NFD

# NFD Control Command specification

NFD management module exposes a command interface as Interest-Data exchange.

Commands provided over this interface are useful for querying or changing the state of NFD forwarder.

## Request format

A request to the command interface is an Interest under `ndn:/nfd` prefix.

A request Interest has at least four Name components.

The first four components are:

1. "nfd" in UTF-8

2. *nfdid*, forwarder's public key digest

3. *verb*, the command verb in UTF-8

4. *options*, the arguments to the command

### Signed request and Unsigned request

Most commands require a signature to be included in the Name.

The signature format is defined in [[Signed Interests]] spec.

A signed request Interest has seven Name components.

Certain commands that do not change the forwarder state do not require a signature.

An unsigned request Interest has four Name components.

Each individual command specification defines whether a request Interest using that command verb should be signed or not.

### Options

The *option* component contains arguments to the command as a TLV.

This component is required even if the command verb does not need any arguments.

In that case, this component would have zero length.

Each individual command specification defines the format of the options TLV.

The TLV-TYPE numbers used in this TLV should be allocated from application range, and are not required to be unique across different command verbs.

## Response format

A response from the command interface is a Data that matches the request Interest.

Each individual command specification defines the format inside the Data payload.

### Negative response

A negative response follows the following convention inside the Data payload.

    StatusResponse ::= STATUS-RESPONSE-TYPE TLV-LENGTH

                         StatusCode

                         StatusText?

                         ...

    StatusCode     ::= STATUS-CODE-TYPE TLV-LENGTH

                         nonNegativeInteger

    StatusText     ::= STATUS-TEXT TLV-LENGTH

                         string in UTF-8

**StatusCode** generally follows HTTP convention. Common codes include:

StatusCode | Description

-----------|------------------------

400        | Arguments are incorrect

401        | Signed request is required for command, but unsigned request is passed

403        | Signing key is not authorized for this command

404        | Command verb is not supported

In **StatusResponse**, additional elements are allowed at the end.

Each individual command specification defines whether and what can present.

## TLV-TYPE assignments

Type                                        | Assigned value    | Assigned value (hex)

------------------------------------------- | ----------------- | --------------------

StatusResponse                              | 130               | 0x82

StatusCode                                  | 139               | 0x8b

StatusText                                  | 140               | 0x8c