Autoficon - Automatic filetype convertor

1.1. Purpose
The purpose of this SDS is to describe the design and function of our software.
The software is designed in a modular way. This document describes the various modules of the software and their functionalities. This document also gives the relationships between the various modules.

1.2. Document conventions
All level 1, 2 and 3 headings are written using font “Times New Roman” font size 14.
All textual matter using “Times new Roman” font size “12”.

1.3. Scope of the development Project
The main purpose of the Autoficon is to make the process of file conversion simpler. The file type can be converted by just renaming the file i.e. changing the extension. It runs as a daemon which monitors for any file system alteration event in the users HOME directory. When a file system alteration event occurs the file type conversions will be made based on the extension. Presently our aim is to support conversion for image types. As and when the user renames a file (currently only image files) the daemon automatically detects it and carries out the necessary conversion. The user need not intervene in the conversion process.

1.4. Definitions, Acronyms and Abbreviations
FAM              File Alteration Monitor
PID                 Process ID
PPID              Parent Process ID
UID                User ID

1.5. References
1. http://oss.sgi.com/projects/fam/doc.html

2. System Architecture Description

2.1. Overview of the modules

Fig.(1) Various Modules of the Software

The software can be divided in to 3 main modules

· The Spy

· The Transformer

· The Subscriber

These modules also have sub-modules which will also be discussed.

2.1.1. The Spy:

The Spy module can be considered as a server module.
The main work of the Spy is to monitor the file system for changes and inform it to the transformer.

Parent Spy:

The Parent Spy keeps track of the user logins and logouts.
It forks a child Spy when new user logs in.
It kills a child spy when no instance of an user exist.
Informs the Transformer about file creation details that is obtained from the Child Spy.

Child Spy:

Each user has a corresponding Child Spy.
The Child Spy monitors the user’s home directories for any file create and delete events.
It maintains the list of user directories being monitored.
In case of any events it informs to the Parent Spy.

The Spy module can again be split in to following modules

User Information Module:

Maintains the list of users who have logged in and their instance count(ie number of logins).
It keeps track of user logins using the Subscriber module.
It finds the user logout by monitoring the proc file system

File Monitoring Module:

· This module is responsible for monitoring the file system.

2.1.2. The Transformer:

· The Transformer module takes care of the file type transformation.

· It maintains a list of plug-ins available to carry out the conversion

2.1.3. The Subscriber

· It is a simple module which registers to the Spy when the use logs in.

· It sends the Process ID and the Users Home directory to the Spy.

2.2. Structure and Relationships

Fig (2) User Registration

Fig (3) File Monitoring

Fig (4) File Monitoring – 2

Fig (5) File Transformation

2.3. User Interface issues

The users are

3. Detailed Description of the Components

3.1. Spy Module

Type	This is the module for monitoring and informing file system changes. It has two sub-modules as mentioned before
Purpose	The purpose of this module is Monitor the file System Maintain the user information
Function	The functions of this modules are Maintaining a user list Monitoring the file system and reporting it to the Transformer Monitoring for user logins and logouts
Subordinates	The subordinate of this modules are User Information Module File Monitoring Module
Dependencies	This module depends on the Subscriber module to identify a user login.
Interfaces	The Spy module communicates with other modules using Unix IPC (Message queues).
Resources	The module uses all the resources used by the sub-ordinate modules
Processing	The processing of the module is the sum processing of the subordinatemodules
Data	-- NA --

3.1.1. User Information Module

Type	This module is a part of the Spy module
Purpose	The purpose of this module is to maintain the user information .i.e. users who have logged in and are using the service by running the Subscriber
Function	The functions of this module are To monitor for user login and logout To maintain the user instance count
Subordinates	-- NA --
Dependencies	This module requires the Subscriber module to know about a user login
Interfaces	-- NA --
Resources	This module makes use of the information available in the /proc file system
Processing	This module does the following When a user logs in the subscriber module is invoked. The subscriber module contacts this module with the use information such as UID, PPID of the Subscriber, Home directory of the user etc. The module checks whether the user is already logged in. If the user is new a Child spy is forked. When a user logout is detected, it reduces the user instance count. If the user instance count becomes zero, it terminates the child spy running for that user.
Data	User Information Structure UID Home directory Number of user instances Linked list of PPID of Subscribers

