src/UserGuide/Master/Tree/API/Programming-MQTT.md - iotdb-docs - Git at Google

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 # MQTT Protocol

 ## 1. Overview

 [MQTT](Message Queuing Telemetry Transport)(http://mqtt.org/) is a lightweight messaging protocol designed for IoT and low-bandwidth environments. It operates on a Publish/Subscribe (Pub/Sub) model, enabling efficient and reliable bidirectional communication between devices. Its core objectives are low power consumption, minimal bandwidth usage, and high real-time performance, making it ideal for unstable networks or resource-constrained scenarios (e.g., sensors, mobile devices).

 IoTDB provides deep integration with the MQTT protocol, fully compliant with MQTT v3.1 (OASIS International Standard). The IoTDB server includes a built-in high-performance MQTT Broker module, eliminating the need for third-party middleware. Devices can directly write time-series data into the IoTDB storage engine via MQTT messages.

 <img style="width:100%; max-width:800px; max-height:600px; margin-left:auto; margin-right:auto; display:block;" src="/img/github/78357432-0c71cf80-75e4-11ea-98aa-c43a54d469ce.png">

 [Programming-MQTT.md](Programming-MQTT.md)
 ## 2. Built-in MQTT Service
 The Built-in MQTT Service provide the ability of direct connection to IoTDB through MQTT. It listen the publish messages from MQTT clients
  and then write the data into storage immediately.
 The MQTT topic corresponds to IoTDB timeseries.
 The messages payload can be format to events by `PayloadFormatter` which loaded by java SPI, and the default implementation is `JSONPayloadFormatter`.
 The default `json` formatter support two json format and its json array. The following is an MQTT message payload example:

 ```json
  {
       "device":"root.sg.d1",
       "timestamp":1586076045524,
       "measurements":["s1","s2"],
       "values":[0.530635,0.530635]
  }
 ```
 or
 ```json
  {
       "device":"root.sg.d1",
       "timestamps":[1586076045524,1586076065526],
       "measurements":["s1","s2"],
       "values":[[0.530635,0.530635], [0.530655,0.530695]]
  }
 ```
 or json array of the above two.

 <img style="width:100%; max-width:800px; max-height:600px; margin-left:auto; margin-right:auto; display:block;" src="/img/github/78357469-1bf11880-75e4-11ea-978f-a53996667a0d.png">

 ## 3. MQTT Configurations
 The IoTDB MQTT service load configurations from `${IOTDB_HOME}/${IOTDB_CONF}/iotdb-system.properties` by default.

 Configurations are as follows:

 | **Property**         | DESCRIPTION           | DEFAULT  |
 | ------------- |:-------------:|:------:|
 | `enable_mqtt_service`       | whether to enable the mqtt service | false |
 | `mqtt_host`       | the mqtt service binding host | 127.0.0.1 |
 | `mqtt_port`      | the mqtt service binding port    |   1883 |
 | `mqtt_handler_pool_size` | the handler pool size for handing the mqtt messages      |    1 |
 | **`mqtt_payload_formatter`** | **Formatting method for MQTT message payloads. ****Options: `json` (tree model), `line` (table model).**     |    **json** |
 | `mqtt_max_message_size` | the max mqtt message size in byte|   1048576 |


 ## 4. Coding Examples
 The following is an example which a mqtt client send messages to IoTDB server.

 ```java
 MQTT mqtt = new MQTT();
 mqtt.setHost("127.0.0.1", 1883);
 mqtt.setUserName("root");
 mqtt.setPassword("root");

 BlockingConnection connection = mqtt.blockingConnection();
 connection.connect();

 Random random = new Random();
 for (int i = 0; i < 10; i++) {
     String payload = String.format("{\n" +
             "\"device\":\"root.sg.d1\",\n" +
             "\"timestamp\":%d,\n" +
             "\"measurements\":[\"s1\"],\n" +
             "\"values\":[%f]\n" +
             "}", System.currentTimeMillis(), random.nextDouble());

     connection.publish("root.sg.d1.s1", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
 }

 connection.disconnect();

 ```

 ## 5. Customize your MQTT Message Format

 If you do not like the above Json format, you can customize your MQTT Message format by just writing several lines
 of codes. An example can be found in  [example/mqtt-customize](https://github.com/apache/iotdb/tree/master/example/mqtt-customize)  project.

