D-LAN

h1. Persistent data

h2. Files cache

This file contains all the shared files and theirs SHA-1 hashes. This file is saved in user space after an update of the file list, it is completely loaded at the start of Aybabtu. If some paths of some files doesn't match the shared directory they are discarded.

This file is saved as a binary file serialized by protocol buffer.

You can see the proto file here : source:/application/Protos/files_cache.proto

h3. Size

Here is a size approximation for 50'000 files stored in 1 TB. The overhead of the file format is not taken in account.

<pre>

Nb of files : 50'0000

Total size : 1 TB

Chunk Size : 32 MB

Average file per directory : 50

Average filename and dirname length : 50 char

Size of a hash : 20B

</pre>

<pre>

AverageFileSize = 1*1024^4 / 50'000 = 21MB

Sha1Size = floor(AverageFileSize / 32MB) * 20 * 50'000 = 1 * 20 * 50'000 = 977kB

FilenameSize = 50'000 * 50 * 2 = 4.8MB (2 bytes per char)

DirnameSize = (50'000 / 50) * 50 * 2 = 97kB

TotalSize = 977kB + 4.8MB + 97kB = 5.9MB

</pre>

h2. Queued files and directories

A file containing the queued files and directories is saved in user space. An item from the list may contains a remote peer id and/or the hashes which identify a file. 

As the file cache file (see above), this file is saved as a binary file serialized by protocol buffer.

For more details see the file : source:/application/Protos/queue.proto

h2. Configuration file

here are the persisted data :

* The nick

* The shared folders in read-only 

* The shared folders in read-write

* Core address and password for remote core

There is two ways to persist theses data :

# Using of _QSettings_ : http://doc.trolltech.com/4.5/qsettings.html

# Using a custom file containing data serialized with _Protocol Buffer_ as the file cache

h3. Pros for the first method (_QSettings_)

* Easier to create, not necessary to create a file definition.

* Standard to Qt.

h3. Pros for the second method (_Protocol Buffer_)

* Same method as the two other files.

* All the persisted data is in the same place.