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:

* ``<box 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>``

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

For example, for ``<box 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

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

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    |   |                               |

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

      +---+                       +---+                               |

        |                           |                                 |

        |                           |                                 |