开发部署在云端的设备接入网关服务就不得不提到MQTT，使用MQTT不论是从设备到设备，还是设备到云端服务的双向通讯，都可以获得较好的支持。
MQTT的起源和我的理解
这里基于mosquitto，以一组实际的订阅、发布，使用tcpdump来观察MQTT的通讯。
# 使用tcpdump打印指定MQTT服务器所在端口的报文tcpdump -n -XX -i eth0 port 1883# 订阅指定主题的消息mosquitto_sub -h 172.16.0.12 -t "topic/#" -u user -P password -i "client1"# 发布消息到指定主题mosquitto_pub -h 172.16.0.12 -t "topic/" -u user -P password -i "client3" -m "1234567890123456789012345678901234567890"
tcpdump抓取的报文如下：
启动mosquitto_sub命令获得如下报文：==================================16:33:28.668926 IP SUB.41050 > MQTT.ibm-mqisdp: Flags [S], seq 1177792969, win 29200, options [mss 1424,sackOK,TS val 530570732 ecr 0,nop,wscale 7], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 003c 5872 4000 3806 556b 5147 9713 ac10 .<Xr@.8.UkQG.... 0x0020: 000c a05a 075b 4633 b1c9 0000 0000 a002 ...Z.[F3........ 0x0030: 7210 a45e 0000 0204 0590 0402 080a 1f9f r..^............ 0x0040: ddec 0000 0000 0103 0307 ..........16:33:28.669001 IP MQTT.ibm-mqisdp >SUB.41050: Flags [S.], seq 1053629863, ack 1177792970, win 28960, options [mss 1460,sackOK,TS val 3885354501 ecr 530570732,nop,wscale 7], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 003c 0000 4000 4006 a645 ac10 000c 5147 .<..@.@..E....QG 0x0020: 9713 075b a05a 3ecd 1da7 4633 b1ca a012 ...[.Z>...F3.... 0x0030: 7120 9309 0000 0204 05b4 0402 080a e795 q............... 0x0040: ce05 1f9f ddec 0103 0307 ..........16:33:28.672229 IP SUB.41050 > MQTT.ibm-mqisdp: Flags [.], ack 1, win 229, options [nop,nop,TS val 530570735 ecr 3885354501], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 5873 4000 3806 5572 5147 9713 ac10 .4Xs@.8.UrQG.... 0x0020: 000c a05a 075b 4633 b1ca 3ecd 1da8 8010 ...Z.[F3..>..... 0x0030: 00e5 320e 0000 0101 080a 1f9f ddef e795 ..2............. 0x0040: ce05 ..16:33:28.672280 IP SUB.41050 > MQTT.ibm-mqisdp: Flags [P.], seq 1:42, ack 1, win 229, options [nop,nop,TS val 530570735 ecr 3885354501], length 41 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 005d 5874 4000 3806 5548 5147 9713 ac10 .]Xt@.8.UHQG.... 0x0020: 000c a05a 075b 4633 b1ca 3ecd 1da8 8018 ...Z.[F3..>..... 0x0030: 00e5 37b7 0000 0101 080a 1f9f ddef e795 ..7............. 0x0040: ce05 1027 0006 4d51 4973 6470 03c2 003c ...'..MQIsdp...< 0x0050: 0007 636c 6965 6e74 3100 0563 636e 6574 ..client1..ccnet 0x0060: 0009 6363 6e65 7430 3930 31 ..ccnet090116:33:28.672313 IP MQTT.ibm-mqisdp > SUB.41050: Flags [.], ack 42, win 227, options [nop,nop,TS val 3885354505 ecr 530570735], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0034 d3a1 4000 4006 d2ab ac10 000c 5147 .4..@.@.......QG 0x0020: 9713 075b a05a 3ecd 1da8 4633 b1f3 8010 ...[.Z>...F3.... 0x0030: 00e3 31e3 0000 0101 080a e795 ce09 1f9f ..1............. 0x0040: ddef ..16:33:28.672562 IP MQTT.ibm-mqisdp > SUB.41050: Flags [P.], seq 1:5, ack 42, win 227, options [nop,nop,TS val 3885354505 ecr 530570735], length 4 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0038 d3a2 4000 4006 d2a6 ac10 000c 5147 .8..@.@.......QG 0x0020: 9713 075b a05a 3ecd 1da8 4633 b1f3 8018 ...[.Z>...F3.... 0x0030: 00e3 11d5 0000 0101 080a e795 ce09 1f9f ................ 0x0040: ddef 2002 0000 ......16:33:28.675753 IP SUB.41050 > MQTT.ibm-mqisdp: Flags [.], ack 5, win 229, options [nop,nop,TS val 530570739 ecr 3885354505], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 5875 4000 3806 5570 5147 9713 ac10 .4Xu@.8.UpQG.... 0x0020: 000c a05a 075b 4633 b1f3 3ecd 1dac 8010 ...Z.