 Steps:
 1. Create a java project, and add dependency:
 ```xml
         <dependency>
             <groupId>org.apache.iotdb</groupId>
             <artifactId>iotdb-server</artifactId>
             <version>2.0.4-SNAPSHOT</version>
         </dependency>
 ```
 2. Define your implementation which implements `org.apache.iotdb.db.protocol.mqtt.PayloadFormatter`
 e.g.,

 ```java
 package org.apache.iotdb.mqtt.server;

 import io.netty.buffer.ByteBuf;
 import org.apache.iotdb.db.protocol.mqtt.Message;
 import org.apache.iotdb.db.protocol.mqtt.PayloadFormatter;

 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;

 public class CustomizedJsonPayloadFormatter implements PayloadFormatter {

     @Override
     public List<Message> format(String topic, ByteBuf payload) {
         // Suppose the payload is a json format
         if (payload == null) {
             return null;
         }

         String json = payload.toString(StandardCharsets.UTF_8);
         // parse data from the json and generate Messages and put them into List<Meesage> ret
         List<Message> ret = new ArrayList<>();
         // this is just an example, so we just generate some Messages directly
         for (int i = 0; i < 2; i++) {
             long ts = i;
             Message message = new Message();
             message.setDevice("d" + i);
             message.setTimestamp(ts);
             message.setMeasurements(Arrays.asList("s1", "s2"));
             message.setValues(Arrays.asList("4.0" + i, "5.0" + i));
             ret.add(message);
         }
         return ret;
     }

     @Override
     public String getName() {
         // set the value of mqtt_payload_formatter in iotdb-system.properties as the following string:
         return "CustomizedJson";
     }
 }
 ```
 3. modify the file in `src/main/resources/META-INF/services/org.apache.iotdb.db.protocol.mqtt.PayloadFormatter`:
   clean the file and put your implementation class name into the file.
   In this example, the content is: `org.apache.iotdb.mqtt.server.CustomizedJsonPayloadFormatter`
 4. compile your implementation as a jar file: `mvn package -DskipTests`


 Then, in your server:
 1. Create ${IOTDB_HOME}/ext/mqtt/ folder, and put the jar into this folder.
 2. Update configuration to enable MQTT service. (`enable_mqtt_service=true` in `conf/iotdb-system.properties`)
 3. Set the value of `mqtt_payload_formatter` in `conf/iotdb-system.properties` as the value of getName() in your implementation
   , in this example, the value is `CustomizedJson`
 4. Launch the IoTDB server.
 5. Now IoTDB will use your implementation to parse the MQTT message.

 More: the message format can be anything you want. For example, if it is a binary format,
 just use `payload.forEachByte()` or `payload.array` to get bytes content.

 ## 6. Caution

 To avoid compatibility issues caused by a default client_id, always explicitly supply a unique, non-empty client_id in every MQTT client.
 Behavior varies when the client_id is missing or empty. Common examples:
 1. Explicitly sending an empty string
    • MQTTX: When client_id="", IoTDB silently discards the message.
    • mosquitto_pub: When client_id="", IoTDB receives the message normally.
 2. Omitting client_id entirely
    • MQTTX: IoTDB accepts the message.
    • mosquitto_pub: IoTDB rejects the connection.
    Therefore, explicitly assigning a unique, non-empty client_id is the simplest way to eliminate these discrepancies and ensure reliable message delivery.
	<!--

	Licensed to the Apache Software Foundation (ASF) under one
	or more contributor license agreements. See the NOTICE file
	distributed with this work for additional information
	regarding copyright ownership. The ASF licenses this file
	to you under the Apache License, Version 2.0 (the
	"License"); you may not use this file except in compliance
	with the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing,
	software distributed under the License is distributed on an
	"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
	KIND, either express or implied. See the License for the
	specific language governing permissions and limitations
	under the License.

