MQTT AT Commands

[中文]

• Introduction

• AT+MQTTUSERCFG: Set MQTT user configuration

• AT+MQTTLONGCLIENTID: Set MQTT client ID

• AT+MQTTLONGUSERNAME: Set MQTT username

• AT+MQTTLONGPASSWORD: Set MQTT password

• AT+MQTTCONNCFG: Set configuration of MQTT connection

• AT+MQTTALPN: Set MQTT Application Layer Protocol Negotiation (ALPN)

• AT+MQTTSNI: Set MQTT Server Name Indication (SNI)

• AT+MQTTCONN: Connect to MQTT Brokers

• AT+MQTTPUB: Publish MQTT Messages in string

• AT+MQTTPUBRAW: Publish long MQTT messages

• AT+MQTTSUB: Subscribe to MQTT topics

• AT+MQTTUNSUB: Unsubscribe from MQTT topics

• AT+MQTTCLEAN: Close MQTT connections

• MQTT AT Error Codes

• MQTT AT Notes

Introduction

Important

The default AT firmware supports all the AT commands mentioned on this page. If you don’t need ESP32 to support MQTT commands, you can compile the ESP-AT project by following the steps in Compile ESP-AT Project Locally documentation. In the project configuration during the fifth step, make the following selections:

• Disable Component config -> AT -> AT MQTT command support

AT+MQTTUSERCFG: Set MQTT User Configuration

Set Command

Function:

Set MQTT User Configuration.

Command:

AT+MQTTUSERCFG=<LinkID>,<scheme>,<"client_id">,<"username">,<"password">,<cert_key_ID>,<CA_ID>,<"path">

Response:

OK

Parameters

• <LinkID>: currently only supports link ID 0.

• <scheme>:

  • 1: MQTT over TCP.

  • 2: MQTT over TLS (no certificate verify).

  • 3: MQTT over TLS (verify server certificate).

  • 4: MQTT over TLS (provide client certificate).

  • 5: MQTT over TLS (verify server certificate and provide client certificate).

  • 6: MQTT over WebSocket (based on TCP).

  • 7: MQTT over WebSocket Secure (based on TLS, no certificate verify).

  • 8: MQTT over WebSocket Secure (based on TLS, verify server certificate).

  • 9: MQTT over WebSocket Secure (based on TLS, provide client certificate).

  • 10: MQTT over WebSocket Secure (based on TLS, verify server certificate and provide client certificate).

• <client_id>: MQTT client ID. Maximum length: 256 bytes.

• <username>: the username to login to the MQTT broker. Maximum length: 64 bytes.

• <password>: the password to login to the MQTT broker. Maximum length: 64 bytes.

• <cert_key_ID>: certificate ID. Currently, ESP-AT only supports one certificate for ID 0.

• <CA_ID>: CA ID. Currently, ESP-AT only supports one CA for ID 0.

• <path>: the path of the resource. Maximum length: 32 bytes.

Note

• The length of the entire AT command should be less than 256 bytes.

• If <scheme> is configured to 3, 5, 8, or 10, in order to check the server certificate validity period, please make sure ESP32 has obtained the current time before sending the AT+MQTTCONN command. (You can send AT+CIPSNTPCFG command to configure SNTP and obtain the current time, and send AT+CIPSNPTIME? command to query the current time.)

AT+MQTTLONGCLIENTID: Set MQTT Client ID

Set Command

Function:

Set MQTT Client ID.

Command:

AT+MQTTLONGCLIENTID=<LinkID>,<length>

Response:

OK

>

This response indicates that AT is ready for receiving MQTT Client ID. You should enter the Client ID, and when the Client ID length reaches the <length> value, the system returns:

OK

Parameters

• <LinkID>: currently only supports link ID 0.

• <length>: MQTT client ID length. Range: [1,1024].

Notes

• The command AT+MQTTUSERCFG can also set MQTT client ID. The differences between the two commands include:

  • You can use AT+MQTTLONGCLIENTID to set a relatively long client ID since there is a limitation on the length of the AT+MQTTUSERCFG command.

  • You should set AT+MQTTLONGCLIENTID after setting the AT+MQTTUSERCFG command.

AT+MQTTLONGUSERNAME: Set MQTT Username

Set Command

Function:

Set MQTT username.

Command:

AT+MQTTLONGUSERNAME=<LinkID>,<length>

Response:

OK

>

This response indicates that AT is ready for receiving MQTT username. You should enter the MQTT username, and when the MQTT username length reaches the <length> value, the system returns:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <length>: MQTT username length. Range: [1,1024].

