Document& args = *method_call.arguments();
+
+    // TODO(awdavies): There's quite a wealth of arguments supplied with this
+    // method, and they should be inspected/used.
+    const rapidjson::Value& client_id_json = args[0];
+    const rapidjson::Value& client_config = args[1];
+    if (client_id_json.IsNull()) {
+      result->Error(kBadArgumentError, "Could not set client, ID is null.");
+      return;
+    }
+    if (client_config.IsNull()) {
+      result->Error(kBadArgumentError,
+                    "Could not set client, missing arguments.");
+    }
+    int client_id = client_id_json.GetInt();
+    active_model_ = std::make_unique<TextInputModel>(client_id, client_config);
+  } else if (method.compare(kSetEditingStateMethod) == 0) {
     if (!method_call.arguments() || method_call.arguments()->IsNull()) {
       result->Error(kBadArgumentError, "Method invoked without args");
       return;
     }
     const rapidjson::Document& args = *method_call.arguments();
 
-    if (method.compare(kSetClientMethod) == 0) {
-      // TODO(awdavies): There's quite a wealth of arguments supplied with this
-      // method, and they should be inspected/used.
-      const rapidjson::Value& client_id_json = args[0];
-      const rapidjson::Value& client_config = args[1];
-      if (client_id_json.IsNull()) {
-        result->Error(kBadArgumentError, "Could not set client, ID is null.");
-        return;
-      }
-      if (client_config.IsNull()) {
-        result->Error(kBadArgumentError,
-                      "Could not set client, missing arguments.");
-      }
-      int client_id = client_id_json.GetInt();
-      active_model_ =
-          std::make_unique<TextInputModel>(client_id, client_config);
-    } else if (method.compare(kSetEditingStateMethod) == 0) {
-      if (active_model_ == nullptr) {
-        result->Error(
-            kInternalConsistencyError,
-            "Set editing state has been invoked, but no client is set.");
-        return;
-      }
-      auto text = args.FindMember(kTextKey);
-      if (text == args.MemberEnd() || text->value.IsNull()) {
-        result->Error(kBadArgumentError,
-                      "Set editing state has been invoked, but without text.");
-        return;
-      }
-      auto selection_base = args.FindMember(kSelectionBaseKey);
-      auto selection_extent = args.FindMember(kSelectionExtentKey);
-      if (selection_base == args.MemberEnd() ||
-          selection_base->value.IsNull() ||
-          selection_extent == args.MemberEnd() ||
-          selection_extent->value.IsNull()) {
-        result->Error(kInternalConsistencyError,
-                      "Selection base/extent values invalid.");
-        return;
-      }
-      active_model_->SetEditingState(selection_base->value.GetInt(),
-                                     selection_extent->value.GetInt(),
-                                     text->value.GetString());
-    } else {
-      // Unhandled method.
-      result->NotImplemented();
+    if (active_model_ == nullptr) {
+      result->Error(
+          kInternalConsistencyError,
+          "Set editing state has been invoked, but no client is set.");
+      return;
+    }
+    auto text = args.FindMember(kTextKey);
+    if (text == args.MemberEnd() || text->value.IsNull()) {
+      result->Error(kBadArgumentError,
+                    "Set editing state has been invoked, but without text.");
       return;
     }
+    auto selection_base = args.FindMember(kSelectionBaseKey);
+    auto selection_extent = args.FindMember(kSelectionExtentKey);
+    if (selection_base == args.MemberEnd() || selection_base->value.IsNull() ||
+        selection_extent == args.MemberEnd() ||
+        selection_extent->value.IsNull()) {
+      result->Error(kInternalConsistencyError,
+                    "Selection base/extent values invalid.");
+      return;
+    }
+    active_model_->SetEditingState(selection_base->value.GetInt(),
+                                   selection_extent->value.GetInt(),
+                                   text->value.GetString());
+  } else {
+    result->NotImplemented();
+    return;
   }
   // All error conditions return early, so if nothing has gone wrong indicate
   // success.

