repo-ng

Repo Protocol Specification

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

Repo is persistent storage of data objects model in NDN. 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

The repo could be viewed as the data container of the data objects. It will register some specific prefixes of data objects it holds into NFD (NDN Forwarding 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 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 insertation is also supported in the insertation 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 defined to have following components:

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

* ``insert`` refers to insert data objects

* ``<data name>`` refers to specific name of data that will be inserted

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

* ``<timestamp>``

* ``<random-value>``

* ``<SignatureInfo>``

* ``<SignatureValue>``

<name of repo> and <data name> can be divided by serveral continious ``/`` according to specific defination.

For example, for ``<name of repo>`` as ``/ucla/cs/repo`` and ``<data name>`` as ``/vedio/Forrest Gump``, the data object is defined as following:

    /ucla/cs/repo/insert/vedio/Forrest Gump/<timestamp>/<random-value>/<SignatureInfo>/<SignatureValue>

### SegmantationInfo

    SegmantationInfo      ::= SEGMENTATIONINFO-TYPE TLV-LENGTH

                               StartBlockId?

                               FinalBlockId?

    StartBlockId          ::= STARTBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

    EndBlockId            ::= FINALBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

### Insertion status check

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

The name semantics is defined to have following components:

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

* ``insert check`` refers to insert data objects

* ``<data name>`` refers to specific name of data that will be inserted

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

* ``<timestamp>``

* ``<random-value>``

* ``<SignatureInfo>``

* ``<SignatureValue>``

The insertion status is enocoded as a TLV echoded block in content block in data packet. The TLV block format is as follows:

    InsertStatus          ::= INSERTSTATUS-TYPE TLV-LENGTH

                               StatusCode?

                               StartBlockId?

                               FinalBlockId?

                               InsertNum?

    StatusCode            ::= STATUSCODE-TYPE TLV-LENGTH

                                nonNegativeInteger    

    StartBlockId          ::= STARTBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

    EndBlockId            ::= FINALBLOCKID-TYPE TLV-LENGTH

                                nonNegativeInteger

    InsertNum             ::= INSERTNUM-TYPE TLV-LENGTH

                                nonNegativeInteger

StatusCode indicates the status of insertation. InsertNum represents how many data has been intersted into the repo.

StatusCode Definition:

``StatusCode`` | Description

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

``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

### 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.

    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 Selectors

    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)

The definitions of delete command selectors is the same as the selectors of conventional [selectors](http://named-data.net/doc/ndn-tlv/interest.html#selectors). The difference is that this delete command selectors will return any data packets that comforms to the selectors. If selectors are not presented, the repo will just delete the data of exact name. So, for example, if somebody wants to delete all the data under certain prefix, at least, MinSuffixComponents should be set to 0.

### 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