Networking, Part 3: Building a simple TCP Client - lyuanschool/SystemProgramming GitHub Wiki
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
int main(int argc, char **argv)
{
int s;
int sock_fd = socket(AF_INET, SOCK_STREAM, 0);
struct addrinfo hints, *result;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_INET; /* IPv4 only */
hints.ai_socktype = SOCK_STREAM; /* TCP */
s = getaddrinfo("www.illinois.edu", "80", &hints, &result);
if (s != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
exit(1);
}
connect(sock_fd, result->ai_addr, result->ai_addrlen);
char *buffer = "GET / HTTP/1.0\r\n\r\n";
printf("SENDING: %s", buffer);
printf("===\n");
write(sock_fd, buffer, strlen(buffer));
char resp[1000];
int len = read(sock_fd, resp, 999);
resp[len] = '\0';
printf("%s\n", resp);
return 0;
}Example output:
SENDING: GET / HTTP/1.0
===
HTTP/1.1 200 OK
Date: Mon, 27 Oct 2014 19:19:05 GMT
Server: Apache/2.2.15 (Red Hat) mod_ssl/2.2.15 OpenSSL/1.0.1e-fips mod_jk/1.2.32
Last-Modified: Fri, 03 Feb 2012 16:51:10 GMT
ETag: "401b0-49-4b8121ea69b80"
Accept-Ranges: bytes
Content-Length: 73
Connection: close
Content-Type: text/html
Provided by Web Services at Public Affairs at the University of Illinois
The example above demonstrates a request to the server using Hypertext Transfer Protocol. A web page (or other resources) are requested using the following request:
GET / HTTP/1.0
There are four parts (the method e.g. GET,POST,...); the resource (e.g. / /index.html /image.png); the proctocol "HTTP/1.0" and two new lines (\r\n\r\n)
The server's first response line describes the HTTP version used and whether the request is successful using a 3 digit response code:
HTTP/1.1 200 OK
If the client had requested a non existing file, e.g. GET /nosuchfile.html HTTP/1.0
Then the first line includes the response code is the well-known 404 response code:
HTTP/1.1 404 Not Found