Repo Protocol Specification » History » Revision 14
Revision 13 (Shuo Chen, 02/19/2014 10:06 AM) → Revision 14/136 (Shuo Chen, 02/19/2014 10:32 AM)
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 Requester sends insert command to authorize the command; if authorization does not fail immediately, go to step 3
repo.
2. send a negative response indicating authorization failure, and abort these steps Repo checks this insert command.
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 2.1 Repo validates the this command interest. If invalidated, a negative response indicating malformed command, and abort these steps data object contained invalidated status code will be responded.
6. wait for authorization completion
7. if authorization fails, go to step 2
8. send 2.2 Repo checks the name of the interest. If a positive response indicating insert data with the name same with the name or prefix of the data in command interest exists in repo, this command interest 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
store retrieved Data packet
if retrieved Data packet rejected. A data object contains FinalBlockId, and FinalBlockId is less than EndBlockId, let EndBlockId the status code will be FinalBlockId responded.
if 2.3 Repo checks whether the last component of Name data is greater than or equal to EndBlockId, abort these steps
increment the last component of Name
go to step 16 segmented.
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 | | |
| | <==================== | | |
+---+ +---+ |
| | |
| | |