[F3..>..... 0x0030: 00e5 31d9 0000 0101 080a 1f9f ddf3 e795 ..1............. 0x0040: ce09 ..16:33:28.675772 IP SUB.41050 > MQTT.ibm-mqisdp: Flags [P.], seq 42:56, ack 5, win 229, options [nop,nop,TS val 530570739 ecr 3885354505], length 14 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0042 5876 4000 3806 5561 5147 9713 ac10 .BXv@.8.UaQG.... 0x0020: 000c a05a 075b 4633 b1f3 3ecd 1dac 8018 ...Z.[F3..>..... 0x0030: 00e5 46b6 0000 0101 080a 1f9f ddf3 e795 ..F............. 0x0040: ce09 820c 0001 0007 6363 6e65 742f 2300 ........ccnet/#.16:33:28.675823 IP MQTT.ibm-mqisdp > SUB.41050: Flags [P.], seq 5:10, ack 56, win 227, options [nop,nop,TS val 3885354508 ecr 530570739], length 5 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0039 d3a3 4000 4006 d2a4 ac10 000c 5147 .9..@.@.......QG 0x0020: 9713 075b a05a 3ecd 1dac 4633 b201 8018 ...[.Z>...F3.... 0x0030: 00e3 a1b8 0000 0101 080a e795 ce0c 1f9f ................ 0x0040: ddf3 9003 0001 00 .......16:33:28.719501 IP SUB.41050 > MQTT.ibm-mqisdp: Flags [.], ack 10, win 229, options [nop,nop,TS val 530570783 ecr 3885354508], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 5877 4000 3806 556e 5147 9713 ac10 .4Xw@.8.UnQG.... 0x0020: 000c a05a 075b 4633 b201 3ecd 1db1 8010 ...Z.[F3..>..... 0x0030: 00e5 3197 0000 0101 080a 1f9f de1f e795 ..1............. 0x0040: ce0c ..
终止mosquitto_sub命令获得如下报文：=================================16:29:54.745664 IP 81.71.151.19.40510 > 172.16.0.12.ibm-mqisdp: Flags [F.], seq 58, ack 12, win 229, options [nop,nop,TS val 530356809 ecr 3885119146], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 e1fc 4000 3806 cbe8 5147 9713 ac10 .4..@.8...QG.... 0x0020: 000c 9e3e 075b 0e6c ea6f 989b b7f8 8011 ...>.[.l.o...... 0x0030: 00e5 1a34 0000 0101 080a 1f9c 9a49 e792 ...4.........I.. 0x0040: 36aa 6.16:29:54.745761 IP 172.16.0.12.ibm-mqisdp > 81.71.151.19.40510: Flags [F.], seq 12, ack 59, win 227, options [nop,nop,TS val 3885140578 ecr 530356809], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0034 fbe4 4000 4006 aa68 ac10 000c 5147 .4..@.@..h....QG 0x0020: 9713 075b 9e3e 989b b7f8 0e6c ea70 8011 ...[.>.....l.p.. 0x0030: 00e3 c67c 0000 0101 080a e792 8a62 1f9c ...|.........b.. 0x0040: 9a49 .I16:29:54.751445 IP 81.71.151.19.40510 > 172.16.0.12.ibm-mqisdp: Flags [.], ack 13, win 229, options [nop,nop,TS val 530356812 ecr 3885140578], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 e1fd 4000 3806 cbe7 5147 9713 ac10 .4..@.8...QG.... 0x0020: 000c 9e3e 075b 0e6c ea70 989b b7f9 8010 ...>.[.l.p...... 0x0030: 00e5 c677 0000 0101 080a 1f9c 9a4c e792 ...w.........L.. 0x0040: 8a62 .b
# 执行mosquitto_pub后得到的报文如下：16:36:40.721513 IP 81.71.151.19.41390 > 172.16.0.12.ibm-mqisdp: Flags [S], seq 2807988728, win 29200, options [mss 1424,sackOK,TS val 530762785 ecr 0,nop,wscale 7], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 003c 5dd0 4000 3806 500d 5147 9713 ac10 .<].@.8.P.QG.... 0x0020: 000c a1ae 075b a75e 81f8 0000 0000 a002 .....[.^........ 