A C++ client-server banking system built on TCP sockets with multithreading, signal handling, and structured request/response messaging. The system is split into three independent servers and one interactive client.

• Client

  • Interactive CLI for users
  • Connects to all servers
  • Supports retries, graceful shutdown, and signal-safe transactions

• Finance Server

  • Manages bank accounts
  • Supports deposit, withdraw, balance checks
  • Accrues interest across all accounts using a thread pool

• File Server

  • Handles file upload and download
  • Optional file-extension allowlist
  • Stores files in a local storage/ directory

• Logging Server

  • Records all user actions to a log file
  • Thread-safe file writes

• TCP-based request/response protocol
• Length-prefixed wire format
• Thread pools for concurrency
• Mutex-protected shared state
• Graceful shutdown via signals (SIGINT, SIGCHLD, SIGALRM)
• Retry logic for failed client operations

• LOGIN
• LOGOUT
• DEPOSIT
• WITHDRAW
• BALANCE
• EARN_INTEREST
• UPLOAD_FILE
• DOWNLOAD_FILE
• QUIT

Requires:

• g++ (C++11)
• pthreads
• Linux or Unix-like OS

Build everything:

make

Clean build artifacts:

make clean

Start each server in its own terminal before launching the client.

./finance [-p PORT] [-m MAX_ACCOUNTS] [-t THREADS]

Defaults:

• Port: 8000
• Max accounts: 100
• Threads: 4

./file [-p PORT] [-t THREADS] [ALLOWED_EXTENSIONS...]

Defaults:

• Port: 8001
• Threads: 4
• If no extensions are provided, all are allowed

./logging [-p PORT] [-f LOG_FILE] [-t THREADS]

Defaults:

• Port: 8002
• Log file: system.log
• Threads: 4

./client [OPTIONS]

Options:

• --finance-host HOST
• --finance-port PORT
• --file-host HOST
• --file-port PORT
• --logging-host HOST
• --logging-port PORT
• -r, --retries N
• -h, --help

Defaults connect to localhost on ports 8000, 8001, and 8002.

• Login
• Deposit
• Withdraw
• View balance
• Upload file
• Download file
• Logout
• Server status
• Accrue interest
• Exit

Request format

TYPE|USER_ID|AMOUNT|FILENAME|DATA

Response format

SUCCESS|BALANCE|DATA|MESSAGE

Messages use a 4-byte length prefix (network byte order).

• SIGINT: graceful shutdown (second SIGINT forces exit)
• SIGCHLD: server process tracking
• SIGALRM: timeout support

Signal events are logged to signals.log.

• Accounts are created lazily on first use
• Interest accrual applies 1% to all positive balances
• File storage is local and not sandboxed
• Designed for instructional and architectural purposes