block.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <assert.h>

int main(int argc, char *argv[]) {
	size_t n;
	int sock;
	struct sockaddr_in servaddr;
	unsigned char block_addr[5];
	int ret;
	int off;
	int block_rate;

	if (argc != 3) {
		printf("Usage: provide an <IP address< <block rate>\n");
		exit(0);
	}

	block_rate = atoi(argv[2]);
	if (block_rate < 0 || block_rate > 100) {
		printf("block rate must be between 0 and 100\n");
		exit(0);
	}

	block_addr[4] = (unsigned char)block_rate;

	ret = sscanf(argv[1], "%hhu.%hhu.%hhu.%hhu%n", 
		&block_addr[0], &block_addr[1], &block_addr[2], &block_addr[3], &off);

	if (ret != 4 || argv[1][off] != '\0') {
		printf("couldn't understand addr %s\n", argv[1]);
		exit(0);
	}
	printf("Blocking: %d.%d.%d.%d\n", 
		(int)block_addr[0], (int)block_addr[1], (int)block_addr[2], (int)block_addr[3]);

	sock = socket(AF_INET, SOCK_DGRAM, 0);
	if (sock < 0) {
		perror("socket creation failed");
		exit(0);
	}


	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(100);
	servaddr.sin_addr.s_addr = inet_addr("100.100.100.100");


	n = sendto(sock, block_addr, 5, 0, (struct sockaddr*)&servaddr, sizeof(servaddr));
	if (n != 5) {
		perror("send error");
	}

	close(sock);
	return 0;
}