NFD

# Control Command

**Control Command** is a mechanism of [[Management|NFD Management protocol]]. This mechanism is useful for altering the state of the forwarder.

This document defines the request and response format of such commands, and how they should be signed and authenticated.

## Request format

Control commands are [[ndn-cxx:CommandInterest|Command Interests]] under a NFD management prefix.

The Name for a request Interest has the following form:

    /<prefix>/<management-module>/<command-verb>/<control-parameters>/<command-interest-components>

* *prefix* is a NFD management prefix.

  Unless otherwise noted, all commands use `/localhost/nfd` prefix.

  Each individual command MAY specify additional prefixes under which that command could be accepted.

* *management-module* is the name of management module to which the command needs to be dispatched.

* *command-verb* is the command to be executed.

* *control-parameters* is a ControlParameters TLV block wrapped in a NameComponent.

* *command-interest-components* are four additional components defined by [[ndn-cxx:CommandInterest|Command Interest]] spec.

### ControlParameters

ControlParameters block contains arguments to the command.

    ControlParameters   ::= CONTROL-PARAMETERS-TYPE TLV-LENGTH

                              Name?

                              FaceId?

                              Uri?

                              LocalUri?

                              Origin?

                              Cost?

                              Capacity?

                              Flags?

                              Mask?

                              Strategy?

                              ExpirationPeriod?

                              FacePersistency?

    ; Name is defined in NDN packet format specification

    FaceId              ::= FACE-ID-TYPE TLV-LENGTH

                              nonNegativeInteger

    Uri                 ::= URI-TYPE TLV-LENGTH

                              RFC3986 URI in UTF-8 encoding

    LocalUri            ::= LOCAL-URI-TYPE TLV-LENGTH

                              RFC3986 URI in UTF-8 encoding

    Origin              ::= ORIGIN-TYPE TLV-LENGTH

                              nonNegativeInteger

    Cost                ::= COST-TYPE TLV-LENGTH

                              nonNegativeInteger

    Capacity            ::= CAPACITY-TYPE TLV-LENGTH 

                              nonNegativeInteger

    Flags               ::= FLAGS-TYPE TLV-LENGTH 

                              nonNegativeInteger

    Mask                ::= MASK-TYPE TLV-LENGTH 

                              nonNegativeInteger

    Strategy            ::= STRATEGY-TYPE TLV-LENGTH

                              Name

    ExpirationPeriod    ::= EXPIRATION-PERIOD-TYPE TLV-LENGTH

                              nonNegativeInteger  

    ; FacePersistency is defined in FaceMgmt section

This definition exhausts all possible fields used in existing commands.

Each individual command MUST specify:

* a list of required fields: those fields MUST be present

* a list of optional fields: those fields MAY be present

* the semantics of each required and optional field

A field that is neither required nor optional for a command MUST NOT be present in a ControlParameter given to that command.

Each individual command MAY impose additional constraints on certain fields.

### Flags and Mask

Various commands collect multiple attributes into the **Flags** field as an inclusive OR.

Each individual command that uses Flags field MUST define the meaning of each bit. In such definition, the least significant bit is denoted as "bit 0".

The **Mask** field, if accepted by a command, indicates which attributes are being updated.

In such cases, Flags field and Mask field must be both present or both omitted in the request.

Bits in the Mask field is arranged in the same order as the Flags field.

For example, if a command defines two flags at bit 0 and bit 1 and also accepts Mask field, a request containing "Flags=0x02 Mask=0x02" specifies bit 1 as "true" and specifies bit 0 as "don't care, leave at default, or keep unchanged"; this request is equivalent to a request containing "Flags=0x03 Mask=0x02".

If a command does not accept the **Mask** field, it SHOULD interpret every flag bit, and there is no "don't care" bits.

## Response format

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

The payload of this Data is a ControlResponse block.

    ControlResponse ::= CONTROL-RESPONSE-TYPE TLV-LENGTH

                          StatusCode

                          StatusText

                          <body>

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

                          nonNegativeInteger

    StatusText      ::= STATUS-TEXT-TYPE TLV-LENGTH

                          string in UTF-8

    <body>          ::= zero or more arbitrary TLV blocks

### StatusCode

StatusCode loosely follows the HTTP semantics described in [RFC 7231](https://tools.ietf.org/html/rfc7231#section-6).

* Codes between 100 and 399 represent a success.

* Codes between 400 and 499 represent a client error.

* Codes between 500 and 599 represent a server error.

Common codes include:

StatusCode | Description

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

200        | OK

400        | ControlParameters is incorrect

403        | Command Interest is not authorized

404        | Resource (e.g., face, prefix, ...) not found

501        | Module or verb is not supported

503        | Service not available

Each individual command MAY define additional codes.

### \<body>

Additional elements are allowed at the end of ControlResponse.

Each individual command MAY define the type and meaning of \<body>.

Unless otherwise defined by an individual command,

\<body> is the ControlParameters passed into this command for all successful responses,

and \<body> is empty for all failure responses.

## TLV-TYPE assignments

Type                                        | Assigned value    | Assigned value (hex)

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

ControlParameters                           | 104               | 0x68

FaceId                                      | 105               | 0x69

Uri                                         | 114               | 0x72

LocalUri                                    | 129               | 0x81

Origin                                      | 111               | 0x6f

Cost                                        | 106               | 0x6a

Capacity                                    | 131               | 0x83

Flags                                       | 108               | 0x6c

Mask                                        | 112               | 0x70

Strategy                                    | 107               | 0x6b

ExpirationPeriod                            | 109               | 0x6d

ControlResponse                             | 101               | 0x65

StatusCode                                  | 102               | 0x66

StatusText                                  | 103               | 0x67

(reserved, formerly LocalControlFeature)    | 110               | 0x6e