Overview

PeerCon is a peer-to-peer desktop sharing application built entirely with Java JDK, utilizing no external dependencies.
I started this project while studying Netty. I wanted to explore pure Java networking (Java NIO) without relying on abstraction layers like Netty. I aim to understand the core mechanisms of low-level networking, including UDP hole punching and non-blocking I/O.

Screenshots

This shows a screen being shared with another PC in real time.

Architecture

- The server handles requests using a selector and worker-thread architecture. - The client uses blocking channels because the request volume is not high. - After a connection is established via UDP hole punching, screen sharing is implemented by capturing the screen and transmitting the captured frames between peers.

Learnings

Server

• Understood the roles of STUN and TURN servers in direct peer-to-peer communication environments.
• Learned when to use blocking I/O and why a selector is needed to manage multiple sockets with non-blocking I/O.
• Identified the limitations of P2P communication under symmetric NAT/router environments and the need for a TURN server.
• Designed a custom protocol and handled raw data directly.
• Implemented TCP and UDP communication using Java NIO.

Client

• Built screen capture and compression features using Java’s Robot class.
• Implemented direct communication through NAT hole punching.
• Investigated issues caused by symmetric NAT environments and applied appropriate workarounds.
• Understood why private IP-based communication is needed when peers are under the same public IP.
• Designed a custom protocol and handled raw data directly.
• Built TCP and UDP communication features using Java NIO.

How to run

git clone https://github.com/clapppp/PeerCon-client.git
cd PeerCon-client/target
java -jar client-1.0.jar