{"id":459,"date":"2015-09-08T14:30:31","date_gmt":"2015-09-08T14:30:31","guid":{"rendered":"7fe1f8abaad094e0b5cb1b01d712f708"},"modified":"2015-09-08T14:30:31","modified_gmt":"2015-09-08T14:30:31","slug":"","status":"publish","type":"post","link":"https:\/\/www.xiaobo.li\/notes\/archives\/459","title":{"rendered":"mqtt\u7b14\u8bb0"},"content":{"rendered":"

MQTT\uff08Message Queue Telemetry Transport\uff09,\u9065\u6d4b\u4f20\u8f93\u534f\u8bae\uff0c\u63d0\u4f9b\u8ba2\u9605\/\u53d1\u5e03\u6a21\u5f0f\uff0c\u66f4\u4e3a\u7b80\u7ea6\u3001\u8f7b\u91cf\uff0c\u6613\u4e8e\u4f7f\u7528\uff0c\u9488\u5bf9\u53d7\u9650\u73af\u5883\uff08\u5e26\u5bbd\u4f4e\u3001\u7f51\u7edc\u5ef6\u8fdf\u9ad8\u3001\u7f51\u7edc\u901a\u4fe1\u4e0d\u7a33\u5b9a\uff09\uff0c\u53ef\u4ee5\u7b80\u5355\u6982\u62ec\u4e3a\u7269\u8054\u7f51\u6253\u9020\uff0c\u5b98\u65b9\u603b\u7ed3\u7279\u70b9\u5982\u4e0b\uff1a<\/p>\n

1.\u4f7f\u7528\u53d1\u5e03\/\u8ba2\u9605\u6d88\u606f\u6a21\u5f0f\uff0c\u63d0\u4f9b\u4e00\u5bf9\u591a\u7684\u6d88\u606f\u53d1\u5e03\uff0c\u89e3\u9664\u5e94\u7528\u7a0b\u5e8f\u8026\u5408\u3002\r\n2. \u5bf9\u8d1f\u8f7d\u5185\u5bb9\u5c4f\u853d\u7684\u6d88\u606f\u4f20\u8f93\u3002\r\n3. \u4f7f\u7528 TCP\/IP \u63d0\u4f9b\u7f51\u7edc\u8fde\u63a5\u3002\r\n4. \u6709\u4e09\u79cd\u6d88\u606f\u53d1\u5e03\u670d\u52a1\u8d28\u91cf\uff1a\r\n    \u201c\u81f3\u591a\u4e00\u6b21\u201d\uff0c\u6d88\u606f\u53d1\u5e03\u5b8c\u5168\u4f9d\u8d56\u5e95\u5c42 TCP\/IP \u7f51\u7edc\u3002\u4f1a\u53d1\u751f\u6d88\u606f\u4e22\u5931\u6216\u91cd\u590d\u3002\u8fd9\u4e00\u7ea7\u522b\u53ef\u7528\u4e8e\u5982\u4e0b\u60c5\u51b5\uff0c\u73af\u5883\u4f20\u611f\u5668\u6570\u636e\uff0c\u4e22\u5931\u4e00\u6b21\u8bfb\u8bb0\u5f55\u65e0\u6240\u8c13\uff0c\u56e0\u4e3a\u4e0d\u4e45\u540e\u8fd8\u4f1a\u6709\u7b2c\u4e8c\u6b21\u53d1\u9001\u3002\r\n    \u201c\u81f3\u5c11\u4e00\u6b21\u201d\uff0c\u786e\u4fdd\u6d88\u606f\u5230\u8fbe\uff0c\u4f46\u6d88\u606f\u91cd\u590d\u53ef\u80fd\u4f1a\u53d1\u751f\u3002\r\n    \u201c\u53ea\u6709\u4e00\u6b21\u201d\uff0c\u786e\u4fdd\u6d88\u606f\u5230\u8fbe\u4e00\u6b21\u3002\u8fd9\u4e00\u7ea7\u522b\u53ef\u7528\u4e8e\u5982\u4e0b\u60c5\u51b5\uff0c\u5728\u8ba1\u8d39\u7cfb\u7edf\u4e2d\uff0c\u6d88\u606f\u91cd\u590d\u6216\u4e22\u5931\u4f1a\u5bfc\u81f4\u4e0d\u6b63\u786e\u7684\u7ed3\u679c\u3002\r\n5. \u5c0f\u578b\u4f20\u8f93\uff0c\u5f00\u9500\u5f88\u5c0f\uff08\u56fa\u5b9a\u957f\u5ea6\u7684\u5934\u90e8\u662f 2 \u5b57\u8282\uff09\uff0c\u534f\u8bae\u4ea4\u6362\u6700\u5c0f\u5316\uff0c\u4ee5\u964d\u4f4e\u7f51\u7edc\u6d41\u91cf\u3002\r\n6. \u4f7f\u7528 Last Will \u548c Testament \u7279\u6027\u901a\u77e5\u6709\u5173\u5404\u65b9\u5ba2\u6237\u7aef\u5f02\u5e38\u4e2d\u65ad\u7684\u673a\u5236\u3002<\/code><\/pre>\n
MQTT 3.1\u534f\u8bae\u5728\u7ebf\u7248\u672c\uff1a http:\/\/public.dhe.ibm.com\/software\/dw\/webservices\/ws-mqtt\/mqtt-v3r1.html<\/a><\/span><\/p>\n
\u5b98\u65b9\u4e0b\u8f7d\u5730\u5740\uff1a http:\/\/public.dhe.ibm.com\/software\/dw\/webservices\/ws-mqtt\/MQTT_V3.1_Protocol_Specific.pdf<\/a><\/span><\/p>\n
PDF\u7248\u672c\uff0c42\u9875\uff0c\u4e0d\u7b97\u591a\u3002<\/p>\n
\u76ee\u524dMQTT\u5927\u5bb6\u90fd\u7528\u5728\u4e86\u624b\u673a\u63a8\u9001\uff0c\u53ef\u80fd\u8fd8\u6709\u5f88\u591a\u7684\u4f7f\u7528\u65b9\u5f0f\uff0c\u6709\u5f85\u8fdb\u4e00\u6b65\u7684\u63a2\u7d22\u3002<\/p>\n
 <\/p>\n
\u56fa\u5b9a\u5934\u90e8<\/h2>\n
\u56fa\u5b9a\u5934\u90e8\uff0c\u4f7f\u7528\u4e24\u4e2a\u5b57\u8282\uff0c\u517116\u4f4d\uff1a<\/p>\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\nMessage Type<\/td>\nDUP flag<\/td>\nQoS level<\/td>\nRETAIN<\/td>\n<\/tr>\n
byte 2<\/td>\nRemaining Length<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u7b2c\u4e00\u4e2a\u5b57\u8282(byte 1)<\/h3>\n
\u6d88\u606f\u7c7b\u578b(4-7)\uff0c\u4f7f\u75284\u4f4d\u4e8c\u8fdb\u5236\u8868\u793a\uff0c\u53ef\u4ee3\u886816\u79cd\u6d88\u606f\u7c7b\u578b\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Mnemonic<\/th>\nEnumeration<\/th>\nDescription<\/th>\n<\/tr>\n<\/thead>\n
Reserved<\/td>\n0<\/td>\nReserved<\/td>\n<\/tr>\n
CONNECT<\/td>\n1<\/td>\nClient request to connect to Server<\/td>\n<\/tr>\n
CONNACK<\/td>\n2<\/td>\nConnect Acknowledgment<\/td>\n<\/tr>\n
PUBLISH<\/td>\n3<\/td>\nPublish message<\/td>\n<\/tr>\n
PUBACK<\/td>\n4<\/td>\nPublish Acknowledgment<\/td>\n<\/tr>\n
PUBREC<\/td>\n5<\/td>\nPublish Received (assured delivery part 1)<\/td>\n<\/tr>\n
PUBREL<\/td>\n6<\/td>\nPublish Release (assured delivery part 2)<\/td>\n<\/tr>\n
PUBCOMP<\/td>\n7<\/td>\nPublish Complete (assured delivery part 3)<\/td>\n<\/tr>\n
SUBSCRIBE<\/td>\n8<\/td>\nClient Subscribe request<\/td>\n<\/tr>\n
SUBACK<\/td>\n9<\/td>\nSubscribe Acknowledgment<\/td>\n<\/tr>\n
