This is the third of the future of machines 34 An article

The original address ：http://t.csdn.cn/DwLgX

1. The theme Topic

The topic level separator is used to introduce the structure into the topic name . If there is , It divides the topic name into multiple “ Subject level ”.

give an example ： Valve status data topic ：/topic/valve/state

Topic filters for subscriptions can contain special wildcards , Allows you to subscribe to more than one topic at a time .

Wildcards can be used in topic filters , But not in the subject name [MQTT-4.7.1-1] Use in

1.1 Topic level separator

• Forward slash (‘/’ U+002F) Used to separate each level in the topic tree , And provide a hierarchy for topic names .
• The topic level separator can appear anywhere in the topic filter or topic name .

topicName:/topic/valve/upload
topicFilter:/topic/valve/#

• Adjacent topic level separator （2 A continuous ’/'） Indicates zero length topic level .

topicName:/topic/valve//control

1.2. Multi level wildcards #

• Number symbols (‘#’ U+0023) It's a wildcard , You can match any number of levels in the topic . Multi level wildcards represent parents and any number of children .
• Multi level wildcards must Specified separately Or in the After the topic level separator Appoint .
• In any case , It must be a topic filter [MQTT-4.7.1-2] Specified in the The last character
  give an example ：
  • List of topics
    • sport/tennis/player1
    • sport/tennis/player1/ranking
    • sport/tennis/player1/score/wimbledon

1.3 Single level wildcards +

plus (‘+’ U+002B) It's a wildcard , Match only one topic level .

• Where it is used , it Must occupy the entire level of the filter
• Multiple levels in the topic filter use , And can be used with multi-level wildcards
  give an example ：
  • List of topics
    • sport/tennis/player1
    • sport/tennis/player1/ranking
    • sport/tennis/player1/score/wimbledon

1.4 $ The special theme at the beginning

• Multi level wildcards # And single level wildcards + Cannot match to $ The special theme at the beginning ;
• $Special\; topics\; at\; the\; beginning\; are\; often\; used\; for\; special\; control\; purposes\; ,\; for\; example$SYS/, The client cannot be defined with $ The subject at the beginning
• If the client needs to subscribe $The\; subject\; at\; the\; beginning\; ,\; Need\; a\; separate\; subscription$ The theme , Usage is as follows ：
  • for example $The\; name\; of\; the\; topic\; is\; ：$SYS/monitor/Clients, Then the client subscription topic filter can be set to ： $SYS/monitor/+ or $SYS/monitor/#
• The client wants to receive from $SYS/ Start with a theme that doesn't start with $ The message of the beginning topic , It must also subscribe to “#” and “$SYS/#”

1.5 Subject grammar

• All topic names and topic filters must be at least one character long [MQTT-4.7.3-1], Subject rating identifier ’/' Also accounted for 1 Bytes
• Topic name and topic filter Case sensitive
• Topic names and topic filters can Include spaces character
• Lead or follow “/” Create different topic names or topic filters
  • topic and /topic、topic and topic/ Neither pair has the same subject name
• Contains only “/” The subject name or subject filter of the character is valid
• Topic names and topic filters must not contain empty characters (Unicode U+0000) [ Unicode ] [MQTT-4.7.3-2]
• The topic name and topic filter are UTF-8 Encoded string , Their code must not exceed 65535 byte [MQTT-4.7.3-3]. See the first 1.5.3 section

2. Error handling

Unless otherwise stated , If the server or client encounters Agreement violations , It must close the network connection it receives the control packet that causes the protocol violation [MQTT-4.8.0-1].

Client or server implementations may encounter problems that prevent successful processing MQTT Transient error of packet （ For example, if the internal buffer is full ）.

If the client or server is Process inbound control packets Transient error encountered while , It must close the network connection that receives the control packet [MQTT-4.8.0-2]. If the server detects a transient error , It should not disconnect or have any other impact on its interaction with any other client

《MQTT Quick start series 》 Fast navigation ：

• 【MQTT From getting started to improving series | 01】 from 0 To 1 Quickly build MQTT Test environment
• 【MQTT From getting started to improving series | 02】MQTT3.1.1TLS The encrypted
• 【MQTT From getting started to improving series | 03】 One article mastery MQTT3.1.1 Agreement framework
• 【MQTT From getting started to improving series | 04】MQTT Application Protocol CONNECT
• 【MQTT From getting started to improving series | 05】MQTT3.1.1 And PUBLISH Publish workflow
• 【MQTT From getting started to improving series | 06】MQTT3.1.1 And SUBSCRIBE Subscription workflow
• 【MQTT From getting started to improving series | 07】MQTT3.1.1 Link keep alive and disconnect

Write at the end ：

• Blog profile ： focus AIoT field , Chasing the pulse of the future era , Record the technological growth on the way ！
• Column Introduction ： from 0 To 1 master MQTT Distributed protocol .
• Face the crowd ： Zero basic programming enthusiast
• Column plan ： Next, we will gradually publish a series of blog posts into artificial intelligence , Coming soon
  • Python Zero foundation quick start series
  • Quick start Python Data Science Series
  • Artificial intelligence development environment building series
  • Machine learning series
  • Object detection quick start series
  • Automatic driving object detection series
  • …