# MQTT Publish

You can invoke a UbiFunction by publishing data through MQTT. This makes it possible to integrate devices and gateways that may have a non-editable JSON payload that is not compatible with our [native MQTT broker](https://docs.ubidots.com/v1.6/reference/mqtt) or our [HTTP Data Ingestion API](https://docs.ubidots.com/v1.6/reference/http).

Because the UbiFunctions MQTT broker is shared across all functions, subscription requests are not supported **and only the MQTT Publish method is accepted**. Accordingly, all subscription requests are rejected.

{% hint style="success" %}
If you'd like to have a private MQTT broker mapped to a UbiFunction, [please reach out to our sales team](mailto:sales@ubidots.com). In this case, subscribe actions can be supported.
{% endhint %}

{% hint style="info" %}
The UbiFunction method must be set to `POST`.
{% endhint %}

Here are the MQTT settings needed to invoke a UbiFunction over MQTT:

| MQTT Settings | Value                                                   |
| ------------- | ------------------------------------------------------- |
| **URL**       | `functions.ubidots.com`                                 |
| **Port**      | <p>1883 for plain MQTT.<br>8883 for MQTT over TLS.</p>  |
| **Topic**     | `/prv/<your-username>/<function-label>`                 |
| **Username**  | Your account username                                   |
| **Password**  | Valid Token from your Ubidots account.                  |
| **ClientID**  | Any random string. Preferably longer than 15 characters |

### Topic structure

To trigger a UbiFunction through MQTT, the publish topic must follow this structure:

```
/prv/<username>/<function-label>
```

Where:

* `<username>` is your Ubidots account username.
* `<function-label>` is the function name in lowercase, with spaces replaced by dashes.

The base topic corresponds to the UbiFunction HTTPS Endpoint URL's path, as seen in the image below:

<figure><img src="/files/kkFxkFwhJGw6MjTzieae" alt=""><figcaption></figcaption></figure>

#### **Advanced Topics**

Additional topic levels are supported. To add more levels, simply add a forward slash ("`/`") after the base topic:

```
/prv/<username>/<function-label>/<level-1>/···/<level-N>
```

Where:

* `<level-N>` is any additional UTF-8 encoded string that you want to add to the topic.

Topics have the following limits:

| Topic Limits | Limit           |
| ------------ | --------------- |
| Length       | 1500 characters |
| Levels       | 10              |

### UbiFunction `args`

When triggering a UbiFunction through MQTT, you receive a JSON object in the `args` variable of the `main` function. The object has this structure:

```
{
  "topic": "<topic>",
  "payload": "<payload>",
  "from_client_id": "<client_id>",
}
```

Where:

| Key              | Type   | Value description                                          |
| ---------------- | ------ | ---------------------------------------------------------- |
| topic            | String | The multilevel publication topic                           |
| payload          | String | The payload sent by the device in the publication message. |
| from\_client\_id | String | The client ID used in the MQTT connection.                 |

### Certificates

Ubidots supports SSL V1.1, TLS V1.2, and V1.3. You can download our root certificates in different formats:

* [PEM file](https://z.cdn.ubidots.com/ustatic/certs/roots.pem): Certificate chain with two root certificates from our certificate authorities (CAs).
* [DER file](https://z.cdn.ubidots.com/ustatic/certs/roots.der): Same as the PEM file, with an alternative encoding.
* [CRT file](https://z.cdn.ubidots.com/ustatic/certs/roots.crt): Same as the PEM file, with a different extension. Often referred to as **.crt**, **.cert** or **.cer**.

### Examples

{% tabs %}
{% tab title="Port 1883" %}

```bash
mosquitto_pub \
-p 1883 \ 
-h functions.ubidots.com \
-t "/prv/<username>/<function-name>" \
-m '{"token": "TOKEN", "device": "device-label", "variable-label": value}' \
-u "<username>" \
-P "TOKEN" \
-q 1 -d
```

{% endtab %}

{% tab title="Port 8883" %}

```bash
mosquitto_pub \
-p 8883 \ 
-h functions.ubidots.com \
-t "/prv/<username>/<function-name>" \
-m '{"token": "TOKEN", "device": "device-label", "variable-label": value}' \
-u "<username>" \
-P "TOKEN" \
-q 1 -d \
--cafile /Users/user/Documents/Ubidots/roots.pem
```

{% endtab %}
{% endtabs %}


---

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