UNSUBSCRIBE<\/td>\n10<\/td>\nClient Unsubscribe request<\/td>\n<\/tr>\n
UNSUBACK<\/td>\n11<\/td>\nUnsubscribe Acknowledgment<\/td>\n<\/tr>\n
PINGREQ<\/td>\n12<\/td>\nPING Request<\/td>\n<\/tr>\n
PINGRESP<\/td>\n13<\/td>\nPING Response<\/td>\n<\/tr>\n
DISCONNECT<\/td>\n14<\/td>\nClient is Disconnecting<\/td>\n<\/tr>\n
Reserved<\/td>\n15<\/td>\nReserved<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u9664\u53bb0\u548c15\u4f4d\u7f6e\u5c5e\u4e8e\u4fdd\u7559\u5f85\u7528\uff0c\u517114\u79cd\u6d88\u606f\u4e8b\u4ef6\u7c7b\u578b\u3002<\/p>\n
DUP flag\uff08\u6253\u5f00\u6807\u5fd7\uff09<\/h3>\n
\u4fdd\u8bc1\u6d88\u606f\u53ef\u9760\u4f20\u8f93\uff0c\u9ed8\u8ba4\u4e3a0\uff0c\u53ea\u5360\u7528\u4e00\u4e2a\u5b57\u8282\uff0c\u8868\u793a\u7b2c\u4e00\u6b21\u53d1\u9001\u3002\u4e0d\u80fd\u7528\u4e8e\u68c0\u6d4b\u6d88\u606f\u91cd\u590d\u53d1\u9001\u7b49\u3002\u53ea\u9002\u7528\u4e8e\u5ba2\u6237\u7aef\u6216\u670d\u52a1\u5668\u7aef\u5c1d\u8bd5\u91cd\u53d1PUBLISH, PUBREL, SUBSCRIBE \u6216 UNSUBSCRIBE\u6d88\u606f\uff0c\u6ce8\u610f\u9700\u8981\u6ee1\u8db3\u4ee5\u4e0b\u6761\u4ef6\uff1a<\/p>\n
 \u5f53QoS > 0\r\n \u6d88\u606f\u9700\u8981\u56de\u590d\u786e\u8ba4<\/code><\/pre>\n
\u6b64\u65f6\uff0c\u5728\u53ef\u53d8\u5934\u90e8\u9700\u8981\u5305\u542b\u6d88\u606fID\u3002\u5f53\u503c\u4e3a1\u65f6\uff0c\u8868\u793a\u5f53\u524d\u6d88\u606f\u5148\u524d\u5df2\u7ecf\u88ab\u4f20\u9001\u8fc7\u3002<\/p>\n
QoS(Quality of Service,\u670d\u52a1\u8d28\u91cf)<\/h3>\n
\u4f7f\u7528\u4e24\u4e2a\u4e8c\u8fdb\u5236\u8868\u793aPUBLISH\u7c7b\u578b\u6d88\u606f\uff1a<\/p>\n\n\n\n\n\n\n\n\n
QoS value<\/th>\nbit 2<\/th>\nbit 1<\/th>\nDescription<\/th>\n<\/tr>\n<\/thead>\n
0<\/td>\n0<\/td>\n0<\/td>\n\u81f3\u591a\u4e00\u6b21<\/td>\n\u53d1\u5b8c\u5373\u4e22\u5f03<\/td>\n<=1<\/td>\n<\/tr>\n
1<\/td>\n0<\/td>\n1<\/td>\n\u81f3\u5c11\u4e00\u6b21<\/td>\n\u9700\u8981\u786e\u8ba4\u56de\u590d<\/td>\n>=1<\/td>\n<\/tr>\n
2<\/td>\n1<\/td>\n0<\/td>\n\u53ea\u6709\u4e00\u6b21<\/td>\n\u9700\u8981\u786e\u8ba4\u56de\u590d<\/td>\n=1<\/td>\n<\/tr>\n
3<\/td>\n1<\/td>\n1<\/td>\n\u5f85\u7528\uff0c\u4fdd\u7559\u4f4d\u7f6e<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
RETAIN(\u4fdd\u6301)<\/h3>\n
\u4ec5\u9488\u5bf9PUBLISH\u6d88\u606f\u3002\u4e0d\u540c\u503c\uff0c\u4e0d\u540c\u542b\u4e49\uff1a<\/p>\n
1<\/strong>\uff1a\u8868\u793a\u53d1\u9001\u7684\u6d88\u606f\u9700\u8981\u4e00\u76f4\u6301\u4e45\u4fdd\u5b58\uff08\u4e0d\u53d7\u670d\u52a1\u5668\u91cd\u542f\u5f71\u54cd\uff09\uff0c\u4e0d\u4f46\u8981\u53d1\u9001\u7ed9\u5f53\u524d\u7684\u8ba2\u9605\u8005\uff0c\u5e76\u4e14\u4ee5\u540e\u65b0\u6765\u7684\u8ba2\u9605\u4e86\u6b64Topic name\u7684\u8ba2\u9605\u8005\u4f1a\u9a6c\u4e0a\u5f97\u5230\u63a8\u9001\u3002<\/p>\n
\u5907\u6ce8\uff1a\u65b0\u6765\u4e4d\u5230\u7684\u8ba2\u9605\u8005\uff0c\u53ea\u4f1a\u53d6\u51fa\u6700\u65b0\u7684\u4e00\u4e2aRETAIN flag = 1\u7684\u6d88\u606f\u63a8\u9001\u3002<\/p>\n
0<\/strong>\uff1a\u4ec5\u4ec5\u4e3a\u5f53\u524d\u8ba2\u9605\u8005\u63a8\u9001\u6b64\u6d88\u606f\u3002<\/p>\n
\u5047\u5982\u670d\u52a1\u5668\u6536\u5230\u4e00\u4e2a\u7a7a\u6d88\u606f\u4f53(zero-length payload)\u3001RETAIN = 1\u3001\u5df2\u5b58\u5728Topic name\u7684PUBLISH\u6d88\u606f\uff0c\u670d\u52a1\u5668\u53ef\u4ee5\u5220\u9664\u6389\u5bf9\u5e94\u7684\u5df2\u88ab\u6301\u4e45\u5316\u7684PUBLISH\u6d88\u606f\u3002<\/p>\n
Remaining Length\uff08\u5269\u4f59\u957f\u5ea6\uff09<\/h3>\n
\u5728\u5f53\u524d\u6d88\u606f\u4e2d\u5269\u4f59\u7684byte(\u5b57\u8282)\u6570\uff0c\u5305\u542b\u53ef\u53d8\u5934\u90e8\u548c\u8d1f\u8377<\/span>(\u5185\u5bb9)\u3002<\/p>\n
\u5355\u4e2a\u5b57\u8282\u6700\u5927\u503c\uff1a01111111\uff0c16\u8fdb\u5236\uff1a0x7F\uff0c10\u8fdb\u5236\u4e3a127\u3002<\/p>\n
MQTT\u534f\u8bae\u89c4\u5b9a\uff0c\u7b2c\u516b\u4f4d\uff08\u6700\u9ad8\u4f4d\uff09\u82e5\u4e3a1\uff0c\u5219\u8868\u793a\u8fd8\u6709\u540e\u7eed\u5b57\u8282\u5b58\u5728\u3002<\/p>\n
MQTT\u534f\u8bae\u6700\u591a\u5141\u8bb84\u4e2a\u5b57\u8282\u8868\u793a\u5269\u4f59\u957f\u5ea6\u3002\u6700\u5927\u957f\u5ea6\u4e3a\uff1a0xFF,0xFF,0xFF,0x7F\uff0c\u4e8c\u8fdb\u5236\u8868\u793a\u4e3a:11111111,11111111,11111111,01111111\uff0c\u5341\u8fdb\u5236\uff1a268435455 byte=261120KB=256MB=0.25GB \u56db\u4e2a\u5b57\u8282\u4e4b\u95f4\u503c\u7684\u8303\u56f4\uff1a<\/p>\n\n\n\n\n\n\n\n\n
Digits<\/th>\nFrom<\/th>\nTo<\/th>\n<\/tr>\n<\/thead>\n
1<\/td>\n0 (0x00)<\/td>\n127 (0x7F)<\/td>\n<\/tr>\n
2<\/td>\n128 (0x80, 0x01)<\/td>\n16 383 (0xFF, 0x7F)<\/td>\n<\/tr>\n
3<\/td>\n16 384 (0x80, 0x80, 0x01)<\/td>\n2 097 151 (0xFF, 0xFF, 0x7F)<\/td>\n<\/tr>\n
