Justin Yang

11/30/24

1. Getting Started

First, I needed to understand what I'm trying to build. I reviewed the TCP/IP and OSI network models and their layers on this video: https://youtu.be/CRdL1PcherM?si=dMnGLPY4UCzL2Rt7.

Next, I needed to figure out what network proxies were which this video helped with: https://youtu.be/4NB0NDtOwIQ?si=DhqFThDD__a7VSCP.

I was still confused on what a TCP proxy was specifically, so I asked Perplexity "is a tcp proxy just a reverse proxy?". I had the wrong idea because apparently reverse proxies operate on layer 7 and TCP proxies operate on layer 4.

TCP Proxy	Reverse Proxy
Operates at transport layer (Layer 4)	Can operate at application layer (Layer 7)
Primarily forwards TCP segments	Can modify and inspect traffic
Limited to TCP protocol	Supports multiple protocols
Basic traffic forwarding	Advanced features like SSL encryption, caching

This gave me a little more insight into what a TCP proxy is, but I'm still unclear. I kept asking perplexity more questions and came to the conclusion that a TCP proxy is just a program that manages TCP traffic between two computers, and does any variety of tasks with the traffic it intercepts (https://www.perplexity.ai/page/what-is-a-tcp-proxy-trk3L64lRbePJMG_DeJLMw).

12/4/24

2. Building a TCP Proxy

Now that I have a rough idea of what a TCP proxy is, I need to actually build one.

I found an article online on how to build a TCP proxy in python: https://thepythoncode.com/article/building-a-tcp-proxy-with-python#implementation, read through its explanations, and the code.

I'm unfamiliar with the python standard libraries for networking, so I watched this helpful tutorial: https://youtu.be/3QiPPX-KeSc?si=BRabx8Pf4wc9MOlj. And also watched this short video which helped clear up what network sockets are for me: https://youtu.be/_FVvlJDQTxk?si=As96U5tOPdnifpj_ (I also realized sockets not the same as WebSockets 😅).

Then I made the basic structure for my TCP proxy and a testing suite for it with Perplexity.

To add the CLI functionality, I made a main program for the TCP proxy file as well. To add signal handling, I used python's signal, sys, and logging libraries.

After all that, I updated the test file to reflect changes made to the proxy.

Unfortunately, I this is as far as I'm getting 🥲. I was caught up by a few other projects and a final tomorrow so I didn't have much time to spend on the TCP proxy :p.

If I had more time to work on this project though, I would:

• Make sure I understand all the code, a lot was generated.
• Make the test suite more thorough.
• Test to make sure it works across different operating systems (although python should work everywhere).
• Try making something to automatically detect the optimal buffer size to use, rather than a constant value.
• Check if the proxy works with API calls.

Thanks for giving me the opportunity to learn more about networking and considering me for your internship position!

3. Instructions + Additional

Instructions for running

1. Have python3 installed.
2. Same as given instructions. i.e. To run tcp_proxy.py: python3 tcpproxy.py --ip 127.0.0.1 --port 5555 --server "192.168.5.2:80" from the project root folder. To run test_tcp_proxy.py: python3 test_tcp_proxy.py.

Citations

See citation.md

Light Links

This project was made for Light Links Inc.'s software intern assessment. Instructions can be found in assessment.pdf.