Tcp

“tessenger” is my unsw networks assignment: a multi-client chat server in raw c — server.c (583 lines) and client.c (253), no libraries beyond pthreads and the bsd socket api (Kernighan, Brian W. and Ritchie, Dennis M., 1988). it does authentication with timed lockout, private and group messaging, presence, audit logs, and a udp side channel for peer-to-peer file transfer. this page walks the architecture, weaves in the socket theory the assignment was designed to teach, and then does something the assignment never required: an honest concurrency audit of my own submission, with the bugs demonstrated live. 𐃏

the internet is a triumph of indirection: no layer trusts the one below to be reliable, timely, or even present, and yet a packet leaves your laptop, crosses a dozen autonomous systems owned by companies that actively dislike each other, and arrives. 𐃏 this page walks the stack bottom-up, then follows one HTTP request through DNS, TCP, and TLS to see every layer earn its keep.