4<\/td>\n2 097 152 (0x80, 0x80, 0x80, 0x01)<\/td>\n268 435 455 (0xFF, 0xFF, 0xFF, 0x7F)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u5176\u5b9e\u6362\u4e2a\u65b9\u5f0f\u7406\u89e3\uff1a\u7b2c1\u5b57\u8282\u7684\u57fa\u6570\u662f1\uff0c\u800c\u7b2c2\u5b57\u8282\u7684\u57fa\u6570\uff1a128\uff0c\u4ee5\u6b64\u7c7b\u63a8\uff0c\u7b2c\u4e09\u5b57\u8282\u7684\u57fa\u6570\u662f\uff1a128*128=2\u768414\u6b21\u65b9\uff0c\u7b2c\u56db\u5b57\u8282\u662f\uff1a128*128*128=2\u768421\u6b21\u65b9\uff1b<\/p>\n
\u4f8b\u5982\uff0c\u9700\u8981\u8868\u8fbe321=2*128+65.\uff082\u5b57\u8282\uff09\uff1a10100001 0000 0011.<\/p>\n
\uff08\u548c\u6211\u4eec\u7406\u89e3\u7684\u4f4e\u4f4d\u8fd0\u7b97\u653e\u7f6e\u987a\u5e8f\u4e0d\u4e00\u6837\uff0c\u7b2c\u4e00\u4e2a\u5b57\u8282\u662f\u4f4e\u4f4d\uff0c\u540e\u7eed\u5b57\u8282\u662f\u9ad8\u4f4d\uff0c\u4f46\u5b57\u8282\u5185\u90e8\u672c\u8eab\u662f\u4f4e\u4f4d\u53f3\u8fb9\uff0c\u9ad8\u4f4d\u5de6\u8fb9\uff09\u3002<\/p>\n
\u53ef\u53d8\u5934\u90e8<\/h2>\n
\u56fa\u5b9a\u5934\u90e8\u4ec5\u5b9a\u4e49\u4e86\u6d88\u606f\u7c7b\u578b\u548c\u4e00\u4e9b\u6807\u5fd7\u4f4d\uff0c\u4e00\u4e9b\u6d88\u606f\u7684\u5143\u6570\u636e\uff0c\u9700\u8981\u653e\u5165\u53ef\u53d8\u5934\u90e8\u4e2d\u3002\u53ef\u53d8\u5934\u90e8\u5185\u5bb9\u5b57\u8282\u957f\u5ea6 + Playload\/\u8d1f\u8377\u5b57\u8282\u957f\u5ea6 = \u5269\u4f59\u957f\u5ea6\u3002<\/p>\n
\u53ef\u53d8\u5934\u90e8\uff0c\u5305\u542b\u4e86\u534f\u8bae\u540d\u79f0\uff0c\u7248\u672c\u53f7\uff0c\u8fde\u63a5\u6807\u5fd7\uff0c\u7528\u6237\u6388\u6743\uff0c\u5fc3\u8df3\u65f6\u95f4\u7b49\u5185\u5bb9\u3002<\/p>\n
\u53ef\u53d8\u5934\u90e8\u5c45\u4e8e\u56fa\u5b9a\u5934\u90e8\u548cpayload\u4e2d\u95f4\u3002<\/p>\n
\u53ef\u53d8\u5269\u4f59\u957f\u5ea6\uff08remaing length\uff09\u4e0d\u662f\u53ef\u53d8\u5934\u90e8\u7684\u4e00\u90e8\u5206\uff0c\u5f53\u7136\u8be5\u957f\u5ea6\u503c\u4e5f\u662f\u4ece\u53ef\u53d8\u5934\u90e8\u5f00\u59cb\u8ba1\u7b97\uff0c\u5305\u542b\u53ef\u53d8\u5934\u90e8\u7684\u957f\u5ea6+payload\u7684\u957f\u5ea6\u3002<\/span><\/p>\n
\u53ef\u53d8\u5934\u90e8\u7684\u5b57\u6bb5\u5982\u4e0b\uff1a<\/p>\n
\u534f\u8bae\u540d\u79f0<\/strong><\/span>\uff1a MQTT <\/span>CONNECT<\/a> <\/span>message. UTF\u7f16\u7801\uff1a\u5982 MQIsdp, capitalized.<\/p>\n
\u534f\u8bae\u7248\u672c<\/strong><\/span>\uff1a8\u4f4d\u65e0\u7b26\u53f7\uff0c\u5f53\u524d\u4f7f\u7528\uff1a3 (0x03)\uff0c\u5982\u4e0b:<\/p>\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
 <\/td>\nProtocol Version<\/td>\n<\/tr>\n
 <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
Connect flags<\/h3>\n
Clean session, Will, Will QoS, Retain flags \u8be5\u5b57\u6bb5\u7684\u8bbe\u7f6e<\/p>\n
\u4e00\u4e2a\u5b57\u8282\u8868\u793a\uff0c\u9664\u4e86\u7b2c1\u4f4d\u662f\u4fdd\u7559\u672a\u4f7f\u7528\uff0c\u5176\u5b837\u4f4d\u90fd\u5177\u6709\u4e0d\u540c\u542b\u4e49\u3002<\/p>\n
\u4e1a\u52a1\u4e0a\u5f88\u91cd\u8981\uff0c\u5bf9\u6d88\u606f\u603b\u4f53\u6d41\u7a0b\u5f71\u54cd\u5f88\u5927\uff0c\u9700\u8981\u7262\u8bb0\u3002<\/p>\n
 <\/p>\n
Clean session flag<\/h3>\n
Position:<\/strong> <\/span>bit 1 \uff0c\u8fde\u63a5\u6807\u5fd7.<\/p>\n
0\uff1aserver\u9700\u8981\u5b58\u50a8client\u7684\u8ba2\u9605\u3002\u5305\u62ec\u5b58\u50a8Qos 1\u548c2\u7684\u8ba2\u9605\u4e3b\u9898\uff08\u5f53client\u91cd\u8fde\u65f6\u80fd\u5c06\u6d88\u606f\u53d1\u9001\uff09\uff1b\u5f53\u8fde\u63a5\u4e22\u5931\u7684\u65f6\u5019 \u670d\u52a1\u5668\u5fc5\u987b\u7ef4\u62a4\u6b63\u5728\u53d1\u9001\u7684\u6d88\u606f\u7684\u72b6\u6001\u76f4\u5230\u5ba2\u6237\u7aef\u91cd\u65b0\u8fde\u63a5\u5230\u670d\u52a1\u5668\u3002<\/p>\n
1\uff1aserver MUST\u5ffd\u7565\u4e4b\u524d\u7ef4\u62a4\u5173\u4e8eclient\u7684\u4fe1\u606f\uff0c\u5e76\u4e14\u5c06\u8be5connection\u5f53\u6210clean\u7684\u3002server MUST \u5ffd\u7565\u4efb\u4f55client\u65ad\u5f00\u7684\u72b6\u6001\u3002<\/p>\n
 <\/div>\n
\u539f\u6587\u7ffb\u8bd1\u4e0d\u80fd\uff0c\u6240\u4ee5\u53c2\u8003\u4e86\u4e0b\u4e00\u4f4d\u5927\u725b\u7684\u8868\u8fbe\uff1a<\/p>\n
0\uff0c\u8868\u793a\u5982\u679c\u8ba2\u9605\u7684\u5ba2\u6237\u673a\u65ad\u7ebf\u4e86\uff0c\u8981\u4fdd\u5b58\u4e3a\u5176\u8981\u63a8\u9001\u7684\u6d88\u606f\uff08QoS\u4e3a1\u548cQoS\u4e3a2\uff09\uff0c\u82e5\u5176\u91cd\u65b0\u8fde\u63a5\u65f6\uff0c\u9700\u5c06\u8fd9\u4e9b\u6d88\u606f\u63a8\u9001\uff08\u82e5\u5ba2\u6237\u7aef\u957f\u65f6\u95f4\u4e0d\u8fde\u63a5\uff0c\u9700\u8981\u8bbe\u7f6e\u4e00\u4e2a\u8fc7\u671f\u503c\uff09\u3002 <\/span>
\n1\uff0c\u65ad\u7ebf\u670d\u52a1\u5668\u5373\u6e05\u7406\u76f8\u5173\u4fe1\u606f\uff0c\u91cd\u65b0\u8fde\u63a5\u4e0a\u6765\u4e4b\u540e\uff0c\u4f1a\u518d\u6b21\u8ba2\u9605\u3002<\/p>\n
Will Flag<\/h5>\n
