# FCommandMeta

## 基本信息
- **类型**: USTRUCT(BlueprintType)
- **父类**: (none)
- **源文件**: Plugins/CharacterControl/Source/CharacterControl/Public/CommandEndpoint.h
- **模块**: CharacterControl

## 功能概述
Metadata header for every command packet. Carries CommandID (int32, from UInputAction), HopLimit (uint8, mutable, decremented per router hop), bIsContinuous (bool, routing strategy selector), bIsUpward (bool, upward propagation flag).

## 设计用意
Routing envelope - decouples "what the command is" (payload) from "how it travels" (hop limit, direction). HopLimit prevents broadcast storms in router graphs. Upward flag supports parent-child router topologies.

## 职责范围
Carries routing metadata for one command packet. Embedded in FCommandPacket::Meta. Decremented at each router hop.

## 项目内依赖
| 依赖项 | 关系 | 源文件 |
|--------|------|--------|
| (none) | | |

## 对外接口
FCommandMeta 是嵌入在 FCommandPacket::Meta 中的数据容器，所有字段通过 UPROPERTY(BlueprintReadOnly) 暴露给蓝图。调用者不直接构造 FCommandMeta，而是由 UCommandInputComponent::BuildPacket 在输入事件触发时自动填充。路由过程中 UCommandRouter::ReceiveCommand 会递减 HopLimit。

- **CommandID** (int32, BlueprintReadOnly): 由 BuildPacket 从 UInputAction::GetUniqueID() 填充，标识命令来源
- **HopLimit** (uint8, mutable, BlueprintReadOnly): 每经过一层路由递减 1，耗尽则丢包。BuildPacket 对连续命令设为 3、离散命令设为 5
- **bIsContinuous** (bool, BlueprintReadOnly): 决定路由分发策略（连续走 RouteContinuousCommand，离散走 RouteDiscreteCommand）
- **bIsUpward** (bool, BlueprintReadOnly): 上行传播标志，在上级路由器中决定是否同时投递本地和向上转发

## 使用方法
FCommandMeta 作为 FCommandPacket 的成员由 BuildPacket 构建，在 CommandRouter 中消费：

- **构建**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandInputComponent.cpp:70-72` -- BuildPacket 设置 CommandID、bIsContinuous、HopLimit（连续 3、离散 5）
- **跳数递减**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandRouter.cpp:16-21` -- ReceiveCommand 检查 HopLimit 并在 >0 时递减
- **上行传播跳数递减**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandRouter.cpp:155` -- 上行命令在路由器层面再递减一次
- **路由策略选择**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandRouter.cpp:23-30` -- 根据 bIsContinuous 选择 RouteContinuousCommand 或 RouteDiscreteCommand

## 用例
- **BuildPacket 构建**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandInputComponent.cpp:70-72` -- 输入触发时根据 FInputCommand::bIsContinuous 设置 Meta 各字段，连续命令 HopLimit=3，离散命令 HopLimit=5
- **HopLimit 防护**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandRouter.cpp:16-18` -- ReceiveCommand 入口处首先检查 HopLimit，<=0 直接丢包，防止广播风暴
- **逐跳递减**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandRouter.cpp:21` -- 每经过一个路由器，mutable 的 HopLimit 减 1，确保命令不会无限传播
- **上行转发**: `Plugins/CharacterControl/Source/CharacterControl/Private/CommandRouter.cpp:148-155` -- 当 bIsUpward 为 true 时，先投递本地（清除上行标志），再向上级路由器转发