# LoRaWAN Custom Decoder

### Overview

The **LoRaWAN Custom Device Decoder** allows you to **write your own decoder function** to process incoming LoRaWAN uplink messages. 

This provides flexibility to handle **custom payload formats** that are not available as pre-built templates.

### How It Works

{% @mermaid/diagram content="graph LR;
A\[LoRaWAN Device Sends Data] --> B{Decoder Function Available?};

B -- No --> C{If Incoming Payload is Valid JSON?};
C -- Yes --> D\[Store JSON Data in Qubitro];
C -- No --> E\[Requires a Decoder Function];

B -- Yes --> F\[Apply Custom Decoder];
F --> G\[Store Decoded Data in Qubitro];

%% Style Adjustments
style A fill:#d9d9d9,stroke:#000,color:#000;
style B fill:#f2f2f2,stroke:#000,color:#000;
style C fill:#f2f2f2,stroke:#000,color:#000;
style F fill:#e0e0e0,stroke:#000,color:#000;
style G fill:#e0e0e0,stroke:#000,color:#000;" %}

{% hint style="warning" %}
If a [Transformation Function](https://qubitro.gitbook.io/qubitro-documentation/platform/functions/transformation-function) is enabled, data will be processed before storage. The decoder applies first, and then any defined transformation function modifies the data before it is stored in Qubitro.
{% endhint %}

### Tips

JavaScript payload formatters allow you to write functions to encode or decode messages. These functions are executed using a **JavaScript ECMAScript 5.1 runtime**.

* **Avoid** non-trivial logic or polyfills; they may not be supported.
* Use arithmetic operations and bit shifts to convert binary data into readable fields.
* Keep payload formatters simple and lightweight.

{% hint style="success" %}
Need help reviewing your custom formatter? Our team can assist in checking your code for compatibility. Reach out via the [Support Page](https://qubitro.gitbook.io/qubitro-documentation/help-center).
{% endhint %}

### Function Schema

A **decoder function** processes raw **uplink messages** and returns a **JSON object** containing the decoded fields.

```javascript
function decoder(input) {
  // Your decoding logic here
}
```

{% hint style="danger" %}
The function name and parameter name cannot be modified.
{% endhint %}

#### Function Parameters

The decoder function has a single parameter: input. Qubitro automatically provides this parameter, which contains three properties:

* **Metadata**: A dynamic object containing metadata from the LNS provider (e.g., RSSI, SNR, timestamp). The structure varies depending on the provider.
* **fPort**: The LoRaWAN fPort used for the uplink.
* **Bytes**: A byte array representing the raw payload from the uplink message.

#### Example: Accessing Function Parameters

```javascript
function decoder(input) {
    var bytes = input.bytes;  // Get the raw payload
    var fPort = input.fPort;  // Get the fPort value
    var metadata = input.metadata; // Get metadata from the LNS provider
    return {};
}
```

#### Return Values

{% hint style="warning" %}
To ensure compatibility with Qubitro’s no-code suite, the output should be a key-value JSON object.
{% endhint %}

For example, if the payload represents temperature, the function can extract and return it as follows:

```javascript
function decoder(input) {
  const bytes = input.bytes;
  const fPort = input.fPort;
  const metadata = input.metadata;

  // Convert bytes to temperature value
  const temperature = ((bytes[0] << 8) + bytes[1]) / 100;

  return {
    "temperature": temperature,
    "metadata": metadata
  };
}
```

### Creating a Custom Decoder Function

{% stepper %}
{% step %}
**Select the Function Type**

1. Open the **device details page** in the **Qubitro Portal**.
2. Click the **Functions** tab.
3. Click **Create function** and select **Decoder Function**.
4. Choose **LoRaWAN Custom Device** as the formatter type.
   {% endstep %}

{% step %}
**Write the Decoder Code**

1. Enter your **custom decoder function** in the editor.
2. Modify the formatter code to match your device’s payload.

<figure><img src="/files/owcEkBDFvVI0jaIRwZGX" alt="" width="563"><figcaption></figcaption></figure>
{% endstep %}

{% step %}
**Save and Apply the Function**

1. Click **Save and complete** to apply the decoder function.
2. The function will now **process all incoming data** for this device automatically.
   {% endstep %}
   {% endstepper %}

## FAQs

<details>

<summary>I created the function, but my device data is not decoded correctly. What should I do?</summary>

If your function is active but the data is not decoded correctly, check the following:

* Ensure that the payload format matches your decoder logic.
* Use the **Test** feature in the function editor to validate sample data.
* Check the **device logs** to see if raw data is being received.

If you need assistance, our team can **review your custom formatter code**. Open a [ticket](https://qubitro.gitbook.io/qubitro-documentation/help-center) from the Support Page.

</details>

<details>

<summary>I don’t see my device listed. Can Qubitro help me?</summary>

Absolutely! If your device does not appear after setting up the integration, **open a** [**support ticket**](https://qubitro.gitbook.io/qubitro-documentation/help-center), and our team will assist you in troubleshooting the issue.

</details>

<details>

<summary>Can I use a custom decoder with any LNS provider?</summary>

Yes! Qubitro’s **LoRaWAN Custom Device Decoder** works with **any LNS provider**, including **Loriot, The Things Stack, and ChirpStack**. As long as the device sends data, your decoder function will process it.

</details>

<details>

<summary>Can the Qubitro team help me write a custom decoder?</summary>

While Qubitro provides flexibility for writing custom decoders, our team can **review your formatter code** to ensure compatibility and suggest improvements. Feel free to reach out via the [Support Page](https://qubitro.gitbook.io/qubitro-documentation/help-center).

</details>


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