repo-ng

Repo Protocol Specification

===========================

A Repo supports the network by preserving content and responding to Interests requesting content that it holds. A Repo can exist in any node, and is recommended if applications in that node need to preserve data. The NDN repo protocol is a specification of repo operations including reading, insertion and deletion of data objects in repo.

Repo semantics is based on [Command Interests](http://redmine.named-data.net/projects/nfd/wiki/Command_Interests) with signed commponents an the end of the name and basic common semantics of NDN. 

When some operation of repo including insertion and deletion of data objects is requested, a command interest is sent. The command interest is the interest as command of insertion and deletion and signed as form of command interest for access control. The repo will response the command with the data object.

The repo protocol can be categorized in three sections of reading, insertion and deletion of data objects.

## Repo Reading Specification

Repo registers prefixes of data objects it holds into NDN fowarding deamon and the repo will respond the data with such prefixes.

A standard interest is used to fetch content from the repo. The repo will respond when the name of the interest matches the prefix it registered in NFD. If the content in repo matches the interests, it will respond with the data object. When the interest is not matched, it will not respond.

The protocol is listed as bellow

If there is a matching data object:

    Requester                     Repo

        |                           |

        |                           |

        |         Interest          |

     t1 |-------------------------->|

        |                           |

        |        Data Object        |

     t2 |<==========================|

        |                           |

        |                           |

        |                           |

If there is no matching data object:

    Requester                     Repo

        |                           |

        |                           |

        |         Interest          |

     t1 |-------------------------->|

        |                           |

        |                           |

        |                           |

## Repo Command

For insertion, deletion and other operations of repo, these commands are encoded in the form of [sigend command interest](http://redmine.named-data.net/projects/nfd/wiki/Command_Interests). The semantics of repo command interest is as follows:

The name semantics is defined to have following components:

* ``<name of repo>`` refers to specific name of repo

* ``<command verb>`` refers to the name of command

* ``<RepoCommandParameters>`` refers to parameters of repo command

The following components are components of singed interest for access control:

* ``<timestamp>``

* ``<random-value>``

* ``<SignatureInfo>``

* ``<SignatureValue>``

For name of the repo /ucla/cs/repo/, the command will be defined as this:

    /ucla/cs/repo/<command verb>/<RepoCommandParameters>/<timestamp>/<random-value>/<SignatureInfo>/<SignatureValue>

### RepoCommandParameters

    RepoCommandParameters  ::= REPOCOMMANDPARAMETERS-TYPE TLV-LENGTH

                               Name?

                               StartBlockId?

                               EndBlockId?

    Name ::= NAME-TYPE TLV-LENGTH NameComponent*

    NameComponent ::= NAME-COMPONENT-TYPE TLV-LENGTH BYTE+

    StartBlockId          ::= STARTBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

    EndBlockId            ::= ENDBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

### Repo Command Selectors

Repo command supports parts of interest selectors of interest to indicate which contents to process. The definition of standard NDN selectors is described in [NDN Selectors Doc](http://named-data.net/doc/ndn-tlv/interest.html#selectors). The concrete definitions of both standard NDN selectors and repo command selectors are the same. The difference between standard NDN interest and Repo Command interest that, the standard NDN selectors just matches **one** data packet that conforms to the selector conditions, but repo command selectors would matches **any** data packets. For example, if Interest is expressed for /ndn/edu and Exclude specifies one name component ucla, in standard NDN interest, the data producers will first exclude all the data packets with prefix /ndn/edu but not /ndn/edu/ucla, and then just selects one data packet. In repo command interest, it will select all the data packets with prefix /ndn/edu but not /ndn/edu/ucla.

Repo command supports parts of standard NDN interests including MinSuffixComponents, MaxSuffixComponents, PublisherPublicKeyLocator, Exclude. If command contains other selectors, repo will ignore these not supported selectors. In addition, selectors are just supported in delete command. If other commands contains selectors, repo will ignore selectors when processing these commands.

The form of selectors is as follows:

    Selectors             ::= SELECTORS-TYPE TLV-LENGTH

                               MinSuffixComponents?

                               MaxSuffixComponents?

                               PublisherPublicKeyLocator?

                               Exclude?

    MinSuffixComponents   ::= MIN-SUFFIX-COMPONENTS-TYPE TLV-LENGTH

                               nonNegativeInteger

    MaxSuffixComponents   ::= MAX-SUFFIX-COMPONENTS-TYPE TLV-LENGTH

                               nonNegativeInteger

    PublisherPublicKeyLocator ::= KeyLocator

    Exclude               ::= EXCLUDE-TYPE TLV-LENGTH Any? (NameComponent (Any)?)+

    Any                   ::= ANY-TYPE TLV-LENGTH(=0)

### Repo trust model

The trust model of repo depends on people who deploy the repo service, such as PKI. Repo can specify their own verification policies, and data consumers can specify their own trust anchors. The NDN [FAQ](http://named-data.net/project/faq/#How_does_NDN8217s_8220trust_management8221_work) shows how NDN trust managment works.