0x0030: 7210 8378 0000 0204 0590 0402 080a 1fa2 r..x............ 0x0040: cc21 0000 0000 0103 0307 .!........16:36:40.721585 IP 172.16.0.12.ibm-mqisdp > 81.71.151.19.41390: Flags [S.], seq 4236199326, ack 2807988729, win 28960, options [mss 1460,sackOK,TS val 3885546554 ecr 530762785,nop,wscale 7], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 003c 0000 4000 4006 a645 ac10 000c 5147 .<..@.@..E....QG 0x0020: 9713 075b a1ae fc7f 459e a75e 81f9 a012 ...[....E..^.... 0x0030: 7120 9e41 0000 0204 05b4 0402 080a e798 q..A............ 0x0040: bc3a 1fa2 cc21 0103 0307 .:...!....16:36:40.724732 IP 81.71.151.19.41390 > 172.16.0.12.ibm-mqisdp: Flags [.], ack 1, win 229, options [nop,nop,TS val 530762788 ecr 3885546554], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 5dd1 4000 3806 5014 5147 9713 ac10 .4].@.8.P.QG.... 0x0020: 000c a1ae 075b a75e 81f9 fc7f 459f 8010 .....[.^....E... 0x0030: 00e5 3d46 0000 0101 080a 1fa2 cc24 e798 ..=F.........$.. 0x0040: bc3a .:16:36:40.724750 IP PUB.41390 > MQTT.ibm-mqisdp: Flags [P.], seq 1:42, ack 1, win 229, options [nop,nop,TS val 530762788 ecr 3885546554], length 41 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 005d 5dd2 4000 3806 4fea 5147 9713 ac10 .]].@.8.O.QG.... 0x0020: 000c a1ae 075b a75e 81f9 fc7f 459f 8018 .....[.^....E... 0x0030: 00e5 40ef 0000 0101 080a 1fa2 cc24 e798 ..@..........$.. 0x0040: bc3a 1027 0006 4d51 4973 6470 03c2 003c .:.'..MQIsdp...< 0x0050: 0007 636c 6965 6e74 3300 0563 636e 6574 ..client3..ccnet 0x0060: 0009 6363 6e65 7430 3930 31 ..ccnet090116:36:40.724787 IP 172.16.0.12.ibm-mqisdp > 81.71.151.19.41390: Flags [.], ack 42, win 227, options [nop,nop,TS val 3885546557 ecr 530762788], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0034 f9a2 4000 4006 acaa ac10 000c 5147 .4..@.@.......QG 0x0020: 9713 075b a1ae fc7f 459f a75e 8222 8010 ...[....E..^.".. 0x0030: 00e3 3d1c 0000 0101 080a e798 bc3d 1fa2 ..=..........=.. 0x0040: cc24 .$16:36:40.724978 IP 172.16.0.12.ibm-mqisdp > 81.71.151.19.41390: Flags [P.], seq 1:5, ack 42, win 227, options [nop,nop,TS val 3885546557 ecr 530762788], length 4 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0038 f9a3 4000 4006 aca5 ac10 000c 5147 .8..@.@.......QG 0x0020: 9713 075b a1ae fc7f 459f a75e 8222 8018 ...[....E..^.".. 0x0030: 00e3 1d0e 0000 0101 080a e798 bc3d 1fa2 .............=.. 0x0040: cc24 2002 0000 .$....16:36:40.728114 IP 81.71.151.19.41390 > 172.16.0.12.ibm-mqisdp: Flags [.], ack 5, win 229, options [nop,nop,TS val 530762791 ecr 3885546557], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 5dd3 4000 3806 5012 5147 9713 ac10 .4].@.8.P.QG.... 0x0020: 000c a1ae 075b a75e 8222 fc7f 45a3 8010 .....[.^."..E... 0x0030: 00e5 3d13 0000 0101 080a 1fa2 cc27 e798 ..=..........'.. 0x0040: bc3d .=16:36:40.728144 IP PUB.41390 > MQTT.ibm-mqisdp: Flags [P.], seq 42:82, ack 5, win 229, options [nop,nop,TS val 530762791 ecr 3885546557], length 40 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 005c 5dd4 4000 3806 4fe9 5147 9713 ac10 .\].@.8.O.QG.... 0x0020: 000c a1ae 075b a75e 8222 fc7f 45a3 8018 .....[.^."..E... 0x0030: 00e5 a8af 0000 0101 080a 1fa2 cc27 e798 .............'.. 0x0040: bc3d 3026 0006 6363 6e65 742f 3132 3334 .=0&..ccnet/1234 0x0050: 3536 3738 3930 3132 3334 3536 3738 3930 5678901234567890 0x0060: 3132 3334 3536 3738 3930 123456789016:36:40.728146 IP 81.71.151.19.41390 > 172.16.0.12.ibm-mqisdp: Flags [FP.], seq 82:84, ack 5, win 229, options [nop,nop,TS val 530762791 ecr 3885546557], length 2 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0036 5dd5 4000 3806 500e 5147 9713 ac10 .6].