3.1.2. File Monitoring Module

Type	This is a part of the Spy module
Purpose	The purpose of this module is to monitor the file system and report it to the Parent Spy or Transformer
Function	The functions done by this module are Maintain a list of directories being monitored Monitoring and informing the file system events (FILE_CREATION & FILE_DELETION)
Subordinates	-- NA --
Dependencies	-- NA --
Interfaces	-- NA --
Resources	The module uses FAM to monitor the files. ( inotify and gamin are also in consideration)
Processing	The module does the following processing When a new user is logging, it recursively travels into the user’s home directory and register them with FAM. When a new file is created inside user’s home directory, it checks if it is a directory. If it is a directory, the newly created directory is registered. If it is an ordinary file it informs the Parent Spy which in turn informs the Transformer.
Data	The structure of the file information is: File name ( with full path ) FAM connection number Each Child Spy maintains a list of above information for the corresponding user.

3.2. Transformer Module

Type	This module carries out the file type conversion, if necessary
Purpose	The purpose of this module is to convert the file type of the file reported by the Spy
Function	The functions performed by the module are Identify the file type to check for possible conversion If file type conversion is necessary and it is possible carry out the conversion
Subordinates	-- NA --
Dependencies	-- NA --
Interfaces	-- NA --
Resources	The Transformer requires image handling libraries such as libtiff, libjpeg, libpng, DevIL etc. The module uses a plug-in list file.
Processing	The module does the following processing When the Transformer is run it creates a list of available plug-ins When a FILE_CREATED is reported by the Spy, fork a Child Transformer The following are done in the child process The current file type is identified. The current extension is identified The following take place when the extension and file format do not match The Transformer searches for a matching plug-in to carry out the conversion. If a plug-in is found it carries out the conversion.
Data	The Transformer maintains a list of plug-ins. The information stored about the plug-ins are Plug-in version Source format Target format Location of the plug-in library

3.3. Subscriber Module

Type	This module register a user with the Spy, when he user logs in.
Purpose	The purpose of this module is to inform the Spy about a user login
Function	The functions of this module are Inform the Spy the User’s home directory Inform the spy its PPID
Subordinates	-- NA --
Dependencies	-- NA --
Interfaces	Uses Unix IPC to communicate with the Spy.
Resources	-- NA --
Processing	The processing done by this module is Obtain the User Information and inform it to the Spy
Data	-- NA --

4. Reuse and Relationship with other products
The modules used in this software can be reused with any other software. The plugins used for converting a file from one type to another can be made use by other softwares.
The software uses some open source code and libraries for image conversion and file system monitoring.

5. Design Decisions and Tradeoffs
The number of directories that can be monitored in a Users home directory is limited by the capability of FAM. FAM allows a maximum of 1000 active requests at a time for each process. Hence it was decided to fork a Child Spy for each new user.

6.     Pseudocode for components
6.1 Spy
if ( UserLoginDetected )
            if ( NewUser )
                       CreateNewUserInfo();
                       fork();
            endif
else
            IncreaseUserInstanceCount();
endif
if ( UserLogoutDetected )
             DecreaseUserInstanceCount();
             if ( UserInstanceCount == 0 )
                        KillChildSpy();
             endif
endif

// Inside the child spy
RegisterAllUserDirectories();
WaitForEvent();
if ( FileCreated )
              if ( FileIsDirectory )
                         AddToMonitorList();
              else
                          ReportToParentSpy();
               endif
endif
if ( SIGTERM )
               UnregisterAllDirectories();
               Exit();
endif

6.2 Transformer
BuildPluginList();
WaitForEvent();
if ( FileCreated ) //message sent by the Spy
                 filetype=CheckForFiletype();
                 fileext=GetFileExtension();
              if ( filetype != fileext )
                              FindPlugin();
                              if ( PluginFound )
                                                 ConvertFiletype();
                              endif
                  endif
endif

Appendices
---- NA ---