PDS_Project (m1)

Students: Giuseppe Toscano (280086) - Luca Nicosia (269565)

GitHub link: https://github.com/LucaNicosia/PDS_Project

1. Needed packages

• SQLITE3: sudo apt-get install libsqlite3-dev
• CRYPTOPP: sudo apt-get install libcrypto++-dev libcrypto++-doc libcrypto++-utils

2. Needed initial folders and files

  /client_folder
    /DB
    /executable_dir
      /client_directory
      PDS_Project_Client (executable)
    /Log
      log.txt

  /server_folder
    /DB
      /users
    /executable_dir
      /server_directory
      PDS_Project_Server (executable)
    /Log
      log.txt

2.1 Description of initial folders

• DB: contains all db files (e.g. user1.db, user2.db, ...)
• executable_dir: contains the executable file and client_directory/server_directory that contains users data
• Log: contains the log file

3. Parameters of the executable files

• PDS_Project_Server: PORT (e.g. 5111)
• PDS_Project_Client: PORT username password FETCH/RESTORE(e.g. 5111 user1 pass FETCH)

  The program can be executed in two different modes:

  1. FETCH: replicates all user actions on client directory in server directory
  2. RESTORE: delete all local files and restore all data contained in the server directory

4. Internal structures

4.1 Database

Two db types:

• username.db
  • directory (path, name)
  • file (path, name, hash)
• users.db
  • users (username, password, salt)

The field password of users is not the real password but the salted digest computed with the library cryptopp

4.2 Communication protocol

• FETCH MODE:

    CLIENT                                                SERVER                                                                                       
    CONNECT username password mode ->
                                                          <- CONNECT-OK
    CONNECT-OK ->
                                                          if (!correct password)
                                                          <- wrong username or password
    return
                                                          else
                                                          <- DIGEST server_db_digest
                                                          endif
    if (client_db_digest == server_db_digest)
    Database up to date ->                                 
                                                          <- server_db_ok
    else
    GET-DB ->   
                                                          <- sendFile(server_db)
    ... compare the two databases ...
    for each different directory:
    DIR path action ->              
                                                          <- DONE
  
    for each different file:
    FILE path action ->
                                                          if (action == 'erased')
                                                          <- DONE
                                                          else  
                                                          <- READY
                                                          endif
    if (action != 'erased')
    FILE path length_file ->                    
                                                          <- OK
    sendFile(path) ->             
                                                          <- DONE
    endif
    endif
    ... starting folder monitoring ...
  

• RESTORE MODE: like FETCH MODE but the file/directory transfering is in the opposite direction.

4.3 Communication.h

This library contains primitives to send and receive messages and files between two hosts.

4.4 File.h, File.cpp, Directory.h and Directory.cpp

These two classes are used to represent a simplified view of the filesystem with some more addons (e.g. file digest).

4.5 Socket.h, Socket.cpp, SocketServer.h and SocketServer.cpp

These two classes are used to perform a TCP connection between two hosts. There is a customizable timeout for each message.

4.6 MyCryptoLibrary.h

This library is used to compute the digest of a file or a string.

4.7 Utilities.h

This library contains the Logger class that is used to write on the log file.

4.8 FileWatcher.h

This library is used to monitor a specific directory in the client space and react to each modification.

4.9 Database.h

This library is used to perform queries on databases using SQLITE3.

4.10 Exceptions.h

This library contains definitions of different types of exception:

• general_exception
• socket_exception
• filesystem_exception (derived from general_exception)
• database_exception (derived from general_exception)

5. Processes and Threads

5.1 Processes

5.1.1 Client

At the beginning the client process performs a fork():

• father: display on console the child status received from the pipe (e.g. 'connection succeed', e.g. 'wrong username or password'). It is used to make the child a zombie process
• child: executes the main program and sends its status via pipe

5.1.2 Server

At the beginning the server process performs a fork():

• father: dies (it is used to make the child a zombie process)
• child: executes the main program

5.2 Threads

5.2.1 Client

• main thread: executes the main program and creates the below threads
• FileWatcher thread: setup and starts the FileWatcher
• monitor thread: monitors the status of the FileWatcher and opens or closes server connection

5.2.2 Server

• main thread: listens on socket port and creates the below threads
• user thread: a thread is instantiated for each user that connects to the server (until the number of connected users reach a threshold). This thread executes the main program.