@.8.P.QG.... 0x0020: 000c a1ae 075b a75e 824a fc7f 45a3 8019 .....[.^.J..E... 0x0030: 00e5 5cdf 0000 0101 080a 1fa2 cc27 e798 ..\..........'.. 0x0040: bc3d e000 .=..16:36:40.728230 IP MQTT.ibm-mqisdp > SUB.41050: Flags [P.], seq 96:136, ack 62, win 227, options [nop,nop,TS val 3885546560 ecr 530753903], length 40 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 005c d3a9 4000 4006 d27b ac10 000c 5147 .\..@.@..{....QG 0x0020: 9713 075b a05a 3ecd 1e07 4633 b207 8018 ...[.Z>...F3.... 0x0030: 00e3 e34f 0000 0101 080a e798 bc40 1fa2 ...O.........@.. 0x0040: a96f 3026 0006 6363 6e65 742f 3132 3334 .o0&..ccnet/1234 0x0050: 3536 3738 3930 3132 3334 3536 3738 3930 5678901234567890 0x0060: 3132 3334 3536 3738 3930 123456789016:36:40.728288 IP 172.16.0.12.ibm-mqisdp > 81.71.151.19.41390: Flags [.], ack 85, win 227, options [nop,nop,TS val 3885546561 ecr 530762791], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0034 f9a4 4000 4006 aca8 ac10 000c 5147 .4..@.@.......QG 0x0020: 9713 075b a1ae fc7f 45a3 a75e 824d 8010 ...[....E..^.M.. 0x0030: 00e3 3ce6 0000 0101 080a e798 bc41 1fa2 ..<..........A.. 0x0040: cc27 .'16:36:40.728367 IP 172.16.0.12.ibm-mqisdp > 81.71.151.19.41390: Flags [F.], seq 5, ack 85, win 227, options [nop,nop,TS val 3885546561 ecr 530762791], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0034 f9a5 4000 4006 aca7 ac10 000c 5147 .4..@.@.......QG 0x0020: 9713 075b a1ae fc7f 45a3 a75e 824d 8011 ...[....E..^.M.. 0x0030: 00e3 3ce5 0000 0101 080a e798 bc41 1fa2 ..<..........A.. 0x0040: cc27 .'16:36:40.731431 IP 81.71.151.19.41050 > 172.16.0.12.ibm-mqisdp: Flags [.], ack 136, win 229, options [nop,nop,TS val 530762794 ecr 3885546560], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 5880 4000 3806 5565 5147 9713 ac10 .4X.@.8.UeQG.... 0x0020: 000c a05a 075b 4633 b207 3ecd 1e2f 8010 ...Z.[F3..>../.. 0x0030: 00e5 54ce 0000 0101 080a 1fa2 cc2a e798 ..T..........*.. 0x0040: bc40 .@16:36:40.731575 IP 81.71.151.19.41390 > 172.16.0.12.ibm-mqisdp: Flags [.], ack 6, win 229, options [nop,nop,TS val 530762795 ecr 3885546561], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 0000 4000 3806 ade5 5147 9713 ac10 .4..@.8...QG.... 0x0020: 000c a1ae 075b a75e 824d fc7f 45a4 8010 .....[.^.M..E... 0x0030: 00e5 3cdf 0000 0101 080a 1fa2 cc2b e798 ..<..........+.. 0x0040: bc41 .A
去掉TCP握手和收报报文的常规交互，可知道MQTT订阅发布的完整时序如下：
MQTT发布订阅的实际交互时序图
可以看到AUHT、SUB、PUB、SEND_MESSAGE的报文非常精简，基本只是对必须传送的字段增加了两个字节的长度，因此其对带宽是非常节省的。
再分析下支持websockets时的通讯时序# 启动对9001端口的监视tcpdump -n -XX -i eth0 port 9001# 订阅指定主题的消息mosquitto_sub -h 172.16.0.12 -t "topic/#" -u user -P password -i "client1"
#编写一个基于websockets访问mqtt的页面，如下亲测通过； 点击init按钮<html><head><script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/paho-mqtt/1.0.2/mqttws31.js"></script></head><body><script>var mqtt;var host = '81.71.87.37';var port = 9001; // onConnect 事件function onConnect() {console.log('connected.');/*var raw_message = 'Hello World!';message = new Paho.MQTT.Message(raw_message);message.destinationName = 'ccnet/up/abc';console.log('sending message: ' + raw_message );mqtt.send(message);*/ // 订阅 download