C Socket Examples

Minimal TCP, UDP, and HTTPS client examples matching the Python versions in ../python/.

Build

TCP/UDP (no extra deps):

cc -o 01-basic-tcp-server 01-basic-tcp-server.c
cc -o 02-basic-tcp-client 02-basic-tcp-client.c
cc -o 03-basic-udp-server 03-basic-udp-server.c
cc -o 04-basic-udp-client 04-basic-udp-client.c
cc -o 06-domain-to-ip 06-domain-to-ip.c
cc -o 07-ioctl-link-layer 07-ioctl-link-layer.c

HTTPS client (requires OpenSSL):

cc -o 05-https-client 05-https-client.c -lssl -lcrypto

On macOS with Homebrew OpenSSL, you may need:

cc -I$(brew --prefix openssl)/include -L$(brew --prefix openssl)/lib \
   -o 05-https-client 05-https-client.c -lssl -lcrypto

Or build all at once (TCP/UDP only; HTTPS needs the OpenSSL flags above):

for f in 0*.c; do cc -o "${f%.c}" "$f"; done

Run

TCP (run server first, then client in another terminal):

./01-basic-tcp-server    # Terminal 1
./02-basic-tcp-client    # Terminal 2

UDP (run server first, then client):

./03-basic-udp-server    # Terminal 1
./04-basic-udp-client    # Terminal 2

HTTPS client (no server needed; talks to real HTTPS sites):

./05-https-client www.example.com
./05-https-client www.example.com /

Domain name to IP (DNS lookup):

./06-domain-to-ip www.example.com
./06-domain-to-ip localhost

ioctl link-layer (query network interfaces; Linux-oriented):

./07-ioctl-link-layer              # list all interfaces
./07-ioctl-link-layer eth0         # single interface

TCP/UDP examples use 127.0.0.1:8080 by default. Requires a POSIX environment (macOS, Linux, etc.). See 10-security/02-https-how-it-works.md for how HTTPS communication works.