Made by Muraru Stefan

This project is licensed under the MIT License - feel free to use, modify, and share it!

C++ Local File Sharing Server

🚧 Current status: Multi-file support implementation in progress...

A simple, high-performance command-line utility written in C++ to share files from a Linux or Windows machine to any device with a web browser (optimized for iPhone/iOS) over a local network.

Features

• Zero Dependencies: Uses standard C++17 and POSIX sockets.
• High Speed: Efficient memory buffering for fast transfers.
• Mobile Optimized: Specifically tuned to handle Safari (iOS) connection behaviors and HTTP headers.
• Reliable: Handles SIGPIPE signals and multiple browser handshake requests.

How it Works

The program creates a basic HTTP server using TCP Sockets. It listens for incoming connections, handles the HTTP GET request, and streams the file as a binary octet-stream, forcing the browser to trigger a download.

Installation & Usage

First download the file "server.cpp"

How to compile the project:

Linux

g++ -std=c++17 server.cpp -o file_server

Windows

is required to add the flag "-lws2_32".

g++ server.cpp -o server.exe -lws2_32

you can also use the MinGW or g++ compiler.

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How to run the command (server side)

To share a file, pass its path as an argument when launching the program. If the filename has spaces, wrap it in quotes:

Linux

Run the server on Linux requires sudo to bind to port 80

sudo ./file_server "your_file.pdf/.jpeg/ecc..."

Windows

.\server.exe your_file.jpg

IMPORTANT: Firewall Note: When running the server for the first time, Windows might prompt you to allow the application through the Firewall. Ensure you grant access to "Private" and/or "Public" networks for the connection to work.

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The server will start, display your local IP address, and stay active (listening on port 8080) until you manually stop it with Ctrl+c

Hot to download (client side)

Ensure both the PC and the Phone are connected to the same Wi-Fi network

1. Start the server on your PC by using the commands written above
2. Find the IP: The program will print your local IP in the terminal (e.g., 192.168.1.106).
3. Open browser: On your iPhone, Android, or another PC, open Safari/Chrome and type:

   http://192.168.1.xxx:80
   

   (Replace 192.168.1.xxx with the IP shown in your terminal).
4. HTTP ONLY: You must use http:// and NOT https://. Most mobile browsers try to force HTTPS, which will cause a connection error because this server does not use SSL.
5. Save: A download prompt will appear on your screen. Click "Download" to save the file to your "Files" or "Downloads" folder.

Critical Troubleshooting & Security

1. The Firewall (UFW) - "Connection Refused" If your phone says "Impossible to connect", the Linux firewall is likely blocking port 80. You can open the specific port with:

   • To allow connection: sudo ufw allow 80/tcp
   • To check status: sudo ufw status
   • To block again later: sudo ufw delete allow 80/tcp

2. The "3 Success Messagges" Mystery When downloading on iOS/Safari, the terminal might print "Transfer Successful" 3 times. This is normal behavior:

   • Request 1: Safari checks the file headers (metadata) to show the download prompt.
   • Request 2: Safari performs a quick stability test of the connection.
   • Request 3: The actual data download takes place. The server handles each "ping" as a successful interaction.

Technical Deep Dive (What I Learned)

• Socket Management: Implementation of the socket(), bind(), listen(), and accept() lifecycle.
• HTTP Protocol: manual crafting of HTTP/1.1 headers. Specifically:
  • Content-Type: application/octet-stream: Forces the browser to treat data as a binary file.
  • Content-Disposition: attachment; filename="...": Forces the "Save as" prompt with the original name.
• Buffer & Memory: Files are streamed in 16KB chunks using std::vector<char>, allowing for high-speed transfers without filling up the RAM, even for large files.
• Request Clearing: The server reads the client's request buffer (recv) before responding to ensure the TCP window is clear, preventing protocol synchronization errors.

Roadmap & Upcoming Goals

You can follow the detailed progress of the work on my Project Board.

• Full Translation (Done): Converting all code comments and system logs from Italian to English to make the project international.
• Cross-Platform Support (Windows) (In progress): Implementation of the Winsock2 libraries to make the server compatible with Windows systems as well as Linux.
• Multi-file Support: Implemented the ability to share entire folders or multiple files at once.
• Web Interface (UI): Replaced the direct download with a minimal HTML page for a better mobile user experience.
• HTTPS Security: OpenSSL integration to secure data transfer within the local network.
• Progress Bar: Real-time display of the loading percentage in the terminal.

A Project Done (and in progress) By Stefan Muraru.