Reason Code 与 Properties 目录（MQTT 5）

依据 OASIS MQTT 5.0 §2.2.2 Properties、§2.4 Reason Code 及各控制报文章节整理
完整规范性定义以正式 HTML/PDF 为准：
https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html
MQTT 3.1.1 无本目录所述 Properties / 细粒度 Reason Code 体系

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1. Reason Code 使用位置

报文	是否常见带 Reason
CONNACK	Connect Reason Code
PUBACK / PUBREC / PUBREL / PUBCOMP	发布流 Reason
SUBACK / UNSUBACK	每订阅/每过滤一项
DISCONNECT	断开原因
AUTH	认证步骤结果

0x00 在多数上下文表示成功；0x80 及以上通常表示错误（具体以该报文章节表格为准）。

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2. 常用 Reason Code 速查（跨报文高频）

Code	名称（英文习惯）	典型场景
0x00	Success / Normal disconnection / Granted QoS0	成功
0x01	Granted QoS 1	SUBACK
0x02	Granted QoS 2	SUBACK
0x04	Disconnect with Will Message	DISCONNECT
0x10	No matching subscribers	PUBACK/PUBREC
0x11	No subscription existed	UNSUBACK
0x18	Continue authentication	AUTH
0x19	Re-authenticate	AUTH
0x80	Unspecified error	多处
0x81	Malformed Packet	解析失败
0x82	Protocol Error	协议违规
0x83	Implementation specific error	实现特定
0x84	Unsupported Protocol Version	CONNACK
0x85	Client Identifier not valid	CONNACK
0x86	Bad User Name or Password	CONNACK
0x87	Not authorized	鉴权失败
0x88	Server unavailable	CONNACK
0x89	Server busy	CONNACK / DISCONNECT
0x8A	Banned	CONNACK
0x8B	Server shutting down / Keep Alive timeout	视报文
0x8C	Bad authentication method	CONNACK
0x8D	Session taken over	DISCONNECT
0x8F	Topic Filter invalid	SUBACK 等
0x90	Topic Name invalid	PUBLISH 相关
0x91	Packet Identifier in use	订阅/发布
0x93	Receive Maximum exceeded	流控
0x94	Topic Alias invalid	PUBLISH
0x95	Packet too large	包长
0x97	Quota exceeded	配额
0x99	Payload format invalid	载荷格式
0x9A	Retain not supported	CONNACK/相关
0x9B	QoS not supported	CONNACK
0x9C	Use another server	重定向
0x9D	Server moved	重定向
0x9E	Shared Subscriptions not supported	SUBACK
0x9F	Connection rate exceeded	CONNACK
0xA1	Subscription Identifiers not supported	SUBACK
0xA2	Wildcard Subscriptions not supported	SUBACK

同一数值在不同报文中的官方名称可能略有差别；排障时以该报文章节的 Reason Code 表为准。

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3. Property Identifier 目录（常用）

ID	属性名	值类型	典型报文
0x01	Payload Format Indicator	Byte	PUBLISH, Will
0x02	Message Expiry Interval	Four Byte	PUBLISH, Will
0x03	Content Type	UTF-8 String	PUBLISH, Will
0x08	Response Topic	UTF-8 String	PUBLISH, Will
0x09	Correlation Data	Binary	PUBLISH, Will
0x0B	Subscription Identifier	Var Byte Int	SUBSCRIBE, PUBLISH
0x11	Session Expiry Interval	Four Byte	CONNECT, CONNACK, DISCONNECT
0x12	Assigned Client Identifier	UTF-8 String	CONNACK
0x13	Server Keep Alive	Two Byte	CONNACK
0x15	Authentication Method	UTF-8 String	CONNECT, CONNACK, AUTH
0x16	Authentication Data	Binary	CONNECT, CONNACK, AUTH
0x17	Request Problem Information	Byte	CONNECT
0x18	Will Delay Interval	Four Byte	Will Properties
0x19	Request Response Information	Byte	CONNECT
0x1A	Response Information	UTF-8 String	CONNACK
0x1C	Server Reference	UTF-8 String	CONNACK, DISCONNECT
0x1F	Reason String	UTF-8 String	多种 ACK/DISCONNECT
0x21	Receive Maximum	Two Byte	CONNECT, CONNACK
0x22	Topic Alias Maximum	Two Byte	CONNECT, CONNACK
0x23	Topic Alias	Two Byte	PUBLISH
0x24	Maximum QoS	Byte	CONNACK
0x25	Retain Available	Byte	CONNACK
0x26	User Property	UTF-8 String Pair	多处（可重复）
0x27	Maximum Packet Size	Four Byte	CONNECT, CONNACK
0x28	Wildcard Subscription Available	Byte	CONNACK
0x29	Subscription Identifier Available	Byte	CONNACK
0x2A	Shared Subscription Available	Byte	CONNACK

未列出的 Identifier 见规范完整表；实现必须忽略无法识别属性或按规范报错（视报文规则）。

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4. 与本库其它文档

主题	文档
报文总结构	10-MQTT控制报文格式总览.md
连接	11
发布/QoS	12
订阅	13
心跳/断开/认证	14
5.0 特性综述	04-MQTT5新特性.md
正式规范链接	09-规范与资料索引.md

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5. 合规声明

本目录为便于联调的速查整理。字段强制条件、默认值、哪些属性可重复、错误时关闭连接还是仅丢包等，一律以 OASIS MQTT 5.0 正式文本对应章节的 Normative 表述为准。