Network Programming

Four network servers written from scratch in C++ over BSD sockets, progressing from a single-client remote shell to a concurrent multi-user server, an HTTP/CGI server, and a SOCKS4 proxy.

Projects

1-npshell/ — remote shell with pipes

A shell (npshell.cpp, 363 lines) supporting ordinary pipes, numbered pipes (|N / !N — pipe output to a command N lines later), and file redirection, executing external commands via fork/exec with correct pipe plumbing between children.

2-concurrent-servers/ — three concurrency models

The same multi-user "remote working station" server implemented three ways, to compare concurrency architectures:

• np_simple — one process per connection (fork per client)
• np_single_proc (762 lines) — single process, all clients multiplexed with select()
• np_multi_proc (725 lines) — process per client with shared memory + FIFOs for cross-user pipes and broadcast messaging

3-http-cgi-server/ — HTTP server + CGI

An HTTP server (http_server.cpp) that parses requests and dispatches to CGI programs, plus a CGI console (cgi_server.cpp, 387 lines) built on Boost.Asio that opens multiple concurrent SSH-like sessions and streams their output into an HTML panel. Includes a minimal Boost.Asio echo-server example.

4-socks4-proxy/ — SOCKS4/4A proxy with firewall

A SOCKS4 proxy (socks_server.cpp, 353 lines) supporting both CONNECT and BIND modes, with a configurable firewall (socks.conf) that permits/denies connections by operation and destination.

Concepts demonstrated

BSD sockets, fork/exec process management, select() multiplexing, inter-process communication (shared memory, FIFOs, pipes), HTTP and CGI, the SOCKS4 protocol, and Boost.Asio's asynchronous model — the core toolkit of concurrent network back ends.

Build

Each project has its own Makefile:

cd 2-concurrent-servers && make
./np_single_proc 8000        # then telnet/nc to localhost 8000

Context

Coursework for Network Programming at NYCU (Spring 2024), taught by Prof. I-Chen Wu. Each project directory is my own implementation against the course specification; the shell command binaries (noop, number, removetag) are small provided test utilities. Cleaned up (compiled binaries, course spec PDFs, and editor configs removed) and documented for release.