# ndncatchunks and ndnputchunks

**ndncatchunks** and **ndnputchunks** are a pair of programs to transfer a file as Data segments.

* **ndnputchunks** is a producer program that reads a file from the standard input, and makes
  it available as NDN Data segments.  It appends version and segment number components
  to the specified name, according to the
  [NDN naming conventions](http://named-data.net/publications/techreports/ndn-tr-22-ndn-memo-naming-conventions/).

* **ndncatchunks** is a consumer program that fetches Data segments of a file, optionally
  discovering the latest version of the file, and writes the content of the retrieved file to
  the standard output.

## Version discovery methods in ndncatchunks

* `fixed`    : sends an interest attempting to find a data packet with the
               specified prefix and version number. A version component must be present at the
               end of the user-specified NDN name.

* `realtime` : sends discovery interests to fetch metadata of the solicited content from which
               the data version will be resolved.
               The version number of the solicited content is included in the name of returned
               metadata data packet.
               For more information about the packet format and naming convention of interest and
               data packets for realtime version discovery, please refer to:
[Realtime Data Retrieval (RDR) protocol wiki page](https://redmine.named-data.net/projects/ndn-tlv/wiki/RDR)

The default discovery method is `realtime`.

## Interest pipeline types in ndncatchunks

* `fixed`: maintains a fixed-size window of Interests in flight; the window size is configurable
           via a command line option and defaults to 1.

* `aimd` : sends Interests using an additive-increase/multiplicative-decrease (AIMD) algorithm to
           control the window size. By default, a Conservative Loss Adaptation algorithm is adopted
           combining with the AIMD algorithm, that is, at most one window decrease will be
           performed per round-trip-time. For details please refer to:
  [A Practical Congestion Control Scheme for Named Data
  Networking](https://www.researchgate.net/publication/306259672_A_Practical_Congestion_Control_Scheme_for_Named_Data_Networking)

The default Interest pipeline type is `aimd`.

## Usage examples

### Publishing

The following command will publish the text of the GPL-3 license under the `/localhost/demo/gpl3`
prefix:

    ndnputchunks ndn:/localhost/demo/gpl3 < /usr/share/common-licenses/GPL-3

To find the published version you have to start ndnputchunks with the `-p` command line option,
for example:

    ndnputchunks -p ndn:/localhost/demo/gpl3 < /usr/share/common-licenses/GPL-3

This command will print the published version to the standard output.

To publish data with a specific version, you must append a version component to the end of the
prefix. The version component must follow the aforementioned NDN naming conventions.
For example, the following command will publish the version `%FD%00%00%01Qc%CF%17v` of the
`/localhost/demo/gpl3` prefix:

    ndnputchunks ndn:/localhost/demo/gpl3/%FD%00%00%01Qc%CF%17v < /usr/share/common-licenses/GPL-3

If the version component is not valid, a new well-formed version will be generated and appended
to the supplied NDN name.


### Retrieval

To retrieve the latest version of a published file, the following command can be used:

    ndncatchunks ndn:/localhost/demo/gpl3

This command will use the realtime method to discover the version number of the file.

To fetch a specific version of a published file, you can use the `fixed` version discovery method.
In this case the version needs to be supplied as part of the name. For example, if the version
is known to be `%FD%00%00%01Qc%CF%17v`, the following command will fetch that exact version of the
file:

    ndncatchunks -d fixed ndn:/localhost/demo/gpl3/%FD%00%00%01Qc%CF%17v


For more information, run the programs with `--help` as argument.