Notes

• The command AT+MQTTUSERCFG can also set MQTT username. The differences between the two commands include:

  • You can use AT+MQTTLONGUSERNAME to set a relatively long username since there is a limitation on the length of the AT+MQTTUSERCFG command.

  • You should set AT+MQTTLONGUSERNAME after setting the command AT+MQTTUSERCFG.

AT+MQTTLONGPASSWORD: Set MQTT Password

Set Command

Function:

Set MQTT password.

Command:

AT+MQTTLONGPASSWORD=<LinkID>,<length>

Response:

OK

>

This response indicates that AT is ready for receiving MQTT password. You should enter the MQTT password, and when the MQTT password length reaches the <length> value, the system returns:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <length>: MQTT password length. Range: [1,1024].

Notes

• The command AT+MQTTUSERCFG can also set MQTT password. The differences between the two commands include:

  • You can use AT+MQTTLONGPASSWORD to set a relatively long password since there is a limitation on the length of the AT+MQTTUSERCFG command.

  • You should set AT+MQTTLONGPASSWORD after setting the command AT+MQTTUSERCFG.

AT+MQTTCONNCFG: Set Configuration of MQTT Connection

Set Command

Function:

Set configuration of MQTT Connection.

Command:

AT+MQTTCONNCFG=<LinkID>,<keepalive>,<disable_clean_session>,<"lwt_topic">,<"lwt_msg">,<lwt_qos>,<lwt_retain>

Response:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <keepalive>: timeout of MQTT ping. Unit: second. Range [0,7200]. The default value is 0, which will be force-changed to 120 s.

• <disable_clean_session>: set MQTT clean session. For more details about this parameter, please refer to the section Clean Session in MQTT Version 3.1.1.

  • 0: enable clean session.

  • 1: disable clean session.

• <lwt_topic>: LWT (Last Will and Testament) message topic. Maximum length: 128 bytes.

• <lwt_msg>: LWT message. Maximum length: 128 bytes.

• <lwt_qos>: LWT QoS, which can be set to 0, 1, or 2. Default: 0.

• <lwt_retain>: LWT retain, which can be set to 0 or 1. Default: 0.

AT+MQTTALPN: Set MQTT Application Layer Protocol Negotiation (ALPN)

Set Command

Function:

Set MQTT Application Layer Protocol Negotiation (ALPN).

Command:

AT+MQTTALPN=<LinkID>,<alpn_counts>[,<"alpn">][,<"alpn">][,<"alpn">]

Response:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <alpn_counts>: the number of <”alpn”> parameters. Range: [0,5].

• 0: clean the MQTT ALPN configuration.

• [1,5]: set the MQTT ALPN configuration.

• <”alpn”>: you can send more than one ALPN in ClientHello to the server.

Notes

• The length of the entire AT command should be less than 256 bytes.

• MQTT ALPN will be effective only if the MQTT connection is based on TLS or WSS.

• You should set AT+MQTTALPN after setting the command AT+MQTTUSERCFG.

Example

AT+CWMODE=1
AT+CWJAP="ssid","password"
AT+CIPSNTPCFG=1,8,"ntp1.aliyun.com","ntp2.aliyun.com"
AT+MQTTUSERCFG=0,5,"ESP32","espressif","1234567890",0,0,""
AT+MQTTALPN=0,2,"mqtt-ca.cn","mqtt-ca.us"
AT+MQTTCONN=0,"192.168.200.2",8883,1

AT+MQTTSNI: Set MQTT Server Name Indication (SNI)

Set Command

Function:

Set MQTT Server Name Indication (SNI).

Command:

AT+MQTTSNI=<LinkID>,<"sni">

Response:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <”sni”>: MQTT Server Name Indication. You can send it in ClientHello to the server.

Notes

• The length of the entire AT command should be less than 256 bytes.

• MQTT SNI will be effective only if the MQTT connection is based on TLS or WSS.

• You should set AT+MQTTSNI after setting the command AT+MQTTUSERCFG.

Example

AT+CWMODE=1
AT+CWJAP="ssid","password"
AT+CIPSNTPCFG=1,8,"ntp1.aliyun.com","ntp2.aliyun.com"
AT+MQTTUSERCFG=0,5,"ESP32","espressif","1234567890",0,0,""
AT+MQTTSNI=0,"my_specific_prefix.iot.my_aws_region.amazonaws.com"
AT+MQTTCONN=0,"my_specific_prefix.iot.my_aws_region.amazonaws.com",8883,1

AT+MQTTCONN: Connect to MQTT Brokers

Query Command

Function:

Query the MQTT broker that ESP32 are connected to.