topicvar subOptions = {qos: 1,onSuccess: onSubscribe};mqtt.subscribe('ccnet/#', subOptions);}function onSend() {console.log('onSend.');var raw_message = 'Hello World!';message = new Paho.MQTT.Message(raw_message);message.destinationName = 'ccnet/up/abc';console.log('sending message: ' + raw_message );mqtt.send(message);} // 订阅主题成功事件function onSubscribe(context) {console.log('subscribe success');console.log(context);} // 连接失败事件function onFailure(message) {console.log('connect failed.');} // onMessageArrived 事件function onMessageArrived(message) {console.log('new message arrived...');console.log(message.payloadString);} // 建立 MQTT websocket 连接function MQTTconnect() {console.log('connecting to ' + host + ':' + port);mqtt = new Paho.MQTT.Client(host, port, 'clientid');var options = {timeout: 3,onSuccess: onConnect,onFailure: onFailure,userName: 'ccnet',password: 'ccnet0901',mqttVersion: 4};mqtt.onMessageArrived = onMessageArrived;mqtt.connect(options);}</script><input type="button" value="Init" onclick="javascript:MQTTconnect();"/> <input type="button" value="Send" onclick="javascript:onSend();"/></body></html>
# 发布消息到指定主题mosquitto_pub -h 172.16.0.12 -t "topic/" -u user -P password -i "client3" -m "1234567890123456789012345678901234567890"
TCPDUMP抓取的报文如下：
# 点击WEB页面上的Init按钮之后18:11:49.183098 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [S], seq 3659468570, win 64240, options [mss 1360,nop,wscale 8,nop,nop,sackOK], length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0034 7b4e 4000 7206 65a0 0e96 6cbb ac10 .4{N@.r.e...l... 0x0020: 000c c737 2329 da1f 0f1a 0000 0000 8002 ...7#).......... 0x0030: faf0 797b 0000 0204 0550 0103 0308 0101 ..y{.....P...... 0x0040: 0402 ..18:11:49.183188 IP 172.16.0.12.etlservicemgr > 14.150.108.187.50999: Flags [S.], seq 3730879023, ack 3659468571, win 29200, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0034 0000 4000 4006 1357 ac10 000c 0e96 .4..@.@..W...... 0x0020: 6cbb 2329 c737 de60 b22f da1f 0f1b 8012 l.#).7.`./...... 0x0030: 7210 7157 0000 0204 05b4 0101 0402 0103 r.qW............ 0x0040: 0307 ..18:11:49.223085 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [.], ack 1, win 515, length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0028 7b4f 4000 7206 65ab 0e96 6cbb ac10 .({O@.r.e...l... 0x0020: 000c c737 2329 da1f 0f1b de60 b230 5010 ...7#).....`.0P. 0x0030: 0203 2237 0000 .."7..18:11:49.247331 IP Browser.50999 > MQTT.etlservicemgr: Flags [P.], seq 1:511, ack 1, win 515, length 510 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0226 7b50 4000 7206 63ac 0e96 6cbb ac10 .&{P@.r.c...l... 0x0020: 000c c737 2329 da1f 0f1b de60 b230 5018 ...7#).....`.0P. 0x0030: 0203 d122 0000 4745 5420 2f6d 7174 7420 ..."..GET./mqtt. 0x0040: 4854 5450 2f31 2e31 0d0a 486f 7374 3a20 HTTP/1.1..Host:. 0x0050: 3831 2e37 312e 3837 2e33 373a 3930 3031 81.71.87.37:9001 0x0060: 0d0a 436f 6e6e 6563 7469 6f6e 3a20 5570 ..Connection:.Up 0x0070: 6772 6164 650d 0a50 7261 676d 613a 206e grade..Pragma:.n 0x0080: 6f2d 6361 6368 650d 0a43 6163 6865 2d43 o-cache..Cache-C 0x0090: 6f6e 7472 6f6c 3a20 6e6f 2d63 6163 6865 ontrol:.no-cache 0x00a0: 0d0a 5573 6572 2d41 6765 6e74 3a20 4d6f ..User-Agent:.Mo 0x00b0: 7a69 6c6c 612f 352e 3020 2857 696e 646f zilla/5.0.