## Repo Command Response

Repo command response is the response data packet of repo command interest. The response contains statuscode to indicate the status of command process and other information. A TLV-encoded block called ``RepoCommandResponse`` is encoded in content of the data packet.

    RepoCommandResponse   ::= INSERTSTATUS-TYPE TLV-LENGTH

                               StatusCode?

                               StartBlockId?

                               EndBlockId?

                               InsertNum?

                               DeleteNum?

    StatusCode            ::= STATUSCODE-TYPE TLV-LENGTH

                                nonNegativeInteger    

    StartBlockId          ::= STARTBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

    EndBlockId            ::= ENDBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

    InsertNum             ::= INSERTNUM-TYPE TLV-LENGTH

                                nonNegativeInteger

    DeleteNum             ::= DELETENUM-TYPE TLV-LENGTH

                                nonNegativeInteger

## Repo Insertion Specification

Insertion specification is for some client and application to insert data objects into certain NDN repo. A command interest as insertion command will be sent to the repo. This command interest is a signed interest and will be validated with access control policy defined by the repo. When the interested is validated and name of the data is not existed in the repo. The repository will reponse with a data object containing OK status and start to send the interest to fetch the data to insert.

Segmented data insertion is also supported in the insertion protocol. Segmantation info is defined as a TLV-encoded SegmantationInfo block. If the content is segmented, the final segment id will be encoded in this block.

### Insertion command interest semantics

The name semantics is follows the format of the repo command. The <command verb> is defined as ``insert``.

For example, for ``<name of repo>`` as ``/ucla/cs/repo``, the following is an example:

    /ucla/cs/repo/insert/<RepoCommandParameters>/<timestamp>/<random-value>/<SignatureInfo>/<SignatureValue>

### Insertion status check

During the insertion progress, the requester could send insertion status check command to check the status of the insertion progress. This status check command is also signed interest. The semantics of insertion status check command is shown as follows:

<command verb> equals to ``insert check``. For example:

    /ucla/cs/repo/insert check/<RepoCommandParameters>/<timestamp>/<random-value>/<SignatureInfo>/<SignatureValue>

### Insertatation status response

This insert status data object could be the response data object of both insert command and insert check command. It will follow the format of repo command response.

StatusCode indicates the status of insertion. InsertNum represents how many data has been intersted into the repo. StartBlockId and EndBlockId is the start and end segment id of data inserted. InsertNum is the how many data segments have been inserted.

For insert cammand, status code will be set according to definition below, StartBlockId and EndBlockId will be set according to the insert command.

For insert check command, status code will be set according to definition below, StartBlockId and EndBlockId will be set according to the insert command, insertnum will be set according to insertion progress.

StatusCode Definition:

``StatusCode`` | Description

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

``100``        | The command is OK. can start to fetch the data

``200``        | All the data has been inserted

``300``        | This insertion is in progress

``401``        | This insertion check is invalidated

``404``        | No such this insertion is in progress

``505``        | status check command is not supported

### Protocol Process

1. start to authorize the command; if authorization does not fail immediately, go to step 3

2. send a negative response indicating authorization failure, and abort these steps

3. if both StartBlockId and EndBlockId are missing, go to step 6

4. if both StartBlockId and EndBlockId are present, and StartBlockId is less than or equal to EndBlockId, go to step 6

5. send a negative response indicating malformed command, and abort these steps

6. wait for authorization completion

7. if authorization fails, go to step 2

8. send a positive response indicating insert is in progress

9. if both StartBlockId and EndBlockId are present, go to step 15

10. start to retrieve Name

11. wait for retrieval completion

12. if retrieval fails, abort these steps

13. store retrieved Data packet

14. abort these steps

15. append StartBlockId to Name

16. start to retrieve Name

17. wait for retrieval completion

18. if retrieval fails, abort these steps

19. store retrieved Data packet

20. if retrieved Data packet contains FinalBlockId, and FinalBlockId is less than EndBlockId, let EndBlockId be FinalBlockId

21. if the last component of Name is greater than or equal to EndBlockId, abort these steps

22. increment the last component of Name

23. go to step 16

Implementation MAY pipeline the Interests.

### Repo command progress report

Implementation MAY publish a notification of status regarding insert progress. The process of status check is as follows:

1. start to authorize the insert status command

2. send a negative response indicating authorization failure, and abort these steps

3. start to check the progress of the insert with the data name in the command. If no such progress is found, go to 4. or go to 5.