	-->
	# MQTT Protocol

	## 1. Overview

	[MQTT](Message Queuing Telemetry Transport)(http://mqtt.org/) is a lightweight messaging protocol designed for IoT and low-bandwidth environments. It operates on a Publish/Subscribe (Pub/Sub) model, enabling efficient and reliable bidirectional communication between devices. Its core objectives are low power consumption, minimal bandwidth usage, and high real-time performance, making it ideal for unstable networks or resource-constrained scenarios (e.g., sensors, mobile devices).

	IoTDB provides deep integration with the MQTT protocol, fully compliant with MQTT v3.1 (OASIS International Standard). The IoTDB server includes a built-in high-performance MQTT Broker module, eliminating the need for third-party middleware. Devices can directly write time-series data into the IoTDB storage engine via MQTT messages.

	<img style="width:100%; max-width:800px; max-height:600px; margin-left:auto; margin-right:auto; display:block;" src="/img/github/78357432-0c71cf80-75e4-11ea-98aa-c43a54d469ce.png">

	[Programming-MQTT.md](Programming-MQTT.md)
	## 2. Built-in MQTT Service
	The Built-in MQTT Service provide the ability of direct connection to IoTDB through MQTT. It listen the publish messages from MQTT clients
	and then write the data into storage immediately.
	The MQTT topic corresponds to IoTDB timeseries.
	The messages payload can be format to events by `PayloadFormatter` which loaded by java SPI, and the default implementation is `JSONPayloadFormatter`.
	The default `json` formatter support two json format and its json array. The following is an MQTT message payload example:

	```json
	{
	"device":"root.sg.d1",
	"timestamp":1586076045524,
	"measurements":["s1","s2"],
	"values":[0.530635,0.530635]
	}
	```
	or
	```json
	{
	"device":"root.sg.d1",
	"timestamps":[1586076045524,1586076065526],
	"measurements":["s1","s2"],
	"values":[[0.530635,0.530635], [0.530655,0.530695]]
	}
	```
	or json array of the above two.

	<img style="width:100%; max-width:800px; max-height:600px; margin-left:auto; margin-right:auto; display:block;" src="/img/github/78357469-1bf11880-75e4-11ea-978f-a53996667a0d.png">

	## 3. MQTT Configurations
	The IoTDB MQTT service load configurations from `${IOTDB_HOME}/${IOTDB_CONF}/iotdb-system.properties` by default.

	Configurations are as follows:

	\| Property \| DESCRIPTION \| DEFAULT \|
	\| ------------- \|:-------------:\|:------:\|
	\| `enable_mqtt_service` \| whether to enable the mqtt service \| false \|
	\| `mqtt_host` \| the mqtt service binding host \| 127.0.0.1 \|
	\| `mqtt_port` \| the mqtt service binding port \| 1883 \|
	\| `mqtt_handler_pool_size` \| the handler pool size for handing the mqtt messages \| 1 \|
	\| `mqtt_payload_formatter` \| Formatting method for MQTT message payloads. Options: `json` (tree model), `line` (table model). \| json \|
	\| `mqtt_max_message_size` \| the max mqtt message size in byte\| 1048576 \|


	## 4. Coding Examples
	The following is an example which a mqtt client send messages to IoTDB server.

	```java
	MQTT mqtt = new MQTT();
	mqtt.setHost("127.0.0.1", 1883);
	mqtt.setUserName("root");
	mqtt.setPassword("root");

	BlockingConnection connection = mqtt.blockingConnection();
	connection.connect();

	Random random = new Random();
	for (int i = 0; i < 10; i++) {
	String payload = String.format("{\n" +
	"\"device\":\"root.sg.d1\",\n" +
	"\"timestamp\":%d,\n" +
	"\"measurements\":[\"s1\"],\n" +
	"\"values\":[%f]\n" +
	"}", System.currentTimeMillis(), random.nextDouble());

	connection.publish("root.sg.d1.s1", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
	}

	connection.disconnect();

	```

	## 5. Customize your MQTT Message Format

	If you do not like the above Json format, you can customize your MQTT Message format by just writing several lines
	of codes. An example can be found in [example/mqtt-customize](https://github.com/apache/iotdb/tree/master/example/mqtt-customize) project.