Command:

AT+MQTTCONN?

Response:

+MQTTCONN:<LinkID>,<state>,<scheme><"host">,<port>,<"path">,<reconnect>
OK

Set Command

Function:

Connect to an MQTT broker.

Command:

AT+MQTTCONN=<LinkID>,<"host">,<port>,<reconnect>

Response:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <host>: MQTT broker domain. Maximum length: 128 bytes.

• <port>: MQTT broker port. Maximum: port 65535.

• <path>: path. Maximum length: 32 bytes.

• <reconnect>:

  • 0: MQTT will not reconnect automatically. If MQTT connection established and then disconnected, you cannot use this command to reestablish MQTT connection. Please send AT+MQTTCLEAN=0 command to clean MQTT connection first, reconfigure the connection parameters, and then establish a new MQTT connection.

  • 1: MQTT will reconnect automatically. It takes more resources.

• <state>: MQTT state.

  • 0: MQTT uninitialized.

  • 1: already set AT+MQTTUSERCFG.

  • 2: already set AT+MQTTCONNCFG.

  • 3: connection disconnected.

  • 4: connection established.

  • 5: connected, but did not subscribe to any topic.

  • 6: connected, and subscribed to MQTT topics.

• <scheme>:

  • 1: MQTT over TCP.

  • 2: MQTT over TLS (no certificate verify).

  • 3: MQTT over TLS (verify server certificate).

  • 4: MQTT over TLS (provide client certificate).

  • 5: MQTT over TLS (verify server certificate and provide client certificate).

  • 6: MQTT over WebSocket (based on TCP).

  • 7: MQTT over WebSocket Secure (based on TLS, verify no certificate).

  • 8: MQTT over WebSocket Secure (based on TLS, verify server certificate).

  • 9: MQTT over WebSocket Secure (based on TLS, provide client certificate).

  • 10: MQTT over WebSocket Secure (based on TLS, verify server certificate and provide client certificate).

AT+MQTTPUB: Publish MQTT Messages in String

Set Command

Function:

Publish MQTT messages in string to a defined topic. If the amount of data you publish is relatively large, and the length of a single AT command has exceeded the threshold of 256, please use the AT+MQTTPUBRAW command.

Command:

AT+MQTTPUB=<LinkID>,<"topic">,<"data">,<qos>,<retain>

Response:

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <topic>: MQTT topic. Maximum length: 128 bytes.

• <data>: MQTT message in string.

• <qos>: QoS of message, which can be set to 0, 1, or 2. Default: 0.

• <retain>: retain flag.

Notes

• The length of the entire AT command should be less than 256 bytes.

• This command cannot send data \0. If you need to send \0, please use the command AT+MQTTPUBRAW instead.

Example

AT+CWMODE=1
AT+CWJAP="ssid","password"
AT+MQTTUSERCFG=0,1,"ESP32","espressif","1234567890",0,0,""
AT+MQTTCONN=0,"192.168.10.234",1883,0
AT+MQTTPUB=0,"topic","\"{\"timestamp\":\"20201121085253\"}\"",0,0  // When sending this command, please pay attention to whether special characters need to be escaped.

AT+MQTTPUBRAW: Publish Long MQTT Messages

Set Command

Function:

Publish long MQTT messages to a defined topic. If the amount of data you publish is relatively small, and the length of a single AT command is not greater than the threshold of 256, you also can use the AT+MQTTPUB command.

Command:

AT+MQTTPUBRAW=<LinkID>,<"topic">,<length>,<qos>,<retain>

Response:

OK
>

The symbol > indicates that AT is ready for receiving serial data, and you can enter the data now. When the requirement of message length determined by the parameter <length> is met, the transmission starts.

If the transmission is successful, AT returns:

+MQTTPUB:OK

Otherwise, it returns:

+MQTTPUB:FAIL

Parameters

• <LinkID>: only supports link ID 0 currently.

• <topic>: MQTT topic. Maximum length: 128 bytes.

• <length>: length of MQTT message. The maximum length is limited by available memory.

• <qos>: QoS of the published message, which can be set to 0, 1, or 2. Default is 0.

• <retain>: retain flag.

AT+MQTTSUB: Subscribe to MQTT Topics

Query Command

Function:

List all MQTT topics that have been already subscribed.

