Docs++ - Distributed File System

A simplified shared document system similar to Google Docs, implemented in C with support for concurrency and access control.

---

🚀 Features

🧩 Core Functionalities (150 Marks)

• ✅ View files with flags (-a, -l, -al)
• ✅ Read file content
• ✅ Create new files
• ✅ Write to files with sentence-level locking
• ✅ Undo last changes
• ✅ Get file metadata and information
• ✅ Delete files
• ✅ Stream content word-by-word
• ✅ List all users
• ✅ Access control (add/remove read/write permissions)
• ✅ Execute file content as shell commands

⚙️ System Requirements (40 Marks)

• ✅ Data persistence across server restarts
• ✅ Access control enforcement
• ✅ Comprehensive logging system
• ✅ Error handling with clear error codes
• ✅ Efficient search using Trie data structure (O(m) complexity)
• ✅ LRU caching for recent file lookups

---

🏗️ Architecture

• Name Server (NM) – Central coordinator managing file metadata and routing
• Storage Servers (SS) – Handle actual file storage and operations
• Clients – User interface for file operations

---

🔧 Compilation

make

This will compile three executables:

• name_server
• storage_server
• client

---

▶️ Running the System

1. Start Name Server

./name_server

The Name Server will start on port 8080.

2. Start Storage Servers

# Terminal 2
./storage_server 127.0.0.1 9001 10001

# Terminal 3
./storage_server 127.0.0.1 9002 10002

3. Start Client(s)

# Terminal 4
./client

Enter your username when prompted, then use the available commands.

---

💻 Available Commands

Command	Description	Example
VIEW	List accessible files	VIEW
VIEW -a	List all files	VIEW -a
VIEW -l	List files with details	VIEW -l
VIEW -al	List all files with details	VIEW -al
READ <filename>	Read file content	READ test.txt
CREATE <filename>	Create new file	CREATE newfile.txt
WRITE <filename> <sent_idx>	Write to a specific sentence index	WRITE test.txt 0
DELETE <filename>	Delete file	DELETE oldfile.txt
INFO <filename>	Get file information	INFO test.txt
STREAM <filename>	Stream file word-by-word	STREAM test.txt
LIST	List all users	LIST
ADDACCESS -R <file> <user>	Add read access	ADDACCESS -R test.txt user2
ADDACCESS -W <file> <user>	Add write access	ADDACCESS -W test.txt user2
REMACCESS <file> <user>	Remove access	REMACCESS test.txt user2
EXEC <filename>	Execute file as shell script	EXEC script.txt
UNDO <filename>	Undo last change	UNDO test.txt
HELP	Show help	HELP
EXIT	Exit client	EXIT

---

🧪 Testing

Run the automated test suite:

chmod +x test.sh
./test.sh

The test script will:

1. Compile the project
2. Start all necessary servers
3. Run 15+ automated tests
4. Display results with pass/fail status
5. Clean up processes and files

---

🧠 Key Implementation Details

🔍 Efficient Search

• Trie data structure for O(m) file lookups (m = filename length)
• LRU cache (100-entry capacity) for recent searches
• Hash-based fallback for edge cases

🧵 Concurrency

• Multi-threading using pthreads for handling multiple clients
• Mutex locks for protecting shared data structures
• Sentence-level locking for concurrent file editing

🔐 Access Control

• Owner always has read/write access
• Read access allows viewing content
• Write access includes read permissions
• Access lists stored in file metadata

💾 Data Persistence

• Files stored in ./storage/
• Undo history in ./storage/.undo/
• Metadata maintained by Name Server

⚠️ Error Handling

Error Code	Meaning
ERR_FILE_NOT_FOUND	File doesn't exist
ERR_ACCESS_DENIED	Insufficient permissions
ERR_FILE_EXISTS	File already exists
ERR_SENTENCE_LOCKED	Sentence being edited by another user
ERR_INDEX_OUT_OF_RANGE	Invalid sentence/word index
ERR_SS_NOT_AVAILABLE	Storage server unavailable

---

🌐 Network Architecture

Client(s) <--TCP--> Name Server <--TCP--> Storage Server(s)
   |                                          |
   +--------------- Direct TCP ---------------+
          (for READ, WRITE, STREAM ops)

---

📂 Project Structure

docs_plus_plus/
├── common.h              # Shared data structures and constants
├── common.c              # Common utility functions
├── name_server.c         # Name Server implementation
├── storage_server.c      # Storage Server implementation
├── client.c              # Client implementation
├── Makefile              # Build configuration
├── test.sh               # Automated testing script
└── README.md             # Project documentation

---

⚠️ Limitations

• Single undo per file (no multi-level undo)
• No folder hierarchy (bonus feature not implemented)
• No fault tolerance or replication (bonus feature)
• Name Server failure means system failure
• Maximum: 100 clients, 10 storage servers

---

🚧 Future Enhancements

• Hierarchical folder structure
• Multi-level undo with checkpoints
• Fault tolerance with replication
• Request-access mechanism
• Name Server redundancy

---

👥 Authors

Implemented as part of the Operating Systems and Networks (OSN) course project at IIIT Hyderabad.

---

📜 License

Educational use only.

---

🧭 Usage Instructions

Compile everything

make

Run in separate terminals

# Terminal 1
./name_server

# Terminal 2
./storage_server 127.0.0.1 9001 10001

# Terminal 3
./storage_server 127.0.0.1 9002 10002

# Terminal 4
./client

Run tests

chmod +x test.sh
./test.sh