Networking in C · advanced · ~15 min

A tiny HTTP GET client

Send an HTTP/1.0 request over a TCP connection, then read and parse the response status line.

Lesson

How HTTP/1.0 works

HTTP/1.0 is a text-based protocol that runs on top of TCP. Because it is text, you can write a request as a plain string and read the reply the same way.

The exchange has three steps:

Connect a TCP socket to the server.
Write the request. A minimal GET request looks like this:
```
GET /path HTTP/1.0\r\nHost: example\r\n\r\n
```
Each line ends with \r\n (carriage return + line feed). The blank line at the end (an extra \r\n) tells the server the request is finished.
Read the response from the same socket.

Stay on localhost

For the C-platform exercises, only target localhost. The test harness starts a local server in a separate thread for you to connect to.

Never point such a client at third-party hosts without explicit permission.

Code examples

const char *req = "GET / HTTP/1.0\r\nHost: localhost\r\n\r\n";
write(s, req, strlen(req));
char buf[4096]; ssize_t n = read(s, buf, sizeof buf - 1);
buf[n] = 0; puts(buf);

Summary

Key takeaways

HTTP/1.0 is a plain-text protocol carried over TCP.
A request is: connect, write GET /path HTTP/1.0 with \r\n line endings and a trailing blank line, then read the reply.
In these exercises, connect only to localhost (the harness runs a local test server).
Do not run the client against third-party hosts without permission.