> For the complete documentation index, see [llms.txt](https://docs.iotmp.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.iotmp.io/iotmp/messages/describe.md).

# Describe Resources

This message enables discovering remote [resources ](/iotmp/definitions.md#resources)defined both in client and server. Resources can be defined dynamically by clients and servers. As described in the [resources ](/iotmp/definitions.md#resources)definition, a resource is basically like a function that can be executed like in RPC (Remote Procedure Call). As a "function" it can receive parameters, inputs, and provide an output. 

This message allows discovering such resources, like its names, function type, if they support streaming, required parameters, etc.

## Request

### Header

<table><thead><tr><th width="168.33333333333331">Field</th><th width="93">Value</th><th>Description</th></tr></thead><tbody><tr><td><strong>Message Type</strong></td><td>0x07</td><td>Describe Resources</td></tr><tr><td><strong>Message Size</strong></td><td><a href="/pages/-MD0eHPhqzDOIPgDvpwS#varint">varint</a></td><td>Remaining Message Length</td></tr></tbody></table>

### Body

<table><thead><tr><th width="163">Name</th><th width="84">Field</th><th width="100">Type<select><option value="0c77f58c89ed4decabfda2706eab0ed3" label="any" color="blue"></option><option value="6e677f5f03024d73956cdc02b81f1ef0" label="varint" color="blue"></option></select></th><th width="115" data-type="checkbox">Mandatory</th><th>Description</th></tr></thead><tbody><tr><td><strong>Stream Id</strong></td><td>0x01</td><td><span data-option="6e677f5f03024d73956cdc02b81f1ef0">varint</span></td><td>true</td><td><a href="/pages/-MD0eHPhqzDOIPgDvpwS#stream-identifier">Stream identifier</a>.</td></tr><tr><td><strong>Parameters</strong></td><td>0x02</td><td><span data-option="0c77f58c89ed4decabfda2706eab0ed3">any</span></td><td>false</td><td>Params</td></tr><tr><td><strong>Resource</strong> </td><td>0x04</td><td><span data-option="0c77f58c89ed4decabfda2706eab0ed3">any</span></td><td>false</td><td><a href="/pages/-MD0eHPhqzDOIPgDvpwS#resource-definition">Resource identifier</a>. It should be a string or a resource identifier. If not sent, the target endpoint should report all available resources.</td></tr></tbody></table>

{% hint style="info" %}
If not resource is specified, the target endpoint should list all available resources.
{% endhint %}

## Response (All Resources)

If no resource is specified while sending the Describe Resources message, the target endpoint should list all available resources,

### Ok

If the request succeed, the remote endpoint should return an [Ok Message](/iotmp/messages/ok.md) with the following payload:

```javascript
{
  "relay": {
    "fn": 2
    "id": 0
  },
  "temperature": {
    "fn": 3
    "id": 1
  },
  "reset" : {
    "fn": 1,
    "st": false,
    "id": 2
}
```

In such document each key represents the resource name

<table><thead><tr><th width="166">Describe Field</th><th width="82">Key</th><th width="173">Value</th><th width="116" data-type="checkbox">Mandatory</th><th>Description</th></tr></thead><tbody><tr><td>Function Type</td><td><strong>fn</strong></td><td><p><strong>1</strong> : function without parameters</p><p><strong>2</strong> : function with input</p><p><strong>3</strong>: function with output</p><p><strong>4</strong>: function with input and output</p></td><td>true</td><td>Provides information about the function type, i.e., if it requires and input, provides an output, none, or both of them.</td></tr><tr><td>Parameters</td><td><strong>pr</strong></td><td><p><strong>true</strong>: requires parameters</p><p><strong>false</strong>: no parameters required</p></td><td>false</td><td>Determines if the resource requires parameters to be executed. By default, if not specified, the resource does not require parameters to be executed.</td></tr><tr><td>Stream</td><td><strong>st</strong></td><td><p><strong>true</strong>: support Stream</p><p><strong>false</strong>: no stream support</p></td><td>false</td><td>Determines if the resource can be used with the Streams functionality. By default, if not specified, the stream support is enabled.</td></tr><tr><td>Resource identifier</td><td><strong>id</strong></td><td>varint</td><td>false</td><td>An alternative numeric resource identifier, instead of a name, that can be used to call this resource. </td></tr></tbody></table>

### Error

The resources cannot be described, i.e., no support for describing resources.

## Response (Single Resource)

If a resource is specified while sending the Describe Resources message, the target endpoint should reply with the resource details.

### Ok

If the request succeed, the remote endpoint should return an [Ok Message](/iotmp/messages/ok.md) with the following payload:

```json
{
  "in": true
}
```

```json
{
  "out": 22.33
}  
```

```json
{
  "in": 0
  "out": 25
}
```

### Error

The resource cannot be described, i.e, it does not exists.