\u5b9a\u4e49\u4e86\u5ba2\u6237\u7aef\uff08\u6ca1\u6709\u4e3b\u52a8\u53d1\u9001DISCONNECT\u6d88\u606f\uff09\u51fa\u73b0\u7f51\u7edc\u5f02\u5e38\u5bfc\u81f4\u8fde\u63a5\u4e2d\u65ad\u7684\u60c5\u51b5\u4e0b\uff0c\u670d\u52a1\u5668\u9700\u8981\u505a\u7684\u4e00\u4e9b\u63aa\u65bd\u3002<\/p>\n
\u7b80\u800c\u8a00\u4e4b\uff0c\u5c31\u662f\u5ba2\u6237\u7aef\u9884\u5148\u5b9a\u4e49\u597d\uff0c\u5728\u81ea\u5df1\u5f02\u5e38\u65ad\u5f00\u7684\u60c5\u51b5\u4e0b\uff0c\u6240\u7559\u4e0b\u7684\u6700\u540e\u9057\u613f\uff08Last Will\uff09\uff0c\u4e5f\u79f0\u4e4b\u4e3a\u9057\u5631\uff08Testament\uff09\u3002 \u8fd9\u4e2a\u9057\u5631\u5c31\u662f\u4e00\u4e2a\u7531\u5ba2\u6237\u7aef\u9884\u5148\u5b9a\u4e49\u597d\u7684\u4e3b\u9898\u548c\u5bf9\u5e94\u6d88\u606f\uff0c\u9644\u52a0\u5728CONNECT\u7684\u53ef\u53d8\u5934\u90e8\u4e2d\uff0c\u5728\u5ba2\u6237\u7aef\u8fde\u63a5\u51fa\u73b0\u5f02\u5e38\u7684\u60c5\u51b5\u4e0b\uff0c\u7531\u670d\u52a1\u5668\u4e3b\u52a8\u53d1\u5e03\u6b64\u6d88\u606f\u3002<\/p>\n
\u53ea\u6709\u5728Will Flag\u4f4d\u4e3a1\u65f6\uff0c<\/span>Will Qos\u548cWill Retain\u624d\u4f1a\u88ab\u8bfb\u53d6\uff0c\u6b64\u65f6\u6d88\u606f\u4f53Playload\u4e2d\u8981\u51fa\u73b0Will Topic\u548cWill Message\u5177\u4f53\u5185\u5bb9\uff0c\u5426\u5219\uff0cWill QoS\u548cWill Retain\u503c\u4f1a\u88ab\u5ffd\u7565\u6389\u3002<\/p>\n
Will Qos<\/h5>\n
\u4e24\u4f4d\u8868\u793a\uff0c\u548cPUBLISH\u6d88\u606f\u56fa\u5b9a\u5934\u90e8\u7684QoS level\u542b\u4e49\u4e00\u6837\u3002<\/p>\n
\u82e5\u6807\u8bc6\u4e86Will Flag\u503c\u4e3a1\uff0c\u90a3\u4e48Will QoS\u5c31\u4f1a\u751f\u6548\uff0c\u5426\u5219\u4f1a\u88ab\u5ffd\u7565\u6389\u3002<\/p>\n
Will RETAIN<\/h5>\n
\u5982\u679c\u8bbe\u7f6eWill Flag\uff0cWill Retain\u6807\u5fd7\u5c31\u662f\u6709\u6548\u7684\uff0c\u5426\u5219\u5b83\u5c06\u88ab\u5ffd\u7565\u3002<\/p>\n
\u5f53\u5ba2\u6237\u7aef\u610f\u5916\u65ad\u5f00\u670d\u52a1\u5668\u53d1\u5e03\u5176Will Message\u4e4b\u540e\uff0c\u670d\u52a1\u5668\u662f\u5426\u5e94\u8be5\u7ee7\u7eed\u4fdd\u5b58\u3002\u8fd9\u4e2a\u5c5e\u6027\u548cPUBLISH\u56fa\u5b9a\u5934\u90e8\u7684RETAIN\u6807\u5fd7\u542b\u4e49\u4e00\u6837\uff0c\u8fd9\u91cc\u5148\u63a0\u8fc7\u3002<\/p>\n
User name \u548c password Flag\uff1a<\/h5>\n
\u7528\u4e8e\u6388\u6743\uff0c\u4e24\u8005\u8981\u4e48\u4e3a0\u8981\u4e48\u4e3a1\uff0c\u5426\u5219\u90fd\u662f\u65e0\u6548\u3002\u90fd\u4e3a0\uff0c\u8868\u793a\u5ba2\u6237\u7aef\u53ef\u81ea\u7531\u8fde\u63a5\/\u8ba2\u9605\uff0c\u90fd\u4e3a1\uff0c\u8868\u793a\u8fde\u63a5\/\u8ba2\u9605\u9700\u8981\u6388\u6743\u3002<\/p>\n
 <\/p>\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
 <\/strong><\/span><\/td>\nUser Name Flag<\/strong><\/span><\/td>\nPassword Flag<\/strong><\/span><\/td>\nWill Retain<\/strong><\/span><\/td>\nWill QoS<\/strong><\/span><\/td>\nWill Flag<\/strong><\/span><\/td>\nClean Session<\/strong><\/span><\/td>\nReserved<\/strong><\/span><\/td>\n<\/tr>\n
 <\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n <\/td>\nx<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
 <\/p>\n
Playload\/\u6d88\u606f\u4f53\/\u8d1f\u8377<\/h3>\n
\u6d88\u606f\u4f53\u4e3b\u8981\u662f\u4e3a\u914d\u5408\u56fa\u5b9a\/\u53ef\u53d8\u5934\u90e8\u547d\u4ee4\uff08\u6bd4\u5982CONNECT\u53ef\u53d8\u5934\u90e8User name\u6807\u8bb0\u82e5\u4e3a1\u5219\u9700\u8981\u5728\u6d88\u606f\u4f53\u4e2d\u9644\u52a0\u7528\u6237\u540d\u79f0\u5b57\u7b26\u4e32\uff09\u800c\u5b58\u5728\u3002<\/p>\n
CONNECT\/SUBSCRIBE\/SUBACK\/PUBLISH\u7b49\u6d88\u606f\u6709\u6d88\u606f\u4f53\u3002PUBLISH\u7684\u6d88\u606f\u4f53\u4ee5\u4e8c\u8fdb\u5236\u5f62\u5f0f\u5bf9\u5f85\u3002<\/p>\n
MQTT\u534f\u8bae\u53ea\u5141\u8bb8\u5728PUBLISH\u7c7b\u578b\u6d88\u606f\u4f53\u4e2d\u4f7f\u7528\u81ea\u5b9a\u4e49\u7279\u6027\uff0c\u5728\u56fa\u5b9a\/\u53ef\u53d8\u5934\u90e8\u60f3\u52a0\u5165\u81ea\u5b9a\u4e49\u79c1\u6709\u7279\u6027\u662f\u4e0d\u5141\u8bb8\u7684\u3002<\/p>\n
\u8fd9\u4e5f\u662f\u4e3a\u4e86\u534f\u8bae\u514d\u4e8e\u6d41\u4e8e\u5f62\u5f0f\uff0c\u53d8\u5f97\u5f88\u5206\u88c2\u4e5f\u4e3a\u4e86\u517c\u987e\u73b0\u6709\u5ba2\u6237\u7aef\u7b49\u3002\u6bd4\u5982\u652f\u6301\u538b\u7f29\u7b49\uff0c\u90a3\u5c31\u53ef\u4ee5\u5728Playload\u4e2d\u5b9a\u4e49\u6570\u636e\u652f\u6301\uff0c\u5728\u5e94\u7528\u4e2d\u8fdb\u884c\u8bfb\u53d6\u5904\u7406\u3002<\/p>\n
\u8fd9\u90e8\u5206\u4f1a\u5728\u540e\u9762\u8be6\u7ec6\u8bba\u8ff0\u3002<\/p>\n
\u6d88\u606f\u6807\u8bc6\u7b26\/\u6d88\u606fID<\/h3>\n
\u56fa\u5b9a\u5934\u4e2d\u7684QoS level\u6807\u5fd7\u503c\u4e3a1\u62162\u65f6\u624d\u4f1a\u5728\uff1aPUBLISH\uff0cPUBACK\uff0cPUBREC\uff0cPUBREL\uff0cPUBCOMP\uff0cSUBSCRIBE\uff0cSUBACK\uff0cUNSUBSCRIBE\uff0cUNSUBACK\u7b49\u6d88\u606f\u7684\u53ef\u53d8\u5934\u4e2d\u51fa\u73b0\u3002<\/p>\n