(Windo 0x00c0: 7773 204e 5420 3130 2e30 3b20 5769 6e36 ws.NT.10.0;.Win6 0x00d0: 343b 2078 3634 2920 4170 706c 6557 6562 4;.x64).AppleWeb 0x00e0: 4b69 742f 3533 372e 3336 2028 4b48 544d Kit/537.36.(KHTM 0x00f0: 4c2c 206c 696b 6520 4765 636b 6f29 2043 L,.like.Gecko).C 0x0100: 6872 6f6d 652f 3130 312e 302e 3439 3531 hrome/101.0.4951 0x0110: 2e36 3720 5361 6661 7269 2f35 3337 2e33 .67.Safari/537.3 0x0120: 360d 0a55 7067 7261 6465 3a20 7765 6273 6..Upgrade:.webs 0x0130: 6f63 6b65 740d 0a4f 7269 6769 6e3a 206e ocket..Origin:.n 0x0140: 756c 6c0d 0a53 6563 2d57 6562 536f 636b ull..Sec-WebSock 0x0150: 6574 2d56 6572 7369 6f6e 3a20 3133 0d0a et-Version:.13.. 0x0160: 4163 6365 7074 2d45 6e63 6f64 696e 673a Accept-Encoding: 0x0170: 2067 7a69 702c 2064 6566 6c61 7465 0d0a .gzip,.deflate.. 0x0180: 4163 6365 7074 2d4c 616e 6775 6167 653a Accept-Language: 0x0190: 207a 682d 434e 2c7a 683b 713d 302e 390d .zh-CN,zh;q=0.9. 0x01a0: 0a53 6563 2d57 6562 536f 636b 6574 2d4b .Sec-WebSocket-K 0x01b0: 6579 3a20 7938 796a 3756 7858 624b 576f ey:.y8yj7VxXbKWo 0x01c0: 4f45 6962 3248 7176 4b51 3d3d 0d0a 5365 OEib2HqvKQ==..Se 0x01d0: 632d 5765 6253 6f63 6b65 742d 4578 7465 c-WebSocket-Exte 0x01e0: 6e73 696f 6e73 3a20 7065 726d 6573 7361 nsions:.permessa 0x01f0: 6765 2d64 6566 6c61 7465 3b20 636c 6965 ge-deflate;.clie 0x0200: 6e74 5f6d 6178 5f77 696e 646f 775f 6269 nt_max_window_bi 0x0210: 7473 0d0a 5365 632d 5765 6253 6f63 6b65 ts..Sec-WebSocke 0x0220: 742d 5072 6f74 6f63 6f6c 3a20 6d71 7474 t-Protocol:.mqtt 0x0230: 0d0a 0d0a ....18:11:49.247360 IP 172.16.0.12.etlservicemgr > 14.150.108.187.50999: Flags [.], ack 511, win 237, length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010:电脑 0028 653f 4000 4006 ae23 ac10 000c 0e96 .(e?@.@..#...... 0x0020: 6cbb 2329 c737 de60 b230 da1f 1119 5010 l.#).7.`.0....P. 0x0030: 00ed 214f 0000 ..!O..18:11:49.323395 IP 172.16.0.12.etlservicemgr > 14.150.108.187.50999: Flags [P.], seq 1:160, ack 511, win 237, length 159 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 00c7 6540 4000 4006 ad83 ac10 000c 0e96 ..e@@.@......... 0x0020: 6cbb 2329 c737 de60 b230 da1f 1119 5018 l.#).7.`.0....P. 0x0030: 00ed df2c 0000 4854 5450 2f31 2e31 2031 ...,..HTTP/1.1.1 0x0040: 3031 2053 7769 7463 6869 6e67 2050 726f 01.Switching.Pro 0x0050: 746f 636f 6c73 0d0a 5570 6772 6164 653a tocols..Upgrade: 0x0060: 2057 6562 536f 636b 6574 0d0a 436f 6e6e .WebSocket..Conn 0x0070: 6563 7469 6f6e 3a20 5570 6772 6电脑164 650d ection:.Upgrade. 0x0080: 0a53 6563 2d57 6562 536f 636b 6574 2d41 .Sec-WebSocket-A 0x0090: 6363 6570 743a 204a 6845 6544 4534 6468 ccept:.JhEeDE4dh 0x00a0: 6462 2b4b 6a47 4f52 452b 595a 7176 424b db+KjGORE+YZqvBK 0x00b0: 2f34 3d0d 0a53 6563 2d57 6562 536f 636b /4=..Sec-WebSock 0x00c0: 6574 2d50 726f 746f 636f 6c3a 206d 7174 et-Protocol:.mqt 0x00d0: 740d 0a0d 0a t....18:11:49.392070 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [P.], seq 511:557, ack 160, win 514, length 46 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0056 7b54 4000 7206 6578 0e96 6cbb ac10 .V{T@.r.ex..l... 0x0020: 000c c737 2329 da1f 1119 de60 b2cf 5018 ...7#).....`..P. 0x0030: 0202 7640 0000 82a8 a399 adbd b3bf adb9 ..v@............ 电脑 0x0040: eec8 f9e9 a75b ad81 a391 ced1 cafc c3c9 .....[.......... 0x0050: cafd adb8 c0fa c3d8 d799 a4de c0f7 c8c9 ................ 