networking protocols are complicated

book: TCP/IP Illustrated, Volume 1, by Stevens (600 pages)
person: what if I just want to download a cat picture?

Unix systems have an API called the “socket API” that makes it easier to make network connections

Unix: you don’t need to know how TCP works. I’ll take care of it!

here’s what getting a cat picture with the Socket API looks like:

1. Create a socket: fd= socket(AF_INET, SOCK-STREAM...)
2. Connect to an IP/port: connect (fd, 12.13.14.15:80)
3. Make a request: write (fd, "GET /cat.png HTTP/I.I...)
4. Read the response: cat-picture= read (fd...)

Every HTTP library uses sockets under the hood

$curl awesome.com
Python: requests.get("yay.us")"
(sockets)

person: oh, cool, I could write an HTTP library too if I wanted*. Neat!
* SO MANY edge cases though! :)

AF_INET? What’s that?

AF-INET means basically “internet socket”: it lets you connect to other computers on the internet using their IP address.

The main alternative is AF-UNIX (“unix domain socket”) for connecting to programs on the same computer.

3 kinds of internet (AF INET) sockets:

1. SOCK_STREAM = TCP (curl uses this)
2. SOCK_DGRAM = UDP (dig (DNS) uses this)
3. SOCK.RAW = just let me send IP packets. I will implement my own protocol. (ping uses this)