\u4e00\u4e2a16\u4f4d\u65e0\u7b26\u53f7\u4f4d\u7684short\u7c7b\u578b\u503c\uff08\u503c\u4e0d\u80fd\u4e3a 0\uff0c0\u505a\u4fdd\u7559\u4f5c\u4e3a\u65e0\u6548\u7684\u6d88\u606fID\uff09\uff0c\u4ec5\u4ec5\u8981\u6c42\u5728\u4e00\u4e2a\u7279\u5b9a\u65b9\u5411\uff08\u670d\u52a1\u5668\u53d1\u5f80\u5ba2\u6237\u7aef\u4e3a\u4e00\u4e2a\u65b9\u5411\uff0c\u5ba2\u6237\u7aef\u53d1\u9001\u5230\u670d\u52a1\u5668\u7aef\u4e3a\u53e6\u4e00\u4e2a\u65b9\u5411\uff09\u7684\u901a\u4fe1\u6d88\u606f\u4e2d\u5fc5\u987b\u552f\u4e00\u3002\u6bd4\u5982\u5ba2\u6237\u7aef\u53d1\u5f80\u670d\u52a1\u5668\uff0c\u6709\u53ef\u80fd\u5b58\u5728\u670d\u52a1\u5668\u53d1\u5f80\u5ba2\u6237\u7aef\u4f1a\u540c\u65f6\u5b58\u5728\u91cd\u590d\uff0c\u4f46\u4e0d\u788d\u4e8b\u3002<\/p>\n
\u53ef\u53d8\u5934\u90e8\u4e2d\uff0c\u9700\u8981\u4e24\u4e2a\u5b57\u8282\u7684\u987a\u5e8f\u662fMSB(Most Significant Bit) LSB(Last\/Least Significant Bit)\uff0c\u7ffb\u8bd1\u6210\u4e2d\u6587\u5c31\u662f\uff0c\u6700\u9ad8\u6709\u6548\u4f4d\uff0c\u6700\u4f4e\u6709\u6548\u4f4d\u3002\u6700\u9ad8\u6709\u6548\u4f4d\u5728\u6700\u4f4e\u6709\u6548\u4f4d\u5de6\u8fb9\/\u4e0a\u9762\uff0c\u8868\u793a\u8fd9\u662f\u4e00\u4e2a\u5927\u7aef\u5b57\u8282\/\u7f51\u7edc\u5b57\u8282\u5e8f\uff0c\u7b26\u5408\u4eba\u7684\u9605\u8bfb\u4e60\u60ef\uff0c\u9ad8\u4f4d\u5728\u6700\u5de6\u8fb9\u3002<\/p>\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
 <\/td>\nMessage Identifier MSB<\/td>\n<\/tr>\n
 <\/td>\nMessage Identifier LSB<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
<\/code>\u6700\u5927\u957f\u5ea6\u53ef\u4e3a\uff1a 65535<\/p>\n
UTF-8\u7f16\u7801<\/h3>\n
\u6709\u5173\u5b57\u7b26\u4e32\uff0cMQTT\u91c7\u7528\u7684\u662f\u4fee\u6539\u7248\u7684UTF-8\u7f16\u7801\uff0c\u4e00\u822c\u5f62\u5f0f\u4e3a\u5982\u4e0b\uff1a<\/p>\n\n\n\n\n\n\n\n
bit<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\nString Length MSB<\/td>\n<\/tr>\n
byte 2<\/td>\nString Length LSB<\/td>\n<\/tr>\n
bytes 3 ...<\/td>\nEncoded Character Data<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
 <\/p>\n
 \u6700\u540e\u7684\u7ed3\u6784\u5982\u4e0b\uff1a<\/p>\n
 <\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
 <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
Fixed header\/\u56fa\u5b9a\u5934\u90e8<\/strong><\/td>\n<\/tr>\n
 <\/td>\n <\/td>\nMessage Type(1)<\/td>\nDUP flag<\/td>\nQoS level<\/td>\nRETAIN<\/td>\n<\/tr>\n
\n
byte 1<\/div>\n<\/td>\n
 <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n<\/tr>\n
byte 2<\/td>\nRemaining Length<\/td>\n<\/tr>\n
Variable header<\/strong>\/\u53ef\u53d8\u5934\u90e8<\/td>\n<\/tr>\n
Protocol Name<\/td>\n<\/tr>\n
byte 1<\/td>\nLength MSB (0)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 2<\/td>\nLength LSB (6)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n<\/tr>\n
byte 3<\/td>\n'M'<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n<\/tr>\n
byte 4<\/td>\n'Q'<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n<\/tr>\n
byte 5<\/td>\n'I'<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n<\/tr>\n
byte 6<\/td>\n's'<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
byte 7<\/td>\n'd'<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 8<\/td>\n'p'<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
Protocol Version Number<\/td>\n<\/tr>\n
byte 9<\/td>\nVersion (3)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
Connect Flags<\/td>\n<\/tr>\n
 <\/td>\nUser Name Flag<\/td>\nPassword Flag<\/td>\nWill Retain<\/td>\nWill QoS<\/td>\nWill Flag<\/td>\nClean Session<\/td>\nReserved<\/td>\n<\/tr>\n
\n
byte 10<\/div>\n<\/td>\n
1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n1<\/td>\nx<\/td>\n<\/tr>\n
Keep Alive timer<\/td>\n<\/tr>\n
byte 11<\/td>\nKeep Alive MSB (0)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 12<\/td>\nKeep Alive LSB (10)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n<\/tr>\n
Playload\/\u6d88\u606f\u4f53<\/strong><\/td>\n<\/tr>\n
\n
Client Identifier(\u5ba2\u6237\u7aefID)<\/p>\n
1-23\u4e2a\u5b57\u7b26\u957f\u5ea6\uff0c\u5ba2\u6237\u7aef\u5230\u670d\u52a1\u5668\u7684\u5168\u5c40\u552f\u4e00\u6807\u5fd7\uff0c\u5982\u679c\u5ba2\u6237\u7aefID\u8d85\u51fa23\u4e2a\u5b57\u7b26\u957f\u5ea6\uff0c\u670d\u52a1\u5668\u9700\u8981\u8fd4\u56de\u7801\u4e3a2\uff0c\u6807\u8bc6\u7b26\u88ab\u62d2\u7edd\u54cd\u5e94\u7684CONNACK\u6d88\u606f\u3002

\n\u5904\u7406QoS\u7ea7\u522b1\u548c2\u7684\u6d88\u606fID\u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528\u5230\u3002

\n\u5fc5\u586b\u9879\u3002<\/td>\n<\/tr>\n
\n
Will Topic<\/p>\n