0x0060: 93a0 9d8c ....18:11:49.392100 IP 172.16.0.12.etlservicemgr > 14.150.108.187.50999: Flags [.], ack 557, win 237, length 0 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0028 6541 4000 4006 ae21 ac10 000c 0e96 .(eA@.@..!...... 0x0020: 6cbb 2329 c737 de60 b2cf da1f 1147 5010 l.#).7.`.....GP. 0x0030: 00ed 2082 0000 ......18:11:49.392352 IP 172.16.0.12.etlservicemgr > 14.150.108.187.50999: Flags [P.], seq 160:166, ack 557, win 237, length 6 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 002e 6542 4000 4006 ae1a ac10 000c 0e96 ..eB@.@......... 0x0020: 6cbb 2329 c737 de60 b2cf da1f 1147 5018 l.#).7.`.....GP. 0x0030: 00ed 7e6d 0000 8204 2002 00电脑00 ..~m........18:11:49.443110 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [.], ack 166, win 514, length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0028 7b56 4000 7206 65a4 0e96 6cbb ac10 .({V@.r.e...l... 0x0020: 000c c737 2329 da1f 1147 de60 b2d5 5010 ...7#)...G.`..P. 0x0030: 0202 1f67 0000 ...g..18:11:49.451571 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [P.], seq 557:577, ack 166, win 514, length 20 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 003c 7b57 4000 7206 658f 0e96 6cbb ac10 .<{W@.r.e...l... 0x0020: 000c c737 2329 da1f 1147 de60 b2d5 5018 ...7#)...G.`..P. 0x0030: 0202 5568 0000 828e 2670 37fd a47c 37fc ..Uh....&p7..|7. 0x0040: 2677 549e 4815 43d2 0571 &wT.H.C..q18:11:49.451667 IP 172.16.0.12.etlservicemgr > 14.150.108.187.50999: Flags [P.], seq 166:173, ack 577, win 237, length 7 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 002f 6543 4000 4006 ae18 ac10 000c 0e96 ./eC@.@......... 0x0020: 6cbb 2329 c737 de60 b2d5 da1f 115b 5018 l.#).7.`.....[P. 0x0030: 00ed 0d4f 0000 8205 9003 0001 01 ...O.........18:11:49.543376 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [.], ack 173, win 514, length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0028 7b59 4000 7206 65a1 0e96 6cbb ac10 .({Y@.r.e...l... 0x0020: 000c c737 2329 da1f 115b de60 b2dc 5010 ...7#)...[.`..P. 0x0030: 0202 1f4c 0000 ...L..# 点击Send按钮之后18:16:59.642995 IP Browser.50999 > MQTT.etlservicemgr: Flags [P.], seq 677:711, ack 249, win 514, length 34 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 004a 7c2e 4000 7206 64aa 0e96 6cbb ac10 .J|.@.r.d...l... 0x0020: 000c c737 2329 da1f 11bf de60 b328 5018 ...7#).....`.(P. 0x0030: 0202 736b 0000 829c 69c7 926a 59dd 9266 ..sk....i..jY..f 0x0040: 0aa4 fc0f 1de8 e71a 46a6 f009 21a2 fe06 ........F...!... 0x0050: 06e7 c505 1bab f64b .......K18:16:59.643148 IP MQTT.etlservicemgr > Browser.50999: Flags [P.], seq 249:279, ack 711, win 237, length 30 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0046 654b 4000 4006 adf9 ac10 000c 0e96 .FeK@.@......... 0x0020: 6cbb 2329 c737 de60 b328 da1f 11e1 5018 l.#).7.`.(....P. 0x0030: 00ed ce09 0000 821c 301a 000c 6363 6e65 ........0...ccne 0x0040: 742f 7570 2f61 6263 4865 6c6c 6f20 576f t/up/abcHello.Wo 0x0050: 726c 6421 rld!18:16:59.743220 IP 14.150.108.187.50999 > 172.16.0.12.etlservicemgr: Flags [.], ack 279, win 514, length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0028 7c30 4000 7206 64ca 0e96 6cbb ac10 .(|0@.r.d...l... 0x0020: 000c c737 2329 da1f 11e1 de60 b346 5010 ...7#).....`.FP. 0x0030: 0202 1e5c 0000 ...\..