4. reponse status with status code of 404

5. ckeck te status of insertion. return the status data content

### Protocol diagram:

    Requester                     Repo                          Data producer

        |                           |                                 |

        |                           |                                 |

      +---+  Insert command       +---+                               |

      |   | --------------------> |   |                               |

      +---+                       |   |                               |

        |                         |   |                               |

      +---+   Confirm start       |   |                               |

      |   | <==================== |   |                               |

      +---+   Reject command      +---+                               |

        |     (with status code)    |                                 |

        |                         +---+     Interest for Data       +---+

        |                         |   | --------------------------> |   |

        |                         +---+                             |   |

        |                           |                               |   |

        |                         +---+       Data segment          |   |

        |                         |   | <========================== |   |

        |                         +---+                             +---+

        |                           |                                 |

        |                           ~                                 ~

        |                           ~                                 ~

        |                           |                                 |

        |                         +---+     Interest for Data       +---+

        |                         |   | --------------------------> |   |

        |                         +---+                             |   |

        |                           |                               |   |

        |                         +---+       Data segment          |   |

        |                         |   | <========================== |   |

        |                         +---+                             +---+

        |                           |                                 |

        |                           |                                 |

        |                           ~                                 ~

        |                           ~                                 ~

        |                           |                                 |

        |                           |                                 |

        |                           |                                 |

      +---+   Status interest     +---+                               |

      |   | --------------------> |   |                               |

      +---+                       |   |                               |

        |                         |   |                               |

      +---+    Status response    |   |                               |

      |   | <==================== |   |                               |

      +---+                       +---+                               |

        |                           |                                 |

        |                           |                                 |

## Repo Deletion Specification

Deletion of one content object or content objects under certain prefix are both supported in repo specification. Selectors are used to select multiple content objects. These selectors are different from conventional [selectors](http://named-data.net/doc/ndn-tlv/interest.html#selectors) of interest packet. The conventional selecors of interest would select one data packet of repo. Selecors of delete command will return any data packets which applies for these selectors.

### Deletion command interest semantics

Deletion command interest follows the format of the repo command. For example:

    /ucla/cs/repo/delete/<RepoCommandParameters>/<timestamp>/<random-value>/<SignatureInfo>/<SignatureValue>

### Deletion Command Selectors

Deletion command selectors follows the [repo command selectors](http://redmine.named-data.net/projects/repo-ng/wiki/Repo_Protocol_Specification#Repo-Command-Selectors).

### Deletion status check

During the deletion progress, the requester could send deletion status check command to check the status of the deletion progress. This status check command is also signed interest. The semantics of deletion status check command follows the format of repo command. ``<command verb>`` equals to ``delete check``. For example:

    /ucla/cs/repo/delete/<RepoCommandParameters>/<timestamp>/<random-value>/<SignatureInfo>/<SignatureValue>

### Deletion status response

This delete status data object could be the response data packet of both delete command and delete check command. The name of data packet is the same as that of command.The deletion status is enocoded as a TLV echoded block in content block in data packet. The TLV block format follows RepoCommandResponse.

StatusCode indicates the status of deletion. DeleteSum is the sum of the deletion. DeleteNum represents how many data has been deleted.

StatusCode Definition:

``StatusCode`` | Description

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

``200``        | All the data has been deleted

``300``        | This deletion is in progress

``401``        | This deletion check is invalidated

``404``        | No such this deletion is in progress

``505``        | status check command is not supported

### Protocol process

1. start to authorize the command; if authorization does not fail immediately, go to step 3

2. send a negative response indicating authorization failure, and abort these steps

3. check whether selectors are presented. If selectors are presented, go to step 4, or select the data packet of the exact name of command. If some data is selected, go to step 6. If no data selected, go to step 5

4. select all the data packets that comforms to data name of the command and the selectors. If some data packets are selected, go to step 6. Or no data selected, go to step 5.

5. send a negative response and abort the delete transaction.

6. wait for authorization completion

7. if authorization fails, go to step 2

8. start to delete the selected data. If deletion success, return positive reponse, or return negative response and abort the deletion.

Implementation MAY publish a notification of status regarding delete progress. The process of status check is as follows:

1. start to authorize the delete status command

2. send a negative response indicating authorization failure, and abort these steps

3. start to check the progress of the delete with the data name in the command. If no such progress is found, go to 4. or go to 5.

4. reponse status with status code of 404

5. ckeck te status of delete. return the status data content

### Protocol diagram:

    Requester                     Repo 

        |                           |                                 

        |                           |                                 

      +---+  Delete command       +---+                               

      |   | --------------------> |   |                               

      +---+                       +---+                               

        |                           |                                 

        |                           |                                 

        |                           |                                 

      +---+   Status interest     +---+                               

      |   | --------------------> |   |                               

      +---+                       |   |                               

        |                         |   |                               

      +---+    Status response    |   |                               

      |   | <==================== |   |                               

      +---+                       +---+                               

        |                           |                                 

        |                           |                                 

        |                           |                                 

      +---+   Confirm Deletion    +---+                               

      |   | <==================== |   |                               

      +---+   Reject command      +---+                               

        |     (with status code)    |    

        |                           |