Will Flag\u503c\u4e3a1\uff0c\u8fd9\u91cc\u4fbf\u662fWill Topic\u7684\u5185\u5bb9\u3002QoS\u7ea7\u522b\u901a\u8fc7Will QoS\u5b57\u6bb5\u5b9a\u4e49\uff0cRETAIN\u503c\u901a\u8fc7Will RETAIN\u6807\u8bc6\uff0c\u90fd\u5b9a\u4e49\u5728\u53ef\u53d8\u5934\u91cc\u9762\u3002<\/td>\n<\/tr>\n
\n
Will Message<\/p>\n
Will Flag\u82e5\u8bbe\u4e3a1\uff0c\u8fd9\u91cc\u4fbf\u662fWill Message\u5b9a\u4e49\u6d88\u606f\u7684\u5185\u5bb9\uff0c\u5bf9\u5e94\u7684\u4e3b\u9898\u4e3aWill Topic\u3002\u5982\u679c\u5ba2\u6237\u7aef\u610f\u5916\u7684\u65ad\u5f00\u89e6\u53d1\u670d\u52a1\u5668PUBLISH\u6b64\u6d88\u606f\u3002
\n\u957f\u5ea6\u6709\u53ef\u80fd\u4e3a0\u3002
\n\u5728CONNECT\u6d88\u606f\u4e2d\u7684Will Message\u662fUTF-8\u7f16\u7801\u7684\uff0c\u5f53\u88ab\u670d\u52a1\u5668\u53d1\u5e03\u65f6\u5219\u4f5c\u4e3a\u4e8c\u8fdb\u5236\u7684\u6d88\u606f\u4f53\u3002<\/td>\n<\/tr>\n
\n
User Name<\/p>\n
\u5982\u679c\u8bbe\u7f6eUser Name\u6807\u8bc6\uff0c\u53ef\u4ee5\u5728\u6b64\u8bfb\u53d6\u7528\u6237\u540d\u79f0\u3002\u4e00\u822c\u53ef\u7528\u4e8e\u8eab\u4efd\u9a8c\u8bc1\u3002\u534f\u8bae\u5efa\u8bae\u7528\u6237\u540d\u4e3a\u4e0d\u591a\u4e8e12\u4e2a\u5b57\u7b26\uff0c\u4e0d\u662f\u5fc5\u987b\u3002<\/td>\n<\/tr>\n
\n
Password<\/p>\n
\u5982\u679c\u8bbe\u7f6ePassword\u6807\u8bc6\uff0c\u4fbf\u53ef\u8bfb\u53d6\u7528\u6237\u5bc6\u7801\u3002\u5efa\u8bae\u5bc6\u7801\u4e3a12\u4e2a\u5b57\u7b26\u6216\u8005\u66f4\u5c11\uff0c\u4f46\u4e0d\u662f\u5fc5\u987b\u3002<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
 <\/p>\n
\u5fc3\u8df3\u65f6\u95f4(Keep Alive timer)<\/h5>\n
\u4ee5\u79d2\u4e3a\u5355\u4f4d\uff0c\u5b9a\u4e49\u670d\u52a1\u5668\u7aef\u4ece\u5ba2\u6237\u7aef\u63a5\u6536\u6d88\u606f\u7684\u6700\u5927\u65f6\u95f4\u95f4\u9694\u3002\u4e00\u822c\u5e94\u7528\u670d\u52a1\u4f1a\u5728\u4e1a\u52a1\u5c42\u6b21\u68c0\u6d4b\u5ba2\u6237\u7aef\u7f51\u7edc\u662f\u5426\u8fde\u63a5\uff0c\u4e0d\u662fTCP\/IP\u534f\u8bae\u5c42\u9762\u7684\u5fc3\u8df3\u673a\u5236(\u6bd4\u5982\u5f00\u542fSOCKET\u7684SO_KEEPALIVE\u9009\u9879)\u3002 \u4e00\u822c\u6765\u8bb2\uff0c\u5728\u4e00\u4e2a\u5fc3\u8df3\u95f4\u9694\u5185\uff0c\u5ba2\u6237\u7aef\u53d1\u9001\u4e00\u4e2aPINGREQ\u6d88\u606f\u5230\u670d\u52a1\u5668\uff0c\u670d\u52a1\u5668\u8fd4\u56dePINGRESP\u6d88\u606f\uff0c\u5b8c\u6210\u4e00\u6b21\u5fc3\u8df3\u4ea4\u4e92\uff0c\u7ee7\u800c\u7b49\u5f85\u4e0b\u4e00\u8f6e\u3002\u82e5\u5ba2\u6237\u7aef\u6ca1\u6709\u6536\u5230\u5fc3\u8df3\u53cd\u9988\uff0c\u4f1a\u5173\u95ed\u6389TCP\/IP\u7aef\u53e3\u8fde\u63a5\uff0c\u79bb\u7ebf\u3002 16\u4f4d\u4e24\u4e2a\u5b57\u8282\uff0c\u53ef\u770b\u505a\u4e00\u4e2a\u65e0\u7b26\u53f7\u7684short\u7c7b\u578b\u503c\u3002\u6700\u5927\u503c\uff0c2^16-1 = 65535\u79d2 = 18\u5c0f\u65f6\u3002\u6700\u5c0f\u503c\u53ef\u4ee5\u4e3a0\uff0c\u8868\u793a\u5ba2\u6237\u7aef\u4e0d\u65ad\u5f00\u3002\u4e00\u822c\u8bbe\u4e3a\u51e0\u5206\u949f\uff0c\u6bd4\u5982\u5fae\u4fe1\u5fc3\u8df3\u5468\u671f\u4e3a300\u79d2\u3002<\/p>\n
Will Message\u7f16\u7801<\/h5>\n
Will Message\u5728CONNECT Payload\/\u6d88\u606f\u4f53\u4e2d\uff0c\u4f7f\u7528UTF-8\u7f16\u7801\u3002\u5047\u8bbe\u5185\u5bb9\u4e3a\u201cabcd\u201d\uff0c\u5927\u6982\u5982\u4e0b\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n\n
 <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\nLength MSB (0)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 2<\/td>\nLength LSB (4)<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n
byte 3<\/td>\n'a' (0x61)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n<\/tr>\n
byte 4<\/td>\n'b' (0x62)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n<\/tr>\n
byte 5<\/td>\n'c' (0x63)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
byte 6<\/td>\n'd' (0x64)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u6709\u4e00\u70b9\u9700\u8981\u8bb0\u4f4f\uff0cPUBLISH\u7684Payload\/\u6d88\u606f\u4f53\u4e2d\u4ee5\u4e8c\u8fdb\u5236\u7f16\u7801\u4fdd\u5b58\u3002<\/p>\n
\u67d0\u523b\u5ba2\u6237\u7aef\u5f02\u5e38\u5173\u95ed\u89e6\u53d1\u670d\u52a1\u5668\u4f1aPUBLISH\u6b64\u6d88\u606f\u3002\u90a3\u4e48\u670d\u52a1\u5668\u4f1a\u76f4\u63a5\u628abyte3-byte6\u4e4b\u95f4\u5b57\u7b26\u53d6\u51fa\uff0c\u4fdd\u5b58\u4e3a\u4e8c\u8fdb\u5236\uff0c\u9644\u52a0\u5230PUBLISH\u6d88\u606f\u4f53\u4e2d\uff0c\u5927\u6982\u5b58\u50a8\u5982\u4e0b\uff1a<\/p>\n\n\n\n\n\n\n\n\n
 <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
byte 1<\/td>\n'a' (0x61)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n<\/tr>\n
byte 2<\/td>\n'b' (0x62)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n<\/tr>\n
byte 3<\/td>\n'c' (0x63)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n<\/tr>\n
byte 4<\/td>\n'd' (0x64)<\/td>\n0<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u53e6\u5916\uff0cMQTT 3.1\u534f\u8bae\u5bf9Will message\u7684\u8bf4\u660e\u5f88\u5bb9\u6613\u5f15\u8d77\u8bef\u89e3\uff0c3.1.1\u8349\u6848\u5df2\u7ecf\u5f97\u5230\u4fee\u6b63\u3002<\/p>\n