	Steps:
	1. Create a java project, and add dependency:
	```xml
	<dependency>
	<groupId>org.apache.iotdb</groupId>
	<artifactId>iotdb-server</artifactId>
	<version>2.0.4-SNAPSHOT</version>
	</dependency>
	```
	2. Define your implementation which implements `org.apache.iotdb.db.protocol.mqtt.PayloadFormatter`
	e.g.,

	```java
	package org.apache.iotdb.mqtt.server;

	import io.netty.buffer.ByteBuf;
	import org.apache.iotdb.db.protocol.mqtt.Message;
	import org.apache.iotdb.db.protocol.mqtt.PayloadFormatter;

	import java.nio.charset.StandardCharsets;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.List;

	public class CustomizedJsonPayloadFormatter implements PayloadFormatter {

	@Override
	public List<Message> format(String topic, ByteBuf payload) {
	// Suppose the payload is a json format
	if (payload == null) {
	return null;
	}

	String json = payload.toString(StandardCharsets.UTF_8);
	// parse data from the json and generate Messages and put them into List<Meesage> ret
	List<Message> ret = new ArrayList<>();
	// this is just an example, so we just generate some Messages directly
	for (int i = 0; i < 2; i++) {
	long ts = i;
	Message message = new Message();
	message.setDevice("d" + i);
	message.setTimestamp(ts);
	message.setMeasurements(Arrays.asList("s1", "s2"));
	message.setValues(Arrays.asList("4.0" + i, "5.0" + i));
	ret.add(message);
	}
	return ret;
	}

	@Override
	public String getName() {
	// set the value of mqtt_payload_formatter in iotdb-system.properties as the following string:
	return "CustomizedJson";
	}
	}
	```
	3. modify the file in `src/main/resources/META-INF/services/org.apache.iotdb.db.protocol.mqtt.PayloadFormatter`:
	clean the file and put your implementation class name into the file.
	In this example, the content is: `org.apache.iotdb.mqtt.server.CustomizedJsonPayloadFormatter`
	4. compile your implementation as a jar file: `mvn package -DskipTests`


	Then, in your server:
	1. Create ${IOTDB_HOME}/ext/mqtt/ folder, and put the jar into this folder.
	2. Update configuration to enable MQTT service. (`enable_mqtt_service=true` in `conf/iotdb-system.properties`)
	3. Set the value of `mqtt_payload_formatter` in `conf/iotdb-system.properties` as the value of getName() in your implementation
	, in this example, the value is `CustomizedJson`
	4. Launch the IoTDB server.
	5. Now IoTDB will use your implementation to parse the MQTT message.

	More: the message format can be anything you want. For example, if it is a binary format,
	just use `payload.forEachByte()` or `payload.array` to get bytes content.

	## 6. Caution

	To avoid compatibility issues caused by a default client_id, always explicitly supply a unique, non-empty client_id in every MQTT client.
	Behavior varies when the client_id is missing or empty. Common examples:
	1. Explicitly sending an empty string
	• MQTTX: When client_id="", IoTDB silently discards the message.
	• mosquitto_pub: When client_id="", IoTDB receives the message normally.
	2. Omitting client_id entirely
	• MQTTX: IoTDB accepts the message.
	• mosquitto_pub: IoTDB rejects the connection.
	Therefore, explicitly assigning a unique, non-empty client_id is the simplest way to eliminate these discrepancies and ensure reliable message delivery.