Command:

AT+MQTTSUB?

Response:

+MQTTSUB:<LinkID>,<state>,<"topic1">,<qos>
+MQTTSUB:<LinkID>,<state>,<"topic2">,<qos>
+MQTTSUB:<LinkID>,<state>,<"topic3">,<qos>
...
OK

Set Command

Function:

Subscribe to defined MQTT topics with defined QoS. Multiple topics are available for subscription (up to 10 topics can be subscribed).

Command:

AT+MQTTSUB=<LinkID>,<"topic">,<qos>

Response:

OK

When AT receives MQTT messages of the subscribed topic, it will prompt:

+MQTTSUBRECV:<LinkID>,<"topic">,<data_length>,data

If the topic has been subscribed before, it will prompt:

ALREADY SUBSCRIBE

Parameters

• <LinkID>: only supports link ID 0 currently.

• <state>: MQTT state.

  • 0: MQTT uninitialized.

  • 1: already set AT+MQTTUSERCFG.

  • 2: already set AT+MQTTCONNCFG.

  • 3: connection disconnected.

  • 4: connection established.

  • 5: connected, but subscribe to no topic.

  • 6: connected, and subscribed to MQTT topics.

• <topic>: the topic that is subscribed to.

• <qos>: the QoS that is subscribed to.

AT+MQTTUNSUB: Unsubscribe from MQTT Topics

Set Command

Function:

Unsubscribe the client from defined topics. This command can be called multiple times to unsubscribe from different topics.

Command:

AT+MQTTUNSUB=<LinkID>,<"topic">

Response:

OK

If the topic has not been subscribed, AT will prompt:

NO UNSUBSCRIBE

OK

Parameters

• <LinkID>: only supports link ID 0 currently.

• <topic>: MQTT topic. Maximum length: 128 bytes.

AT+MQTTCLEAN: Close MQTT Connections

Set Command

Function:

Close the MQTT connection and release the resource.

Command:

AT+MQTTCLEAN=<LinkID>

Response:

OK

Parameter

• <LinkID>: only supports link ID 0 currently.

MQTT AT Error Codes

The MQTT Error code will be prompted as ERR CODE:0x<%08x>.