\u76f8\u5173\u8bf4\u660e\uff1a<\/p>\n
http:\/\/mqtt.org\/wiki\/doku.php\/willmessage<\/em>utf8_support<\/p>\n
https:\/\/tools.oasis-open.org\/issues\/browse\/MQTT-2<\/p>\n
\u8fde\u63a5\u5f02\u5e38\u4e2d\u65ad\u901a\u77e5\u673a\u5236<\/h3>\n
CONNECT\u6d88\u606f\u4e00\u65e6\u8bbe\u7f6e\u5728\u53ef\u53d8\u5934\u90e8\u8bbe\u7f6e\u4e86Will flag\u6807\u8bb0\uff0c\u90a3\u5c31\u542f\u7528\u4e86Last-Will-And-Testament\u7279\u6027\uff0c\u6b64\u7279\u6027\u5f88\u8d5e\u3002<\/p>\n
\u4e00\u65e6\u5ba2\u6237\u7aef\u51fa\u73b0\u5f02\u5e38\u4e2d\u65ad\uff0c\u4fbf\u4f1a\u89e6\u53d1\u670d\u52a1\u5668\u53d1\u5e03Will Message\u6d88\u606f\u5230Will Topic\u4e3b\u9898\u4e0a\u53bb\uff0c\u901a\u77e5Will Topic\u8ba2\u9605\u8005\uff0c\u5bf9\u65b9\u56e0\u5f02\u5e38\u9000\u51fa\u3002<\/p>\n
\u63a5\u6536CONNECT\u540e\u7684\u54cd\u5e94\u52a8\u4f5c<\/h3>\n
\u63a5\u6536\u5230CONNECT\u6d88\u606f\u4e4b\u540e\uff0c\u670d\u52a1\u5668\u5e94\u8be5\u8fd4\u56de\u4e00\u4e2aCONNACK\u6d88\u606f\u4f5c\u4e3a\u54cd\u5e94\uff1a<\/p>\n
    \n
  1. \u82e5\u5ba2\u6237\u7aef\u7ed5\u8fc7CONNECT\u6d88\u606f\u76f4\u63a5\u53d1\u9001\u5176\u5b83\u7c7b\u578b\u6d88\u606f\uff0c\u670d\u52a1\u5668\u5e94\u5173\u95ed\u6b64\u975e\u6cd5\u8fde\u63a5 \u82e5\u5ba2\u6237\u7aef\u53d1\u9001CONNECT\u4e4b\u540e\u672a\u6536\u5230CONNACT\uff0c\u9700\u8981\u5173\u95ed\u5f53\u524d\u8fde\u63a5\uff0c\u7136\u540e\u91cd\u65b0\u8fde\u63a5<\/li>\n
  2. \u76f8\u540cClient ID\u5ba2\u6237\u7aef\u5df2\u8fde\u63a5\u5230\u670d\u52a1\u5668\uff0c\u5148\u524d\u5ba2\u6237\u7aef\u5fc5\u987b\u65ad\u5f00\u8fde\u63a5\u540e\uff0c\u670d\u52a1\u5668\u624d\u80fd\u5b8c\u6210\u65b0\u7684\u5ba2\u6237\u7aefCONNECT\u8fde\u63a5 \u5ba2\u6237\u7aef\u53d1\u9001\u65e0\u6548\u975e\u6cd5CONNECT\u6d88\u606f\uff0c\u670d\u52a1\u5668\u9700\u8981\u5173\u95ed<\/li>\n<\/ol>\n
    CONNACK<\/h2>\n
    \u4e00\u4e2a\u5b8c\u6574\u7684CONNACK\u6d88\u606f\u5927\u81f4\u5982\u4e0b\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
     <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
    Fixed header\/\u56fa\u5b9a\u5934\u90e8<\/strong><\/td>\n<\/tr>\n
    byte 1<\/td>\n <\/td>\nMessage type (2)<\/td>\nDUP flag<\/td>\nQoS flags<\/td>\nRETAIN<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n<\/tr>\n
    byte 2<\/td>\n <\/td>\nRemaining Length (2)<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n1<\/td>\n0<\/td>\n<\/tr>\n
    Variable header<\/strong>\/\u53ef\u53d8\u5934\u90e8<\/td>\n<\/tr>\n
    Topic Name Compression Response<\/td>\n<\/tr>\n
    byte 1<\/td>\nReserved values. Not used.<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n<\/tr>\n
    Connect Return Code<\/td>\n<\/tr>\n
    byte 2<\/td>\nReturn Code<\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \u53ef\u53d8\u5934\u90e8\u7b2c\u4e00\u4e2a\u5b57\u8282\u4e3a\u4fdd\u7559\uff0c\u65e0\u751a\u7528\u5904\u3002\u7b2c\u4e8c\u4e2a\u5b57\u8282\u4e3a\u8fde\u63a5\u63e1\u624b\u8fd4\u56de\u7801\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
    \u8fd4\u56de\u503c<\/td>\n16\u8fdb\u5236<\/td>\n\u542b\u4e49<\/td>\n<\/tr>\n<\/thead>\n
    0<\/td>\n0x00<\/td>\nConnection Accepted<\/td>\n<\/tr>\n
    1<\/td>\n0x01<\/td>\nConnection Refused: unacceptable protocol version<\/td>\n<\/tr>\n
    2<\/td>\n0x02<\/td>\nConnection Refused: identifier rejected<\/td>\n<\/tr>\n
    3<\/td>\n0x03<\/td>\nConnection Refused: server unavailable<\/td>\n<\/tr>\n
    4<\/td>\n0x04<\/td>\nConnection Refused: bad user name or password<\/td>\n<\/tr>\n
    5<\/td>\n0x05<\/td>\nConnection Refused: not authorized<\/td>\n<\/tr>\n
    6-255<\/td>\n <\/td>\nReserved for future use<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \u53ea\u67090-5\u76ee\u524d\u88ab\u4f7f\u7528\u5230\uff0c\u5176\u4ed6\u503c\u6709\u5f85\u65e5\u540e\u4f7f\u7528\u3002\u4e00\u822c\u8fd4\u56de\u503c\u4e3a0x00\uff0c\u8868\u793a\u8fde\u63a5\u5efa\u7acb\u3002\u975e\u6cd5\u7684\u8bf7\u6c42\uff0c\u9700\u8981\u8fd4\u56de\u76f8\u5e94\u7684\u6570\u503c\u3002<\/p>\n
    \u4ece\u4e0a\u9762\u770b\u51fa\uff0c\u4e00\u4e2aCONNACT\uff0c\u56db\u4e2a\u5b57\u8282\u8868\u793a\u3002\u4e00\u4e2a\u6b63\u5e38\u7684CONNACT\u6d88\u606f\u5b9e\u9645\u5185\u5bb9\u53ef\u80fd\u5982\u4e0b\uff1a 0x20 0x02 0x00 0x00<\/p>\n
    \u82e5\u662f\u5728\u79c1\u6709\u534f\u8bae\u4e2d\uff0c\u4e24\u4e2a\u5b57\u8282\u5c31\u8db3\u591f\u4e86\u3002<\/p>\n
