Reliable Files Transfer

The source code and some specifications will be omitted per UCSC’s policy.

During the Winter 2025, I had a chance to take a network programming class of CSE156. One of my favorite’s class assignments was to create a program transferring files over UDP socket. The goal was to learn the importance and the reason why each TCP field exists, since the assignment forced me to basically reimplement a reliable protocol over unreliable transport link from scratch. The result was a packet structure that is similar to TCP packets, and control flows that assembled TCP.

• Make a reliable transferring over unreliable transfer protocol (UDP).
• Each UDP packet size must be lower than a specific number.
• Can handle dropped packets, duplicate packets, unordered packets.
• Can handle multiple transfers at once, so multiplexing.
• Must be relatively fast for large files, so keeping an entire 1GB file buffer inside memory is out of the equation.

C++ with standard library only. Writing on UDP must be done on socket-level only.

Not only did I learn more on socket programming and TCP, I also learned how to handle buffers. With many layers of abstraction and fragmentation from limited packet size, constructing partially complete buffer with interactiveness is a must.