# 执行发布消息命令之后17:56:50.992944 IP MQTT.etlservicemgr > Browser.50939: Flags [P.], seq 205:247, ack 675, win 237, length 42 0x0000: feee 809f 3247 5254 00e4 a55c 0800 4500 ....2GRT...\..E. 0x0010: 0052 e2f9 4000 4006 303f ac10 000c 0e96 .R..@.@.0?...... 0x0020: 6cbb 2329 c6fb c3b7 103a 2e40 d9e6 5018 l.#).....:.@..P. 0x0030: 00ed aaae 0000 8228 3026 0006 6363 6e65 .......(0&..ccne 0x0040: 742f 3132 3334 3536 3738 3930 3132 3334 t/12345678901234 0x0050: 3536 3738 3930 3132 3334 3536 3738 3930 567890123456789017:56:51.100524 IP 14.150.108.187.50939 > 172.16.0.12.etlservicemgr: Flags [.], ack 247, win 514, length 0 0x0000: 5254 00e4 a55c feee 809f 3247 0800 4568 RT...\....2G..Eh 0x0010: 0028 77db 4000 7206 691f 0e96 6cbb ac10 .(w.@.r.i...l... 0x0020: 000c c6fb 2329 2e40 d9e6 c3b7 1064 5010 ....#).@.....dP. 0x0030: 0202 bffd 0000 ......
可看到基于websockets的通讯整体协作图如下：
MQTT在websockets下的工作模
可以看到除了在建立websockets时，有较大的http头信息，其余仍然很精简。而且websocket已经对Browser上送的AUTH、SUB、PUB进行了加密处理，但是对于下发到Browser的信息并没有进行加密处理
使用Mosquitto搭建支持Websockets的MQTT服务这里使用了mosquitto-2.0.11，下载源码后，修改下config.mk文件，将WITH_WEBSOCKETS打开，如下
# Build with websockets support on the broker.WITH_WEBSOCKETS:=yes
这里是在centos下工作的，如果没有websockets库，需要安装
yum install libwebsockets* -y
然后就是一路的make，make install，之后配置下LD_LIBRARY_PATH的环境变量，就可以开始工作了。
LD_LIBRARY_PATH=:/root/setup/mosquitto-2.0.11/lib:/root/setup/cJSON-1.7.14
配置mosquitto环境，可建立一个专门的目录，将mosquitto.conf文件拷贝过来修改，目录结构如下：
<root@VM-0-12-centos:/mqtt>tree.|-- aclfile # 访问控制文件|-- log # 日志文件目录| `-- mosquitto.log|-- mosquitto # mqtt运行目录| |-- mosquitto.db| `-- pid.pid|-- mosquitto.conf #配置文件！！！IMPORTANT`-- pwfile # 用户的密码文件
#cat aclfile ===========================================================# This affects access control for clients with no username.topic read $SYS/## This only affects clients with username "roger".user rogertopic foo/bar# This affects all clients.pattern write $SYS/broker/connection/%c/state# Add 20210722user ccnettopic read ccnet/#topic write ccnet/#=========================================================# 创建用户密码文件pwfiletouch pwfilemosquitto_passwd pwfile user#cat mosquitto.conf |grep -v "#"=========================================================pid_file /home/release/soft/mqtt/mosquitto/pid.piduser releaseport 1883listener 9001protocol websocketsbind_interface eth0persistence true persistence_location /home/release/soft/mqtt/mosquittoallow_anonymous falsepassword_file /home/release/soft/mqtt/pwfile acl_file /home/release/soft/mqtt/aclfile
运行Mosquitto
mosquitto -c mosquitto.conf -d
MQTT有很多实现，Mosquitto的魅力在于小而美。有很多开源的实现，基于nodejs、java等，也有商业版本的，更有一些云服务商直接将之PaaS化了。
例如，阿里云将MQTT定义为这样子。一些公司直接基于mqtt搭建其上的物模型，超赞！
阿里云的MQTT服务
电脑 电脑