    \u5f88\u591a\u65f6\u5019\uff0c\u5ba2\u6237\u7aef\u548c\u670d\u52a1\u5668\u7aef\u5728\u6ca1\u6709\u6d88\u606f\u4f20\u9012\u65f6\uff0c\u4f1a\u4e00\u76f4\u4fdd\u6301\u7740\u8fde\u63a5\u3002\u867d\u7136\u4e0d\u80fd\u4f9d\u9760TCP\u5fc3\u8df3\u673a\u5236\uff08\u6bd4\u5982SO_KEEPALIVE\u9009\u9879\uff09\uff0c\u4e1a\u52a1\u5c42\u9762\u5b9a\u4e49\u5fc3\u8df3\u673a\u5236\uff0c\u4f1a\u8ba9\u8fde\u63a5\u72b6\u6001\u68c0\u6d4b\u3001\u63a7\u5236\u66f4\u4e3a\u76f4\u89c2\u3002<\/p>\n
     <\/h2>\n
    PINGREQ<\/h2>\n
    \u7531\u5ba2\u6237\u7aef\u53d1\u9001\u5230\u670d\u52a1\u5668\u7aef\uff0c\u8bc1\u660e\u81ea\u5df1\u8fd8\u5728\u4e00\u76f4\u8fde\u63a5\u7740\u5462\u3002\u4e24\u4e2a\u5b57\u8282\uff0c\u56fa\u5b9a\u503c\u3002<\/p>\n\n\n\n\n\n\n\n\n\n
     <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
    Fixed header\/\u56fa\u5b9a\u5934\u90e8<\/strong><\/td>\n<\/tr>\n
    byte 1<\/td>\n <\/td>\nMessage type (12)<\/td>\nDUP flag<\/td>\nQoS flags<\/td>\nRETAIN<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n0<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n<\/tr>\n
    byte 2<\/td>\n <\/td>\nRemaining Length (0)<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \u5ba2\u6237\u7aef\u4f1a\u5728\u4e00\u4e2a\u5fc3\u8df3\u5468\u671f\u5185\u53d1\u9001\u4e00\u6761PINGREQ\u6d88\u606f\u5230\u670d\u52a1\u5668\u7aef\u3002<\/p>\n
    \u5fc3\u8df3\u9891\u7387\u5728CONNECT\u53ef\u53d8\u5934\u90e8\u201cKeep Alive timer\u201d\u4e2d\u5b9a\u4e49\u65f6\u95f4\uff0c\u5355\u4f4d\u4e3a\u79d2\uff0c\u65e0\u7b26\u53f716\u4f4dshort\u8868\u793a\u3002<\/p>\n
    PINGRESP<\/h2>\n
    \u670d\u52a1\u5668\u6536\u5230PINGREQ\u8bf7\u6c42\u4e4b\u540e\uff0c\u4f1a\u7acb\u5373\u54cd\u5e94\u4e00\u4e2a\u4e24\u4e2a\u5b57\u8282\u56fa\u5b9a\u683c\u5f0f\u7684PINGRESP\u6d88\u606f\u3002<\/p>\n\n\n\n\n\n\n\n\n\n
     <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
    Fixed header\/\u56fa\u5b9a\u5934\u90e8<\/strong><\/td>\n<\/tr>\n
    byte 1<\/td>\n <\/td>\nMessage type (13)<\/td>\nDUP flag<\/td>\nQoS flags<\/td>\nRETAIN<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n1<\/td>\n1<\/td>\n0<\/td>\n1<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n<\/tr>\n
    byte 2<\/td>\n <\/td>\nRemaining Length (0)<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \u670d\u52a1\u5668\u4e00\u822c\u82e5\u57281.5\u500d\u7684\u5fc3\u8df3\u5468\u671f\u5185\u63a5\u6536\u4e0d\u5230\u5ba2\u6237\u7aef\u53d1\u9001\u7684PINGREQ\uff0c\u53ef\u8003\u8651\u5173\u95ed\u5ba2\u6237\u7aef\u7684\u8fde\u63a5\u63cf\u8ff0\u7b26\u3002\u6b64\u65f6\u7684\u5173\u95ed\u8fde\u63a5\u7684\u884c\u4e3a\u548c\u63a5\u6536\u5230\u5ba2\u6237\u7aef\u53d1\u9001DISCONNECT\u6d88\u606f\u7684\u5904\u7406\u884c\u4e3a\u4e00\u81f4\uff0c\u4f46\u5bf9\u5ba2\u6237\u7aef\u7684\u8ba2\u9605\u4e0d\u4f1a\u4ea7\u751f\u5f71\u54cd\uff08\u4e0d\u4f1a\u6e05\u9664\u5ba2\u6237\u7aef\u8ba2\u9605\u6570\u636e\uff09\uff0c\u8fd9\u4e2a\u9700\u8981\u7262\u8bb0\u3002<\/p>\n
    \u82e5\u5ba2\u6237\u7aef\u53d1\u9001PINGREQ\u4e4b\u540e\u7684\u4e00\u4e2a\u5fc3\u8df3\u5468\u671f\u5185\u63a5\u6536\u4e0d\u5230PINGRESP\u6d88\u606f\uff0c\u53ef\u8003\u8651\u5173\u95edTCP\/IP\u5957\u63a5\u5b57\u8fde\u63a5\u3002<\/p>\n
    DISCONNECT<\/h2>\n
    \u5ba2\u6237\u7aef\u4e3b\u52a8\u53d1\u9001\u5230\u670d\u52a1\u5668\u7aef\uff0c\u8868\u660e\u5373\u5c06\u5173\u95edTCP\/IP\u8fde\u63a5\u3002\u6b64\u65f6\u8981\u6c42\u670d\u52a1\u5668\u8981\u5b8c\u6574\u3001\u5e72\u51c0\u7684\u8fdb\u884c\u65ad\u5f00\u5904\u7406\uff0c\u4e0d\u80fd\u4ec5\u4ec5\u7c7b\u4f3c\u4e8e\u5173\u95ed\u8fde\u63a5\u63cf\u8ff0\u7b26\u7c7b\u4f3c\u8349\u8349\u5904\u7406\u4e4b\u3002 \u9700\u8981\u4e24\u4e2a\u5b57\u8282\uff0c\u503c\u56fa\u5b9a\uff1a<\/p>\n\n\n\n\n\n\n\n\n\n
     <\/th>\nDescription<\/th>\n7<\/th>\n6<\/th>\n5<\/th>\n4<\/th>\n3<\/th>\n2<\/th>\n1<\/th>\n0<\/th>\n<\/tr>\n<\/thead>\n
    Fixed header\/\u56fa\u5b9a\u5934\u90e8<\/strong><\/td>\n<\/tr>\n
    byte 1<\/td>\n <\/td>\nMessage type (14)<\/td>\nDUP flag<\/td>\nQoS flags<\/td>\nRETAIN<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n1<\/td>\n1<\/td>\n1<\/td>\n0<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\nx<\/td>\n<\/tr>\n
    byte 2<\/td>\n <\/td>\nRemaining Length (0)<\/td>\n<\/tr>\n
     <\/td>\n <\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \u670d\u52a1\u5668\u8981\u6839\u636e\u5148\u524d\u6b64\u5ba2\u6237\u7aef\u5728\u53d1\u9001CONNECT\u6d88\u606f\u53ef\u53d8\u5934\u90e8Connect flag\u4e2d\u7684\u201cClean session flag\u201d\u6240\u8bbe\u7f6e\u503c\uff0c\u518d\u6b21\u590d\u4e60\u4e00\u4e0b\uff1a<\/p>\n
      \n
    1. \n
      \u503c\u4e3a0\uff0c\u670d\u52a1\u5668\u5fc5\u987b\u5728\u5ba2\u6237\u7aef\u65ad\u5f00\u4e4b\u540e\u7ee7\u7eed\u5b58\u50a8\/\u4fdd\u6301\u5ba2\u6237\u7aef\u7684\u8ba2\u9605\u72b6\u6001\u3002\u8fd9\u4e9b\u72b6\u6001\u5305\u62ec\uff1a<\/p>\n