basic-proxy/main.c

#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include "easysock.h"
#define PROG_NAME "basicproxy"
#define PROG_VER "0.01"
void forward_data(int from_fd, int to_fd) {
	int n = 0;
        char* buffer = malloc(3000*sizeof(char));
	while ((n = recv(from_fd, buffer, 3000, 0)) > 0) { // read data from input socket
        	send(to_fd, buffer, n, 0); // send data to output socket
	}
}

void print_prog_info() {
	printf("%s [Local IP address] [local port] [remote IP address] [remote port]\n",PROG_NAME);
}

void print_version_info() {
	printf("%s %s\n",PROG_NAME,PROG_VER);
}

void print_help_info() {
	printf("\n%s - A simple TCP proxy written in C.\n\n",PROG_NAME);
	printf("Syntax - ");
	print_prog_info();
	printf("[Local IP address] - The local address to bind to\n"
		"[local port] - The local port to listen on\n"
		"[remote IP address] - The remote IP to connect to\n"
		"[remote port] - The remote port to connect to\n");
	printf("\nExample: %s 127.0.0.1 3000 1.2.3.4 5000 - Listen on '127.0.0.1:3000', and forward all data from there to '1.2.3.4:5000'\n\n",PROG_NAME);
}
int main(int argc,char* argv[]) {

/* argv[1] = local address
   argv[2] = local port
   argv[3] = remote address
   argv[4] = remote port */

	if (argc == 2) {
		if (strcmp(argv[1],"-v") == 0 || strcmp(argv[1],"--version") == 0) {
			print_version_info();
			exit(0);
		} else if (strcmp(argv[1],"-h") == 0 || strcmp(argv[1],"--help") == 0) {
			print_help_info();
			exit(0);
		}
	}

	if (argc != 5) {
		print_prog_info();
		exit(230);
	}


	char* local_addr = argv[1];
	int local_port = strtol(argv[2],NULL,10);
	char* remote_addr = argv[3];
	int remote_port = strtol(argv[4],NULL,10);

	int preferred_local_network = check_ip_ver(local_addr);
	int preferred_remote_network = check_ip_ver(remote_addr);
	if (preferred_remote_network < 0) { /* This value will be less than 0 if the remote address is a domain name */
		printf("Using %d for local\nUsing hostname for remote\n",preferred_local_network);
	} else {
		printf("Using %d for local\nUsing %d for remote\n",preferred_local_network,preferred_remote_network);
	}
	if (preferred_local_network == -1) {
		exit(207);  /* If the _local_ address isn't an IP address, then we've got problems. */
	}

	char preferred_transport = 'T';
	struct sockaddr addr_struct;
	int server_sock = create_local(preferred_local_network,preferred_transport,local_addr,local_port,&addr_struct);
	int addrlen;
	if (check_ip_ver(local_addr) == 4) {
		addrlen = sizeof(struct sockaddr_in);
	} else if (check_ip_ver(local_addr) == 6) {
		addrlen = sizeof(struct sockaddr_in6);
	} else {
		exit(207);
	}

	listen(server_sock,50);  /* Arbitrary number, change later */

	printf("Listening on %s:%d\n",local_addr,local_port);

	struct sockaddr remote_addr_struct;
	while (1) {
		int from_client = accept(server_sock,&addr_struct,(socklen_t *)&addrlen);
		int to_server = create_remote(preferred_remote_network,preferred_transport,remote_addr,remote_port,&remote_addr_struct);

		printf("Connection established to %s:%d\n",remote_addr,remote_port);
		if (fork() == 0) {
			/* fork returns 0 for a child, so we're in the child's execution
			   right now */
			close(server_sock);
			if (fork() == 0) {
				forward_data(from_client,to_server);
				exit(0);
			}
			if (fork() == 0) {
				forward_data(to_server,from_client);
				exit(0);
			}
			exit(0);
		}

	}

}