Phase: 2 — Networking Foundations + L4 Goal: Move from application code to the network. Build a TCP server, understand the OSI model from code, and implement the bidirectional proxy that is the foundation of every L4 load balancer and security gateway.
Background in this wiki: the OSI guide (one request through all seven layers); TCP/IP guide Ch 19 (ports and sockets), Ch 20 (UDP), Ch 21–23 (handshake, reliability, closing) with the
dialcheck,stream,udpping, andclosewaitlabs; Linux guide Ch 73 (goroutines vs threads) and Ch 78 (file descriptors and the netpoller).