Error Type	Error Code
AT_MQTT_NO_CONFIGURED	0x6001
AT_MQTT_NOT_IN_CONFIGURED_STATE	0x6002
AT_MQTT_UNINITIATED_OR_ALREADY_CLEAN	0x6003
AT_MQTT_ALREADY_CONNECTED	0x6004
AT_MQTT_MALLOC_FAILED	0x6005
AT_MQTT_NULL_LINK	0x6006
AT_MQTT_NULL_PARAMTER	0x6007
AT_MQTT_PARAMETER_COUNTS_IS_WRONG	0x6008
AT_MQTT_TLS_CONFIG_ERROR	0x6009
AT_MQTT_PARAM_PREPARE_ERROR	0x600A
AT_MQTT_CLIENT_START_FAILED	0x600B
AT_MQTT_CLIENT_PUBLISH_FAILED	0x600C
AT_MQTT_CLIENT_SUBSCRIBE_FAILED	0x600D
AT_MQTT_CLIENT_UNSUBSCRIBE_FAILED	0x600E
AT_MQTT_CLIENT_DISCONNECT_FAILED	0x600F
AT_MQTT_LINK_ID_READ_FAILED	0x6010
AT_MQTT_LINK_ID_VALUE_IS_WRONG	0x6011
AT_MQTT_SCHEME_READ_FAILED	0x6012
AT_MQTT_SCHEME_VALUE_IS_WRONG	0x6013
AT_MQTT_CLIENT_ID_READ_FAILED	0x6014
AT_MQTT_CLIENT_ID_IS_NULL	0x6015
AT_MQTT_CLIENT_ID_IS_OVERLENGTH	0x6016
AT_MQTT_USERNAME_READ_FAILED	0x6017
AT_MQTT_USERNAME_IS_NULL	0x6018
AT_MQTT_USERNAME_IS_OVERLENGTH	0x6019
AT_MQTT_PASSWORD_READ_FAILED	0x601A
AT_MQTT_PASSWORD_IS_NULL	0x601B
AT_MQTT_PASSWORD_IS_OVERLENGTH	0x601C
AT_MQTT_CERT_KEY_ID_READ_FAILED	0x601D
AT_MQTT_CERT_KEY_ID_VALUE_IS_WRONG	0x601E
AT_MQTT_CA_ID_READ_FAILED	0x601F
AT_MQTT_CA_ID_VALUE_IS_WRONG	0x6020
AT_MQTT_CA_LENGTH_ERROR	0x6021
AT_MQTT_CA_READ_FAILED	0x6022
AT_MQTT_CERT_LENGTH_ERROR	0x6023
AT_MQTT_CERT_READ_FAILED	0x6024
AT_MQTT_KEY_LENGTH_ERROR	0x6025
AT_MQTT_KEY_READ_FAILED	0x6026
AT_MQTT_PATH_READ_FAILED	0x6027
AT_MQTT_PATH_IS_NULL	0x6028
AT_MQTT_PATH_IS_OVERLENGTH	0x6029
AT_MQTT_VERSION_READ_FAILED	0x602A
AT_MQTT_KEEPALIVE_READ_FAILED	0x602B
AT_MQTT_KEEPALIVE_IS_NULL	0x602C
AT_MQTT_KEEPALIVE_VALUE_IS_WRONG	0x602D
AT_MQTT_DISABLE_CLEAN_SESSION_READ_FAILED	0x602E
AT_MQTT_DISABLE_CLEAN_SESSION_VALUE_IS_WRONG	0x602F
AT_MQTT_LWT_TOPIC_READ_FAILED	0x6030
AT_MQTT_LWT_TOPIC_IS_NULL	0x6031
AT_MQTT_LWT_TOPIC_IS_OVERLENGTH	0x6032
AT_MQTT_LWT_MSG_READ_FAILED	0x6033
AT_MQTT_LWT_MSG_IS_NULL	0x6034
AT_MQTT_LWT_MSG_IS_OVERLENGTH	0x6035
AT_MQTT_LWT_QOS_READ_FAILED	0x6036
AT_MQTT_LWT_QOS_VALUE_IS_WRONG	0x6037
AT_MQTT_LWT_RETAIN_READ_FAILED	0x6038
AT_MQTT_LWT_RETAIN_VALUE_IS_WRONG	0x6039
AT_MQTT_HOST_READ_FAILED	0x603A
AT_MQTT_HOST_IS_NULL	0x603B
AT_MQTT_HOST_IS_OVERLENGTH	0x603C
AT_MQTT_PORT_READ_FAILED	0x603D
AT_MQTT_PORT_VALUE_IS_WRONG	0x603E
AT_MQTT_RECONNECT_READ_FAILED	0x603F
AT_MQTT_RECONNECT_VALUE_IS_WRONG	0x6040
AT_MQTT_TOPIC_READ_FAILED	0x6041
AT_MQTT_TOPIC_IS_NULL	0x6042
AT_MQTT_TOPIC_IS_OVERLENGTH	0x6043
AT_MQTT_DATA_READ_FAILED	0x6044
AT_MQTT_DATA_IS_NULL	0x6045
AT_MQTT_DATA_IS_OVERLENGTH	0x6046
AT_MQTT_QOS_READ_FAILED	0x6047
AT_MQTT_QOS_VALUE_IS_WRONG	0x6048
AT_MQTT_RETAIN_READ_FAILED	0x6049
AT_MQTT_RETAIN_VALUE_IS_WRONG	0x604A
AT_MQTT_PUBLISH_LENGTH_READ_FAILED	0x604B
AT_MQTT_PUBLISH_LENGTH_VALUE_IS_WRONG	0x604C
AT_MQTT_RECV_LENGTH_IS_WRONG	0x604D
AT_MQTT_CREATE_SEMA_FAILED	0x604E
AT_MQTT_CREATE_EVENT_GROUP_FAILED	0x604F
AT_MQTT_URI_PARSE_FAILED	0x6050
AT_MQTT_IN_DISCONNECTED_STATE	0x6051
AT_MQTT_HOSTNAME_VERIFY_FAILED	0x6052

MQTT AT Notes

• In general, AT MQTT commands responds within 10 s, except the command AT+MQTTCONN. For example, if the router fails to access the Internet, the command AT+MQTTPUB will respond within 10 s. But the command AT+MQTTCONN may need more time due to packet retransmission in a bad network environment.

• If the AT+MQTTCONN is based on a TLS connection, the timeout of each packet is 10 s, and the total timeout will be much longer depending on the handshake packets count.

• When the MQTT connection ends, it will prompt the message +MQTTDISCONNECTED:<LinkID>.

• When the MQTT connection established, it will prompt the message +MQTTCONNECTED:<LinkID>,<scheme>,<"host">,port,<"path">,<reconnect>.

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