shell/platform/windows/text_input_plugin.cc

@@ -117,60 +117,60 @@ void TextInputPlugin::HandleMethodCall(
     // These methods are no-ops.
   } else if (method.compare(kClearClientMethod) == 0) {
     active_model_ = nullptr;
-  } else {
-    // Every following method requires args.
+  } else if (method.compare(kSetClientMethod) == 0) {
     if (!method_call.arguments() || method_call.arguments()->IsNull()) {
       result->Error(kBadArgumentError, "Method invoked without args");
       return;
     }
     const rapidjson::Document& args = *method_call.arguments();
 
-    if (method.compare(kSetClientMethod) == 0) {
-      const rapidjson::Value& client_id_json = args[0];
-      const rapidjson::Value& client_config = args[1];
-      if (client_id_json.IsNull()) {
-        result->Error(kBadArgumentError, "Could not set client, ID is null.");
-        return;
-      }
-      if (client_config.IsNull()) {
-        result->Error(kBadArgumentError,
-                      "Could not set client, missing arguments.");
-        return;
-      }
-      int client_id = client_id_json.GetInt();
-      active_model_ =
-          std::make_unique<TextInputModel>(client_id, client_config);
-    } else if (method.compare(kSetEditingStateMethod) == 0) {
-      if (active_model_ == nullptr) {
-        result->Error(
-            kInternalConsistencyError,
-            "Set editing state has been invoked, but no client is set.");
-        return;
-      }
-      auto text = args.FindMember(kTextKey);
-      if (text == args.MemberEnd() || text->value.IsNull()) {
-        result->Error(kBadArgumentError,
-                      "Set editing state has been invoked, but without text.");
-        return;
-      }
-      auto selection_base = args.FindMember(kSelectionBaseKey);
-      auto selection_extent = args.FindMember(kSelectionExtentKey);
-      if (selection_base == args.MemberEnd() ||
-          selection_base->value.IsNull() ||
-          selection_extent == args.MemberEnd() ||
-          selection_extent->value.IsNull()) {
-        result->Error(kInternalConsistencyError,
-                      "Selection base/extent values invalid.");
-        return;
-      }
-      active_model_->SetEditingState(selection_base->value.GetInt(),
-                                     selection_extent->value.GetInt(),
-                                     text->value.GetString());
-    } else {
-      // Unhandled method.
-      result->NotImplemented();
+    const rapidjson::Value& client_id_json = args[0];
+    const rapidjson::Value& client_config = args[1];
+    if (client_id_json.IsNull()) {
+      result->Error(kBadArgumentError, "Could not set client, ID is null.");
+      return;
+    }
+    if (client_config.IsNull()) {
+      result->Error(kBadArgumentError,
+                    "Could not set client, missing arguments.");
       return;
     }
+    int client_id = client_id_json.GetInt();
+    active_model_ = std::make_unique<TextInputModel>(client_id, client_config);
+  } else if (method.compare(kSetEditingStateMethod) == 0) {
+    if (!method_call.arguments() || method_call.arguments()->IsNull()) {
+      result->Error(kBadArgumentError, "Method invoked without args");
+      return;
+    }
+    const rapidjson::Document& args = *method_call.arguments();
+
+    if (active_model_ == nullptr) {
+      result->Error(
+          kInternalConsistencyError,
+          "Set editing state has been invoked, but no client is set.");
+      return;
+    }
+    auto text = args.FindMember(kTextKey);
+    if (text == args.MemberEnd() || text->value.IsNull()) {
+      result->Error(kBadArgumentError,
+                    "Set editing state has been invoked, but without text.");
+      return;
+    }
+    auto selection_base = args.FindMember(kSelectionBaseKey);
+    auto selection_extent = args.FindMember(kSelectionExtentKey);
+    if (selection_base == args.MemberEnd() || selection_base->value.IsNull() ||
+        selection_extent == args.MemberEnd() ||
+        selection_extent->value.IsNull()) {
+      result->Error(kInternalConsistencyError,
+                    "Selection base/extent values invalid.");
+      return;
+    }
+    active_model_->SetEditingState(selection_base->value.GetInt(),
+                                   selection_extent->value.GetInt(),
+                                   text->value.GetString());
+  } else {
+    result->NotImplemented();
+    return;
   }
   // All error conditions return early, so if nothing has gone wrong indicate
   // success.