> For the complete documentation index, see [llms.txt](https://alex-robenko.gitbook.io/commsdsl-specification/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alex-robenko.gitbook.io/commsdsl-specification/fields/data.md).

# data Field

This field stores and abstracts away value of a raw bytes data. The **\<data>** field has all the [common](/commsdsl-specification/fields/common.md) properties as well as extra properties and elements described below.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <data name="SomeDataField" />
    </fields>
</schema>
```

Such definition of the **\<data>** does **NOT** have any limit on the length of the data, and will consume all the available bytes in the input buffer.

## Default Value

The default value of the **\<data>** field when constructed can be specified using **defaultValue** [property](/commsdsl-specification/properties.md). The value of the property must be case-insestive string of hexadecimal values with even number of characters. The allowed ranges of the characters are: \['0' - '9'], and \['a' - 'f']. The ' ' (space) character is also allowed for convenient separation of the bytes. If not specified, defaults to empty data.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <data name="SomeDataField" defaultValue="0123 45 67 89 ab cd eF" />
    </fields>
</schema>
```

The example above is expected to create approprate raw data abstracting field, containing 8 bytes: \[0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef] when default constructed.

## Fixed Length

In case the data value needs to be serialized using predefined fixed length, use **length** property to specify the required value.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <data name="SomeDataField" length="16" />
    </fields>
</schema>
```

## Length Prefix

Many protocols prefix raw binary data with its length. The **CommsDSL** allows definition of such prefix using **lengthPrefix** child element, which must define prefix as [\<int>](/commsdsl-specification/fields/int.md) field.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <data name="SomeDataField">
            <lengthPrefix>
                <int name="LengthPrefix" type="uint16" />
            </lengthPrefix>
        <data>
    </fields>
</schema>
```

In case the prefix field is defined as external field, **CommsDSL** allows usage of **lengthPrefix** as [property](/commsdsl-specification/properties.md), value of which contains name of the referenced field.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <int name="DataLengthPrefix" type="uint8" />
        <data name="SomeDataField" lengthPrefix="DataLengthPrefix" />
    </fields>
</schema>
```

The **CommsDSL** also supports **detached** length prefix, when there are several other fields in the [\<message>](/commsdsl-specification/messages.md) or in the [\<bundle>](/commsdsl-specification/fields/bundle.md) between the length field and the **\<data>**.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <bundle name=SomeBundle">
            <int name="DataLengthPrefixMember" type="uint16" />
            <int name="SomeOtherFieldMember" type="uint16" />
            <data name="SomeDataFieldMember" lengthPrefix="$DataLengthPrefixMember" />
        </bundle>
    </fields>

    <message name="Msg1" id="1">
        <int name="DataLengthPrefix" type="uint16" />
        <int name="SomeOtherField" type="uint16" />
        <data name="SomeDataField" lengthPrefix="$DataLengthPrefix" />
    </message>
</schema>
```

**NOTE**, the existence of **$** prefix when specifying **lengthPrefix** value. It indicates that the referenced field is a sibling in the containing [\<message>](/commsdsl-specification/messages.md) or the [\<bundle>](/commsdsl-specification/fields/bundle.md) field.

The code generator is expected to take the existence of such detached prefix into account and generate correct code for various field operations (read, write, etc...).

**NOTE**, that **length** and **lengthPrefix** properties are mutually exclusive, i.e. cannot be used together.

Use [properties table](/commsdsl-specification/appendix/data.md) for future references.